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Sulphur availability on interior lodgepole pine sites Kishchuk, Barbara Ellen 1998

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SULPHUR AVAILABILITY ON INTERIOR LODGEPOLE PINE SITES by BARBARA ELLEN KISHCHUK B.S.A., University of Saskatchewan, 1986 M.Sc, McGill University, 1991 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES FACULTY OF FORESTRY DEPARTMENT OF FOREST SCIENCES We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA July 1998 © Barbara Ellen Kishchuk, 1998 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Rt£$f QU£HCg.<> The University of British Columbia Vancouver, Canada Date /2- OMU^T DE-6 (2/88) A B S T R A C T Sulphur deficiencies limit the response of lodgepole pine to nitrogen fertilization on some sites in the British Columbia interior. Soil sulphur properties, foliar nutrition, and response to fertilization were investigated on sulphur-deficient and sulphur-sufficient sites. The soil sulphur constituents most closely associated with sulphur availability were determined. Cycling of soluble inorganic-sulphate through organic-sulphate in mineral soils is the process limiting sulphur availability on sulphur-deficient sites. Sulphur cycling appears to be further limited by low concentrations of organic carbon. A model containing foliar nitrogen, foliar sulphate-sulphur, and soil organic carbon concentrations was a better predictor of lodgepole pine growth response to nitrogen fertilization than a model containing only foliar nitrogen and sulphate-sulphur. Sulphur concentrations in lodgepole pine foliage remained elevated several years after fertilization with sulphate-sulphur. Soil organic-sulphate concentration increased with elemental sulphur fertilization, although seedling biomass was similar on fertilized and unfertilized soils. The susceptibility of interior lodgepole pine sites to sulphur deficiencies is related to both pedogenetic processes and management practices. i i T A B L E OF CONTENTS A B S T R A C T ii T A B L E OF CONTENTS iii LIST OF T A B L E S vii LIST OF FIGURES ix A C K N O W L E D G E M E N T S xi CHAPTER I. INTRODUCTION 1 A . Problem Definition 1 B. Thesis Outline 2 C. Study Design 3 CHAPTER II. SULPHUR C Y C L I N G , SULPHUR NUTRITION, A N D SULPHUR A V A I L A B I L I T Y 7 A . Literature Review 7 1. Sulphur Cycling 7 a. Background to Sulphur Cycling 7 b. Sulphur Cycling in Soils and Plants 7 i. Weathering and Oxidation 9 i i . Reduction 10 ii i . Atmospheric Sulphur 10 iv. Sulphate Adsorption, Precipitation, and Leaching 11 v. Sulphate Uptake and Assimilation 12 vi. Sulphur and Nitrogen Nutrition 15 vii. Evaluation of Sulphur Deficiency 16 viii . Foliar Sulphur Concentrations in Pine 17 ix. Internal Sulphur Cycling 17 x. Soil Organic-Sulphur 19 xi. Sulphur Mineralization 21 xii. Soil Microbial Sulphur 24 2. Sulphur Availability Indices 25 a. Sulphur Availability Indices for Agricultural Soils 26 b. Sulphur Availability Indices for Forest Soils 27 B. Hypothesis and Approach 28 C. Methods 29 1. Soil Nutrient Concentration 29 a. Sampling Procedure 29 b. Soil Analysis 29 i. Soil S Properties 30 i i . Additional Soil Analyses 32 i i i c. Data Collation 33 i. Forest Floor Samples 33 i i . Mineral Soil Samples 33 2. Bulk Density and Soil Nutrient Content.'. .. 34 a. Forest Floor . 34 b. Mineral Soil i . . . . . . 35 3. Mineralizable-S and N (Aerobic Incubation) 36 a. Sampling Procedure 36 b. Incubation Procedure 37 c. Extraction and Analysis 38 4. Nutrient Resorption and Litter S Concentration Sampling 39 5. Foliar Nutrient Concentration 39 6. Correlation of Soil Properties 40 7. Soil and Foliar Data Correlation 40 8. Statistical Analysis 41 a. Soil and Foliar Properties in Prince George and Nelson Regions 41 b. Correlation of Soil Properties 41 c. Soil and Foliar Nutrient Correlations 42 D. Results and Discussion 42 1. Limitations of the Methodology 42 a. Soil S Analyses 42 b. Foliar S0 4-S Analysis 45 2. Soil Nutrient Concentrations 45 a. Forest Floor 53 b. Mineral Soil: B Horizon 55 c. Mineral Soil: C Horizon 58 d. Changes in S Constituents with Profile Depth 59 i. Total-S and C: all sites 59 i i . Total-S and constituents: by site 62 iii . Soluble and total inorganic-S04 83 3. Soil Bulk Density and Soil Nutrient Content 94 4. Correlation of Soil Properties 105 5. Mineralizable-S and N 108 a. Forest Floor 108 b. Mineral Soil 110 6. Foliar Nutrient Resorption and Litter Nutrient Concentration I l l a. Nutrient Resorption I l l b. Litter Nutrient Concentrations I l l iv 7. Soil and Foliar Nutrient Correlations 114 a. Foliar Nutrition 114 b. Relationships of B and C Horizon Soil S Properties to Foliar S0 4-S Concentration 115 c. Relationships of Other B and C Horizon Soil Properties to Foliar S0 4-S Concentration 119 d. Relationships Between F Horizon Properties and Foliar S Concentration 120 e. Relationships Among Soil N , Mineralizable Nutrients and Foliar Nutrients 122 f Relationships of Mineral Soil Nutrient Content to Foliar S0 4-S Concentration 122 8. Further Discussion and Summary 125 CHAPTER III. SULPHUR DEFICIENCIES A N D FERTILIZATION IN FORESTS 130 A. Literature Review 130 1. The Increasing Incidence of Sulphur Deficiencies 130 2. Assessment of Nutrient Status and Predicting Response to Fertilization 130 3. Sulphur Deficiencies in Forest Species 131 4. Lodgepole Pine Response to Fertilization 133 5. Sulphur Deficiencies in Western Canada 135 B. Hypotheses and Approach 135 C. Seedling Bioassay 136 1. Bioassay Establishment and Procedure 136 a. Soils 136 b. Lodgepole Pine Seedlings 137 2. Data Collection 138 a. Soil Chemical Analysis 138 b. Seedling Tissue Biomass and Chemical Analysis 138 3. Statistical Analysis 139 4. Results and Discussion 139 a. Forest Floor Nutrient Concentration 139 b. Mineral Soil Nutrient Concentration 143 c. Seedling Nutrient Status 146 d. Seedling Biomass 148 5. Summary and Conclusions 149 v D. Nutrient Distribution by Foliar Age Class 150 1. Foliar Sampling 150 2. Results and Discussion 151 3. Summary 157 E. Discussion and Conclusions 158 CH A PT ER IV. PREDICTORS OF LODGEPOLE PINE GROWTH RESPONSE TO N FERTILIZATION 159 CH A PT ER V . CONCLUSIONS 167 LITERATURE CITED 170 APPENDICES 197 APPENDIX I. Criteria for site selection 198 APPENDIX II. Soil profile descriptions 199 APPENDIX III. Sulphur and other properties of F horizon material from Prince George and Nelson Region sites 214 APPENDIX IV. Sulphur and other properties of B horizon soil from Prince George and Nelson Region sites 219 APPENDIX V . Sulphur and other properties of C horizon soil from Prince George and Nelson Region sites 223 APPENDIX VI. B and C horizon hand texture, exchangeable cations, CEC, partial base saturation, and pH 227 APPENDIX VII. Exchangeable cations, CEC, and partial base saturation in B horizon soils 238 APPENDIX VIII. Relationship between mineral soil inorganic C concentration and pH 239 APPENDIX IX. Nutrient content of forest floors 240 v i LIST OF T A B L E S Table 1. Study site characteristics 4 Table 2. F horizon S constituents: regional means of concentration, percent of total-S, and percent of organic-S 46 Table 3. B horizon soil S constituents: regional means of concentration, percent of total-S, and percent of organic-S 47 Table 4. C horizon soil S constituents: regional means of concentration, percent of total-S, and percent of organic-S 48 Table 5. F horizon chemical properties: regional means 50 Table 6. B horizon soil chemical properties: regional means 51 Table 7. C horizon soil chemical properties: regional means 52 Table 8. Total-S concentration in forest soils 54 Table 9. Sulphur content of forest soils 96 Table 10. Nutrient content of upper 50 cm of mineral soil 106 Table 11. Pearson correlation coefficients for selected B horizon soil properties 107 Table 12. Regional means of net mineralizable-S04, N H 4 , and N 0 3 , and percent of total-S and N mineralized during 32 d laboratory incubation of forest floor 109 Table 13. Regressions of forest floor mineralizable-S04 and concentrations of selected S constituents 109 Table 14. Regional means of net mineralizable-S04, N H 4 , and N 0 3 , and percent of total-S and N mineralized or immobilized during 32 d laboratory incubation of mineral soil 110 Table 15. Percent resorption of nutrients from needles prior to senescence 112 Table 16. Nutrient concentrations in litter 113 Table 17. Concentrations of S and N in foliage from Prince George and Nelson Regions 115 Table 18. Simple linear regressions of foliar S0 4-S concentration and B and C horizon soil chemical properties 116 Table 19. Simple linear regressions of foliar S concentration and F horizon chemical properties 121 Table 20. Simple linear regressions of foliar N concentration and F, B, and C horizon N constituents 123 v i i Table 21. Simple linear regressions of foliar nutrient concentrations and mineralizable soil nutrients (aerobic laboratory incubation) 124 Table 22. Simple linear regression of foliar S0 4-S concentration and nutrient content of upper 50 cm of mineral soil 124 Table 23. Species with demonstrated or suspected sulphur deficiencies 132 Table 24. Lodgepole pine growth response to single fertilizer application 134 Table 25a. Forest floor S constituent concentrations in the seedling bioassay 140 Table 25b. Forest floor S constituents as proportion of total-S and organic-S in the seedling bioassay. . 140 Table 25c. Forest floor total C, total and extractable N , and element ratios in the seedling bioassay.. . . 142 Table 25d. Forest floor pH, exchangeable cations, and extractable P in the seedling bioassay 142 Table 26a. Mineral soil S constituent concentrations (/ug g'1) in the seedling bioassay 144 Table 26b. Mineral soil S constituents as proportion of total-S and organic-S in the seedling bioassay. . 144 Table 26c. Mineral soil total C, total and extractable N , and element ratios in the seedling bioassay.. . 145 Table 26d. Mineral soil pH, exchangeable cations, and extractable P in the seedling bioassay 145 Table 27. Lodgepole pine seedling nutrient concentration 147 Table 28. Biomass of seedlings in bioassay 149 v i i i LIST OF FIGURES Figure 1. Generalized S cycling 8 Figure 2. Constituents of soil sulphur and summary of their determination 31 Figure 3. S constituents as percent of total-S in B and C horizon soil: Prince George and Nelson Regions 49 Figure 4. Soil S and C properties with depth: all sites 60 Figure 5. S properties in mineral soil a. Meadow Lake 63 b. Tsus Creek 65 c. Gregg Creek 67 d. Cluculz Creek 69 e. Cobb Lake 71 f. Bowron 73 g. Golden 75 h. Upper Gold Creek 77 i . Lower Gold Creek 79 j . Canal Flats 81 Figure 6. Soluble and total inorganic-S04 a. Meadow Lake 84 b. Tsus Creek 85 c. Gregg Creek 86 d. Cluculz Creek 87 e. Cobb Lake 88 f. Bowron 89 g. Golden 90 h. Upper Gold Creek 91 i. Lower Gold Creek 92 j . Canal Flats 93 Figure 7. Soil sulphur content 95 Figure 8. Soil total inorganic-S04 content 97 Figure 9. Soil soluble-S04 content 98 Figure 10. Soil organic-S04 content 99 Figure 11. Soil carbon-bonded-S content 100 Figure 12. Soil organic C content 101 Figure 13. Soil N content 102 Figure 14. Soil extractable P content 103 ix Figure 15. Soil exchangeable cation content 104 Figure 16. Relationship between B horizon soluble-S04 and foliar S0 4-S concentrations 118 Figure 17. Age of oldest needles remaining on trees under fertilizer treatments 152 Figure 18a. Foliar N concentration of all remaining age classes on unfertilized and fertilized trees. . . . 154 Figure 18b. Foliar S concentration of all remaining age classes on unfertilized and fertilized trees. . . . 155 Figure 18c. Foliar S0 4-S concentration of all remaining age classes on unfertilized and fertilized trees 156 Figure 19. Predictors of lodgepole pine growth response to 200 kg ha'1 N fertilization a. B horizon soil properties 161 b. Foliar nutrient properties 162 c. Selected soil and foliar properties 163 d. Best predictors from each group 164 x A C K N O W L E D G E M E N T S I gratefully acknowledge the Science Council of British Columbia and the British Columbia Ministry of Forests for financial support of this project. I extend my sincere appreciation to my supervisory committee for their patience and support: my research supervisor, Dr. Gordon Weetman, and committee members Dr. Cindy Prescott, Dr. Les Lavkulich, Dr. Tim Ballard, and Dr. Michael Feller Mr. Rob Brockley, B.C. Ministry of Forests, was instrumental in facilitating, funding, and supporting this research. He graciously assisted in many steps along the way. I also acknowledge the assistance of other individuals who contributed their time and expertise generously during the course of this research: Dr. Paul Sanborn, B.C. Ministry of Forests Dr. Doug Maynard, Canadian Forest Service Clive Dawson, B.C. Ministry of Forests Research Laboratory Bev Herman, Pacific Soil Analysis Inc. Arlene Gammell, MacMillan Bloedel Forest Sciences Laboratory I would also like to thank the staff at B.C. Ministry of Forests Region and District Offices and at Red Rock Nursery who arranged for refrigerated storage and drying ovens for samples. My deep and sincere appreciation to Cindy Prescott, for personal and academic support. Thanks to the folks at NoFC for a hand along the final stretch. And to my family, friends, and loved ones, I truly thank you for all the help, encouragement and support. Barbara Kishchuk October 1998 x i CHAPTER I. INTRODUCTION 1 A . P R O B L E M DEFINITION If lodgepole pine is "a skinny tree growing on the edge of nowhere" (Hutchinson 1964), then we are now at that edge. Lodgepole pine (Pinus contorta var. latifolia Engelm.) constitutes 36% of the harvested volume of interior B.C. forests, and 25% of all B.C. forests (B.C. Ministry of Forests 1995). Forest fertilization is one element of nutrient management in interior British Columbia forests aimed at improving forest productivity (Brockley et al. 1992). In the past fifteen years, interior forest fertilization research has been directed at evaluating the response of young lodgepole pine stands to fertilization, in conjunction with precommercial thinning (Brockley 1991a). Lodgepole pine stands that regenerate naturally following disturbance by fire, harvesting, or site preparation may be very densely stocked (Fiedler 1986; Eremko 1990). The foremost challenge in the management of lodgepole pine is the treatment of existing stands (Weyermann 1964). Thinning and fertilization of young lodgepole pine stands are the silvicultural options available to increase yield and contribute to balancing the age class distribution of maturing forests (Brockley 1991/3). As nitrogen (N) deficiencies are widespread in interior forests, fertilization research has emphasized N additions. Response of lodgepole pine to N fertilizer has been documented (Weetman et al. 1988; Brockley 1991a, 19916). However, response to N fertilization is variable and is not reliably predicted by measures of stand N status, such as foliar N concentration and soil mineralizable N (Brockley 1990; Weetman et al. 1992). On some sites, growth response of lodgepole pine to N fertilization appears to be limited by low sulphur (S) status, with N additions inducing or aggravating S deficiencies (Brockley 19916; Brockley and Sheran 1994). Fertilization trials have been established by the B.C. Ministry of Forests to specifically evaluate response to N and N+S fertilization treatments (Brockley and Sheran 1994). Forest fertilization involves an investment in the site (Leaf 1974). For fertilization to be feasible with respect to returns on investment, only stands with a high probability of growth response should be treated. This requires the identification of potentially responsive and non-responsive stands, and 2 knowledge of the site properties to which growth response or lack of response can be attributed (Waring and Youngberg 1972; Mika et al. 1992). Costs of fertilization (about $200 ha"1 in the interior) and the associated thinning ($500 ha"1) (B.C. Ministry of Forests 1995) dictate that the maximum potential return on this intensive silvicultural investment be determined. In addition, application of nutrients that are not required or are not applied in the correct balance may unnecessarily increase application costs and may even result in decreased yield (Brockley and Sheran 1994; Hunter and Smith 1996). There is a lack of information about the soil properties that determine the productivity of lodgepole pine (Koch 1996). In particular, there is little understanding of the site and soil properties contributing to S deficiencies in interior B.C. lodgepole pine stands. Foliar total-S and sulphate-S (S0 4-S) concentrations and N:S ratios are presently used to predict the responsiveness of lodgepole pine stands to N fertilization. Although reasonably successful for lodgepole pine (Brockley 1991 i>), these measures do not address the underlying cause of low S status on these sites, nor do they provide insight into relationships between soil S properties, soil S availability, foliar S status, and growth response. The overall objectives of this research were: 1) to identify the soil properties related to S availability in the B.C. interior, and 2) to evaluate soil and foliar properties as predictors for lodgepole pine response to N fertilization. B. THESIS OUTLINE The thesis has five chapters. The first describes the context of the research and the overall study design. The second chapter addresses S cycling and availability in soils. Sulphur cycling is reviewed both in the general context of plant nutrition, and as it relates to forest soils and nutrition. Methods of estimating S availability are discussed. Soil S and other properties of the study sites are summarized, and differences between S-deficient and S-sufficient sites are identified. Finally, relationships between soil S and S availability across the range of sites are discussed. The third chapter is concerned with S fertilization and availability of fertilizer S. Sulphur deficiencies and fertilization in forestry are reviewed, and previous examples of S deficiencies in western 3 Canada and the B.C. interior are outlined. The availability of fertilizer S in a seedling bioassay, and the distribution of S in different age classes of fertilized foliage are discussed. In the fourth chapter, predictors of growth response of lodgepole pine to fertilization are evaluated. The final chapter provides overall conclusions and recommendations for the role of S in nutrient management in the B.C. interior. C. STUDY DESIGN The basis of this study was the comparison of S attributes and S cycling on sites that were either S-deficient or that had adequate S. Ten sites were chosen from B.C. Ministry of Forests N and S fertilization trials for soil and foliage sampling. The fertilization trials were established by R. Brockley, Research Silviculturalist, B.C. Ministry of Forests. Site characteristics are presented in Table 1. A l l sites had pure, even-age, immature lodgepole pine stands originating from fire or harvesting. The stands were 17-33 years old at the time of sampling, and had been planted or previously thinned to densities of 1440 to 2200 stems ha'1. Eight of the trials (EP886.04, EP886.09, and EP886.10) contain single tree plots of 5 m radius (Brockley 1989a; Brockley and Sheran 1994). Two trials (EP886.01) are comprised of fixed area plots (0.06-0.09 ha) containing 50 trees (Brockley 19896). In all cases, fertilizer treatments were applied to the plots in a completely randomized design. A l l stands in the study sites were identified as N deficient on the basis of foliar N data. Fertilization treatments used in the trials included both N alone and N+S treatments. The exception to this was Canal Flats, which had N treatments only. The fertilization trials were established to evaluate 1) the comparative effects of N and N+S fertilization, and 2) various S and N fertilizer materials and application rates. Installations selected for soil and foliar sampling had similar treatments to allow comparison of response data across sites. Treatments selected for this study were 200 kg ha -1 N (primarily as urea), 200 kg ha 1 N plus 50 kg ha -1 S as ammonium sulphate or elemental S, and control (unfertilized). Table 1. Study site characteristics. Sites Biogeoclimatic subzone and association3 Forest district B.C. Ministry of Forests trial Stand Stand age at origin sampling (yr) Prince George Region Meadow Lake (ML) Tsus Creek (TC) Gregg Creek (GC) Cluculz Creek (CC) Cobb Lake (CL) Bowron (B) SBSdw 06" SBSwk 04b SBSdw 04" SBSdw 02b SBSdw 01 b SBSdw 03 b Prince George Prince George Prince George Vanderhoof Vanderhoof EP886.09 #3 EP886.09 #4 EP886.10#2 EP886.09 #5 fire fire EP886.09 #2 harvest harvest harvest Prince George EP886.09 #1 fire 33 29 18 17 18 22 Nelson Region Golden (G) Upper Gold Creek (UGC) Lower Gold Creek (LGC) Canal Flats (CF) ICHmw03 c Golden EP886.01 #13 fire MSdk04 c Cranbrook EP886.09 #7 fire MSdk04 c Cranbrook EP886.01 #12 fire MSdk04 c Invermere EP886.04 #2 fire 22 30 21 31 a Meidinger and Pojar 1991 b Delongetal . 1993 c Braumandl and Curran 1992 5 Table 1. (Continued) Soil association Surficial material Moisture regime8 SI50 Stand density (stem ha-1) Prince George Region Meadow Lake (ML) Barrett-Alixb till with glacio-fluvial pockets submesic 18 2200 Tsus Creek (TC) Ptarmigan0 glaciofluvial submesic 22 2200 Gregg Creek (GC) Deserters'1 till mesic 19 2000 Cluculz Creek (CC) Deserters-Crystal-Alix d till submesic n.a.e 1500 Cobb Lake (CL) Crystal-Barrettd till mesic 19 1440 Bowron (B) Ramseyd glaciofluvial submesic 22 1600 Nelson Region Golden (G) Narboef glaciofluvial subxeric 22 1100 Upper Gold Creek (UGC) Skelly-Kaslog till submesic 20 1100 Lower Gold Creek (LGC) Malpass, Avis 8 fluvial terrace over till submesic 19 2100 Canal Flats (CF) Spillimacheen8 till submesic n.a. 1600 a Meidinger and Pojar 1991 "Lord and Walmsley 1988 c Lord and Green 1985 "Dawson 1989 e data not available fKelley and Holland 1961 8Lacelle 1990 Foliar nutrient concentrations and growth response data from the fertilization trials were used as the basis for identifying the stands as S-deficient or S-sufficient. Foliage from stands characterized as S-deficient met the following conditions: 1) total-S and 2) S0 4-S concentrations below critical levels (0.12 to 0.15%, and 80 ug g"1, respectively), and 3) N:S ratios approaching or above critical levels (14.6) (Ballard and Carter 1985). Sulphur-deficient stands also showed a statistically significant growth response to N+S additions, while no significant growth response to N alone was observed. The S-deficient sites are located in the Prince George Forest Region. Sulphur-sufficient stands are located in the Nelson Forest Region. Stands considered to be S-sufficient had foliar S0 4-S concentrations above critical levels and N:S ratios below critical levels. Significant growth response to N fertilizer treatments occurred in these stands, while no additional response was evident with N+S application. The Canal Flats site was inferred to be S sufficient on the basis of foliar data and a growth response to N alone. Growth response and foliar nutrition data used as criteria for site selection are shown in Appendix I. Although not ruled out by specific fertilization treatments, deficiencies of nutrients other than N or S affecting radial growth response were not suspected at the ten study sites. Soils at the Prince George sites were Podzols, Podzolic Grey Luvisols, Brunisolic Grey Luvisols, and Brunisols. At the Nelson Region sites, soils were Podzols, Grey Luvisols, Brunisolic Grey Luvisols, and Brunisols. Particle size analysis was not done, precluding final soil classifications for some profiles. Detailed properties of soils at the study sites are presented in Appendix II. 7 CHAPTER II. SULPHUR C Y C L I N G , SULPHUR NUTRITION, A N D SULPHUR A V A I L A B I L I T Y A. LITERATURE REVIEW 1. Sulphur Cycling a. Background to Sulphur Cycling Sulphur has historically been either insufficient or present in excess for food and fibre production. Biogeochemical, atmospheric, microbial, and pedospheric sulphur (S) cycles intersect in numerous S-plant interactions that result in inadequate S supply, acute S toxicity, or indirect alterations to nutrient cycling and plant metabolism. Within the soil system alone, S cycling is complex. The complexity arises from two sources. The first is the diversity of natural S compounds and reactions in soils. The general reactivity of S, formation of disulphide bonds in both inorganic and organic compounds (Roy and Trudinger 1970a), the influence of oxidation and reduction on S dynamics (Trudinger 1979), range of S oxidation states (Bohn et al. 1986), association with soil organic matter (Trudinger 1986), and the dominant role of microorganisms in S dynamics (Zinder and Brock 1978; Nihlgard et al. 1994) result in a tremendous variety of S forms and pathways involving S. Cycling of S as a plant nutrient runs concurrently along two avenues: microbial oxidation and reduction reactions that are similar to nitrogen transformations, and the mineral weathering, adsorption-desorption reactions, and precipitation that are similar to phosphorus (P) dynamics. b. Sulphur Cycling in Soils and Plants Many of the more dramatic and economically important S transformations are carried out by distinct microbial populations under specific conditions of soil pH, aeration, metal concentration, and temperature. In moderately acid, well aerated forest soils many of these processes are not relevant and will be mentioned only briefly. Sulphur cycling is outlined in Figure 1. 8 ATMOSPHERIC S jj H 2S, S042", S02 | ABOVE-GROUND S organic-S04 \ | SO/- leaching translocation Figure 1. Generalized S cycling. 9 i. Weathering and Oxidation The original source of soil S is the oxidative weathering of metal sulphide minerals such as iron, nickel, lead, and copper sulphides of hydrothermal or biogenic origin in igneous and sedimentary rocks (Moss 1978; Scott 1985; Ehrlich 1990a; Mulder and Cresser 1994). Pyrite (FeS2) is the major contributor of mineral sulphide to soils (Stevenson 1986). The contribution of S from mineral weathering is generally minor in forest soils, especially those formed on tills and igneous bedrock (Mitchell et al. 1992). However, where inclusions of shale and other sulphide-containing minerals are present in otherwise S-poor parent materials, contributions of inorganic-S from weathering may be significant (Mitchell et al. 1986). Sulphate minerals are also a source of soil S, and are associated with near-surface sedimentary deposits (Nriagu 1978). Examples of sulphate minerals include gypsum (CaS0 4-2H 20), epsomite (MgS0 4-7H 20), and barite (BaS0 4) (Nriagu and Hem 1978). Soil parent material has a significant effect on the S concentration in soils (Dight 1973). Of the total S released annually by mineral weathering, approximately 32% is from sulphide minerals, 65% from sulphate minerals, and 3% from other igneous rocks (Smil 1985). Weathering of sulphide minerals proceeds from the most reduced form of inorganic-S (S2_) to sulphate (S0 4 2 ) , the most oxidized. The sulphate ion, S0 4 2 - , will hereafter be referred to as S0 4 . In addition to metal sulphides and polysulphides, reduced forms of inorganic-S in soils include elemental S (S°), hydrogen sulphide (H 2S), sulphite (S0 3 2 ) , thiosulphate (S 20 3 2 _), and tetrathionate (S 40 6 2 ') (Konopka et al. 1986). Reduced inorganic-S is microbially oxidized by chemoautotrophic bacteria (e.g. Thiobacillus spp.), photoautotrophic bacteria (e.g. Chromatium, Chlorobium spp.), and heterotrophic bacteria and fungi (Roy and Trudinger 19706; Ralph 1979; Wainwright 1989; Ehrlich 19906; Germida et al. 1992). 10 i i . Reduction Sulphate and more reduced forms of inorganic-S are reduced to sulphides under anaerobic conditions using S 0 4 as the terminal electron receptor in respiration (e.g. Desulfovibrio, Desulfotomaculum spp.) (Krouse and McCready 1979). This process, in which S is not reduced for metabolic use, is termed dissimilatory S reduction. Reduced inorganic-S forms that are intermediate in mineral weathering, S oxidation, or dissimilatory S reduction are unstable or transient in aerated soils, and are generally limited to anaerobic environments or oxic-anoxic interfaces (Meyer 1977; Anderson 1978). In most forest soils studies, reduced forms of inorganic-S have been assumed to be negligible, and are not well quantified (Mitchell et al. 1992). These S forms may be of seasonal importance on sites subject to water saturation of soil (David et al. 1987). ii i . Atmospheric Sulphur Other inputs of S to soils are as natural atmospheric inputs of H 2S and gaseous organic-S compounds, and natural and anthropogenic inputs of S 0 4 and sulphur dioxide (S0 2) (Trudinger 1986; Binkley and Richter 1987; Smith 1990). Where atmospheric S inputs are high, S cycling dynamics are altered (Johnson 1984; Johnson et al. 1986). Gaseous S (S0 2 , H 2S) is absorbed by foliage, and sulphide gases are volatilized to the atmosphere from plant tissues and from surface soils (Noggle et al. 1986; Ernst 1990; Lakkineni et al. 1990; Smith 1990; Haines 1991). Annual S inputs of as low as 0.5 kg ha 1 yr"1 S have been reported for unpolluted inland areas (Metson 1979). In inland western North America, atmospheric S inputs are generally less than 7 kg ha"1 yr"1 S, and are unlikely to contribute significantly to the S requirements of plants (Walker 1969; Mitchell et al. 1986; Rochelle et al. 1987). 11 iv. Sulphate Adsorption, Precipitation, and Leaching Sulphate is the main form of ihorganic-S in most soils, including forest soils (Mitchell et al. 1992). Inorganic-S04 is present as soluble-S04 (in solution) and as adsorbed S 0 4 . Mechanisms of anion adsorption are electrostatic attraction to a positively charged colloid surface (non-specific anion exchange), and specific adsorption (ligand exchange) (Johnson and Cole 1980). Sulphate is adsorbed by both of these mechanisms, or a combination (Hue et al. 1985; Marsh et al. 1987; Harrison et al. 1989a; Marcano-Martinez and McBride 1989). Adsorbed S 0 4 is desorbed from colloids as solution S 0 4 is removed (Barber 1995). Sulphate adsorption is associated with materials of variable surface charge, such that positive charge on colloids increases with decreasing pH, and anion adsorption is favoured (Johnson and Cole 1980). There is a well established inverse relationship between soil solution pH and S 0 4 adsorption (Couto et al. 1979; Parfitt 1982; Nodvin et al. 1986; Courchesne and Hendershot 1989). The approximate pH range in which S 0 4 adsorption occurs is between 4 and 6.5 (Kamprath et al. 1956; Williams and Steinbergs 1962; Fuller etal. 1987; Gundersen and Beier 1988). Colloids contributing to a pH-dependent surface charge associated with S 0 4 adsorption include allophanic material, hydrous oxides of iron (Fe) and aluminum (Al), and kaolinitic materials (Chao et al. 1964; Parfitt and Smart 1978; Rajan 1979; Rao and Sridharan 1984; Singh 1984; Xue and Harrison 1991). Extractable Fe and/or A l and S 0 4 adsorption are positively correlated (Johnson and Todd 1983; Fuller et al. 1985; Neary et al. 1987; Harrison et al. 1989a; MacDonald and Hart 1990). The contribution of Fe and A l hydrous oxides to S 0 4 adsorption is expected to be greater in more developed or weathered soils than in less weathered soils (Chao et al. 1962; Johnson et al. 1979; Rochelle et al. 1987). Competition for adsorption sites by phosphate or other anions may limit S 0 4 adsorption (Tabatabai 1985). There is a negative influence of organic matter on S 0 4 adsorption, even where Fe and A l oxides are present (Johnson and Todd 1983; Singh and Johnson 1986; Courchesne.and Landry 1994; Kooner et al. 1995). This may be due either to competition for adsorption sites by organic ligands (Gobran and Nilsson 1988; Evans and Anderson 1990), or to organic coating of the oxide surface (Johnson et al. 1979; Fuller et 12 al. 1985). The relative influence of Fe and A l oxides and organic matter changes with profile depth, such that surface horizons rich in organic matter exhibit less S 0 4 adsorption than subsurface horizons with greater A l and Fe content (Johnson and Todd 1983; Neary et al. 1987; Macdonald and Hart 1990; Mulder and Cresser 1994). The nature of the organic matter influences the rate of decomposition and production of soluble organics and thus the degree to which S 0 4 adsorption is inhibited (Motavalli et al. 1993). Sulphate adsorption is one of the mechanisms by which high atmospheric S inputs are retained in forest soils (Johnson et al. 1982; Fuller et al. 1985). The reversibility of S 0 4 adsorption under decreased atmospheric inputs is variable, and S 0 4 flushes, prolonged S 0 4 release, or limited S 0 4 release to the soil solution may result (Harrison et al. 1989a, 19896; Mitchell et al. 1992; Gustafson and Jacks 1993; Mulder and Cresser 1994; Boxman et al. 1995). Sulphate minerals are precipitated in soils under conditions associated with large acidic S inputs. At very low pH and high S 0 4 concentration, Al-hydroxy-S0 4 minerals are precipitated , such as basaluminite (Al 4(OH) 1 0SO 4), jurbanite (A10HS0 4), and alunite (KA1 3 0H 6 (S0 4 ) 2 ) (Adams and Rawajfih 1977; Ulrich et al. 1980; Weaver et al. 1985; Khanna et al. 1987; Gundersen and Beier 1988; Courchesne and Hendershot 1990). In calcareous soils, S 0 4 may be co-precipitated as an impurity with calcium carbonate, forming an insoluble inorganic-S04 pool (Williams and Steinbergs 1962; Roberts and Bettany 1985). Gypsum and epsomite are precipitated from dissolved S 0 4 salts, and insoluble barite is precipitated in the presence of barium and S 0 4 (Cairns and Richer 1960; Birkeland 1984). Sulphate not retained by other mechanisms is readily leached from the soil profile (Johnson et al. 1982; Tisdale et al. 1986; Bolan et al. 1988). v. Sulphate Uptake and Assimilation Sulphur uptake by plants and most microorganisms is as the S 0 4 ion from soil solution, which must be reduced for metabolic use (Konopka et al. 1986; Anderson 1990). Plant S 0 4 uptake, and microbial S 0 4 assimilation (immobilization), are collectively referred to as assimilatory S reduction, and are the most important biological S reactions (Trudinger 1979). Some microorganisms are unable to reduce 13 S 0 4 and require more reduced forms of inorganic or organic-S for uptake (Zinder and Brock 1978; Konopka et al. 1986). Uptake of soluble-S04 by plants is by active transport and is not particularly sensitive to pH (Mengel and Kirkby 1987; Ferrari et al. 1990). Sulphate uptake by trees is not enhanced by ectomycorrhizal association under low S conditions, likely due to ready diffusion of soluble-S04 directly to the root surface (Morrison 1963a; 19636). Preference of vesicular-arbuscular (VA) mycorrhizal fungi for reduced inorganic-S substrates was attributed to the fungal requirement for reduced S (Hepper 1984). No information is available on the acquisition of organic-S by mycorrhizae, although it was hypothesized as the reason for the presence of reduced organic-S (cysteine) in Fagus sylvatica roots (Herschbach and Rennenberg 1996). There is limited evidence for uptake of organic-S directly by plants roots in a bacterial association (Nissen and Benson 1964; Nissen 1968). Element "confusion" in S 0 4 uptake and metabolism occurs with selenium (Se) (as selenate Se042", selenite S e 0 3 2 , and selenide Se2"), and molybdenum (as molybdate Mo0 4 2") (Howarth and Stewart 1992). On high Se soils, Se may interfere with S 0 4 uptake causing S deficiency (Mengel and Kirkby 1987). Once absorbed by plant roots, the relatively unreactive S 0 4 ion is transported in the xylem to the leaf, and activated prior to further metabolic activity (Schiff and Hodson 1973; Schiff and Fankhauser 1981; Brunold 1990). Sulphate activation precedes the two main pathways of S metabolism in higher plants: reduction and incorporation into cysteine, and formation of ester sulphates (Thompson et al. 1986). Activation is light-driven, occurs mostly in the chloroplast, and results initially in the formation of APS (adenosine 5'-phosphosulphate) (Schiff 1983). The APS S 0 4 is either reduced and incorporated into cysteine, or further activated to PAPS (adenosine 3'-phosphate 5'-phosphosulphate) (Schiff and Hodson 1973; Brunold 1990). The S 0 4 associated with PAPS is used in the formation of sulphate esters and sulpholipids (Schiff and Hodson 1973; Kleppinger-Sparace et al. 1990). Limited S 0 4 reduction does occur in roots, but is likely unimportant to the overall S requirement of plants (Brunold 1990). Microbial assimilation of S follows similar pathways of activation followed by reduction and cysteine synthesis or formation of sulphate esters (Zinder and Brock 1978; Slaughter 1989). 14 Cysteine is the precursor to reduced S compounds in plants, including methionine and cystine, peptides and proteins, enzymes and co-enzymes, glutathione, and thioredoxins (Thompson et al. 1986). At least 80% of the organic-S in plants is present as protein (Dijkshoorn and van Wijk 1967). In amino acids and other reduced S compounds, S is bonded directly to carbon (C). The role of ester sulphates in plants is less well established (Schiff and Fankhauser 1981; Thompson et al. 1986). Ester sulphates are found in higher plants as choline sulphate, phenol sulphates, flavinoid sulphates, glucosinolates and other compounds, many of which are unique to plants (Fitzgerald 1978; Huxtable 1986; Thompson et al. 1986). The general form of ester sulphates is R-O-SCV, where R is aliphatic or cyclical (Trudinger and Ray 1970a). Their function appears to be as S storage, water solubility of S compounds, increased biological reactivity of assimilated S, and as attractants or repellents of herbivores (Nissen and Benson 1961; Huxtable 1986; Schnug 1990). Ester sulphates are also found in bacteria, fungi, lichens, and algae, where their role is thought to be either structural (as sulphated polysaccharides) or as S storage (Fitzgerald 1978; Schiff and Fankhauser 1981). Sulphate is also stored in plants as the inorganic-S04 ion in vacuoles and as the peptide glutathione (Rennenberg 1984; Binkley and Richter 1987). Ten to twenty percent of total plant S can be present as organic or inorganic-S04 (Cram 1990), although values as high as 60% have been reported (Turner et al. 1980). In addition to ester sulphates, sulphamates of the general form R-N-SOy are found in plants and microorganisms (Roy and Trudinger 1970a; Huxtable 1986). From here on, plant and microbial ester sulphates and sulphamates will be referred to collectively as organic-S04. The distinction between C-bonded-S, and S that is bonded to oxygen (O) or nitrogen (N) (organic-S04) is significant in the cycling of plant residues and other soil organic-S. There are three major functional roles of S in plants: structural (as disulphide bonds in the S-containing amino acids), catalytic (enzymes and co-enzymes), and electrochemical (inorganic and organic-S 0 4 role in charge balance, stability of cell emulsions, water relations, and solubility of organic cell constituents) (Allaway and Thompson 1966; Rennie and Halstead 1977; Clarkson and Hanson 1980; Duke and Reisenauer 1986). 15 vi. Sulphur and Nitrogen Nutrition The ratio of C:N:S:P in plant tissue is approximately 100:10:1:1 (Binkley 1986; Trudinger 1986; Howarth and Stewart 1992). The amount of S assimilated into organic compounds in plants is highly regulated (Leaf 1968; Anderson 1990). The ratio of organic-S and organic N are closely linked to protein synthesis and metabolism, but are less related to organic P metabolism (Clement and Gessel 1985). The determination of a fixed ratio between organic-S and organic N in protein formation, and comparison of species differences in the ratio was first developed by Dijkshoorn and van Wijk (1967) for agricultural plants, and further developed for conifers by Kelly and Lambert (1972). For conifer foliage it is assumed that total N equals organic N , giving an S:N atom weight ratio of 0.030 for Pinus radiata (radiata pine), Picea abies (Norway spruce), and Pseudotsuga menziesii (Douglas-fir), and 0.031 for Pinus nigra (Austrian black pine) (Kelly and Lambert 1972; Turner et al. 1977 Clement and Gessel 1985). The S:N atom weight ratio is relatively fixed for a given species under conditions of varying nutrient supply (Clement and Gessel 1985). Sulphur in excess of that required to balance N in protein formation accumulates as S0 4-S. The presence of organic S0 4-S in conifer foliage has not been conclusively established (Howarth and Stewart 1992). It is assumed that S 0 4 accumulates in conifers as inorganic-S04 only, although the commonly used analysis measures both forms (Johnson 1984). Sulphate concentration in tree foliage has been used as a diagnostic tool for evaluating excess S, S deficiencies, and response to N fertilization (Hesse 1957; Turner et al. 1977, 1979, 1980; Legge et al. 1988; Kaiser et al. 1993; Brockley and Sheran 1994). The ratio of total N:total S in tissue is derived from the same concept, and is also used in the evaluation of S nutrition (Ballard and Carter 1985; Brockley 1996). Where S concentrations are high relative to N , S0 4-S increases, as may the production of S amino acids (Turner et al. 1980; Burke et al. 1992). Sulphur deficiencies result in the accumulation of non-protein N , particularly arginine, which may lead to increased Dothistroma needle cast infection of radiata pine (Duke and Reisenauer 1986; Lambert 1986). 1 6 v i i . Evaluation of Sulphur Deficiency Sulphur deficiency has a basic dysfunctional effect on growth and metabolism (Duke and Reisenauer 1986). The physiological symptoms of S deficiency include inhibition of protein synthesis, impaired chloroplast formation, decreased chlorophyll content, decreased photosythetic activity, and reduced growth rates (Turner 1979; Duke and Reisenauer 1986; Marschner 1986; Mengel and Kirkby 1987). In theory, each plant nutrient is responsible for such specialized functions that specific symptoms develop when the nutrient is limiting (Leaf 1968). In practice, the manifestation of a limiting nutrient is easily lost against the background of nutrient interactions and environmental, genetic, and phenological variability. Visual symptoms of S deficiency are difficult to distinguish from N deficiencies, particularly in field-grown coniferous trees (Leaf 1968; Turner 1979). The difficulty is compounded where both elements are limiting. Visual symptoms of S deficiency include chlorotic younger needles, reduced growth, delayed maturity, brittleness, fine stems and branching, thin spindly needles, and dark, fibrous roots (Leaf 1968; Rennie and Halstead 1977; Turner 1979; Duke and Reisenauer 1986; Marschner 1986; Mengel and Kirkby 1987; Walker 1988; Walker and Gessel 1991). In radiata pine, specific symptoms include terminal bud dieback and yellow needle bases (Lambert and Turner 1977). Tree deformation caused by fungal infection is also indicative of S deficiencies in radiata pine (Lambert et al. 1979). Symptoms of S deficiency may be more obvious in seedlings: short stems and needles, blue-green to yellowish coloring, red needle tips, and blackish, short roots in Pinus sylvestris (Scots pine) (Rennie and Halstead 1977), yellow current needles, lack of apical bud formation, and thick, poorly branched roots in Norway spruce (Ingestad 1959), and twisted or curling needles in Picea glauca (white spruce) and Douglas-fir (van den Driessche 1989). Nutrient deficiency symptoms are consistent across pine species (Ingestad 1960). viii . Foliar Sulphur Concentrations in Pine For Scots pine seedlings grown in nutrient solution, the optimum foliar S concentration was estimated to be 0.15 to 0.20% (Ingestad 1960). Foliar S concentrations in forest-grown lodgepole pine seedlings ranged from 0.12 to 0.21% S (Beaton et al. 1965). Mature conifers have lower foliar S concentrations than most deciduous species, and are considered to be "low S accumulators" (Linzon et al. 1979). Sulphur concentrations in three eastern Canadian pine species ranged from 0.13 to 0.17% (Linzon et al. 1979). Current-year foliar S concentration in 15 to 30-year old lodgepole pine stands in the B.C. interior averaged 0.091% (Brockley and Sheran 1994). For slightly older stands, mean concentrations were in the range of 0.09 to 0.11 % (Beaton et al. 1965). Based on data for radiata pine and Douglas-fir (Kelly and Lambert 1972; Turner et al. 1977), guidelines for the assessment of conifer S status were developed (Ballard and Carter 1985). These guidelines use total foliar S, foliar SCyS, and foliar N:S ratio to evaluate both S status per se, and the potential forN-induced S deficiencies withN fertilization. Foliar total-S concentration below 0.12 to 0.15%, S0 4-S concentration below 80 \ig g'\ and an N:S ratio greater than 14.6 are indicative of poor S nutrition and the potential for worsening of the S status with N fertilization (Ballard and Carter 1985). Lodgepole pine stands with foliar S0 4-S concentrations below 40 ug g"1 have not responded to N fertilization, and it is recommended that S fertilizer be added with N where foliar S0 4-S concentrations are below 60 ug g"' (Brockley 1996). A S0 4-S concentration of > 400 ug g"1 is required for a sustained growth response to N fertilization in Douglas-fir (Turner et al. 1979). ix. Internal Sulphur Cycling In addition to uptake from soil and in some cases, foliar interception, S requirements of conifers are met by internal nutrient redistribution (Turner and Lambert 1980). Sulphur is at least somewhat phloem-mobile (Hill 1980; van den Driessche 1984; Walker 1988). There are conflicting results reported for S redistribution, attributable to differences in species, level of external S supply, phenological stage, and S form. For example, in herbaceous plants with sufficient S supply, S 0 4 appears to be readily 18 transported in the phloem to new shoots (Anderson 1990). Sulphate was shown to accumulate in shoots of radiata pine grown in a S-free medium (Morrison 1963a). Other studies indicate that under S stress S0 4-S is immobile from older shoots but is mobilized from root or stem reserves (Bouma 1967; Cram 1990; Ernst 1990). Unlike reduced N , reduced S can be re-oxidized to S0 4 -S ; however, protein S may not be remobilized under conditions of S deficiency due to reduced protease synthesis (Hill 1980; Marschner 1986). Glutathione is the predominant form of soluble reduced S, and glutathione and cysteine are important in S remobilization and S supply to growing shoots of trees (Rennenberg 1982; Anderson 1990; Rennenberg et al. 1994; Blaschke et al. 1996; Buchanan-Wollaston 1997). A supply of reduced S is required for new shoot growth in the spring, as the activity of enzymes required for S 0 4 assimilation and reduction is insufficient (Schupp and Rennenberg 1992; Suter et al. 1992). Different patterns of reduced S remobilization were observed in coniferous and deciduous species (Herschbach and Rennenberg 1995). Nutrient recycling, particularly nutrient resorption from foliage, occurs both prior to senescence and in non-senescing tissue (Nambiar and Fife 1991). As with N and P, efficient S recycling may be a mechanism of nutrient conservation where S availability is low (Turner and Lambert 1980). Stand-level estimates indicate that on a site with high S availability, Douglas-fir obtained only 8% of the annual S requirement by redistribution, while on a low S site 50 to 70% of Eucalyptus spp. S requirement was met by redistribution (Turner and Lambert 1980). Fourteen percent of the annual S requirement of Pinus taeda (loblolly pine) stand was met by redistribution on a site of unknown S status (Switzer and Nelson 1972). In general, 20 to 30% percent of foliar S is resorbed prior to senescence (Binkley 1986). This figure was observed for Eucalyptus spp. and Betula alleghaniensis (yellow birch) (32%) but is much higher than the 3% observed in Fagus sylvatica (European beech) (Hoyle 1965; Staaf 1982). In contrast to studies showing an inverse relationship between nutrient availability and resorption, studies in pine showed that nutrient resorption did not decrease when nutrient availability was increased (Birk and Vitousek 1986; del Arco et al. 1991). This suggests that there may be species differences in the 19 "aggressiveness" of nutrient utilization between early sucessional conifers like pine and other species (Munsonetal. 1995). Studies in young radiata pine stands showed that as much or more N was resorbed from non-senescing tissue to supply new shoots than was resorbed at senescence (Fife and Nambiar 1984; Nambiar and Fife 1987; 1991). These authors suggested thatN resorption is driven by shoot growth rate and not by external nutrient availability. Proe et al. (1992) showed that internally recycled N in Pinus nigra var. maritima (Corsican pine) maintained the internal N supply at growth-supporting levels. Similarly, S demands of new shoots are also met by the transfer of S from the previous year's needles of Norway spruce when S is not limiting (Schupp et al. 1992). The redistribution dynamics of S under low S conditions are not known. It is likely that the transfer of S from older tissue to younger shoots is limited under low S conditions, where reduced S compounds such as glutathione are lacking. x. Soil Organic-Sulphur Soil organic-S includes intact residues of plant litter, roots, microbial biomass, and soil fauna, their decomposition products, and S compounds produced in situ (Kowalenko 1978; Freney 1986). Organic-S and inorganic-S04 are leached from decomposing conifer litter and the forest floor (Feller 1977; Baker et al. 1989; Homann and Cole 1990; Laskowski et al. 1995). The proportion of different forms of organic-S in forest soils varies widely, largely as a function of a wide range in atmospheric S inputs. In general, at least 90% of soil S is in organic form (Scott 1985). On some sites, organic-S formation is a mechanism of S retention under high S inputs (Strickland and Fitzgerald 1984; Swank et al. 1984; Autry et al. 1990). Most of the organic soil S is found in association with other organic matter, clays, and Fe and A l oxides (Bettany and Stewart 1983). Sulphur mineralization, or the conversion of organic-S to inorganic-S04 for plant uptake and microbial assimilation, is essential in soil-plant S cycling, but poorly quantified (Blair 1971; Krouse and McCready 1979). Less than 10% of the soil S pool is actively cycling (van Praag 1973; Goh and Gregg 1982; McLaren et al. 1985). In this respect, S cycling is similar to N cycling. However, the turnover of S 20 through soil organic matter has an added level of complexity in the existence of two well-defined organic-S fractions: C-bonded-S and organic-S04. Carbon-bonded-S includes cystine and methionine, sulphonates (C-SOy), complex heterocyclic molecules associated with humus, and a large proportion of unknown compounds (Freney 1986; Stevenson 1986; Autry and Fitzgerald 1990). Organic-S04 in soils is comprised of the ester sulphates and sulphamates found in plant tissue, as well as inputs from animal excreta, soil microorganisms, and soil macrofauna (Fitzgerald 1976, 1978; Saggar et al. 1981; Tabatabai 1982; Morgan and Mitchell 1987; Germida et al. 1992). Although organic-S04 inputs from conifer foliage are unknown, the major source of soil organic-S04 is likely to be from microbial production rather than vegetative inputs (David et al. 1987). The division of soil organic-S into organic-S04 and C-bonded-S fractions is commonly applied. This is due in part to its suitability for analytical purposes, although the functional roles of the two groups may not be clear (Howarth and Stewart 1992). The organic-S04 fraction and disulphides are determined by reduction to H 2 S by hydriodic acid (cleavage of the S-O or S-N bond), while C-bonded-S is determined either directly by reduction with Raney-nickel (cleavage of the S-C bond), or indirectly by subtraction of hydriodic-acid reducible-S from total-S (Freney 1961; Lowe and DeLong 1963; Freney et al. 1970; Roy and Trudinger 1970a). A portion of the C-bonded-S is not reduced by Raney-nickel, and is considered to be the most recalcitrant form of organic-S (Lowe 1965; Tabatabai 1996). As with N analysis, chemical fractionations may say more about the source and formation of soil organic matter than its degradation and release of mineral S 0 4 Soil organic sulphates are peripheral components of humic and fulvic acids (Fitzgerald 1978; Bettany et al. 1979). Carbon-bonded-S is more tightly integrated within humic acids, having a role in their structural integrity (McGill and Cole 1981). Humic substances are formed in situ from polyphenols originating with lignin degradation and/or microbially synthesized pigments (Zeikus 1982). Polyphenols enzymatically converted to quinones undergo condensation with amino groups, resulting in the formation of persistant, dark-coloured, high molecular weight humic substances (Stevenson 1982; Stout et al. 1981; Davidson et al. 1995). Cysteine and glutathione S-H groups may be substituted for the amino groups, 21 incorporating S into humic substances (Stevenson 1986). The concentration of S in humic and fulvic acids in cool temperate soils is 0.1 to 0.9%, and 0.1 to 1.7%, respectively (Schnitzer 1978). Although humic materials as a group are quantitatively important, the direct importance of humus S as a nutrient source for plants and microorganisms has not been established (Lowe and Delong 1963; Horth et al. 1988). Soluble organic-S is an important component of the S pool (Homann et al. 1990; David et al. 1995). The fulvic acid fraction of organic matter, and to a lesser extent the humic acids, are associated with the vertical movement of organic matter in both podzolic and luvisolic forest soils (Schnitzer and Gupta 1964; Schnitzer and Dejardins 1969; De Coninck 1980; McKeague et al. 1983). Sulphur is present in both the fulvic and humic acid fractions, although organic-S04 is associated more with fulvic than with humic acid(Freney 1961; Freney et al. 1971; Schnitzer 1978, McGil l and Cole 1981; Vannier and Guillet 1994). Vertical movement and accumulation of fulvic acid and organic-S04 in B and C horizons has been documented on forested luvisolic sites (Schoenau and Bettany 1987; Roberts et al. 1989; Huang and Schoenau 1996). Organic-S accumulated in lower horizons may be susceptible to loss by leaching (Schoenau and Bettany 1987; Huang and Schoenau 1996), maintained as a stable S pool (Mitchell et al. 1989), or further decomposed (Dai et al. 1996). More than 70% of soil S is found in the clay-size fraction, with over 80% of that in the hydriodic-acid reducible form (Anderson et al. 1981; Bettany and Stewart 1983). Eluviation of clay-size material and fulvic acids is associated with the development of luvisolic and podzolic soils, respectively (Rust 1983; McKeague et al. 1983). The presence of organic-S04 in the clay-size and fulvic acid fraction suggests that vertical movement of organic-S04 would not be unexpected in soils undergoing this type of development. Sulphur deficiencies are common in leached, neutral to slightly acidic soils that are low in organic matter (Anderson 1988). xi. Sulphur Mineralization It has been proposed that S mineralization also follows the organic-S04/C-bonded-S dichotomy. McGil l and Cole (1981) presented a dual mechanism for S mineralization based on these 22 fractions. Organic-S04 is mineralized extracelluarly in response to microbial demand for S ("biochemical mineralization"), while the C-S bond is oxidized intracellularly for its energy release, analogously to N ("biological mineralization") (McGill and Cole 1981). The ratio of organic-S04:C-bonded-S reflects the S status of soils, with lower ratios indicative of S depletion by the microbial biomass (McGill and Cole 1981). The mineralization of organic-S04 to inorganic-S04 results from hydrolysis by extracellular sulphatase enzymes (Tabatabai and Bremner 1970a; Fitzgerald 1976; Houghton and Rose 1976; Speir and Ross 1978). There are specific enzymes for the different C configurations in the organic-S04 molecule (Roy and Trudinger 1970c). The general mineralization reaction is: R-O-SCy + H 2 0 - R-OH + H + + S 0 4 2 \ Soil sulphatase enzymes are produced mainly by bacteria and fungi, although plant roots and soil fauna may also be capable of sulphatase production (Speir and Ross 1978). Stable sulphatase/clay-organic complexes provide prolonged sulphatase activity (Speir and Ross 1978; Whalen and Warman 1996a). There is a strong positive correlation between sulphatase activity and soil organic C (Tabatabai and Bremner 19706; Speir and Ross 1978). Arylsulphatase activity decreases with profile depth, due to decreased organic C (Tabatabai 1994). Sulphatase activity has been tested as an indicator of soil quality (Dick 1994; Pankhurst et al. 1995). It is generally assumed that the organic-S04 fraction is more labile than C-bonded-S. However, even within the organic-S04 pool there are various organic-S04 fractions with different mineralization dynamics (Lou and Warman 1992a, 19926). Some organic sulphates are weakly bound on surfaces of humic molecules, while others are occluded within the humic compounds (Lou and Warman 1994; Whalen and Warman 19966). Mineralization of C-bonded-S results from the internal enzymatic catabolism of energy-rich substrates by heterotrophs (McGill and Cole 1981). There are two possible pathways for the degradation 23 of cysteine. The first involves the oxidation of S to S0 3 2" while still attached to the organic molecule, in the simplified form of: HS-CH 2 -CH(NH 2 )-COOH (cysteine) - R-SC-32- - S0 4 2 " (Freney 1967; Trudinger 1986). The second pathway is quantitatively less important and involves the formation of free H 2S under anaerobic conditions: HS-CH 2 -CH(NH 2 )-COOH - H 2 S + N H 3 + pyruvic acid, with the subsequent oxidation of H 2 S to S0 4 2 " where oxygen is present (Freney 1967; Trudinger 1986). A l l of the processes and controls of S mineralization are not completely understood (Freney 1986; Howarth and Stewart 1992). Net mineralization of S occurs when the simultaneous mineralization-immobilization process is dominated by mineralization (Germida et al. 1992). Factors affecting S mineralization are pH, soil moisture, soil temperature, wetting-drying patterns, age of organic residues, presence of plants, and S level in the growth medium (Freney and Spencer 1960; Nicholson 1970; Tabatabai and Bremner 19706; Blair 1971; Biederbeck 1978; Maynard et al. 1984; Freney 1986; Foster 1989; MacDonald et al. 1995). The effects of these factors could be due to their influence on sulphatase enzymes or on the grazing activity of soil fauna (Fitzgerald 1976; Ingham et al. 1985; Germida et al. 1992). The C:S , C:N:S, and C:N:P:S ratios of soils have also been considered as controls on S mineralization. The cycling of C, N , S, and P are linked (Mellilo and Gosz 1983; Vitousek et al. 1988; Howarth and Stewart 1992). Nutrients required by C fixers and the energy in fixed C are cycled through soils, regulating primary production (Nadelhoffer et al. 1995). Although related, transformations of C, N , S, and P are not parallel (Coleman et al. 1983). Unlike C and N , S and P cycles do not have an atmospheric fixation component. Differences in inputs (atmospheric, parent material), losses (leaching), and cycling processes are responsible for variations in organic matter elements ratios (Kowalenko 1978; Paul and Clark 1996). The N:S ratio in soils is relatively 24 constant due to the close relationship between foliar N:S (Khanna and Ulrich 1984). The C:S ratio of soil organic matter is less consistent than the C:N or the N:S ratios (Freney 1986; Paul and Clark 1996). The broadest C:N:S ratios in forested podzolic and luvisolic soils are about 200:12:1 (Paul and Clark 1996). Sulphur mineralization has not been well correlated with total-S, C, o rN, mineralizable N , C:S, N:S, or C:N in many studies (Barrow 1959; Kowalenko and Lowe 1975a; Biederbeck 1978; Freney 1986; Ghani et al. 1991; N'dayegamiye et al. 1994). However, on burned forest sites, Sanborn and Ballard (1990) found good correlations between mineralizable-S and soil properties. The broad relationship between organic matter turnover and mineralizable-S is reflected in the estimate that organic matter with a C:S > 400 shows net S immobilization, and material with C:S < 200 shows net mineralized S (Barrow 1960). Mineralization of S has been observed to be both faster and slower than N from the same substrate (Tabatabai and Al-Khafaji 1980; Homann and Cole 1990). The different mineralization mechanisms for organic-S04 and C-bonded-S, in contrast to the single mechanism for C-N linkages, explains the variable relationship between S and N mineralization (Freney et al. 1962; Kowalenko and Lowe 1975a; McGil l and Cole 1981; Saggar et al. 1981; Bettany and Stewart 1983). Methods used in the estimation of S mineralization, for example leached and non-leached systems, may also explain some of the variation in mineralizable-S results (Maynard et al. 1983; Valeur and Nilsson 1993). xii . Soil Microbial Sulphur Soil microbial biomass refers to bacteria, fungi, algae, and protozoa (Brookes et al. 1985). The microbial biomass comprises up to 5% of the soil organic-S, about 3% of the soil C, and up to 5% of the soil N (Saggar et al. 1981; Strick and Nakas 1984; Chapman 1987; Horwath and Paul 1994; Banerjee and Chapman 1996). Bacteria and fungi constitute at least 70% of this pool, and are the most important organisms in decomposition of organic matter (Brookes et al. 1985; Anderson 1983). Sulphur concentration in bacteria and fungi is about 0.1 to 1 % S , including over 80% as proteins and amino acids and the remainder as sulpholipids, vitamins, and organic-S04-S (Rennie and Halstead 1977; Kowalenko 25 1978; Zinder and Brock 1978; Freney 1986). Fungi are able to accumulate more organic-S04 than bacteria (Saggar et al. 1981; Castellano and Dick 1991). Microbial biomass S is a significant fraction of the actively cycling S (Chapman 1987; Smith and Paul 1990; Banerjee and Chapman 1996). There is a strong relationship between microbial biomass C and S (Chapman 1987; Wu et al. 1994). 2. Sulphur Availability Indices Attempts to link soil sulphur pools with sulphur availability to plants have met with limited success. The soil S cycle involves many pools with different dymamics, and the importance of each pool varies with the soil (Binkley 1986). There are a number of fractions from which inorganic-S04 potentially becomes available. Research on S cycling in soils has mainly been done in two contexts: S deficiencies in agricultural systems, and anthropogenic S inputs to forest ecosystems. Work in agricultural crops has focused on measurements of S availability and rates of S turnover from soil organic matter. Research on S deposition in forest ecosystems has been for the most part unconcerned with the availability of the added S, and has attempted to determine the importance of biotic and abiotic processes in retention of added S. Nutrient availability can be defined in several ways. In the simplest terms, an available nutrient is instantaneously present in the form, quantity, and location that can be utilized by plants (Bundy and Meisinger 1994). For S, this would be estimated as soluble inorganic-S04. A much broader approach defines nutrient availability as the product of site nutrient capital and turnover rate (Edmonds et al. 1990). Changes in nutrient availability result from changes in either the size of the capital or the turnover rate. Intermediate to these approaches is the nutrient supply concept of Chapin et al. (1986). Nutrient supply reflects the flux of nutrients from unavailable to available pools, and is expressed as the degree to which plant growth is constrained by limited supply (Chapin et al. 1986; Binkley and Hart 1989; Binkley and Vitousek 1991). 26 a. Sulphur Availability Indices for Agricultural Soils Both tissue and soil S availability indices have been used in agricultural systems. Foliar indices include total-S concentration, SCyS concentration, S04-S:total-S ratio, N:S ratio, protein and non-protein N:S, and Diagnosis and Recommendation Integrated System (DRIS) ratios (Dijkshoorn and van Wijk 1967; Freney et al. 1977; Sumner 1981; Gaines and Patak 1982; Jones 1986; Scaife and Burns 1986). Most soil S availability indices measure some pool of extractable S, constituting either 1) readily soluble-S04, 2) soluble plus a portion of adsorbed S0 4 , or 3) soluble-S04, adsorbed S0 4 , and a portion of the organic-S (Reisenauer et al. 1973). No extractant is known to remove the entire adsorbed S 0 4 fraction (Blanchar 1986). Extractions for available S may correlate well with plant response, but give little information about the nature of the measured S (Beaton 1968). Extractants include water, chloride salts (KC1, MgCl 2 ,CaCl 2 , LiCl) , sodium phosphate, calcium phosphate, ammonium acetate; sodium acetate, and sodium bicarbonate (Kilmer and Nearpass 1960; Beaton 1968; Scott 1981; Tabatabai 1982; Johnson and Fixen 1990). Water, chloride salts, and the phosphate extractants generally remove only inorganic-S04 (Tabatabai 1992). The anion in the extractant determines the displacement of adsorbed S 0 4 (Kowalenko 1993a). Phosphate extractants remove most of the adsorbed S0 4 , and have been well correlated with S availability in some soils (Spencer and Freney 1960; Jones et al. 1972; Probert 1976; Wada et al. 1994). Acetate and bicarbonate extractants remove a portion of the labile organic-S (Beaton 1968; Tabtabai 1996). Heating releases organic-S, particularly organic-S04, and has been used in conjunction with some extractants (Williams and Steinbergs 1959; Goh and Tsuji 1979; Blair 1993; Tabatabai 1996). Correlating extractable S 0 4 with plant growth is confounded by inputs of mineralized S over the growing season, and by the concurrent immobilization of mineralized S (Freney et al. 1971; Goh and Tsuji 1979; Scott 1981; Watkinson and Kear 1996a). Mineralizable-S has been useful as a S availability index on some soils (Bettany et al. 1974; N'dayegamiye et al. 1994), but less so on others (Tsui and Goh 1979; Watkinson and Kear 1996a). Other indices of S availability include microbial growth, a S 0 4 leaching index, and soil particle size fractions (Spencer and Freney 1960; Jones 1986; N'dayegamiye et al. 1994). 27 The method of S analysis will determine the fraction of S measured, independent of the extractant. Ion chromatography (IC) is specific for the S 0 4 ion (Tabatabai 1992). Other methods of measuring extracted S, such as hydriodic-acid reduction or turbidometric determination of barium-S04 precipitate are not specific to inorganic-S04 and will include organic-S04 (Blanchar 1986; Tabatabai 1992; Kowalenko 1993a). The proportion of the organic-S04 included by these analyses is not known. Sulphur analysis by inductively-coupled plasma atomic emission spectrometry (ICP-AES) measures the total soluble-S fraction (inorganic and organic), and is well correlated with S availability in agricultural and pasture crops (Maynard et al. 1987; Zhao and McGrath 1994; Watkinson and Kear 19966). b. Sulphur Availability Indices for Forest Soils There has been relatively little research on S availability in forest soils. Reasons for considering S availability in forest soils have been to evaluate response to N-fertilization (Turner et al. 1977, 1979; Blake et al. 1988, 1990; Brockley and Sheran 1994), S dynamics under forest management practices (Sanborn and Ballard 1990), and unbalanced atmospheric N and S inputs (Turner et al. 1980; Kelly and Johnson 1982). Foliar S0 4-S concentration has been used most often as an index of S availability on forest sites, and has been used in radiata pine (Lambert and Turner 1977), Douglas-fir (Turner et al. 1977, 1979), and lodgepole pine (Brockley and Sheran 1994; Brockley 1996). Other indices of S availability have used extractable soil S 0 4 (Blake et al. 1988; 1990), S 0 4 capture by ion exchange resins (Krause and Ramlal 1987; Sanborn and Ballard 1990), and mineralizable soil S (Kelly and Johnson 1982; Sanborn and Ballard 1990). 28 B. HYPOTHESIS A N D A P P R O A C H At the outset of this study, the reasons for low availability of S in the Prince George area were entirely unknown. There was no previous information about the soil S properties of these sites. The hypothesis under investigation is that soil properties and aspects of S cycling through soils are responsible for low S availability on these sites. The lack of background information on the S dynamics at these sites dictated that some screening of the causes of low S availability be done initially. Some potential origins of the low S status and mechanisms for preliminary evaluation are listed below. Processes that were not expected to be of major importance on these sites were not investigated; for example, dissimilatory S reduction or high atmospheric S inputs. possible origins of low S availability evaluation parent materials low in S S concentration and content in lowermost (BC or C) horizon large quantity of adsorbed S 0 4 determination of phosphate-extractable S 0 4 low S mineralization estimate of mineralizable-S To evaluate the role of soil properties in S availability, the first step was to identify differences in soils at the S-deficient (Prince George) and S-sufficient (Nelson) sites. This information was required to direct the study toward the relevant aspects of S cycling. The second step was to locate the point or points in S cycling at which S limitations appeared to develop. Finally, relationships between soil properties and S availability were evaluated. The soil and foliar properties in this data set were chosen to achieve a balance between processes controlling soil nutrient availability, and properties which can realistically be measured by forest managers and applied across a range of sites. 29 C. METHODS 1. Soil Nutrient Concentration a. Sampling Procedure Three soil pits were dug in unfertilized areas at each of the ten study sites described in Table 1 in July and August 1992 and August 1993. To minimize disturbance to sample trees, soil pits were located outside plot boundaries. In the installations containing single-tree plots, pits were located between plots, well away from fertilized areas. In the fixed-area installations, pits were located outside control (unfertilized) plot buffer strips. Wherever possible, pits were dug to the depth of the control section (Agriculture Canada Expert Committee on Soil Survey 1987). Soil profiles were described according to B.C. Ministries of the Environment and Forests (1990) and Canadian Soil Information System (Agriculture Canada Expert Committee on Soil Survey 1983) criteria. Surface organic soil (L,F,H) and mineral soil were sampled by horizon following description. Detailed profile information is shown in Appendix II. Soils were classified to the Subgroup level (Appendix II) (Agriculture Canada Expert Committee on Soil Survey 1987). Podzolic horizons were confirmed with chemical data. Samples were kept in plastic bags in coolers with ice packs for the remainder of the day until transfer to refrigerated storage (5° C). Samples were air-dried upon return to the laboratory. Green tissue, woody debris, and cones were removed from forest floor material prior to grinding in a Wiley Mi l l with a 2 mm screen. Mineral soils were passed through a 2 mm sieve. Subsamples of the 2 mm fraction were crushed to a smaller mesh size where required for analyses. A l l concentration data are expressed per unit mass of oven-dry soil (105° C for 24 hr). Concentrations of N H 4 - N and N 0 3 - N are expressed as N H 4 and N 0 3 , respectively. Sulphur constituents are expressed in concentration S. b. Soil Analysis Laboratory analyses were conducted in four locations: the B.C. Ministry of Forests Research Laboratory, Victoria, B.C., Pacific Soil Analysis Inc., Richmond, B.C., MacMillan Bloedel Forest 30 Sciences Laboratory, Nanaimo, B.C., and by the author in the Departments of Forest Science and Soil Science at The University of British Columbia. For all chemical analyses, hidden duplicate samples and reference samples were included to evaluate the precision and accuracy of the procedures. Reference samples were obtained from an International Soil Reference and Information Centre laboratory evaluation study, a Canadian Forest Service cross-laboratory study, and the Department of Soil Science, UBC. Duplication and use of reference samples was also done on an in-house basis within labs. i. Soil S Properties Some forms of soil S are measured directly, while others are determined by subtraction. The determination of S constituents is outlined in Figure 2. Total inorganic-S04 was taken as the total inorganic-S fraction. Inorganic-S forms more reduced than S 0 4 were not determined in this study for two reasons. First, it was assumed that reduced S forms were negligible in these soils. Soils were generally well to rapidly drained, with mottles indicative of gleying present only in lower horizons of six profiles. Reduced S forms were likely present during some portion of the year in those horizons, but neither the length of time which these forms were present, nor whether that time coincided with the time of soil sampling was known. Secondly, oxidation of reduced S forms (other than stable S 2 minerals) would presumably occur during sampling and sample handling. Specific techniques for sampling and processing soils to prevent oxidation of reduced S would need to be employed for these determinations. Total-S was determined with a Leco SC-132 S Analyzer (David et al. 1989). Soluble inorganic-S 0 4 was extracted from forest floor samples in 0.01 MNFLC1 (Maynard et al. 1987) (forest floor soluble-S04). Inorganic-S04 was extracted from separate subsamples of mineral soil in Ca(H 2 P0 4 ) 2 (500 mg P L"1) and distilled, deionized water (Maynard et al. 1987; Kalra and Maynard 1991). Sulphate in extracts was measured by Waters IC. Samples were filtered through a 0.45 pm filter prior to analysis to reduce interferences from mineral or organic colloids (Freney 1958; Tabatabai 1982). Sulphate in the phosphate extract measured by IC is the total inorganic-S04 fraction (Kowalenko 1993a), while S 0 4 removed by 31 TOTAL-S ORG/ iNIC-S INORGANIC-S CARBON-BONDED-S ORGANIC-S04 INORGANIC-S04 hydriodic acid reducible-S REDUCED INORGANIC-S Property Total-S lnorganic-S04 Hydriodic acid reducible-S Organic-S04 Carbon-bonded-S Organic-S Reduced inorganic-S Determination LecoSC-132 Analyzer extraction and measurement by ion chromatography modified Johnson-Nishita procedure on entire soil hydriodic acid reducible-S less inorganic-S04 total-S less hydriodic acid reducible-S organic-S04 plus carbon-bonded-S not determined in this study Figure 2. Constituents of soil sulphur and summary of their determination. 32 water is soluble inorganic-S04 (Fuller et al. 1985). These fractions will be referred to as total inorganic-S0 4 and soluble-S04, respectively. Hydriodic-acid reducible-S (HI-S) was determined colorimetrically in soil by a modified Johnson-Nishita procedure (Johnson and Nishita 1952; Kowalenko and Lowe 1972). Sulphur reduced by hydriodic acid includes both organic and inorganic-S04 forms (Freney 1961; Kowalenko 19936). Organic-S04 was estimated by subtraction of total inorganic-S04 from HI-S (Landers et al. 1983). Carbon-bonded-S values were obtained by subtraction of HI-S from total-S. Total organic-S is the sum of organic-S04 and C-bonded-S. Soluble-S was extracted from forest floor samples in 0.01 M N H 4 C 1 and measured on an A R L 3560 ICP spectrophotometer (Kalra and Maynard 1991). The soluble-S fraction includes the soluble portions of the organic-S04 and C-bonded-S pools, and inorganic-S04 (D. Maynard, personal communication). A l l soil S extractions were done in 10:1 solution to soil ratio. i i . Additional Soil Analyses Soil pH was measured in distilled water and in 0.01 M C a C l 2 (Kalra and Maynard 1991). Total C and N were determined by a Leco CHN-600 Analyzer. Organic C was.determined by wet oxidation (Kalra and Maynard 1991) for mineral soil samples with pH in 0.01 M C a C l 2 > 6.5, as carbonates were suspected. Inorganic C concentration was estimated as the difference between total and organic C concentrations. Element ratios involving C are based on organic C values for all samples. The CaC0 3 equivalent of calcareous soils was determined from the inorganic C concentration. Exchangeable N H 4 and N 0 3 were extracted in 2 M K C 1 and measured on a Technicon Auto Analyzer. Total mineralizable N was determined by anaerobic incubation (Powers 1980). Available P was determined by extraction in Bray-Pl solution, reduction by Murphy and Riley (1962) solution, and measured colorimetrically with a UWVisible spectrophotometer (Kalra and Maynard 1991). 33 Pyrophosphate extractable iron and aluminum were determined by ICP analysis for identification of podzolic B horizons (Agriculture Canada Expert Committee on Soil Survey 1987) (data not shown). Exchangeable calcium (Ca), magnesium (Mg), and potassium (K) were extracted in 1 M N H 4 O A c at pH 7.0 and measured by A R L 3560 ICP spectrophotometry (Kalra and Maynard 1991). To determine cation exchange capacity (CEC), samples were then washed with ethanol and the remaining N H 4 exchanged with 10% NaCl. Ammonium in the leachate solution was measured colorimetrically on a Technicon Auto Analyzer. Partial base saturation is the sum of exchangeable Ca, Mg, and K expressed as a percentage of the CEC. c. Data Collation The soils were sampled by horizon, which vary among pits with respect to identity, depth in the profile, and thickness. To provide a basis for averaging data from individual pits within a site, samples were grouped as follows. i. Forest Floor Samples The forest floor horizons present at these soil pits were thin and variable. F horizons were most consistently observed and were present at 28 of the 30 pit locations. The average thickness of the F horizon across all ten sites (n = 28) was 2 cm. A site mean for forest floor chemical properties was obtained by averaging F horizon data from each of the three pits. Where no F horizon was present at a pit, the mean of the other two pits was used. Regional means are the averages of sites within the Prince George and Nelson Regions. ii . Mineral Soil Samples Data from two depths of mineral soil are considered for nutrient concentration. The first depth is representative of the upper B horizon soil. Data from the first three B horizons per pit were averaged, weighted by horizon thickness. 34 The exception was the Canal Flats site, where only the first B horizon in each pit was used as the pit estimate. For some horizons at this site HI-S concentrations were greater than total-S concentrations. The error lay in the total-S analysis, as discussed further under D. Results and Discussion, 1 a. These values were omitted as a number of further calculations involved subtraction from total-S. For consistency within the site, the first B horizon from each pit was included. The mean depth to the lower boundary of the third B horizon (including A horizons where present) was 52 cm (range 24 to 92 cm) for the Prince George sites (n = 18) and 48 cm (range 26 to 85 cm) for the Nelson sites (n = 12). This portion of the profile reflects the processes of soil development occurring at these sites. The depth-weighted means of B horizon soil properties of the three pits per site were averaged to determine a site mean. Regional means are averages of Prince George Region and Nelson Region site means. The second depth in the profile for which concentration data are presented includes the lowermost horizons sampled. These were either single C horizons (20/30 pits), the depth- weighted mean of IC and IIC horizons (4/10), or B C horizons where C horizon material could not be sampled (6/10). It was assumed that these samples were representative of the soil least affected by pedogenesis, and may reflect characteristics more closely related to parent material properties than samples from higher in the profile. Mean depths to the lower boundaries of the deepest horizons were 97 cm and 112 cm for the Prince George (n = 18) and Nelson Region soils (n = 12), respectively. A mean value for the three pits per site was determined, and site and regional means calculated as above. 2. Bulk Density and Soil Nutrient Content a. Forest Floor Fifteen estimates of forest floor bulk density per site were determined. Forest floor was removed from the upper surface of the F horizon to the forest floor-mineral soil interface within a 20 cm x 20 cm quadrat. The depth of the forest floor was measured at each of the four quadrat corners. The four depths 35 were averaged to obtain a mean forest floor depth per sample. Samples were oven dried at 105° C for 24 hr. Bulk density was calculated as the oven-dry mass of the forest floor volume. The fifteen estimates were averaged to obtain a site mean. b. Mineral Soil Fifteen estimates of surface mineral soil bulk density were made per site. A 7.5 cm x 7.5 cm soil core was taken vertically from the surface of the mineral soil. Samples were placed in plastic bags, and oven dried at 105° C for 24 hr. Bulk density was calculated as the oven-dry mass of the core volume. The fifteen estimates were averaged to obtain a site mean. One estimate of subsurface soil bulk density was taken per site. An undisturbed soil surface was exposed at 10 cm depth. A volume of soil was removed from the 10 cm surface to a depth of 30 cm. The cavity was lined with plastic, and filled with water to up tol 0 cm below the soil surface. The volume of water required to fill the cavity to that depth was recorded. The excavated soil was oven dried, and bulk density was estimated as the oven-dry mass of the cavity volume. Coarse fragment content by volume was estimated visually for each mineral horizon. The mean coarse fragment content of any A horizons present and the first B horizon were used as an estimate of the coarse fragment content of the surface mineral soil. The coarse fragment content of the remaining mineral soil horizons was averaged to obtain an estimate for the lower soil horizons. Carbon, N , P, S constituent, and exchangeable cation contents of the fine soil fraction were calculated for each horizon. Nutrient contents in A and first B horizons were estimated using surface bulk density less surface coarse fragment estimates. Nutrient contents in lower horizons were estimated using subsurface bulk density and subsurface coarse fragment estimates. Nutrient contents of individual horizons within a pit were summed to obtain broader depth classes for graphical representation (forest floor, A horizon, upper three B horizons, lower B and C horizons). For 36 the Canal Flats site, horizons for which nutrient concentrations could be calculated were used in the sum. A depth-weighted average of the three pits per site was determined for each depth class. Sampling was done by horizon, not depth, and the total depth of soil sampled varied with the profde. Detailed comparisons of nutrient contents among sites were not done. However, the nutrient content of the first 50 cm of mineral soil was estimated for comparison between regions. This corresponds to the average depth at which there was a vertical transition in fine root abundance from "plentiful" (10 to 100 dm"2) to "few" (< 10 dm"2) (B.C. Ministries of the. Environment and Forests 1990). Across all soil pits (n = 30), this depth was 48.9 cm. Nutrient contents of mineral horizons above the transition were summed and standardized to 50 cm. Site and regional means were determined as previously described. 3. Mineralizable-S and N (Aerobic Incubation) a. Sampling Procedure Soil samples were collected in August and September 1993 for the laboratory incubation study. One forest floor and one mineral soil sample were collected from each of five control (unfertilized) plots at the ten study sites. Forest floor material (F or FH) was obtained by removing fresh litter and collecting the underlying organic material to the surface of the mineral soil. Care was taken not to include mineral soil in the sample. Green tissue (foliage, moss, etc.), large woody debris, cones and animal droppings were removed from the samples by hand-sorting immediately after sampling. Samples were well mixed and stored in plastic bags. Bulk mineral soil was collected to a depth of 30 cm below the mineral surface. Soils were passed through a 4 mm sieve prior to bagging to remove large roots and coarse fragments. A l l samples were kept in coolers with ice packs for the remainder of the day until transfer to refrigerated storage (5° C). Samples were kept refrigerated until the incubation experiment was established (maximum 15 days). 37 b. Incubation Procedure Four subsamples of each forest floor and mineral soil sample were taken. Mineral soils were sieved (2 mm) and forest floor samples were ground in a Wiley mill with a 2 mm screen. One subsample was used to determine the moisture content of the sample by difference in weight prior to and following drying at 105° C for 24 hr. A second subsample was extracted moist to estimate extractable nutrient concentrations (method following). A third subsample was air-dried for analysis of total N and total-S. The fourth subsample was used to establish an aerobic laboratory soil incubation. A closed incubation system was used to estimate net mineral izable-S04, N H 4 , and N 0 3 , with extractable nutrients measured at the beginning and end of the incubation period (Maynard et al. 1983; Valeur and Nilsson 1993). A constant oven-dry mass equivalent of forest floor (12 g) and mineral soil (42 g) was used for each sample incubation. The ambient moisture contents of each sample were used to determine the amount of field-moist sample to be used for the dry-mass equivalent. The soil was placed in a 1 L plastic tub. Soil samples were brought to a moisture content equivalent to field capacity and 80% of field capacity (Maynard et al. 1983) for forest floor and mineral soil, respectively. Field capacity for each sample was determined by saturating a uniformly filled cylinder of soil and allowing the soil to equilibrate on a tension table under the tension of a 1 m water column for 24 hr. The moisture content at field capacity was estimated as the moisture content of the soil following equilibration, and was determined by difference in mass after drying at 105° C for 24 hr. This method provided a basis for establishing a moisture content for these soils in the disturbed conditions of the incubation. The mass of moist soil at field capacity or 80% of field capacity corresponding to the dry mass equivalent was determined. Samples were brought to that mass by addition of distilled water and mixed well. Each tub was covered with a thin polyethylene bag allowing oxygen and carbon dioxide exchange but minimal moisture loss (Eno 1960; Gordon et al. 1987). The soils were incubated at 22° C for 32 days. A one-month incubation estimates mineralization from the labile soil organic matter pool, with greatest 38 changes in extractable S 0 4 observed within the first 4 wk of incubation (Kowalenko and Lowe 1975a; Binkley and Hart 1989). The samples were reweighed after 14 days and moistened to the original mass. At the end of the incubation, the soils were extracted to determine final extractable S0 4 , N H 4 , and N 0 3 concentrations. c. Extraction and Analysis Subsamples of fresh and incubated soils were extracted similarly for initial and final nutrient concentrations, respectively. Extractable S0 4 , including organic and inorganic-S04 forms, was used as the estimate of mineralizable-S04 (Kowalenko and Lowe 19756). Forest floor samples were extracted in 0.01 M N H 4 C 1 (Maynard et al. 1987) and mineral soils in Ca(H 2 P0 4 ) 2 (500 mg P L"1) (Kalra and Maynard 1991). Ten g of moist soil was shaken in 100 mL of solution for 1 hr, filtered, and refrigerated until analysis. The hydriodic-acid reduction method was used to measure reducible-S in the extracts (Kowalenko and Lowe 1972). Inorganic-S04 was not determined separately for these samples. Results are expressed per unit mass of oven dry soil. Forest floor and mineral soil samples were also extracted in 2 M K C 1 for determination of extractable N H 4 and N 0 3 on an Alpkem RFA 300 Autoanlyser. Total-S was determined on a Leco SCI32 S Analyzer. Total N was determined by a semi-micro Kjeldahl digestion (Canadian Society of Soil Science 1978) and measurement on a Technicon II Auto Analyzer. Net mineralizable nutrient concentrations are calculated as final extractable values less initial values. Negative net mineralizable nutrient values indicate that net immobilization occurred. Five replicate values per site for net mineralizable nutrients, total N , and total-S concentrations were averaged to obtain site means. Regional means are averages of the means from either the six Prince George Region or the four Nelson Region sites. 39 4. Nutrient Resorption and Litter S Concentration Sampling Green foliage was sampled in July and August 1992. At the study sites containing single-tree plots, one tree in each of five control (unfertilized) plots was sampled. In fixed-area plots, five trees immediately outside control plot buffer strips were sampled, distributed across the site. Two branches per tree were removed with a pole pruner from one-third to one-half of the distance from the top to bottom of the live crown (Ballard and Carter 1985). Needles from the oldest remaining age class were removed and placed in plastic bags. Foliage removed from branches of the same tree was combined to form one composite sample per tree. Samples were kept in coolers with ice packs until transfer to refrigerated storage (5° C) at the end of the day, and oven-dried as soon as possible (70° C for 24 hr). In October 1992, fresh needle litter was collected from branches of the same trees that had been sampled for green foliage. Litter samples were kept cool until drying at 70° C for 24 hr. Oven-dried tissue was ground in a Waring blender prior to chemical analysis. Nutrient resorption is calculated as the difference between nutrient concentrations in green foliage and fresh litter, expressed as a percentage of the green foliage concentration. Negative resorption values for S0 4-S indicate greater S0 4-S concentrations in litter than in green tissue. The five replicate values per site for percent nutrient resorption were averaged to obtain site means. Regional means are averages of Prince George Region and Nelson Region site mean. 5. Foliar Nutrient Concentration Total N was measured by Leco CHN-600 Analyzer. Total-S was measured with by Leco SC-132 S Analyzer. Foliar S0 4-S was determined by extraction of boiling tissue in 0.01 M HC1, followed by hydriodic-acid reduction of the extract and colorimetric determination (Sanborn and Ballard 1991). Phosphorus, Ca, Mg, K , and micronutrient cations were determined by microwave digestion and measurement on an A R L 3560 ICP spectrophotometer (Kalra and Maynard 1991). Boron was measured 40 colorimetrically in HC1 following dry ashing. Results are expressed per unit weight of oven-dried tissue (70° C for 24 hr). 6. Correlation of Soil Properties Relationships among B horizon soil properties were determined using correlation analysis. Total-S, organic-S, C-bonded-S, organic-S04, soluble-S04, organic C, and total N values of individual samples from the first three B horizons per pit were used in the correlation analysis. 7. Soil and Foliar Data Correlation To evaluate the relationships between soil properties and foliar S properties across the range of S availability, simple linear regressions were done using foliar S properties as dependent variables, and soil properties as independent variables. Foliar S, SCyS, SCyS, N:S, and N were tested against concentrations of S constituents in F, B , and C horizon soil, and mineralizable-S and N from forest floor and mineral soil. Additional soil chemical properties tested were pH, organic C, total N , C:S, N:S, and C:N ratios, extractable P, N H 4 , and exchangeable Ca. Foliar nutrient data from unfertilized trees measured in the same year as soil sampling were obtained from R. Brockley, B.C. Ministry of Forests. Soil and foliage were sampled separately, so the data for individual soil and foliar samples could not be regressed. Site means for soils and foliage were used in the regressions. Means of three composite samples (n = 5) per site were averaged to obtain foliage site means. Site means of soil nutrient concentration (F, B, and C horizons) as described previously were used in the correlations, except for the Canal Flats site. For soil and foliar correlations at the Canal Flats site, the depth weighted mean of the first three B horizons was used as the pit mean of Hl-S, soluble-S04, total inorganicSCy organic-S04, and organic C concentration. These parameters were measured independently 4 1 of total-S and can be considered individually. Inclusion of three B horizons gives a better estimate of the nutrient concentration for use in the correlations. 8. Statistical Analysis a. Soil and Foliar Properties in Prince George and Nelson Regions Regional differences in soil nutrient concentrations, mineralizable nutrients, foliar nutrient concentrations, and nutrient resorption were determined using a nested analysis of variance (<* = 0.05). In this design, sites were nested within regions (Hicks 1982; Shen 1995). Regional differences were tested against the site-within-region differences. Site-within-region differences were tested against the error from observations within sites. To be significant, the regional differences must be greater than the site-within-region differences, which must in turn be greater than the error associated with individual observations at each site. Site-within-region differences were determined in the analysis. Some of the variability in site properties will be discussed but statistical differences among sites will not be presented. The model was Y=constant + region + site(region) + error. A l l data were tested for homogeneity of variance (<* = 0.01) prior to analysis of variance. Where variances were heterogeneous, data were transformed, and analyses performed on the transformed data. Logarithmic, reciprocal, reciprocal of square root, and arcsine transformations were used. Statistical analyses were done on SPSS 7.0 (SPSS Inc. 1996). b. Correlation of Soil Properties Correlations between soil variables were examined using bivariate correlations (SPSS Inc. 1996). Pearson's correlation coefficient and the significance of the correlation coefficient were determined. 42 c. Soil and Foliar Nutrient Correlations Each combination of soil and foliar properties was tested individually to isolate single properties indicative of S pools having a significant relationship to foliar S. Simple linear regression analyses between soil and foliar site means was done with SPSS, generating an r2 value and a regression analysis of variance (<* = 0.05). D. RESULTS A N D DISCUSSION 1. Limitations of the Methodology a. Soil S Analyses A particular problem in the measurement of soil S is the estimation of a number of constituents indirectly by subtraction. Measurement error for the directly determined components of total-S is then carried through the entire calculation (Wieder et al. 1985; Kowalenko 19936). Specifically, there are no direct methods for measuring the organic-S fractions (Tabatabai 1992). Carbon-bonded-S can be estimated by reduction with Raney-nickel, although not all of the C-bonded-S is recovered (Tabatabai 1996). Carbon-bonded-S is more simply estimated as total-S less HI-S, and organic-S04 is generally estimated as the HI-S fraction less inorganic-S04(Blanchar 1986; Kowalenko 19936). This is a reasonable approach provided 1) there is confidence in all of the directly measured fractions, and 2) the inorganic-S04 removed by P-extraction and measured on the IC accounts for all of the inorganic-S04. Based on the results of duplicate and reference sample analysis, the greatest confidence in the analyses done in this study lies in the HI-S, total inorganicS04, and soluble-S04 fractions. There is uncertainty associated with the total-S values for samples of low concentration. In addition, organic-S04 was likely overestimated in some soils, due to the presence of S 0 4 minerals and reduced inorganic-S. In this study total-S was determined with the Leco SC-132 S Analyzer. David et al. (1989) indicate that the Leco Analyzer is sensitive to S concentrations as low as 7 ug g"1. However, Prietzel et al. (1995) found the Leco Analyzer to underestimate total-S in soils with concentrations less than 80 fig g"1, 43 which was the case for 90% of the B horizon samples in this study. The lowest value for total-S concentration determined here was 60 pg g 1 . Many samples had this value, suggesting that the lower limit of detection had been reached. The Leco has been found to be less precise and accurate than other methods of total-S determination, and it is possibly better suited to broad estimates of S concentration (Tabatabai 1996). The implications of underestimating the total-S concentration is that estimates of fractions determined by subtraction from total-S are no longer accurate. This applies to C-bonded-S and organic-S (Figure 2). For some of the B horizon samples in this study, the values of HI-S exceeded the values for total-S, and these samples were omitted from the site and regional means of S concentrations (discussed under C. Methods, 1 c ii). The samples were from a Nelson Region site (Canal Flats) with high HI-S concentrations, and their removal resulted in underestimates for the Hl-S and organic-S04 fractions. The net result was that regional means for HI-S and organic-S04 concentration did not reflect the contribution of this site, and there were very few regional differences for B horizon soil. These differences were more apparent in the C horizon soil where all data were included. While removal of some of the Canal Flats data allowed calculation of the S constituent concentrations for that site, it did not address the problem of possible underestimation of total-S concentration in the remaining soils. If it is assumed that total-S is underestimated by Leco determination where concentrations are less than 80 pg g"1, as indicated by Prietzel et al. (1995), then determinations at concentrations above 80 pg g - 1 should be more accurate. The maximum B horizon total-S concentration determined in this study was 112 pg g - 1 (Golden, Bm), which is still relatively low. Therefore, while total-S concentrations were likely underestimated in this study, is is also likely that they are actually low. This issue could be further addressed by comparing results from the Leco analysis with results done by other methods of total S determination, or by calibrating the Leco for low S concentrations. Another area of inconsistency was the total inorganic and soluble-S04 concentration in mineral soils. Total inorganic-S04 includes both adsorbed and water soluble-SQ4 (Kowalenko 1993a). Soils vary in 44 their capacity to adsorb S0 4 , and the proportion of phosphate-displaced S 0 4 that is strongly adsorbed varies as well. Adsorbed S 0 4 is determined either by phosphate extraction following water extraction on the same sample (Johnson and Todd 1983) or as the difference between P 0 4 and water extractable S 0 4 on different samples (Fuller et al. 1985). It was initially intended to use the latter approach to estimate adsorbed S 0 4 in this study. However, in 20% of the B horizon samples, soluble-S04 values exceeded total inorganic-S04 values. These were all upper B horizons with a maximum depth of 30 cm, where adsorption is expected to be limited. The relative proportions of soluble and adsorbed S 0 4 removed in the phosphate extraction are not known. Given the range of soil pH and other properties influencing S 0 4 adsorption across these sites, it could not be assumed that adsorption was comparable across sites and that the difference between total inorganic and soluble-S04 represented adsorbed S 0 4 Total inorganic and soluble-S04 were simply used as individual parameters. Total inorganic-S04 concentration in B and C horizon soil varied from below detection to 18 pg g"', representing <1% to 26% of the total soil S. Relationships were weak (r2 < 0.10) between total inorganic-S04 concentration and pyrophosphate extractable A l and Fe, C, and pH of horizons tested for podzolic B status (n = 36). Variable amounts of total inorganic-S04 are also reflected in HI-S values. From 5% to 31% of the B horizon HI-S was total inorganic-S04. The HI-S fraction less total inorganic-S04 is a more consistent property than HI-S for the estimation of organic-S04, provided that all inorganic-S04 is P-extractable. An analytical problem that has been associated with water extraction of S 0 4 is the dispersion of soil colloids and overestimation of S 0 4 by colorimetric and turbidimetric determinations (Adams and Lane 1984; Tabatabai 1992). Water-extractable S 0 4 was determined on these samples by ion chromatography, which is specific for the S 0 4 anion (Kalra and Maynard 1991). Extracts are filtered prior to analysis to reduce interferences. 45 b. Foliar SCyS Analysis The presence of organic-S04 in conifer foliage has neither been established nor disproved (Howarth and Stewart 1992). Unless foliar SCyS analysis is specific for the inorganic-S04 anion, both inorganic and organic forms are measured (Richter and Johnson 1983; Johnson 1984). In this study, SCy S was determined by hydriodic-acid reduction, in which organic and inorganic forms of S 0 4 are recovered (Guthrie and Lowe 1984). The proportions of organic and inorganic foliar SCyS in these stands, their role in S storage, and their relative importance as indicators of S status are not known. 2. Soil Nutrient Concentrations Regional means of F, B, and C horizon soil S constituents are shown in Tables 2, 3, and 4. Proportions of S constituents in mineral soil are also shown in Figure 3. Other chemical properties of the soils are shown in Tables 5, 6, and 7. Statistical analyses were done for regional differences, with results shown in Tables 2 to 7. Site means for soil properties are shown in Appendices III to V . F-horizon properties are shown in Appendix III, and B and C horizon properties are shown by site in Appendices IV and V. Exchangeable cations, CEC, partial base saturation, and pH in individual B and C horizons are shown in Appendix VI. Regional means for these properties in B horizon soil are shown in Appendix VII. No statistical analyses were done for exchangeable cations or CEC in forest floor or mineral soil. Site C:N:S ratios are given for B horizon soil, and CaC0 3 equivalent for B and C horizon soil (Appendices IV and V). Where means result from individual observations (site means), the standard deviation is given with the mean. Where values are averages of means (regional means, site means of weighted averages from soil pits), the standard error of the estimate is given. 46 Table 2. F horizon S constituents: regional means of concentration, percent of total-S, and percent of organic-S. Constituents that are significantly different between regions are in bold type. Constituent Prince George Region Nelson Region total-S (%) 0.12 (0.04) 0.10(0.01) HI-S Cug g 1 ) 309.0 (150.0) a 115.4 (20.3) b forest floor soluble-S04 (>ig g"1) 51.7 (19.2) a 27.1 (3.6) b organic-S04 (/ug gl ) 257.4 (131.2) a 88.4 (17.8) b C-bonded-S (/ug g 1 ) 920.7 (210.7) 937.1 (118.3) organic-S (/ug g 1 ) 1178.1 (337.2) 1025.4(134.5) soluble-S Cug g"1) 71.6(19.0) 57.9(3.3) HI-S as % of total-S 21.5 (4.0) a 10.9 (0.7) b forest floor soluble-S04 as % of total-S 4.0 (0.3) a 2.6 (0.2) b organic-S04 as % of total-S 17.6 (3.9) a 8.3 (0.8) b C-bonded-S as % of total-S 78.5 (4.0) b 89.1 (0. 7) a organic-S as % of total-S 96.0 (0.3) b 97.4 (0.2) a soluble-S as % of total-S 6.1 (0.4) 5.7 (0.7) organic-S04 as % of organic-S 18.3 (4.1) a 8.5 (0.9) b C-bonded-S as % of organic-S 81.7 (4.1) b 91.5 (0.9) a organic-S04:C-bonded-S 0.3 (0.1) a 0.1 (0.01) b Prince George Region: n = 18 (3 pits per site; 6 sites) Nelson Region: n = 12 (3 pits per site; 4 sites) Standard errors are shown in parentheses. Different letters for regional means of the same constituent indicate differences at <* = 0.05. 47 Table 3. B horizon soil S constituents: regional means of concentration, percent of total-S, and percent of organic-S. Constituents that are significantly different between regions are in bold type. Constituent Prince George Region Nelson Region total-S fag g 1 ) 64.0(1.6) 65.4 (2.9) HI-S (Mg g 1 ) 21.0 (3.1) 20.3 (5.7) total inorganic-S04 (/^ g g - 1 ) 3.4(1.3) 2.5 (0.6) soluble-S04 (,ug g'1) 0.8 (0.3) b 2.1 (0.8) a organic-S04 (jxg g 1 ) 17.7 (2.1) 17.8 (5.2) C-bonded-S (pig g 1 ) 43.0 (1.5) b 45.2 (4.5) a organic-S (/ug g"1 ) 61.0(0.9) 62.9(3.0) HI-S as % of total-S 31.6 (3.7) 30.1 (8.2) total inorganic-S04 as % of total-S 4.9(1.8) 3.8(1.0) soluble-S04 as % of total-S 1,2 (0.5) b 3.2 (1.3) a organic-S04 as % of total-S 26.7 (2.6) 26.3 (7.5) C-bonded-S as % of total-S 68.4 (3.7) 70.0 (8.2) organic-S as % of total-S 95.1 (1.8) 96.2(1.0) organic-S04 as % of organic-S 28.4 (3.0) 27.6 (8) C-bonded-S as % of organic-S 71.6 (3.0) 72.4 (8) organic-S04:C-bonded-S 0.5(0.1) 0.5(0.1) Prince George Region: n = 54 (weighted average of first 3 B horizons per pit; 3 pits per site; 6 sites) Nelson Region: n = 36 (weighted average of first 3 B horizons per pit; 3 pits per site; 4 sites) Standard errors are shown in parentheses. Different letters for regional means of the same constituent indicate differences at <* = 0.05. 48 Table 4. C horizon soil S constituents: regional means of concentration, percent of total-S, and percent of organic-S. Constituents that are significantly different between regions are in bold type. Constituent Prince George Region Nelson Region total-S ( M g g 1 ) 61.1 (0.7) 60.0 (0.4) HI-S (^ g g 1 ) 13.7 (1.9) b 25.2 (9.8) a total inorganic-S04 (jxg g"1) 1.1(0.1) 0.8 (0.2) soluble-S04 (p,g g 1 ) 0.5 (0.2) 0.4 (0.1) organic-S04 (jxg g 1 ) 12.6 (1.9) b 24.4 (10.0) a C-bonded-S (fj.g g"1) 47.4 (2.3) a 34.9 (9.6) b organic-S (/ig g 1 ) 60.0 (0.8) 59.2 (5) HI-S as % of total-S 22.5 (3.2) b 41.7 (16.8) a total inorganic-S04 as % of total-S 1.9 (0.2) 1.3(0.4) soluble-S04 as % of total-S 0.8 (0.3) 0.6(0.1) organic-S04 as % of total-S 20.6 (3.2) b 40.4 (16.5) a C-bonded-S as % of total-S 77.5 (3.2) a 58.3 (16.2) b organic-S as % of total-S 98.2 (0.2) 98.7 (0.4) organic-S04 as % of organic-S 21.0 (3.3) b 40.8 (16.6) a C-bonded-S as % of organic-S 79.0 (3.3) a 59.2 (16.6) b organic-S04:C-bonded-S 0.4 (0.1) b 2.2 (1.5) a Prince George Region: n = 18 (3 pits per site; 6 sites) Nelson Region: n = 12 (3 pits per site; 4 sites) Standard errors are shown in parentheses. Different letters for regional means of the same constituent indicate differences at <* = 0.05. 49 oo o N O O (A 0 2 LO O d I I & 8 O ro 0 C/J o 8 8 s • 1 1 C L - O . . c — o S "ff § 5 O c -o % ED § c ° — 0) 00 E _L co co «" o £ -4—• c w 0 I tt c cn a) w c Q 1 g C O) O <D o or 00 c o c o - £ 99 U L CO 50 Table 5. F horizon chemical properties: regional means. Properties that are significantly different between regions are in bold type. Property Prince George Region Nelson Region total C (%) 42.90(1.69) 42.23 (1.07) total N (%) 1.17(0.10) 1.28 (0.12) C:S 423 (62)' 430 (49) N:S 11(1) 12(1) C:N 38(3) 35(3) C:organic-S04 3517 (733)b 5640 (923)a PH (H20) 4.48 (0.16) b 4.87 (0.19) a pH (CaCl2) 4.13 (0.17) b 4.56(0.18)a extractable P (pig g"1) 93.6(12.5) 101.0 (21.6) extractable N H 4 (pig g"') 56.32(8.28) 45.67 (8.39) extractable N 0 3 (pig gA ) 2.54 (0.16) 2.67 (0.40) total mineralizable N (pig g'[) 445.6 (70.3) 381.3 (80.2)a Prince George Region: n = 18 (3 pits per site; 6 sites) Nelson Region: n = 12 (3 pits per site; 4 sites) Standard errors are shown in parentheses. Different letters for regional means of the same constituent indicate differences at « = 0.05. n = 9 51 Table 6. B horizon soil chemical properties: regional means. Properties that are significantly different between regions are in bold type. Property Prince George Region Nelson Region mean organic C (%) 0.63 (0.14) b 1.02 (0.35) a total N (%) 0.07 (0.01) b 0.09 (0.02) a C:S 95 (20) b 153 (52) a N:S 11 (1) b 14 (2) a C:N 8(1) 11(2) C:organic-S04 342 (45) b 547 (83)a pH (H20) 5.50 (0.06) b 6.13 (0.38) a pH (CaCl2) 5.03 (0.04) b 5.65 (0.43) a extractable P {pig g"1) 40.5 (7.4) a 14.1 (7.0) b extractable NH 4 {fj.g g"1) 2.52 (0.32) a 1.97 (0.25) b extractable N O s (p.g g"1) 0.31 (0.03) 0.28 (0.11) total mineralizable N (jxg g"1) 4.4(1.7) 1.8 (0.8)a Prince George Region: n = 54 (weighted average of first 3 B horizons per pit; 3 pits per site; 6 sites) Nelson Region: n = 36 (weighted average of first 3 B horizons per pit; 3 pits per site; 4 sites) Standard errors are shown in parentheses. Different letters for regional means of the same constituent indicate differences at « = 0.05. a n = 9 52 Table 7. C horizon soil chemical properties: regional means. Properties that are significantly different between regions are in bold type. Property Prince George Region Nelson Region organic C (%) 0.18(0.01) 0.24 (0.06) total N (%) 0.05 (0.01) 0.05 (0.001) C:S 30 (3) b 39 (10) a N:S 8(l)b 96 (1) a C:N 4 (0.3) 4(1) C:organic-S04 161 (13) 186 (91) PH (H20) 5.84 (0.06) b 7.46 (0.69) a pH (CaCl2) 5.24 (0.07) b 6.48 (0.64) a extractable P (pig g'1) 11.4 (4.4) a 2.3 (1.0) b extractable NH 4 (pig gl ) 1.70 (0.19) a 0.97 (0.15) b extractable N 0 3 (pig g"1 ) 0.17(0.02) 0.14(0.07) total mineralizable N (pig g~l) 0.9 (0.2) 0.1 (0.1)a Prince George Region: n = 18 (3 pits per site; 6 sites) Nelson Region: n = 12 (3 pits per site; 4 sites) Standard errors are shown in parentheses. Different letters for regional means of the same constituent indicate differences at <* = 0.05. a n = 9 53 a. Forest Floor Total-S concentrations in F horizon were 0.12% and 0.10% for the Prince George and Nelson Regions, respectively (Table 2). The range of F horizon total-S values in this study, 0.05% to 0.37%, is broader than the range of 0.10% to 0.20% given by Mitchell et al. (1992) for forest floor material. Forest floor total-S concentrations from other locations are shown in Table 8. Forest floor total-S concentration was not significantly different between regions. Concentrations of F horizon HI-S, forest floor soluble-S04, and organic-S04 were generally two to three times greater in the Prince George soils than in the Nelson soils. Concentrations of total-S, HI-S, forest floor soluble-S04, and organic-S04 were much higher at one Prince George site (Gregg Creek) than all other sites, contributing to the larger values for this region (Appendix III). Regional means are comparable to a luvisolic lodgepole pine site in Alberta (Mitchell et al. 1986). The HI-S, forest floor soluble-S04, and organic-S04 fractions make up a larger proportion of the total-S in the Prince George Region. Proportions of C-bonded-S and organic-S were significantly greater in the Nelson Region, although concentrations of these fractions did not differ significantly. The concentration of soluble-S in the forest floor and the proportion of total-S were not different between the regions. Organic-S comprises over 96% of the forest floor total-S on these sites. Organic-S04 makes up 18% and 8% of total-S on the Prince George and Nelson sites, respectively. Across a range of sites reported on by Mitchell et al. (1992), organic-S04 accounted for 6% to 54% of forest floor total-S (Mitchell et al. 1992). Carbon-bonded-S made up 79% to 89% of the total-S on the same sites. The proportion of organic-S04 in this study appears to be at the lower end of the range, while the proportion of C-bonded-S is at the upper end. Table 8. Total-S concentration in forest soils Location Forest floor total-S (%) B horizon total-S (M-g g'1) Atmospheric S inputs (kg ha"1 yr 1) Reference Interior B.C. 0.05-0.37 60-112 — this study Alberta 0.06-0.13 167 6 Mitchell etal. 1986 Manning Park, B.C. 0.09 — Chaeand Lowe 1980 Port Alberni, B.C. 0.07 240 8 Sanborn and Ballard 1990 Quebec 0.14 440 — Lowe 1964 Quebec 0.17 258-503 7 Houle and Carignan 1992 Ontario 0.09-0.10 300-440 — Neary etal. 1987 Maine 0.12 200-305 — Dhamala and Mitchell 1995 Maine 0.16-0.22 155-740 — Fasth etal. 1991 New York, New Hampshire 0.16-0.17 303-452 — Schindler etal. 1986 New York 0.2 429-540 10 David etal. 1982 New Mexico 0.06-0.11 — Watwood etal. 1986 North Carolina 0.10-0.13 — Strickland et al. 1987 France 0.21 310-350 50 Vannieretal. 1993 Norway 0.07 — Autry and Fitzgerald 1990 Czech Republic 0.21 128-199 71 Novak and Prechova 1995 55 Organic-S0 4 comprised a greater proportion of organic-S than C-bonded-S in the Prince George Region. The ratio of organic-S04 to C-bonded-S was greater in the Prince George Region, reflecting the greater concentration of organic-S04 in this region. Other forest floor chemical properties were similar in the two regions (Table 5). Total C, total N , C:S, N:S, and C:N were not significantly different between regions. The C to organic-S04 ratio was less in the forest floor from Prince George Region than from the Nelson Region. Forest floor pH was greater at the Nelson region sites, likely due to the influence of the calcareous soil found there. There were no differences in forest floor extractable P, N H 4 , and N 0 3 , or total mineralizable N between regions. b. Mineral Soil: B Horizon Total-S in B horizon soil from both regions was about 65 pg g_ 1 (Table 3). The range of total-S values was 60 to 112 pg g"1. These mineral soil total-S values are extremely low compared to literature values (Table 8). These sites are assumed to have low atmospheric inputs, less than 7 kg ha -1 yr"1 S. Locations with comparably low atmospheric S inputs have two to six times more total-S in mineral soil than was measured in these soils. Another range of total-S concentration in mineral soils from forest sites is 50 to 800 pg g"1 S (Mitchell et al. 1992). Soils in this study are clearly at the lower end of the range, but are comparable to the limited S data from the soil surveys for these soil associations (Dawson 1989; Ministry of Environment data provided by H. Luttmerding). There was no difference between regions in B horizon soil total-S concentration. The most notable difference in S constituents in the B horizon was in the soluble-S04 concentration, which was significantly greater in the Nelson Region soils. The Prince George regional mean of 0.78 pg g"' soluble-S04 is similar to that found for other luvisolic B horizons as given by Roberts and Bettany (1985). In that study, luvisolic soils had the lowest soluble-S04 concentrations across a gradient of soil types. Carbon-bonded-S concentration was the only other B horizon property that was 56 significantly different between the Prince George and Nelson Regions, with greater values in the Nelson soils. Data for some B horizon samples from the Canal Flats (Nelson Region) site were not included. In those samples, HI-S concentrations exceeded total-S concentrations (discussed under D. Results and Discussion, 1 a). The HI-S concentrations at the Canal Flats site were the highest observed in the study (up to 134 (ig g"1 ). Their exclusion lowered the regional mean and decreased regional differences in HI-S and organic-S04 concentrations. Differences in the soluble-S04 concentration between regions were apparently great enough that regional differences were present with only one B horizon from the Canal Flats site included. The proportion of soluble-S04 in total-S was also significantly greater in the Nelson soils (Figure 3). The greatest concentrations and proportions of total inorganic-S04 were found in soils from the Tsus Creek and Bowron sites (Prince George Region) (Appendix IV). These were the most podzolized soils sampled. There was a good relationship between pyrophosphate Fe+Al and total inorganic-S04 concentrations in podzolic B horizons from these sites (r2 = 0.76; n = 10). Concentrations of HI-S were relatively high at these sites. This is in part due to the inclusion of total inorganic-S04 in the HI-S determination, but organic-S04 concentrations at these sites were also among the highest values. Proportions of organic-S04 and C-bonded-S in B horizon total-S were about 26% and 70%, respectively (Table 3; Figure 3). These values are within the ranges of 20% to 30% and 50% to 80% described by Mitchell et al. (1992). Proportions of organic-S04 and C-bonded-S are quite consistent across forest soils having different parent materials and vegetation (Mitchell et al. 1986). Organic-S generally made up over 95% of the total-S in B horizon soils. Organic C was assumed to be equivalent to total C where soil pH was less than 6.5 (CaCl 2 ) . For samples with pH ^ 6.5, the presence of inorganic C as carbonates was suspected. In these samples, organic C was estimated directly, and inorganic C was determined by subtraction of organic C from total C (B. Methods, 1 b ii). Mineral soil pH (> 6.5) was plotted against inorganic C concentration in B and C horizon 57 soils to evaluate the relationship of the total inorganic C fraction to pH (Appendix VIII). The poor relationship indicates that other carbonate properties, for example carbonate reactivity or surface area, may be more closely related to soil pH (Kishchuk 1996). Organic C and total N concentrations were greater in B horizon soil from the Nelson Region than the Prince George Region, as were the C:S and N:S ratios (Table 6). Organic C concentrations in the Prince George soils were extremely low, with 74% of the B horizons having less than 1% organic C. Forest mineral soil C:S ratios in the literature vary widely, ranging from 50 to 500. Lower C:S values were observed in this study, which ranged from 8 to 469. Prince George and Nelson regional C:S means were 95 and 153, respectively, and C:N ratios were 10 or less (Table 6). Site C:N:S ratios ranged from 51:8:1 (Cobb Lake) to 303:20:1 (Canal Flats) (Appendix IV). The ratio of C to organic-S04 was greater in Nelson soils than in Prince George soils, indicating low C relative to the 0rganic-SO4 concentration. Soils at three of the Nelson sites (Golden, Lower Gold Creek and Canal Flats) are derived from calcareous parent materials (Kelley and Holland 1961;Lacelle 1990). Soils at the Canal Flats site are the most calcareous (Appendix IV). Despite the likely presence of CaC0 3 -S0 4 complexes and/or gypsum at these sites, total-S concentrations are about the same as at other sites. However, the presence of gypsum or other sulphate minerals would explain the large HI-S values observed at the Canal Flats site, and to a lesser extent the Golden site. Mineral S 0 4 reduced by hydriodic-acid reduction, but not P-extracted and/or measured on the IC would result in an overestimate of organic-S04. Release of S 0 4 from CaC0 3 -S0 4 co-precipitates is by mineral weathering, at rates determined by mineral solubility (Anderson 1988). In general, these minerals are relatively insoluble and contribute little to plant available S (Williams and Steinbergs 1964; Shan et al. 1997). Bedrock near the Gregg Creek (Prince George Region) site contains ultramafic or serpentine minerals, which is reflected in high Mg concentrations in soils from this site (P. Sanborn, personal communication) (Appendix VI). The influence of these minerals on S properties is not known, but the presence of M g S 0 4 minerals is possible. Concentrations of HI-S and organic-S04 in these soils are similar 58 to those in the calcareous and B f horizons, suggesting that there is a significant component of inorganic-S0 4 . If the inorganic-S04 was in mineral form there would also be an overestimate of organic-S04 at this site. Extractable P and N H 4 were greater in the Prince George soils than in the Nelson soils. Low extractable P concentrations in the Nelson soils are likely attributable to two factors: 1) adsorption or precipitation reactions of P with C a C 0 3 or other carbonate minerals (Kishchuk 1996), and 2) underestimation of extractable P in calcareous soils by extraction in Bray -P l solution (Kalra and Maynard 1991). It is possible that lower N H 4 concentrations at the Nelson sites result from increased nitrification, although this is not reflected in N 0 3 concentrations. Partial percent base saturation values could not be determined for many of the calcareous mineral horizons (Appendix VI). An alternative method of exchangeable cation and CEC determination should have been employed on the calcareous soils (Kalra and Maynard 1991). Upper B horizon pH values were as high as 7.5 (CaCl 2) at these sites, and on a regional basis, pH values were significantly higher in the Nelson soils. The optimum pH for lodgepole pine is about 6 (Koch 1996). c. Mineral Soil: C Horizon As in the F and B horizon soils, there was no difference in total-S concentration in C horizon soil between the S-deficient and S-sufficient regions (Table 4). Sulphur concentrations were slightly lower than in B horizon soil, around 60 ug g"1. Soluble-S04 concentrations were not significantly different between regions in C horizon soil, and were lower than in B horizon soil. There was significantly more HI-S and organic-S04 in Nelson soils than in Prince George soils, and less C-bonded-S, a pattern which would have been evident in B horizon soil if all data had been used. The largest concentrations of HI-S and organic-S 0 4 again occurred at the Golden, Canal Flats, and Gregg Creek sites (Appendix V), suggesting the presence of S 0 4 minerals, and the possible overestimation of organic-SCy 59 Differences in the proportions of these constituents in total-S were similar to concentrations (Figure 3). Organic-S04 made up a greater proportion of the organic-S at the Nelson sites, while C-bonded-S was the largest constituent of organic-S at the Prince George sites. The ratio of organic-S04 to C-bonded-S was clearly greater in the Nelson soils, indicating the heavy demand on the organic-S04 pool by S-limited microbial populations (McGill and Cole 1981). Over 98% of the total-S was organic-S. Organic C concentration was below 0.25% in the C horizons. Carbon:S and N:S ratios were greater in Nelson Region soils (Table 7). Extractable NH 4 and P concentrations were greater in the Prince George soils than in the Nelson soils. Extractable P concentrations were nearly five times greater in Prince George C horizon soil. This is again likely due to the presence of carbonates in some of the Nelson soils. The C a C 0 3 equivalents were greater in C horizons of the three calcareous soils than in B horizons, up to 28% at the Canal Flats site (Appendix V). This is attributable to the accumulation of precipitated carbonates in the lower horizons, and less weathering than in the upper horizons (Kishchuk 1996). Maximum pH values in C horizon soil were 7.5 (CaCl 2). There was somewhat more total inorganic-S04 in C horizon soils at the Tsus Creek and Bowron sites than at other sites (Appendix V). However, there was much more P in soils from these sites than other sites, indicating that P adsorption may be replacing S 0 4 at lower depths. d. Changes in S Constituents with Profile Depth i. Total-S and C: all sites Trends in total-S, organic C, C:S, and the proportion of organic-S from F to C horizons at all sites are shown in Figure 4. The high S concentration (0.30%) in Gregg Creek F horizon is evident in Figure 4a. Total-S concentrations at all sites converge at low values in the upper B horizons. The same is observed for organic C (Figure 4b). The C:S declines more gradually, and less consistently with depth (Figure 4c). Narrower C:S ratios in the B horizon than the F horizon are indicative of S accumulation, which could be either organic or 60 10 a. Total-S . . .A 0 500 1000 1500 2000 2500 3000 3500 total-S (ug g"1) b. Organic C 20 30 % C 40 50 60 o ML ••£}•• TC • A • GC • o - CC • v - CL • o B — • — G — • — UGC — A — LGC CF Figure 4. Soil S and C properties with depth: all sites. F, B, and C horizons are indicated on Y axis. Site abbreviations are defined in Table 1. c. Organic C:S 100 200 300 C:S 400 500 92 94 % of total-S 600 o ML • -D • • TC • A GC • • < > • • CC • • v • CL • o - B — • — G . — • — UGC — A — LGC CF 98 100 Figure 4. (Continued). 62 inorganic-S. The trends observed in Figure 4c are similar whether total or organic-S is used. Narrowest values in the C horizon soil probably do not represent further S accumulation; rather, there is likely a balance reached between the downward movement and accumulation of organic C and total-S. Convergence of C:S ratios at values < 60 in C horizons suggests that these horizons contribute little S. Figure 4d shows the differences among the soils at these sites and their S constituents quite clearly. In the B horizons of the Bowron, Tsus Creek, and Canal Flats soils, there is a striking increase in the proportion of inorganic-S04. In the Bowron and Tsus Creek soils, this is due to S 0 4 adsorption in the B f horizons. In the Canal Flats soil, there is likely an accumulation of inorganic-S04 as gypsum or other precipitated S0 4 . The proportions of B horizon inorganic-S at the Gregg Creek and Lower Gold Creek sites are intermediate to the calcareous and podzolic sites, and the remaining sites. i i . Total-S and Constituents: by site Total-S, organic-S04 and C-bonded-S concentrations and C:S ratio at different horizon depths are shown in Figure 5. Deviations from the trend of decreasing total-S concentration with depth are evident for B f horizons at Tsus Creek, Bowron, and Upper Gold Creek sites (Figures 5b, 5f, and 5h). These increases are small in absolute terms, representing a maximum increase of about 50 pg g"1 . The overall decrease in C:S with depth is evident across all sites (Figure 5a-j). As discussed above, the same trends are observed whether total-S or organic-S are considered, indicating that variations in total-S are driven by organic-S. This is not surprising given that at least 95% of the total-S on these sites is in organic form. Changes in organic-S04 and C-bonded-S concentrations were considered to determine if S accumulation with profile depth, as indicated by narrowing of the C:S ratio, was attributable to these constituents. It is evident from Figure 5 that the trend in the organic-S04 concentration most closely resembles the trend in the C:S ratio. Although there are variations in the C-bonded-S concentration with depth, there appears to be little difference between concentrations at the surface and in the lower profile. C/IIC/BC IIC/BC 60 80 100 total-S (ug g 1 ) 120 140 160 • ML pit 1 • • o-ML pit 2 ML pit 3 Organic C:S 100 200 300 400 C:S 500 600 700 Figure 5a. S properties in mineral soil: Meadow Lake site. 3 pits/site: horizons present listed on Y axis as pit1/pit2/pit3 I I 1 1 1 1 1 1 0 10 20. 30 40 50 60 70 organic-S04 (ug g"1) ML pit 1 ML pit 2 ML pit 3 C-bonded-S Bfj/Bf/Ahj -Bfj/Bm/Bf -Bm/Bm/Bfj -Bm -Bm/C/Bm - r C/IIC/BC -1 / i ' o IIC/BC - > T 1 1 r 20 30 40 50 60 70 80 90 C-bonded-S (ug g"1) Figure 5a. (Continued) Ae Bf Bm1/Bm/Bm1 Bm2/BC/Bm2 A BC/C/BC Ae Bf Bm1/Bm/Bm1 A Bm2/BC/Bm2 BC/C/BC Total-S 55 60 65 —i— 50 70 75 80 total-S (ug g"1) TC pit 1 • o - TC pit 2 TC pit 3 Organic C:S 100 150 C:S 85 90 95 200 250 Figure 5b. S properties in mineral soil: Tsus Creek site. 3 pits/site: horizons present listed on Y axis as pit1/pit2/pit3 66 Organic-S04 0 10 20 30 40 50 60 organic-S0 4 (ug g"1) TC pit 1 • o - TC pit 2 TC pit 3 C-bonded-S 20 25 30 35 40 45 50 55 60 C-bonded-S (ug g"1) Figure 5b. (Continued) Ae/Ahe/Ae Bf/Bm1/Bf -| Bm1/Bm2/Bm1 Bm2/Bm3/Bm2 -| C/BCgj/Cg Cgj -) 0 Ae/Ahe/Ae Bf/Bm1/Bf Bm1/Bm2/Bm1 Bm2/Bm3/Bm2 C/BCgj/Cg Cgj 100 Total-S 200 300 total-S (hq g1) • GO pit 1 GO pit 2 GO pit 3 Organic C:S 100 200 300 C:S 400 500 .. • o 400 500 Figure 5c. S properties in mineral soil: Gregg Creek site. 3 pits/site: horizons present listed on Y axis as pit/pit2/pit3 *Ae Bf/Bm1/Bf Bm1/Bm2/Bm1 Bm2/Bm3/Bm2 C/BCgj/Cg Cgj Ae/Ahe/Ae -\ Bf/Bm1/Bf Bm1/Bm2/Bm1 Bm2/Bm3/Bm2 C/BCgj/Cg -| Cgj o-iC o *GC2 Ahe = 542.7 ug g"1 10 15 20 25 30 35 40 organic-S04 (ug g"1) GC pit 1 • o • GC pit 2 GC pit 3 30 35 40 45 50 55 C-bonded-S (ug g"1) — i — 60 65 Figure 5c. (Continued) 69 Ahe/Ae/Aej Bm1/Bmgj1/Bm1 -\ Bm2/Bmgj2/Bm2 Bm3/Bmgj3/Bmcc Cgj/BCgj/C A Total-S 0 T / " / ' " " i » 1 » \ \ I V 50 60 70 80 90 total-S (ug g1) 100 110 CC pit 1 CO pit 2 T CC pit 3 Ahe/Ae/Aej Bm1/Bmgj1/Bm1 Bm2/Bmgj2/Bm2 Bm3/Bmgj3/Bmcc Cgj/BCgj/C Organic C:S 100 200 300 400 500 600 700 C:S Figure 5d. S properties in mineral soil: Cluculz Creek site. 3 pits/site: horizons present listed on Y axis as pit1/pit2/pit3 Ahe/Ae/Aej A Bm1/Bmgj1/Bm1 Bm2/Bmgj2/Bm2 Bm3/Bmgj3/Bmcc Cgj/BCgj/C A Organic-S04 10 15 20 25 organic-S04 (ug g"1) • CC pit 1 CC pit 2 CC pit 3 30 35 Ahe/Ae/Aej Bm1/Bmgj1/Bm1 Bm2/Bmgj2/Bm2 Bm3/Bmgj3/Bmcc Cgj/BCgj/C C-bonded-S 40 45 50 55 60 65 C-bonded-S (ug g"1) 70 75 Figure 5d. (Continued) Ae Bfj/Bfj/Bg1 -| Bm/Bm1/Bg2 BC/Bm2/BCg C/Bm3 55 Ae Bfj/Bfj/Bg1 Bm/Bm1/Bg2 BC/Bm2/BCg C/Bm3 Total-S 60 65 70 total-S (ug g 1) CL pit 1 CL pit 2 CL pit 3 organic C:S 100 200 300 C:S 75 400 80 500 Figure 5e. S properties in mineral soil: Cobb Lake site. 3 pits/site: horizons present listed on Y axis as pit1/pit2/pit3 72 Ae Bfj/Bfj/Bg1 Bm/Bm1/Bg2 -BC/Bm2/BCg -C/Bm3 H O C H Ae Bfj/Bfj/Bg1 Bm/Bm1/Bg2 BC/Bm2/BCg -C/Bm3 -Organic-S04 10 12 14 16 organic-S04 (ug g"1) CL pit 1 CL pit 2 CL pit 3 C-bonded-S o 18 42 44 46 48 50 52 54 C-bonded-S (ug g"1) —i— 20 22 56 58 60 Figure 5e. (Continued) Ae/Ah/Ae Bf/Ae/Bf Bm1/Ahe/Bm1 Bm2/Bf/Bm2 Bm3/Bm1/Bm3 BC/Bm2/BC -\ C/BC/C C Total-S ' . vo 50 60 70 80 90 100 total-S (ug g1) B pit 1 • o • B pit 2 B pit 3 ...o 110 120 Organic C:S Ae/Ah/Ae -Bf/Ae/Bf -Bm1/Ahe/Bm1 - r ;.o Bm2/Bf/Bm2 - w 9"'' 1 Bm3/Bm1/Bm3 - 6 BC/Bm2/BC - V C/BC/C -C - O 200 400 C:S 600 800 Figure 5f. S properties in mineral soil: Bowron site. 3 pits/site: horizons present listed on Y axis as pit1/pit2/pit3 Ae/Ah/Ae -Organic-S04 o Bf/Ae/Bf -Bm1/Ahe/Bm1 -Bm2/Bf/Bm2 -Bm3/Bm1/Bm3 -\ S " ;.;..o BC/Bm2/BC -•f C/BC/C -C - 0 10 20 30 40 organic-S04 (ug g"1) 50 Bp i t 1 • o- B pit 2 B pit 3 60 70 40 50 60 C-bonded-S (ug g"1) 80 Figure 5f. (Continued) 100 200 300 400 500 total-S (ug g"1) 600 700 800 G pit 1 • o- G pit 2 G p i t 3 Ae/Bm/Bm -Organic C:S \ P Bh/Bmk1/Bh -Bm/Bmk2/Bmk1 -Bmk/Bmk3/Bmk2 -BCk/Bmk4/BCk -Ck/Bmk5/Ck -Bmk6 -BCk - p Ck - 0 50 100 150 200 250 300 C:S Figure 5g. S properties in mineral soil: Golden site. 3 pits/site: horizons present listed on Y axis as pit1/pit2/pit3 76 Ae/Bm/Bm Bh/Bmk1/Bh Bm/Bmk2/Bmk1 H Bmk/Bmk3/Bmk2 BCk/Bmk4/BCk Ck/Bmk5/Ck H Bmk6 BCk Ck Organic-S04 \ o. ></ o. \ . \ • \ < • 0 > < 6-...V ' • ' 0 a 20 40 60 80 organic-S04 (ug g"1) 100 • G pit 1 • o- G pit 2 G pit 3 120 140 Ae/Bm/Bm -Bh/Bmk1/Bh -Bm/Bmk2/Bmk1 Bmk/Bmk3/Bmk2 H BCk/Bmk4/BCk Ck/Bmk5/Ck -Bmk6 -BCk -Ck O C-bonded-S missing value for G2 Bmk6 due to organic S 0 4 > total S values 200 400 C-bonded-S ( u g g" 1 ) 600 800 Figure 5g. (Continued) Ae/Bfj/Bfj Bf/Bm1/Bm1 Bm1/Bm2/Bm2 Bm2/BC1/Bm3 Bm3/BC2/IC BC 50 Ae/Bfj/Bfj Bf/Bm1/Bm1 A Bm1/Bm2/Bm2 Bm2/BC1/Bm3 Bm3/BC2/IC BC — i — 60 100 Total-S — i — 70 80 90 total-S (ug g"1) UGC pit 1 • o - UGC pit 2 UGC pit 3 200 300 C:S 100 110 Organic C:S . . . . . . ^ * ^ r ^ / i / i / 400 500 Figure 5h. S properties in mineral soil: Upper Gold Creek site. 3 pits/site: horizons present listed on Y axis as pit1/pit2/pit3 Organic-S04 Ae/Bfj/Bfj -Bf/Bm1/Bm1 -7 / p - y - ' Bm1/Bm2/Bm2 -Bm2/BC1/Bm3 -/ r o •— \ ; 1 * T l\ \ -Bm3/BC2/IC -BC -T 1 1 1 1 r 0 5 10 15 20 25 30 35 40 organic-S04 (ug g"1) UGC pit 1 • o- UGC pit 2 UGC pit 3 C-bonded-S i 1 1 1 1 1 45 50 55 60 65 70 C-bonded-S (ug g"1) Figure 5h. (Continued) 79 Ahe/Ae/Ahe -Ae/Bh/Ae -Bm1/Bm1/Bfj -Bm2/Bm2/Bm1 -Bm3/Bm3/Bm2 -BC/Bm4/Bm3 -Ck/Bm5/BCgj -I ICk1/Cgj -I t IICk1/IIC - -ICk2 - 0 IICk2 - 0 Total-S Ahe/Ae/Ahe Ae/Bh/Ae Bm1/Bm1/Bfj Bm2/Bm2/Bm1 Bm3/Bm3/Bm2 BC/Bm4/Bm3 Ck/Bm5/BCgj ICk1/Cgj IICk1/IIC ICk2 IICk2 40 60 80 100 120 140 160 — i 1 1 1 180 200 220 240 260 total-S (ug g 1) LGC pit 1 • o- LGC pit 2 LGC pit 3 800 Figure 5i. S properties in mineral soil: Lower Gold Creek site. 3 pits/site: horizons present listed on Y axis as pit1/pit2/pit3 Ahe/Ae/Ahe Ae/Bh/Ae Bm1/Bm1/Bfj Bm2/Bm2/Bm1 -Bm3/Bm3/Bm2 -BC/Bm4/Bm3 Ck/Bm5/BCgj ICk1/Cgj IICk1/IIC ICk2 IICk2 40 organic-S04 (ug g"1) 60 80 LGC pit 1 LGC pit 2 LGC pit 3 Ahe/Ae/Ahe Ae/Bh/Ae Bm1/Bm1/Bfj Bm2/Bm2/Bm1 Bm3/Bm3/Bm2 BC/Bm4/Bm3 Ck/Bm5/BCgj ICk1/Cgj -| IICk1/IIC ICk2 IICk2 20 80 100 120 C-bonded-S (ug g"1) 140 160 Figure 5i. (Continued) Ae/Aej/Ae Bh/Bm/Bh Bmk1 Bmk2 BCk/BCk/BCk1 H Ck/Ck/BCk2 55 Ae/Aej/Ae Bh/Bm/Bh Bmk1 Bmk2 BCk/BCk/BCk1 Ck/Ck/BCk2 60 Total-S 65 70 75 80 total-S (ug g 1) 85 90 CF pit 1 • o- CF pit 2 CF pit 3 Organic C:S 95 100 200 300 C:S 400 500 600 Figure 5j. S properties in mineral soil: Canal Flats site. 3 pits/site: horizons present listed on Y axis as pit1/pit2/pit3 Ae/Aej/Ae Bh/Bm/Bh Bmk1 Bmk2 BCk/BCk/BCk1 A Ck/Ck/BCk2 Organic-S04 20 40 60 80 100 120 140 organic-S04 (ug g"1) CF pit 1 • o • CF pit 2 CF pit 3 C-bonded-S Ae/Aej/Ae -Bh/Bm/Bh -Bmk1 - O ' ' Bmk2 -BCk/BCk/BCk1 - p Ck/Ck/BCk2 -\ missing values due to organic S 0 4 > total S values 10 20 30 40 50 60 70 C-bonded-S (ug g" Figure 5j. (Continued) 83 The overall trend of decreasing organic-S04 concentration with depth did not follow as consistent a pattern as the C:S ratio. Organic-S04 concentrations increased relative to the preceeding horizon in B f horizons (Tsus Creek, Gregg Creek, Cobb Lake, Bowron, Upper Gold Creek), calcareous horizons (Golden, Lower Gold Creek, Canal Flats), or where M g S 0 4 is suspected (Gregg Creek). Organic-S04 concentrations again decreased below these horizons. A further mechanism for increased organic-S04 concentrations with depth occurs in gleyed horizons in the lower profile at Gregg Creek, Cluculz Creek, and Cobb Lake sites. Reduced inorganic-S forms were likely present in these horizons, and forms other than sulphides would be reduced by hydriodic acid, if not oxidized during sample handling (Kowalenko 19936). As with mineral S0 4 , this S would be included in the HI-S determination but would not be subtracted as P-extractable S0 4 . It appears that although the HI-S and total inorganic-S04 measurements are made with confidence, estimates of organic-S04 resulting from these measurements are less certain. For Bf horizons and soils without S 0 4 minerals or gleying, it can probably be assumed that HI-S less total inorganic-S04 provides a good estimate of organic-S04. For the other soils, organic-S04 concentrations have likely been overestimated. This fractionation approach may be suited to more acidic soils than were analyzed in this study. ii i . Soluble and Total Inorganic-SQ1 Trends in soluble and total inorganic-S04 concentrations with depth in mineral soils are shown by site in Figure 6. Overall, both constituents decrease with profile depth. Sharp increases in total inorganic-S 0 4 concentration in B f horizons are evident at the Tsus Creek, Bowron, and Upper Gold Creek sites (Figures 6b, 6f, and 6h). The decreasing trend is more consistent for soluble-S04. Where increases in soluble-S04 occur with depth, it is mostly in horizons where there is an accumulation of organic matter. This is evident for Bowron pit 2 (Ahe), Lower Gold Creek pit 3 (Bfj), and Canal Flats pits 1 and3 (Bh) (Figures 6f 6i, and Soluble-S04 Bfj/Bf/Ahj -Bfj/Bm/Bf ->^  Bm/Bm/Bfj -7 Bm - o' • Bm/C/Bm -C/IIC/BC -IIC/BC -f C 0 \ \ 1 N soluble S 0 4 (ug g ) ML pit 1 ML pit 2 ML pit 3 Bfj/Bf/Ahj \ Bfj/Bm/Bf Bm/Bm/Bfj Bm Bm/C/Bm C/IIC/BC IIC/BC Total inorganic-S04 O 1 i — -• on / ^ .6 J o 1 y Y 2 3 4 5 total inorganic-S04 (ug g"1) Figure 6a. Soluble and total inorganic-S04: Meadow Lake. 3 pits/site: horizons present listed on Y axis as pit1/pit2/pit3 Ae Bf Bm1/Bm/Bm1 Bm2/BC/Bm2 BC/C/BC Soluble-SC> soluble-S04 (ug g" TC pit 1 TC pit 2 TC pit 3 Ae Bf Bm1/Bm/Bm1 Bm2/BC/Bm2 A BC/C/BC Total inorganic-S04 ^ i i i i 8 10 12 14 16 18 total inorganic-S04 (ug g"1) Figure 6b. Soluble and total inorganic-S04: Tsus Creek. 3 pits/site: horizons present listed on Y axis as pit1/pit2/pit3 Ae/Ahe/Ae A Bf/Bm1/Bf Bm1/Bm2/Bm1 Bm2/Bm3/Bm2 A C/BCgj/Cg Cgj Ae/Ahe/Ae Bf/Bm1/Bf Bm1/Bm2/Bm1 Bm2/Bm3/Bm2 -C/BCgj/Cg -Cgj o Soluble-SO, 10 15 20 soluble-S04 (u.g g"1) GC pit 1 • o- GC pit 2 GC pit 3 Total inorganic-S04 — i — 10 15 20 total inorganic-S04 (ug g ) 25 — i — 25 30 30 Figure 6c. Soluble and total inorganic-S04: Gregg Creek. 3 pits/site: horizons present listed on Y axis as pit1/pit2/pit3 87 Ahe/Ae/Aej Bm1/Bmgj1/Bm1 Bm2/Bmgj2/Bm2 Bm3/Bmgj3/Bmcc Cgj/BCgj/C i i i i i i 0 1 2 3 4 5 soluble-S04 (ug g"1) CC pit 1 • o- CC pit 2 CC pit 3 Ahe/Ae/Aej Bm1/Bmgj1/Bm1 Bm2/Bmgj2/Bm2 Bm3/Bmgj3/Bmcc Cgj/BCgj/C i 1 1 r 1 ' i 0 1 2 3 4 5 total inorganic-S0 4 (ug g ) Figure 6d. Soluble and total inorganic-S04: Cluculz Creek. 3 pits/site: horizons present listed on Y axis as pit1/pit2/pit3 C/Bm3 Soluble-S04 Ae Bfj/Bfj/Bg1 Bm/Bm1/Bg2 BC/Bm2/BCg -| C/Bm3 c H 1 1 — 2 3 soluble-S04 (ug g"1) CL pit 1 CL pit 2 T CL pit 3 Total inorganic-S04 .o "•o total inorganic-S04 (ug g'1) Figure 6e. Soluble and total inorganic SO4: Cobb Lake. 3 pits/site: horizons present listed on Y axis as pit1/pit2/pit3 Soluble-S04 1 2 soluble-S0 4 (ug g"1) B pit 1 B pit 2 T B pit 3 Ae/Ah/Ae Bf/Ae/Bf Bm1/Ahe/Bm1 Bm2/Bf/Bm2 Bm3/Bm1/Bm3 BC/Bm2/BC C/BC/C C H Total inorganic-SO. — i 1 1 1 1 1 1 1 — 4 6 8 10 12 14 16 18 total inorganic-S04 (ug g"1) 20 Figure 6f. Soluble and total inorganic SO4: Bowron. 3 pits/site: horizons present listed on Y axis as pit1/pit2/pit3 Ae/Bm/Bm -Soluble-S04 Bh/Bmk1/Bh -Bm/Bmk2/Bmk1 -Bmk/Bmk3/Bmk2 -BCk/Bmk4/BCk -Ck/Bmk5/Ck -Bmk6 - 0 ' " BCk - 0 . . . . . Ck - " " • • 0 soluble-S04 (ug g"1) • G pit 1 G pit 2 T G p i t 3 Ae/Bm/Bm Bh/Bmk1/Bh Bm/Bmk2/Bmk1 Bmk/Bmk3/Bmk2 BCk/Bmk4/BCk Ck/Bmk5/Ck Bmk6 BCk Ck total inorganic-S04 (ug g ) Total inorganic-S04 ..O O.' O Figure 6g. Soluble and total inorganic-SC>4: Golden. 3 pits/site: horizons present listed on Y axis as pit1/pit2/pit3 91 Ae/Bfj/Bfj Bf/Bm1/Bm1 A Bm1/Bm2/Bm2 Bm2/BC1/Bm3 Bm3/BC2/IC BC A Soluble-S04 . .o 1 2 soluble-S04 (ug g"1) UGC pit 1 • o - UGC pit 2 UGC pit 3 Ae/Bfj/Bfj Bf/Bm1/Bm1 Bm1/Bm2/Bm2 Bm2/BC1/Bm3 Bm3/BC2/IC BC Total inorganic-S04 total inorganic-S04 (ug g"1) Figure 6h. Soluble and total inorganic-SC>4: Upper Gold Creek. 3 pits/site: horizons present listed on Y axis as pit1/pit2/pit3 Ahe/Ae/Ahe -Ae/Bh/Ae -Bm1/Bm1/Bfj - cr Bm2/Bm2/Bm1 -Bm3/Bm3/Bm2 - o BC/Bm4/Bm3 -Ck/Bm5/BCgj - *. •7 ICk1/Cgj -IICk1/IIC : ICk2 - 6 IICk2 - o Soluble-SO, 2 4 soluble-S04 (ug g"1) LGC pit 1 • o • LGC pit 2 LGC pit 3 Ahe/Ae/Ahe Ae/Bh/Ae Bm1/Bm1/Bfj Bm2/Bm2/Bm1 Bm3/Bm3/Bm2 BC/Bm4/Bm3 Ck/Bm5/BCgj ICk1/Cgj IICk1/IIC ICk2 IICk2 Total inorganic-S04 > — — • • • o D 10 total inorganic-S04 (u.g g ) Figure 6i. Soluble and total inorganic-SC>4: Lower Gold Creek. 3 pits/site: horizons present listed on Y axis as pit1/pit2/pit3 Ae/Aej/Ae Bh/Bm/Bh Bmk1 Bmk2 BCk/BCk/BCk1 Ck/Ck/BCk2 Soluble-SO, soluble-S0 4 (ug g ) • CF pit 1 • o-CF pit 2 CF pit 3 Ae/Aej/Ae Bh/Bm/Bh Bmk1 Bmk2 BCk/BCk/BCk1 Ck/Ck/BCk2 Total inorganic-S04 2 3 4 5 total inorganic-S04 (ug g"1) Figure 6j. Soluble and total inorganic-S04: Canal Flats. 3 pits/site: horizons present listed on Y axis as pit1/pit2/pit3 94 6j). However, given the low concentrations of soluble-S04, and thus low range in variation it is difficult to know if these increases are meaningful. 3. Soil Bulk Density and Soil Nutrient Content Mean surface soil bulk density (0 to 7.5 cm depth) was 1.1 g cm"3 for Prince George Region soils (n = 90), and 0.8 g cm"3 for the Nelson Region (n = 60). The difference in bulk density between regions was significant (« = 0.01). Mean subsurface bulk densities (10 to 30 cm depth) were 2.1 and 1.7 g cm"3 in Prince George (n = 6) and Nelson (n = 4) Region soils, respectively. Only one estimate of subsurface bulk density was made per site, and was done by excavation. Error may occur in estimates using excavation where the plastic lining the cavity prevents maximum occupation of the cavity with water, due to rough surfaces and crevices resulting from coarse fragments and roots. This would result in an underestimate of soil volume and an overestimate of bulk density. Although many interior B.C. subsoils have high bulk densities (Lewis et al. 1991), the values observed here are likely overestimates. The threshold range for impaired root growth in interior B.C. soils is 1.2 to 1.4 g cm"3 (Lousier 1990), which was exceeded in 14% of the surface soils (n = 150). The coarse fragment content of the soils was highly variable, ranging from 0-90% by volume. Bulk density of the forest floor ranged from 0.03 to 0.40 g cm"3 (n = 150). Sulphur content by site is shown graphically in Figure 7. The mean total-S content of these soils from forest floor to C horizon was 636 kg ha'1, with a range of 399 to 123 3 kg ha"1. Forest floor S content ranged from 28 to 143 kg ha"1 averaging 52 kg ha"1 across the ten sites and accounting for about 8% of the total. Soil S contents from other studies are summarized in Table 9. Comparisons with other studies are difficult, as the treatment of coarse fragments, bulk density, and sampling depths was not standardized (Mitchell et al. 1992). Nonetheless, it is evident that the total-S content of the mineral soils in particular is low compared to other studies. The total inorganic-S04 content of the lower horizons is relatively small (Figure 8), suggesting that S in the lower horizons and parent material does not account for much of the S 95 If) £Z o N i— O N <~> o E 8 s £ « 0) CO IDI S t BL| 6>| c o CO CO CO I— o CO CD o rz CD -i—" o o CD -Q o c 3 Q. (/) 0) TD 6 w I £ i 0 CO i_ 3 CD O) o U_ cT 96 Table 9. Sulphur content of forest soils. Forest floor Mineral soil Location (kg ha 1 S) (kg ha"1 S) Reference Interior B.C. 52 584 (to 1 m) this study Czech Republic 1665 over entire profde to 60 cm Novak and Prechova 1995 France 1886-1979 over entire profile to 1 m Vannieretal. 1993 France 62 463 (to 40 cm) Nysetal . 1990 Europe (<10to 100 kg ha"1 yr"1 S inputs) 8-571 966-2925 (to lm) Erkenberg et al. 1996 various North America 11-150 310 (10 cm) to 3070 Mitchell etal. 1992 and Europe Quebec 119 1242 (to 50 cm) Houle and Carignan 1992 New York State 480 2700 (to 66 cm) David etal. 1982 Australia 80 to 220 (to 66 cm) Turner and Lambert 1980 in these soils. Most of the soluble-S04 is found in the forest floor and B horizons (Figure 9), and most of the organic-S04 is found in the upper B horizon (Figure 10). The much larger organic-S04 content at the Canal Flats site compared to other sites supports the possibility of overestimated 0rganic-SO4 concentration for the Canal Flats soil. Carbon-bonded-S is found in both the upper B and lower B horizons (Figure 11). Despite the probable presence of gypsum in the calcareous soils (Golden, Canal Flats), the S content of • these soils is not particularly high. The much higher S content of the Lower Gold Creek soil is at least in part attributable to the greater depth of soil considered. Organic C content is largest in the forest floor and B horizons (Figure 12), while most of the N is in the B horizons (Figure 13). The vast majority of the extractable P is found in the B horizons, with very little in the forest floor (Figure 14). The bulk of the exchangeable cations are located in the B and C horizons (Figure 15). The nutrient content of the upper 50 cm of mineral soil in each region is shown in Table 10. Total 9 7 L i . ro jd 98 *0S O | U B 6 J O U ! 8|qn|os se s ..eu, 6>| TO -)-> c -+—1 c o o O CO 0) -O O </) O CO CD 0 O tV) 0) j Q CD o s— -*—» X <p 03 5 o oo 0 c O CV) XI CO -t—• o CD i_ x CD O •<3-X o o 00 0 CD -t—I 00 T3 0 ' CD O TJ C D-0 ~o O) 15. £ CD 00 "CD O CD O 99 o o CO CO c o b! W o c -C § O I " £ ro CD CD CO CO i 1 l l l l 100 E a E o CN] CO E o o> E o co E o co E o CD E o •* CD o CO o E o o CN] c o Ml CO CO CD i_ o co O co o C CD -*—< rz o o 00 "O CD "D C o I c o C O _Q T3 TO O CO £ O a. — CD o * 00 ? CD Q. E CO CO S papuoq-Q se s ..eu. 6>| TO o L L as 101 co e o 1_ 00 O C - C § o 2 ? CO CD S c o o m x- N M •— C >- i _ 00 o 0 CD §•1 I II O O CD _ i o CD Z> CD GO o o o CD E o CN CD E o o co E o co E o N CD -3" CD o oo o o CN c o v> CD CD O) o CD CD CD CJ cz 0 ei| 6>| 0001-c 03 c '53 o o X! O •a 03 o "So o an ndi C D s_ — O a. CD o "a 7) 03 c csi "5. t CD oo cn 1_ CD C D O L L CO 102 in c o M if) o c sz - o "g § § m S 5= ° m CQ CO 0 0 0 a < s o !,.BM N 6>i 0001-£ u r -CM CD o CO o co CD o co E o co o o CM c o JO 0 0 O ) 1— o 0 CD 0 o 0 —^• 'co >^  r> •g 0 £ -*-» CD O on o •— SZ Q . 0 o T J 00 O) _C CO "5. E CD CD CO • eg o LL CD 103 o o o o o o o m o 10 o in CO CO CN CM T -o o o cn E u C N E o E o c o E o E o CO o co E o c o o E u o CM o w CD CD E> o CD CD o cz 1 c co n C CD •*—> c o o Q_ _0_> CO u 03 i — X CD O 00 0 CD .2 '55 "S3 2 c Q. CD -a cn c Q. E 03 CO JD O L i . co 1 0 4 E o E o C M £= C D o CO cm Nel I S . CJ) £ o CO T —^ E o E o c o CD E O ) 1_ o o CD C D O E 0 o o C D i— CL E u c o o E o o C M CO -t—' £= 0 c o o c o •4—i CO L.BL| SUOjJBO 9|qB86uBL|0Xa 6>) 0001-o 0 0) CO ab an 0 T 3 0 CD C CO CO ica x: C T 3 c o tt) ex abl pth Q> 0 o sr X 5 CO ha O) C If) o X Q. OD E H — CO (D o CO L_ igu juns tota Li. CO 105 inorganic-S04 and P contents of the surface soil were significantly greater in the Prince George Region soils than the Nelson Region soils. The regional difference in P content is consistent with P concentration differences in the upper B horizons (Table 6), while the difference in total inorganic-S04 content does not reflect a concentration difference between regions (Table 3). There were no significant differences in forest floor nutrient content between the two regions (Appendix IX). 4. Correlation of Soil Properties Soluble-S0 4 is the most active pool of soil S, and is maintained by inputs of mineralized and desorbed S (Johnson and Henderson 1979; Feger 1995). In this study, the concentration of soluble-S04 in B horizon soil was greater at the S-sufficient (Nelson) sites, indicating that there is more S 0 4 available for plant uptake at these sites. The source of S 0 4 entering the soluble pool would be indicative of the factors controlling S availability. The three potential sources of soluble-S04 are C-bonded-S, organic-S04, and total inorganic-S04. Correlations were done among B horizon soil properties to evaluate the contribution of these pools to soluble-S0 4, and to determine the relationships between soluble-S04 and other properties. Correlations were done using individual soil samples from the first three B horizons per pit at all sites. Correlation coefficients are shown in Table 11. Soluble-S04 was significantly correlated with organic-S0 4, organic C, and total N , but was not correlated with C-bonded-S or with total inorganic-S04 This suggests that organic-S04 is the pool most closely related to soluble-S04, and related to S availability. Organic-S04 and C-bonded-S were poorly correlated with each other, while organic-S and C-bonded-S are highly correlated with total-S and with each other. This supports the model of different pathways of S cycling through these organic-S forms (McGill and Cole 1981). There is a significant correlation between total-S and N in these soils. 106 Table 10. Nutrient content of upper 50 cm of mineral soil. Constituents that are significantly different between regions are in bold type. Nutrient (kg ha 1) Prince George Region Nelson Region total-S 285 (30) 272(39) Ffl-S 104(21) 79(31) total inorganic-S04 15 (5) a 7 (2) b soluble-S04 6(3) 6(2) organic-S04 89(20) 71 (29) C-bonded-S 181 (21) 193 (48) organic-S 270(31) 265 (38) C (1000 kg ha 1) 43 (13) • 32(11) . N (1000 kg ha"1) 4(1) 3(1) P 210 (46) a 48 (22) b exchangeable cations3 (1000 kg ha"1) 4(1) 6(2) a Sum of exchangeable Ca, Mg, and K Prince George Region: n = 18 (3 pits per site; 6 sites) Nelson Region: n = 12 (3 pits per site; 4 sites) Standard errors are shown in parentheses. Different letters for regional means of the same constituent indicate differences at « = 0.05. 107 O • — ^- r~-o o o © o vo ON SO o © r-© * o Os I D 00 o 00 t--o o o cs O M l O ON C I i n C O o o o o o o i T 3 <U T 3 C o 6 ON * ON 00 ON | o C/3 SO * ON ON ON Q . a, I (Z3 i ea o Q . cn C o N t/2 ccj ^ O t / 3 i -a <D C o I O O ( o ed 6 0 go B O i o © II o .5 'S o 8 • 4 - * o 108 5. Mineralizable-S andN a. Forest Floor Regional means for mineralizable nutrients in forest floor and mineral soil incubations are shown in Tables 12 and 14. There was a significantly greater concentration of mineralizable-S04 in forest floor from Prince George Region sites than Nelson Region sites (Table 12). This was also reflected in a greater proportion of total-S mineralized at the Prince George sites. Net S 0 4 immobilization (< 10 pg g"1) occurred at two Prince George sites (Meadow Lake, Tsus Creek). The greater mineralizable-S04 concentration corresponds to significantly greater concentrations of HI-S, forest floor soluble-S04, and organic-S04 in Prince George Region than Nelson Region forest floor material (Table 2). Total-S, HI-S, total inorganic-S0 4 , and organic-S04 contents are also greater in Prince George Region forest floor (Appendix IX). In this study, mineralizable-S04 included organic and inorganic-S04 forms. The proportions of organic and inorganic-S04 are not known. Net mineralizable-S04 was positively correlated with forest floor total-S, forest floor soluble-S04 organic-S04, and C-bonded-S concentrations, and negatively correlated with C:S and N:S across all sites (Table 13). Maximum net mineralizable-S04 (367ug g"1) occurred at a C:S ratio of 146 (Gregg Creek site, Prince George Region). The strongest correlation of forest floor mineralizable-S04 was with organic-S04 concentration (r2 = 0.84, p < 0.001). These results suggest that forest floor mineralizable-S04 is more strongly associated with organic-S04than with C-bonded-S. This is consistent with the assumption that organic-S04 is more labile than C-bonded-S, and is more readily mineralized. A greater proportion of inorganic N (combined N H 4 and N 0 3 ) was mineralized from Nelson than Prince George forest floor material. 109 Table 12. Region means of net mineralizable-S04, NH 4 , and N0 3 , and percent of total-S and N mineralized during 32 d laboratory incubation of forest floor. Properties that are significantly different between regions are in bold type. Property Prince George Region Nelson Region net mineralizable-S04 (pig g"1) 85.4 (60.0) a 19.8 (3.7) b net mineralizable N H 4 (pig g"1) 949.1 (391.8) 1114.3 (563.9) net mineralizable N 0 3 (pig g"1) 14.3(20.6) 6.7(7.2) net mineralizable-S04 as % of total-S 4.1 (2.8) a 1.7 (0.1) b net mineralizable N as % of total N a 7.0 (2.7) b 8.4 (4.0) a Prince George Region: n = 30 (5 replicates per site, 6 sites) Nelson Region: n = 20 (5 replicates per site, 4 sites) Standard errors are shown in parentheses. Different letters for region means of the same constituent indicate differences at <* = 0.05. a Mineralizable N is the sum of N H 4 and N 0 3 . Table 13. Regressions of forest floor mineralizable-S04 and concentrations of selected S constituents". Significant regressions (<* = 0.05) are in bold type. S constituent r2 p Regression equation total-S 0.78 0.001 y=-ll 6.67+1509.34x forest floor soluble-S04 0.78 0.001 y=-54.04-2.71x organic-S04 0.84 <0.001 y=-l 8.68+0.4 lx C-bonded-S 0.64 0.006 y=-149.10+0.23x C:S 0.5 0.021 y=341.34-0.65x N:S 0.8 0.001 y=545.65-41.31x organic C 0.001 0.925 y=l 09.66-1.18x a Units of x and y variables shown in Tables 2 and 5 (x), and 12 (y). n - 10 site means (5 replicates per site for mineralizable nutrients; 3 samples per site for S constituent concentrations). 110 b. Mineral Soil There were no significant differences between regions in mineral soil mineralizable nutrients (Table 14). Mineralizable-S04 concentrations in mineral soil were much smaller than in forest floor material. Net immobilization of S 0 4 occurred at four of the six Prince George sites. Low net mineralizable-S 0 4 concentration suggests either little gross S mineralization, high rates of S immobilization, or both. Relationships between mineralizable-S04 and soil properties were not as evident as for the forest floor. Mineral soil mineralizable-S04 was poorly correlated with soil total-S, organic-S04, C-bonded-S, C:S, N:S, and organic C (r2 < 0.10). Net N 0 3 immobilization occurred in soils from the Prince George Region. Table 14. Region means of net mineralizable-S04, NH 4 , and N0 3 , and percent of total-S and N mineralized or immobilized during 32 d laboratory incubation of mineral soil. Property Prince George Region Nelson Region net mineralizable-S04 (,ug g"1) -1.0(1.6) 1.8(1.2) net mineralizable N H 4 (jj.g g"1) 4.0 (2.8) 1.6 (0.8) net mineralizable N 0 3 (pig g"1) -3.0(2.3) 1.8(2.2) net mineralizable-S04 as % of total-S -1.4 (2.4) 2.9 (2.0) net mineralizable N as % of total N a 0.4 (0.6) 0.5 (0.4) Prince George Region: n = 30 (5 replicates per site, 6 sites) Nelson Region: n = 20 (5 replicates per site, 4 sites) Standard errors are shown in parentheses. Negative values indicate net immobilization. a Mineralizable N is the sum of N H 4 and N 0 3 . Ill 6. Foliar Nutrient Resorption and Litter Nutrient Concentration a. Nutrient Resorption At eight of the ten sites, there was no net resorption of S0 4-S prior to senescence (Table 15). At these sites, the concentration of S0 4-S in fresh litter was greater than in the oldest green foliage. The data for S0 4-S resorption were highly variable, and there were no significant differences between regions. In contrast to S0 4-S, total-S concentration was greater in the green foliage than in the litter at all sites, indicating S resorption prior to senescence. These results support observations that the redistribution of S0 4-S is less consistent than that of total-S, and is probably contingent on considerable S0 4-S storage. Average S resorption at the Prince George sites (45%) was greater than at the Nelson sites (32%), supporting a hypothesis of greater S resorption where S availability is low. Values from the Prince George sites were greater than the typical estimate of 20% to 30% S resorption suggested by Binkley (1986) for unspecified forest types. Resorption of both N and P was also significantly greater at the Prince George sites than at the Nelson sites. Average N resorption was estimated at 39 and 31%, for the Prince George and Nelson Regions, respectively. Phosphorus resorption was 54 and 45%, respectively for the two regions. These values are lower than those reported elsewhere for lodgepole pine: 48 to 66% of N and 78% of P (Gower et al. 1989; Prescott et al. 1989). Despite higher P concentrations in soils, resorption of P was greater at the Prince George sites than at the Nelson sites. This suggests that either P resorption may be less sensitive to soil P concentrations than S or N , or that the method of soil P determination used in this study (Bray-Pl) may have been less accurate for the calcareous soils. b. Litter Nutrient Concentrations Nutrient concentrations in litter from the two regions are shown in Table 16. There was no difference in litter S0 4-S concentration between regions. Litter S and N concentrations were significantly lower at the Prince George sites than at the Nelson sites, in agreement with the greater resorption of 112 nutrients at these sites. The observations at these sites support the use of litter S and N concentrations as indicators of S and N availability. There was no difference between regions in litter P concentration. Table 15. Percent resorption of nutrients from needles prior to senescence. Constituents that are significantly different between regions are in bold type. SCyS S_ IV P Prince George Region Meadow Lake -42.1 (28.3) 49.12(4.23) 40.86 (4.90) 57.99 (3.75) Tsus Creek 2.1 (22.4) 44.86 (4.73) 36.26 (7.45) 53.93 (5.69) Gregg Creek -95.2(115.9) 33.24 (9.25) 34.14(4.68) 47.31 (7.47) Cluculz Creek -41.2 (33.4) 48.77(12.68) 39.89 (5.55) 59.91 (7.28) Cobb Lake -26.7 (35.1) 48.86 (6.27) 42.26 (3.43) 51.79 (7.14) Bowron -15.4 (24.3) 43.34(21.62) 37.76 (7.42) 51.75 (4.70) REGIONAL M E A N -36.4(13.6)a 44.70 (2.50) a 38.53 (1.24) a 53.78 (1.87) a Nelson Region Golden -4.0 (46.0) 42.23 (6.62) 40.84 (7.63) 61.01 (3.11) Upper Gold Creek -29.0 (63.6) 28.02 (8.97) 25.29(14.88) 34.41 (8.07) Lower Gold Creek 31.1 (33.1) 30.89 (7.95) 27.04(14.66) 36.02 (3.56) Canal Flats -36.7 (25.4) 24.88 (5.00) 31.22 (6.35) 46.46 (8.84) REGIONAL M E A N -9.6 (15.3) a 31.51 (3.78) b 31.10 (3.48) b 44.48 (6.12) b Prince George Region: n = 30 (5 replicates per site, 6 sites) Nelson Region: n = 20 (5 replicates per site, 4 sites) Standard deviations (site means) and standard errors of the estimate (regional means) are shown in parentheses. Negative values indicate higher nutrient concentrations in litter than in green foliage. Different letters for regional means of the same constituent indicate differences at « = 0.05. 113 Table 16. Nutrient concentrations in litter. Constituents that are significantly different between regions are in bold type. (Mgg-') % Prince George Region Meadow Lake 29.6 (3.3) 0.03 (0.001) 0.51 (0.04) 0.03 (0.004) Tsus Creek 31.0 (5.4) 0.04 (0.001) 0.53 (0.06) 0.04 (0.10) Gregg Creek 47.8(19.8) 0.04 (0.01) 0.57 (0.06) 0.04 (0.01) Cluculz Creek 29.6 (3.3) 0.03 (0.01) 0.52 (0.05) 0.03 (0.01) Cobb Lake 27.0 (5.4) 0.04 (0.01) 0.64 (0.03) 0.05 (0.01) Bowron 29.8(5.8) 0.03 (0.01) 0.52 (0.03) 0.05 (0.004) REGIONAL M E A N 32.7 (3.1) a 0.04 (0.001) b 0.55 (0.02) b 0.04 (0.01) a Nelson Region Golden 30.4 (4.3) 0.04 (0.003) 0.52 (0.06) 0.03 (0.004) Upper Gold Creek 34.8(7.3) 0.05 (0.003) 0.62 (0.08) 0.05 (0.01) Lower Gold Creek 34.8 (9.6) 0.05 (0.004) 0.66 (0.08) 0.06 (0.01) Canal Flats 46.0(14.3) 0.05 (0.01) 0.56 (0.04) 0.03 (0.01) REGIONAL M E A N 36.5 (3.3) a 0.05 (0.002) a 0.59 (0.03) a 0.04 (0.01) a Prince George Region: n = 30 (5 replicates per site, 6 sites) Nelson Region: n = 20 (5 replicates per site, 4 sites) Standard deviations (site means) and standard errors of the estimate (regional means) are shown in parentheses. Different letters for regional means of the same constituent indicate differences at <* = 0.05. 114 7. Soil and Foliar Nutrient Correlations Identification of the mineral soil properties at S-deficient and S-sufficient sites has provided a basis for characterizing these sites and determining the factors underlying the S limitation at the Prince George sites. Correlation analysis of soil and foliar data from all sites was undertaken to explore the relationships between soil properties and foliar nutrition across the range of soil S availability. a. Foliar Nutrition Regional means and p values for comparison of foliar properties between regions are shown in Table 17. Of the three foliar S properties: total-S, S0 4-S and S0 4:S ratio, foliar S0 4-S concentration was considered to be the best indicator of S status on the basis of consistently higher r2 values in correlations with mineral soil properties. For example, there was a significant positive relationship between foliar S0 4 -S and B horizon soluble-S04 (r2 = 0.84; p = 0.001), while the regression of foliar S concentration and B horizon soluble-S04 was poor (r2 = 0.04). Total-S concentrations in foliage were not significantly different between regions, while foliar S0 4-S concentrations were significantly higher in the Nelson Region. Relationships of mineral soil properties to foliar S0 4:S ratios were the same sign but weaker than those found for foliar S0 4-S concentration alone. There were significant differences in S0 4-S and total N concentrations, and S0 4:S and N:S ratios between regions (Table 17). Foliar S0 4 -S concentration and S0 4 :S ratio were significantly greater in Nelson Region foliage than in Prince George Region foliage, while N concentration and N:S ratio were greater in Prince George Region foliage. These results indicate greater S availability at the Nelson Region sites. The foliar nutrient concentrations indicate that foliar total-S concentrations for both regions are well below the critical limit of 0.12 to 0.15% S (Ballard and Carter 1985). Foliar S0 4-S concentrations at sites in the Prince George Region are below the critical level of 80 pg g"1, and N:S ratios are approaching the critical level of 14.6. Nitrogen concentrations in foliage from both regions are below critical levels of 1.55% N for lodgepole pine suggested by Ballard and Carter (1985). 115 Table 17. Concentrations of S and N in foliage from Prince George and Nelson Regions. Properties that are significantly different between regions are in bold type. Constituent Prince George Region Nelson Region total-S (%) 0.09 (0.004) a 0.09 (0.002) a S04-S (ugg1) 59.2 (14.24) b 88.3 (16.95) a S04:S 0.07 (0.01) b 0.10 (0.02) a total N (%) 1.18 (0.06) a 1.01 (0.04) b N:S 13.4 (0.5) a 11.9 (0.5) b Prince George Region: n = 18 (3 replicates per site, 6 sites) Nelson Region: n = 12 (3 replicates per site, 4 sites) Standard errors of the estimate are shown in parentheses. Different letters for regional means of the same constituent indicate differences at <* = 0.05. b. Relationships of B and C Horizon Soil S Properties to Foliar SO^S Concentration Results of correlations with foliar S0 4-S only are presented for B and C horizon soil. The strongest relationship of foliar S0 4-S concentration with a B-horizon soil property occurred with soluble-S04 concentration (r2 = 0.84; p < 0.001) (Table 18). This is the strongest relationship observed for any regression of F, B, or C horizon soil properties with foliar nutrients. The relationship is shown in Figure 16. The critical foliar S0 4-S level of 80 ug g"1 occured at a soluble-S04 concentration of 1 to 2 ug g"1 (Figure 16). This would seem to be close to the minimum values found in soils. Foliar S0 4-S concentrations as low as 32 ug g"1 were observed at the Prince George sites, indicating that soluble-S04 is in very short supply. Foliar S0 4-S concentration was less than 60 ug g"1 at all Prince George Region sites (except Gregg Creek), reinforcing the recommendation that S be added with N where foliar S0 4-S concentration is less than 60 ug g"1 (Brockley 1996). As with the difference in soluble-S04 concentration between regions, sources contributing to the soluble-S04 fraction could provide more information about S cycling on these sites. Relationships between the three pools from which soluble-S04 is released and foliar S0 4-S concentration were considered. There was a significant positive relationship between foliar S0 4-S concentration and B horizon organic-S04 concentration (r2 = 0.46; p = 0.03), while relationships were weak between foliar SQ4-S concentration 116 Table 18. Simple linear regressions of foliar S04-S concentration and B and C horizon soil chemical properties3. Significant regressions (<* = 0.05) are in bold type. B horizon Soil property r2 p Regression equation total-S 0.02 0.702 y=0.30+1.09x HI-S 0.42 0.041 y=41.81+1.15x total inorganic-S04 0.01 0.762 y=75.24-1.58x soluble-S04 0.84 <0.001 y=27.81+38.62x organic-S04 0.46 0.032 y=43.71+1.21x C-bonded-S 0.28 0.12 y=208.61-3.14x organic-S 0.01 0.748 y=6.53+1.04x organic-S04: C-bonded-S 0.29 0.111 y=34.74+78.90x organic C 0.72 0 y=14.32+75.92x organic C:S 0.74 0 y=23.03+0.40x N:S 0.75 0 y=-38.40+9.07x organic C:N 0.56 0.013 y=-4.25+8.72x pH (CaCl 2) 0.04 0.568 y=5.68+12.34x total N 0.75 0 y=-34.67+1335.05x extractable N H 4 <0.01 0.913 y=75.44-2.02x extractable P < 0.01 0.872 y=73.84-0.1 Ox exchangeable Ca 0.1 0.838 y=58.05+3.03x Units of x and y variables shown in Tables 3, 4, 6, and 7 (x), and 17 (y). n = 10 site means: foliar SCyS concentration: 3 samples per site B horizon: 9 samples per site C horizon: 3 samples per site 117 Table 18. (Continued) C horizon Soil property r2 P Regression equation total-S 0.26 0.135 y=796.77-11.97x HI-S 0.45 0.04 y=39.46+1.68x total inorganic-S04 0.09 0.394 y=98.51-28.19x soluble-S04 0.17 0.241 y=48.68+50.05x organic-S04 0.44 0.04 y=41.86+1.63x C-bonded-S 0.48 0.03 y=148.87-1.84x organic-S 0.16 0.257 y=586.77-8.65x organic-S04: C-bonded-S 0.49 0.03 y=58.08+12.10x organic C 0.47 0.03 y=19.83+237.09x organic C:S 0.41 0.05 y=11.76+1.75x N:S 0.28 0:113 y=-31.64+12.30x organic C :N 0.21 0.179 y=12.44+14.35x pH (CaCl 2) 0.17 0.242 y=-13.98+14.79x totalN 0.21 0.179 y=-5.88+1503.58x extractable N H 4 0.07 0.454 y=96.77-17.76x extractable P 0.15 0.272 y=82.22-1.47x exchangeable Ca 0.29 0.107 y=52.76+2.23x 118 Dotted lines indicate soil soluble-S0 4 concentration at 80 ug g"1 foliar S0 4 -S . 160 -, , 0 1 2 3 4 B horizon soluble-S0 4 (u.g g"1) Figure 16. Relationship between foliar S 0 4 - S and B horizon soluble-S0 4 concentrations. 119 and C-bonded-S or total inorganic-S04. In the case of C-bonded-S the relationship was negative. There were also poor relationships between foliar S0 4-S concentration and soil total and organic-S concentrations. Similar relationships were observed in C horizon soil (Table 18). There was a significant positive relationship between foliar S0 4-S and C horizon organic-S04 concentrations , and a significant negative relationship between foliar S0 4-S and C-bonded-S. This was also reflected in the positive relationship between foliar S0 4-S concentration and soil organic-S04: C-bonded-S ratio. There was a significant relationship between foliar S0 4-S and HI-S in both B and C horizons. However, as discussed previously, the inclusion of inorganic-S04 in the HI-S analysis made it a less useful indicator than organic-S04 concentration. c. Relationships of Other B and C Horizon Soil Properties to Foliar SOyS Concentration Relationships between foliar S0 4-S and organic C were apparent in both the B and C horizons (Table 18). In particular, there was a strong relationship between foliar S0 4-S concentration and B horizon organic C concentration (r2 = 0.72; p = 0.002). There were also significant relationships between foliar S0 4-S and soil C:S in both mineral horizons. Despite low concentrations of S and C in the lower horizons, they are nonetheless important to nutrient cycling and fertility (Liski and Westman 1995; Richter and Markewitz 1995). Relationships with foliar S0 4-S involving total N or the N:S ratio appeared to be important in the B horizon only (r2 = 0.75; p = 0.001 for both properties). Relationships between foliar S0 4-S and soil organic C and total N are stronger than for total-S, as indicated by correlations of foliar S0 4-S with individual elements and element ratios. This suggests the role of soil organic matter in S availability in the mineral soil. To examine the effects of calcareous soil properties on foliar S nutrition, foliar S0 4-S concentration was correlated with soil pH and exchangeable Ca. There were no significant relationships between foliar S0 4-S concentration and pH or exchangeable Ca in either B or C horizon soil (Table 18). 120 There were no significant relationships between foliar S0 4-S concentration and extractable N H 4 or P in B or C horizon soil. d. Relationships Between F Horizon Properties and Foliar S Concentration In contrast to the mineral soil, S properties of F horizon were more strongly correlated with foliar total-S concentrations than with foliar SCyS concentrations. This may be explained by the development of forest floor from foliar litter, with F horizon properties reflecting foliar nutrition more than contributing to it directly. Results of regressions between foliar S concentrations and F horizon material are shown in Table 19. There were significant, positive relationships between foliar S and forest floor HI-S, soluble-S04, organic-S04, soluble-S, and organic-S04:C-bonded-S ratio. The strongest relationships involved the two soluble-S fractions: soluble-S04 (r2 = 0.45) and soluble-S (r2 = 0.47). Despite the reasonably good r2 values for these regressions, the slopes of the regression lines are approaching zero (Table 19), indicating little change in foliar S with increasing forest floor S. Relationships between foliar S and total-S, C-bonded-S, and organic-S were not significant. There were no significant relationships between foliar S and C, N , pH, P, Ca, or element ratios. 121 Table 19. Simple linear regressions of foliar S concentration and F horizon chemical properties8. Significant regressions (<* = 0.05) are in bold type. Constituent r2 P Regression equation total-S 0.33 0.083 y=0.08+0.07x H I - S 0.41 0.046 y=0.08+1.8xl0'5x forest floor soluble-S04 0.45 0.035 y=0.08+1.5xl0"4x organic-S04 0.4 0.048 y=0.08+2.0xl0-5x C-bonded-S 0.25 0.142 y=0.08+1.0xl0'5x organic-S 0.33 0.084 y=0.08+7.4xl0"6x soluble-S 0.47 0.028 y=0.08+1.6xl0"4x organic-S04: C-bonded-S 0.42 0.044 y=0.08+0.04x total C 0.32 0.088 y=0.03+0.001x C:S 0.17 0.24 y=0.100-2.7x10"5x N:S 0.35 0.074 y=0.11-0.002x C:N 0.01 0.755 y=0.09-1.3xl0'4x pH (CaCl 2) <0.01 0.953 y=0.09-4.2xl0"4x totalN 0.12 0.318 y=0.07+0.01x extractable N H 4 0.22 0.176 y=0.08+2.0xl0"4x extractable P 0.09 0.393 y=0.09-7.4xl0"5x exchangeable Ca < 0.01 0.884 y=0.09+4.0xl0"5x a Units of x and y variables shown in Tables 2 and 5 (x), and 17 (y). n = 10 site means: foliar S0 4-S concentration: 3 samples per site F horizon: 3 samples per site 122 e. Relationships Among Soil N Mineralizable Nutrients and Foliar Nutrients Results of regressions between foliar N concentration and soil N constituents in all horizons are shown in Table 20. Relationships were weak, and no regressions were significant. Relationships between foliar SO4 -S and mineralizable-S04 and between foliar N and mineralizable N , were not significant (Table 21). In the case of regressions between foliar N and F horizon extractable and mineralizable N , low r2 values and slopes approaching zero emphasize the lack of relationship between these variables. f. Relationships of Mineral Soil Nutrient Content to Foliar SCyS Concentration Significant regressions between foliar S0 4-S concentration and nutrient content of the upper 50 cm of mineral soil are shown in Table 22. Foliar S0 4 -S concentration was significantly correlated with HI-S, soluble-S04, organic-S04, total N and organic C contents. Concentrations of the same constituents were also significantly correlated with foliar S0 4-S (Table 21), indicating that concentration and quantity of nutrients are comparably related to foliar S0 4-S concentration for S and N properties. However, the slope of the regression line for foliar S0 4 -S concentration and soil organic C content is close to zero, indicating little change in foliar S0 4-S with changes in organic C content. The relationship between foliar SCyS and organic C is better expressed by organic C concentration than by content. Table 20. Simple linear regressions of foliar N concentration and F, B, and C horizon N constituents3. 123 Constituent r 2 p Regression equation F horizon total N 0.03 0.633 y=l. 24-0.1 l x extractable N H 4 <0.01 0.855 y=l .08+5.5x1 O^x extractable N 0 3 0.21 0.186 y=1.44-0.13x total mineralizable N < 0.01 0.924 y=l. l l+3.5xl0"5x B horizon total N 0.08 0.424 y=1.30-1.90x extractable N H 4 < 0.01 0.876 y=1.08+0.01x extractable N 0 3 0.02 0.679 y=1.16-0.17x total mineralizableN 0.06 0.545 y=l.09+0.01 x C horizon total N 0.15 0.275 y=1.39-5.40x extractable N H 4 0.05 0.542 y=1.02+0.06x extractable N 0 3 0.06 0.487 y=1.04+0.44x total mineralizable N 0.02 0.755 y=l.ll+0.03x a Units of x and y variables shown in Tables 5, 6, and 7 (x), and 17 (y). n = 10 site means: foliar N concentration: n = 3 samples per site F horizon: n = 3 samples per site B horizon: n = 9 samples per site C horizon: n = 3 samples per site 124 Table 21. Simple linear regressions of foliar nutrient concentrations and mineralizable soil nutrients (aerobic laboratory incubation)9. Regression of: f p Regression equation forest floor foliar S0 4-S and net mineralizable-S04 0.29 0.108 foliar N and net mineralizable N 0.35 0.072 mineral soil foliar SCyS and net mineralizable-S04 0.17 0.243 foliar N and net mineralizable N b 0.03 0.648 a Units of x and y variables shown in Tables 12 and 14 (x), and 17 (y). b Mineralizable N is the sum of N H 4 and N O s . n = 10 site means foliar SCyS and N concentration: n = 3 samples per site mineralizable nutrients: n = 5 replicates per site Table 22. Simple linear regression of foliar SCyS concentration and nutrient content of upper 50 cm of mineral soil\ Significant regressions (<* = 0.05) are in bold type. Constituent r 2 P Regression equation HI-S 0.48 0.026 y=27.79+0.46x soluble-S04 0.71 0.002 y=39.27+5.70x organic-S04 0.55 0.014 y=27.79+0.53x totalN 0.47 0.029 y=14.51+0.02x organic C 0.54 0.015 y=34.28+9.4xl0"4x a Units of x and y variables shown in Tables 10(x) and 17 (y). n = 10 site means: foliar SCyS concentration: n = 3 samples per site nutrient contents: n = 3 pits per site y=60.85+0.17x y=l.21-9.4x10"5x y=70.19+4.20x y=1.10+0.05x 125 8. Further Discussion and Summary Soils from the S-deficient (Prince George) and S-sufficient (Nelson) sites did not differ in total-S concentration. Soluble-S04 concentration in B horizon soils differed between regions, and was the soil S property most strongly related to S availability as indicated by foliar S0 4-S concentration. Of the three pools from which soluble-S04 is generated: total inorganic-S04, organic-S04, and C-bonded-S, organic-S 0 4 appears to be the pool most closely related to soluble-S04 and thus S availability in these soils based on two lines of evidence. First, there is a better relationship between foliar S0 4-S and soil organic-S04 concentration than is observed for total inorganicS04 or C-bonded-S. This is also true for organic-S04 content. Secondly, soluble-S04 is significantly correlated with organic-S04 but not with C-bonded-S or total inorganicS04. The importance of organic-S to S availability on these sites is supported by the strong correlations between soil organic C and foliar S0 4-S concentration, and between organic C and soil soluble-S04. A positive correlation between soluble-S04 and organic C has been found in other forest soils (Neary et al. 1987). Organic C appears to be involved in two separate aspects of S dynamics: the negative influence of organic C on S 0 4 adsorption, and the cycling of S through organic matter. Only the latter appears to be important in this study. The relative importance of the true organic portion of organic-S04 and the contribution from inorganic-S04 sources not accounted for by P-extraction is still unknown. Soil total inorganicS04 concentration, and speculatively, S 0 4 adsorption, did not appear to play an important role in S availability on these sites. Organic-S04 is rapidly cycled in soil and may be more important than C-bonded-S in the actively cycling S pool (Freney 1971; McLaren et al. 1985; Schindler et al. 1986: Shan et al. 1997). Studies using 3 5 S indicate that a portion of the S taken up by plants is from the organic-S04 pool (Freney et al. 1975; Strickland et al. 1987). The major source of soil organic-S04 is production in microbial biomass (David et al. 1987). Incorporation of inorganic-S04 into organic-S04 in forest soils is enhanced by available C supply, either as exogenous C (Fitzgerald et al. 1983) or inherent soluble C (David et al. 1983, 1987; Strickland et al. 1986; 126 Autry et al. 1990). Organic-S04 formation is greater in surface organic and mineral soil horizons than in lower horizons, reinforcing the role of organic matter. (David et al. 1983, 1987; Schindler et al. 1986; Autry et al. 1990). In mineral horizons, organic-S04 is formed in situ in organic rich surface horizons and translocated to lower horizons, (Strickland et al. 1986; David et al. 1987; Schoenau and Bettany 1987; Homann et al. 1990; Dhamala and Mitchell 1995). In this study, parallel trends in C:S and organic-S04 with profile depth suggest that S as organic-S04 is accumulating with depth. Organic-S04 is mineralized in response to microbial demand for S (McGill and Cole 1981). Recently formed organic-S04 is less stable and more susceptible to enzymatic hydrolysis than older fractions (Lou and Warman 19926; Ghani et al. 1993). Where soil S reserves are low, the ratio of organic-S04:C-bonded-S should be low, reflecting high S demand, depletion of the organic-S04 pool, and its immobilization by microbial biomass (McGill and Cole 1981; Strick and Nakas 1984). Microbial S is actively cycling, and is part of the S available for plant uptake (Chapman 1987; Eriksen et al. 1995). Even in soils with very low S status, microbial biomass is not S limited (Chapman 1987), suggesting that immobilization of S from organic-S04 is a powerful S sink. There is a strong relationship between microbial biomass C and S, and incorporation of inorganic-S04 into microbial biomass is enhanced in the presence of an available C source such as cellulose (Saggar et al. 1981; Maynard et al. 1985; Chapman 1987; Wu et al. 1994). There appears to be an interaction among S, available C, and the microbial biomass that may explain the differences in S availability observed on these sites. Three situations involving S or C limitation and the expected net result are suggested: 127 Condition Process Result 1. S not limiting, available C limiting •mineralization of C-bonded-S •surplus S (net S mineralization) 2. Available C not limiting, S limiting •mineralization of organic-S04 •re-immobilization of organic-S04 into microbial biomass •cycling of organic-S04 through microbial biomass. 3. Both S and available C limiting •mineralization of organic-S04 and C-bonded-S •re-immobilization of mineralized S •limited turnover of microbial biomass S The third scenario is consistent with the observations in mineral soil from the Prince George sites, such as low rates of S 0 4 mineralization, low concentrations of organic C, low organic-S04:C-bonded-S ratio, and low C:organic-S04 ratio. On these sites, S limitation is exacerbated by low supply of available C. There is then both a heavy demand on the the most actively cycling S pool by the microbial biomass due to low S conditions, and limited turnover of immobilized S back into active cycling due to C limitation. The net result of a reduction in pool size and a reduction in the rate of cycling is the release of very little inorganic-S04 into the soil solution for plant uptake. The cause of low C availability on these sites may be loss of soil organic matter and microbial biomass C during past fires (Johnson 1992). Fire is also expected to be involved in S losses from these sites. The recovery of microbial biomass C and N , and presumably S, following burning can take as long as ten years (Fritze et al. 1993). The specific fire history of these sites has not been examined here; however, fire has undoubtedly been a factor in their development. Response to N+S fertilization has been particularly evident in fire-origin stands in the interior of B.C. (Brockley 1996). Sulphur is volatilized to S 0 2 during the oxidation of soil organic matter and foliage (Tiedemann 1987; Hungerford et al. 1990; Agee 1993). Sulphur losses to volatilization are greater where a higher proportion of foliar S is in organic form, rather than as inorganic-S04-S (Sanborn and Ballard 1991). Low S availability, and a low proportion of inorganic-S04-S in foliage may be exacerbating S losses on the Prince George sites. 128 Sulphate adsorption decreases with the pH increases that follow burning (Raison and McGarity 1980; Sanborn and Ballard 1990). Sulphur availability is increased in the short-term, but soluble-S04 may be readily leached and removed from the nutrient pool. The effects of fire on S mineralization, either through substrate loss, or temperature and pH effects, are not well understood. Eivazi and Bayan (1996) found repeated burning of forest sites to decrease soil arylsulphatase activity, which would be expected to influence organic-S04 dynamics. Pedogenetic processes are also expected to play a role in S availability on these sites. Fine textured S minerals and illuviation of fine fractions would decrease the S content of the upper profile over time. Translocation of soluble organic-S would further remove labile S and organic matter from the upper profile. These processes are likely occurring on both the Prince George and Nelson sites, accounting for the low total-S concentrations in both locations. Soils on the Prince George sites are more developed than those on the Nelson sites, and it is likely that S-removing processes are more advanced and more evident. It does not appear from these results that soil parent material per se is driving differences in S availability. The S determinations done in this study did not reveal the nature of the primary S minerals, although the presence of S 0 4 minerals (CaC0 3 -S0 4 complexes, gypsum, MgS0 4 ) was suspected at some sites. As well, reduced inorganic-S forms were not determined. If detected, the presence of reduced inorganic-S would be indicative of sulphide minerals. Differences in rates of mineral weathering could provide further insight into differences in S availability in these sites. Little is known about harvesting effects on S and the impacts expected on these sites. Sulphur losses would be expected in biomass removal (Brockley et al. 1992), but this has not been well quantified. Sulphate retention has been shown to increase with decreased pH following accelerated mineralization and nitrification associated with harvesting (Fuller et al. 1987; Mitchell et al. 1989). The effects of harvesting on S mineralization, for example through increased surface temperatures, may also influence S dynamics on these sites. 129 The location of the S-deficient and S-sufficient sites in geographically separate areas raises concerns about pseudoreplication in this study. Possible differences between the Prince George and Nelson Region sites that are relevant to this study include climate, parent material, and genetic variation in lodgepole pine. Climatic differences such as annual precipitation would be expected to influence processes such as soil development and S mineralization. Parent materials also affect soil development, as well as S and other chemical properties of the soils. Nutrient resorption and response to nutrient additions may vary among lodgepole pine genotypes. The issue of S-deficient and S-sufficient sites in different locations could best be addressed by comparing S-sufficent (if present) and S-deficient sites within the Prince George Region, where climatic, parent material, and genetic differences are minimized. 130 CHAPTER III. SULPHUR DEFICIENCIES A N D FERTILIZATION IN FORESTS A. LITERATURE REVIEW 1. The Increasing Incidence of Sulphur Deficiencies Reports of S deficiencies in agriculture began to increase in the late 1960's. More widespread S deficiencies were attributed to increased use of high-analysis fertilizers, decreased use of S as a pesticide, production of S-demanding crops, more intensive crop production and increased yields, and air pollution abatement (Coleman 1966; Beaton 1969; Tisdale etal. 1986; Wainwright 1990). Decreases in S emissions have continued, with as much as 50% reduction over the past decade (Hultberg et al. 1994). A consequence of reduced atmospheric S inputs has been another wave of S deficiencies throughout much of Europe (MacKenzie 1995; Ceccotti 1996). In northern forest ecosystems, the absence of anthropogenic S inputs is often considered to be a predisposing factor to S deficiencies (Leaf 1968; Johnson 1984). Concern about decreased S inputs is related to rates of S 0 4 desorption, changes in S mineralization rates, and watershed recovery (Harrison et al. 1989a, 19896; Gustafson and Jacks 1993; Mulder and Cresser 1994; Houle and Carignan 1995). Soil-based factors contributing to S deficiencies are mineralogy, organic matter content, texture, pH, and hydraulic properties (Beaton 1971; Tisdale et al. 1986). 2. Assessment of Nutrient Status and Predicting Response to Fertilization The nutrient status of a stand indicates the degree to which nutrient requirements for maximum growth are satisfied (Tamm 1964). Nutrient status is evaluated to identify deficiencies and imbalances, assess site quality, and predict response to fertilization. Forest nutrient status is evaluated by visual symptoms, foliar and soil analysis, pot trials and other bioassays, site quality assessment, and fertilizer trials (Mead 1984; Ballard and Carter 1985; Binkley 1986; Carter 1992). Use of more than one technique is advocated where feasible (Swan 1966). The diagnostic and predictive aspects of forest nutrient assessment are not synonymous (Richards and Bevege 1972). Diagnosis requires identification of the factors limiting growth in relation to other 131 available resources, while prediction involves forecasting response to changed environmental conditions, such as increased nutrient availability (Morrison 1974). While foliar and soil analyses are widely used diagnostic tools in forest nutrition, response to increased nutrient availability is the soundest indicator of nutrient limitation (Leaf 1963; Morrison 1974; Ballard and Carter 1985; Chapin etal. 1986; Timmer 1991; Vitousek and Howarth 1991). Response to fertilization also provides the framework for developing predictive relationships. Fertilizer trials, followed by correlation of site variables with growth response and site evaluation are the key steps in developing a nutrient assessment strategy (Binkley 1986). 3. Sulphur Deficiencies in Forest Species Sulphur deficiencies in conifers were first described twenty to forty years ago (Youngberg and Dyrness 1965; Beaton 1966; Lambert and Turner 1977; Turner et al. 1977). Prior to that time, S was not considered to be a limiting nutrient in forests (Tamm 1964; Leaf 1968). Sulphur deficiencies are usually secondary to N deficiencies. Cases where S is the primary limiting element are rare, but have been described for Acacia mimosa plantations in East Africa (Hesse 1957). Demonstration of S deficiency in conifers by the addition of S fertilizers is rare. More frequently, S deficiencies have been inferred from foliar S status, namely foliar SCyS. Foliar SCyS has been closely related to Douglas-fir response to N fertilization, and is moderately useful as a predictor in lodgepole pine (Turner et al. 1979; Brockley 1991b, 1996). Species for which S deficiencies have been investigated are listed in Table 23. In cases where the cause of the S deficiency has been examined, low S parent material has usually been put forth as the underlying mechanism. This was observed for radiata pine sites plantations in Australia, Douglas-fir in western Washington, and ponderosa pine in Oregon. In Australia, S availability increases across the range of weathered granites < extrusives < sedimentary rocks (Lambert and Turner 1977). In western Washington, parent materials were grouped in increasing order of S availability as pumice < basalt < acid igneous ~ glacially derived < sedimentary (Turner 1979). Finally in central and 132 Table 23. Species with demonstrated or suspected sulphur deficiencies Species Pinus contorta Pinus contorta Pinus contorta Location Hinton, A B Interior B C Prince Rupert, BC Reference Pinus contorta Pinus contorta Pseudotsuga menziesii Pinus contorta Pinus ponderosa Pinus radiata Pinus radiata Picea glauca and Picea hybrids Tsuga heterophylla Abies amabilis Pseudotsuga menziesii Pseudotsuga menziesii Picea abies Fagus sylvatica Okanagan Falls, BC Golden, BC Oregon Australia Interior BC Vancouver Island W. Washington and Oregon (field trial) W. Washington and Oregon (greenhouse) Germany Diagnosed on basis of: N vs. N+S fertilization N vs. N+S fertilization' N vs. "complete mix" containing S a N vs. "complete mix" containing S a Foliar S parameters Yang 1985a Yang and Bella 1986 Brockley and Sheran 1994 Yoleetal . 1991 Kishchuk 1997 Smith and Wass 1994 Youngberg and Dymess 1965 Will and Youngberg 1978 Cochran etal. 1979 Lambert and Turner 1977 Swift and Brockley 1994 Weetman etal. 1993 Turner etal. 1977, 1979 N vs. N+S or N+S+P fertilization Foliar S0 4-S N vs. "complete mix" containing S a Foliar S parameters3 Foliar S0 4 -S b N vs. N+S fertilization Addition of M g S 0 4 Blake etal. 1988 Ende and Huttl 1992 a S deficiency induced or aggravated by N fertilizer. b For prediction of response to N fertilization. 133 eastern Oregon, S deficiencies are associated with pumice, ash, and basalt derived soils (Youngberg and Dyrness 1965; Geist 1976; Wil l and Youngberg 1978; Cochran 1989). 4. Lodgepole Pine Response to Fertilization Although lodgepole pine will grow on nutrient poor sites, it also shows exceptional response to improved nutrient conditions (Weetman et al. 1985). Fertilization of lodgepole pine has been used in young stands before crown closure, and in older stands closer to harvest age. Growth response of lodgepole pine to N alone and in combination with other elements has been demonstrated in interior B.C., Alberta, and the interior US Northwest. The range of growth responses to fertilization is summarized in Table 24. Direct comparisons are difficult because response to fertilization is variable, and response measures vary among studies. Growth responses range from about 10 to 50% basal area increase, and from 20 to 100% volume increase under various fertilizer treatments (Table 24). Growth response to a single fertilizer N application to lodgepole pine appears to last from three to four years (Boyd et al. 1975; Bella 1978; Mcintosh 1982; Brockley 1996). In some cases, inconsistent growth response of lodgepole pine to N fertilization has been associated with inducible deficiencies of other nutrients. In addition to S, secondary deficiencies of P, K , and boron (B) have been observed (Cochran 1979; Cochran et al. 1979; Yang 19856; Brockley 1990). Pine responds well to S additions relative to other species (Turner and Lambert 1980). Several studies have shown a greater response of lodgepole pine to N+S treatment compared to N alone (Yang 1985a; Brockley and Sheran 1994). Six-year diameter growth response to N+S was as much as 21% greater than to N alone (R. Brockley, unpublished data). In an optimum nutrition trial, repeated fertilization with N and a "complete-mix" fertilizer resulted in 50% increases in stand basal area and volume eight years after the last fertilization (Kishchuk 1997). The S in the fertilizer mix was responsible for the large and sustained growth response. 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Sulphur Deficiencies in Western Canada In contrast to the US Pacific Northwest and Australia, S deficiencies in western Canada are not clearly associated with a particular geologic parent material. In our glaciated soils formed on variable surficial materials, soil-forming processes control soil properties (Lavkulich 1978; Ryder 1978). In western Canada S deficiencies are associated with luvisolic soils. Luvisolic soils form on a variety of fine-textured parent materials including lacustrine clays, tills, and alluvial deposits (Bentley et al. 1971; Valentine and Lavkulich 1978). Sulphur deficiencies were first described in Canada in the 1920's at what are now the Breton Plots in central Alberta (Robertson 1979; Beaton and Soper 1986). Agricultural S deficiencies are widespread on luvisolic soils throughout the Prairie Provinces and B.C. As much as 30% of the cultivated land in the Prairie Provinces is S deficient, including up to 70% of the luvisolic soils (Bettany and Janzen 1984; Beaton and Soper 1986). Sulphur deficiencies have also been described in lodgepole pine on luvisolic soils in Alberta (Yang 1985a). Sulphur deficiencies occur in B.C. on luvisolic soils in the Peace River, Cariboo, Okanagan, Central Interior, and East Kootenay regions (Beaton et al. 1966; Halstead and Rennie 1977). Deficiencies have been documented in grains, forages and oilseed crops (Beaton and Soper 1986). Range and forages on luvisolic soils in the interior have responded well to S fertilization (Freyman and van Ryswyk 1969; Wikeem et al. 1993). B. HYPOTHESES A N D A P P R O A C H Mechanisms involved in growth response to S fertilization were investigated by examining soil nutrient availability and foliar nutrient concentrations in existing fertilization trials. Two aspects of nutrient cycling are considered. The first is a bioassay of lodgepole pine seedlings grown in soils collected from field fertilization trials, based on previous studies evaluating the nutrient supplying capacity of different substrates (Van Cleve and Harrison 1985; Van Cleve et al. 1986; Prescott et al. 1992). The hypothesis under consideration is that seedling growth and nutrition are improved by changes in soil nutrient availability resulting from fertilization. 136 Secondly, nutrient concentrations in foliage of all remaining age classes of fertilized and unfertilized trees were determined (Crane and Banks 1992; Mead and Preston 1994). The null hypotheses examined here were that foliar concentrations of N , S and SCyS do not change with increasing needle age, and that trends in foliar nutrition are unchanged under fertilization. C. SEEDLING BIOASSAY 1. Bioassay Establishment and Procedure A bioassay of lodgepole pine seedlings was established to determine the effects of S additions on soil S properties and seedling nutrition and growth. The specific objectives of the bioassay were 1) to identify changes in the S properties of soils from lodgepole pine sites one or two years following S fertilization, and 2) to determine lodgepole pine seedling biomass and tissue chemistry after growing in fertilized soils for 16 months. a. Soils In the fall of 1991, forest floor and mineral soil were sampled seperately from three installations (sites) in the Prince George Region that had been fertilized in either 1989 (Cobb Lake, Tsus Creek) or 1990 (Cluculz Creek). Experimental design of the trials and results from the Cobb Lake and Tsus Creek sites are described in Brockley and Sheran (1994). Soils were sampled from four treatments at each installation: 1) control (no fertilizer) 2) 200 kg ha 1 N (as urea and NH 4C1): N-only 3) 200 kg ha 1 N plus 50 kg ha 1 S as S 0 4 (as urea and (NH 4 ) 2 S0 4 ): N+S04 4) 200 kg ha"1 N plus 50 kg ha"1 S as S° (as urea, NH 4C1, and a degradable S° - sodium bentonite prill): N+S°. These treatments are a subset of those used in the field trial. No chemical analyses of the soils from these fertilizer installations had been done prior to this study. In addition to determining the effects of these 137 treatments on seedling growth and nutrition, these data provide an initial look at the effects of the fertilizer treatments on soil S properties. Forest floor and mineral soil samples were collected from each of ten plots in each treatment at each site. Samples were kept in coolers with ice-packs and then refrigerated (both approximately 5° C) until bioassay establishment (< 1 wk). Field-moist mineral soils were sieved to 4 mm and forest floor samples were sorted to remove large woody debris and cones. Subsamples were taken for moisture content determination, bioassay establishment, and chemical analysis. Additional soil samples were collected at each site to determine the mean ratio of forest floor to mineral soil to 10 cm depth. This ratio was used to establish a constant proportion of forest floor and mineral soil for each pot in the bioassay. Three soil cores were taken in each treatment at each site by removing an intact block of soil of a fixed volume ( 1 0 x 1 0 x 1 0 cm). Litter (L horizon) material was removed from each block, and the remaining soil was separated into two components: FH and mineral soil. Field-moist weights and moisture contents of the F H and mineral soil samples were determined. The ratio of mineral soil to F H weight on a dry weight basis was determined for each site, and was used to determine the moist weight of mineral and F H material to be used in each pot. Ten replicates of each site and treatment combination were established. Field-moist mineral soil and F H material were gently mixed in 7-inch diameter plastic pots. b. Lodgepole Pine Seedlings Lodgepole pine seeds from a registered seedlot were obtained from the B.C. Ministry of Forests Seed Centre, Surrey, B.C. Seeds were stratified by placing them on moist filter paper for 24 hr, on dry filter paper for 24 hr, and in cold storage (4°C) for 14 days. Seeds were then placed on moist filter paper at room temperature until they germinated (4-12 days). When sufficient seeds had germinated, six germinants were planted in each prepared pot in early September 1991. Pots were positioned randomly on a bench in the Plant Science Greenhouse, U B C . Pots were watered by hand daily for the first 21 days, after which time a daily automatic watering system was used. Incandescent lights were on daily for 8 hr from 138 September 1991 to May 1992 and in October 1992. Seedling growth was continued through the winter to utilize mineralized S. Within the first few weeks of the trial, substantial mouse damage occurred, in the form of unearthing and removal of the remaining seed portion of the germinants. More seed was obtained, stratified, and germinated in late September. The new germinants were placed in the pots in early October, to again bring the total number of germinants per pot to six. About 30% of the germinants were replaced. Consequently, there were random age differences of approximately one month among seedlings. In January 1992, seedlings were thinned to three per pot. The remaining seedlings were harvested in January 1993. At harvest, entire seedlings were removed from pots. Roots and shoots were separated at the root collar, and roots were thoroughly washed in tap water. 2. Data Collection a. Soil Chemical Analysis Forest floor and mineral soil samples were analyzed at the time of bioassay establishment. Fresh soils were extracted with 2 M K C 1 , and the extractant analyzed for N H 4 and N 0 3 on an Alpkem RFA 300 Autoanalyzer. The remainder of the subsamples were air-dried, sieved to 2 mm, and analyzed for total-S, HI-S, total inorganic and soluble-S04, total C and N , pH, available P, and exchangeable cations (II C. Methods, 1 b i , ii) b. Seedling Tissue Biomass and Chemical Analysis Tissue was oven-dried at 70° C for 24 hr. Total seedling biomass (root plus shoot) was determined, and summed for the three seedlings per pot. Shoot samples were separated into green foliage, senescent foliage, and stems. Only green foliage was chemically analyzed. Foliage was composited by pot and ground in a Waring blender prior to chemical analysis. Tissue was analyzed for S, S0 4-S, N , P, Ca, Mg, K , and micronutrients (II C. Methods, 5). 139 3. Statistical Analysis Analysis of variance was used to determine fertilizer treatment differences. As all sites were in the Prince George (S-deficient) Region, sites were considered as blocks in a randomized block design analysis of variance (SPSS Inc. 1996). Treatment differences in seedling biomass and tissue and soil chemistry are reported. 4. Results and Discussion a. Forest Floor Nutrient Concentration Forest floor total-S concentration did not differ statistically among treatments (Table 25a). Although the N+S° treatment mean is more than three times greater than other treatment means, variability of total-S values within the treatment precluded statistical differences. Greater variability of soil S concentration in the N+S° treatment, especially relative to the (NH 4 ) 2 S0 4 treatment, is likely due to the coarser size of S° - sodium bentonite prills compared to (NH 4 ) 2 S0 4 crystals (Brockley and Sheran 1994). Greater forest floor total-S concentration in the N+S° treatment is attributable to the slow release of S from S° by microbial oxidation, and its subsequent transfer or transformation within the soil (Janzen and Bettany 1986). Forest floor total-S concentration in the N+S° treatment did not correspond among sites to the time since fertilization. The highest and lowest concentrations of total-S occurred at the sites fertilized two years prior to sampling (0.16%, 0.59%; Cobb Lake and Tsus Creek, respectively), while concentrations were intermediate at the site fertilized the previous year (0.28%, Cluculz Creek). This suggests that first, there may be site-specific rates of S° oxidation within the forest floor controlled by moisture or other factors; and second, S° oxidation in these forest floors is not complete one to two years following fertilization. Concentrations of forest floor HI-S and organic-S04 were significantly greater in the N+S° treatment than in the control and the N-only treatments (Table 25a). Organic-S concentration in the N+S° treatment was also much greater than in the other treatments, although variability may have again obscured significant treatment differences. Evidently, concentrations of organic-S constituents increased in the N+S° CO i o 1 e>0 CO • T 3 U T 3 G O X) i U o oo s S3 WD i -O s ° ,2 CD CO o <U "G O CO co "ea , v CM ~ ID ON ID VO r-" 0 0 <N p^ ^ « N—' 0 0 0 0 -H O CO ID co v© vo CM VO as OS' O co cn CM •* ID CO CO p^ r-" t-; — • VO co CO © ID ID VO VO co 0 0 0 0 0 0 CM X ! © " X •*" VO co X i £ C M ON o © CO CM o o o © o o o o c o o G o CO IT) X i es p-co r~" o CM o o CM ON C M C M IO fO © C M CM 00 o VO C M l - H ^—^ CM ID CM © 0 0 ID CM CM ^ — ' N — ' O r - 0 0 — VO © CO CM CM p-es ON" <r" CO •<9-O C M CO © CO o CO z z co + Z o </] o c fl> S 3 0> G — a> c U £ to o tS -g .a co c3 - ~ <U to 2 O | CD § JS CD Q to CO 'co eS o "a. c G | -s o .SP 'co a> IS Q . O es O 60 ii C O ii JS CO '2 es o •a a cs oo "es o « M .2 * r 2 o o a. x> 2 .s a. CO C O s s .* ts -ft! P R c u a> CO 8 o u o x> 5 5 c-« 2 o X i CM 2 93 H l?r 00 &o 5 e> "3 1 ^ CO X) 4) I I1? - 1 o 1 o o O CO CO I o 'c CS M CO X ) 4> X I s o X i O CO 6? o 8 ° o CO CO o o CM o X i o p^ C M X i o co C M c o o o ir, o o C3V c o CO o C5 e« CM ir. o O X l - H © V-^ S — ^ co X X p-' X «o X X X X i X X i vo co o CO + z ON © i <i © © o* co p-ir, vo cs p-VO CM CM CO co p-© © o © CM 0 0 p-P-^  ON o\ vd ON o\ cs cs cs X i ON p~ CM p-_ © ©^ CM vd ON X 00 VO* co" co X X X VO cs co co co co ' N CO P-~ • s i " ©• © © ' © ' v—' —^' —^' 0 0 co co ON CM CM' co CM' CO vq ON I/O © © s—' v^ s—' —^' ON vq P-; ID CO CM 0 0 ON CO CO + Z 'co CO a) Q . cfl ts "S. 141 treatment. This appears to be more attributable to organic-S04 than C-bonded-S. This is supported by the greater proportion of organic-S composed of organic-S0 4, and the greater organic-S04 :C-bonded-S ratio in the N+S° treatment (Table 25b). Concentrations of forest floor HI-S and organic-S04 in the N+S0 4 treatment were intermediate to and not statistically different from the other treatments. This partem indicates the persistence of S° and the more rapid loss of S 0 4 from the forest floor. There were no differences in forest floor soluble-S04, C-bonded-S, or organic-S concentrations among treatments. Although not statistically different from the control treatment, lowest mean concentrations of HI-S and organic-S04 occurred in the N-only treatment. This suggests that these constituents may have been more depleted with the addition of N-only than with the addition of N+S0 4 or N+S°. The proportion of total-S comprised of organic-S04 was greater in the N+S° treatment than in the other treatments, while the proportion of C-bonded-S was lower (Table 25b). There were no differences in the proportion of HI-S, forest floor soluble-S04, or organic-S among treatments. Partially oxidized S° forms would be reduced by hydriodic acid, possibly resulting in an overestimation of HI-S and organic-S04 concentrations in the N+S° treatment. However, HI-S and organic-S 0 4 concentrations in the N+S° treatment are an order of magnitude greater than in the other treatments (Table 25a), indicating that overestimation is unlikely to alter the results. Total forest floor C concentration and C:N ratio did not vary among treatments (Table 25c). Total and extractable N concentrations were greatest in the N-only treatment although differences were not significant. Differences in N:S and C:S ratios among treatments are attributable to differences in S (Table 25c). The N:S ratio was significantly lower in the N+S° treatment than in the other treatments. The C:S ratio was lower in the N+S° treatment than in the N-only treatment, but was not statistically different from the control or the N+S0 4 treatments. Forest floor pH measured in water was significantly greater in the N-only and N+S0 4 treatments than in the control (Table 25d). No differences in pH were evident in pH measured in CaCl 2 . A decrease in forest floor pH in the N+S° treatment was expected due to acidification during S° oxidation (Maynard et al. 1986; Nyborg and Mahli 1991). However, pH changes associated with 142 ,cu •5 § 6 0 cu S3 cu '-5 cu D. o S3 S3 o of _e cu cu ce O •a Z ju 3 « cu S3 CU e S3 o CU o. o S3 o im o © o fa u CN 3 S3 H cu 4 0 CC CJ Z CJ o z eo 3. z CJ c cu E cu 40 S3 ab 42 S3 X ON 9 0 C M ON IT, ' NO O NO ON © f > CM S3 S3 S3 42 o s © © C N -^^  C N C M NO ?—\ CN CM" CN" -^^  CN CN © CM cn cn cn on T P ^ i CM" T ? CO T t CN o © © © ^—' —' VO ,_ VO T t © C N on on on in ON o 4 = c o U NO in on CM © © CM o Z o cc + z on T t in in CN ON m © on ON ON © on T t NO © T t CN CN O^ m in © © © © © © © © 0 0 in /—V on ON 0 0 on in r~ CM T t T t Tt^ CM © CM 0 0 CM © 0 0 on CM in T t in on on on on C C + Z in © 8 IS cu o c cu cu 5J 3 e <D C is cu S3 r -n. c S3 cu 4 3 CU S3 o cn • — D. S3 — cn cn cu g fc . i s cu ll 41 _ C C C Q a cu cu cu 4 0 c cu I 0 0 cu S3 cn cu cu D. O >> S3 cn cn S3 O DC CU cu a, JJ S3 S3 cu •o a S3 S3 CU — s S3 CU en cu B G . S3 « J ffi .S s - ^ O RT o cn 43 *^ C C ^ CU cn S ai £ O cu 43 T 5 ir, ON s S3 H 0 0 (=0 3. w o 6 0 S3 O 0 0 4 4 CJ X a. O CN E C B a 42 42 S3 43 S3 S3 \ ON © ON C M 00 <-! w s -^ IT . ON ON ON T f IT; NO © 0 0 NO in in T t CN © CN on in ON —^' ^_ 0 0 CM on on CN ON ON ON © in 0 0 NO 0 0 vo T ? © © " CN ^ i © © © © v—' ,_ © 0 0 NO T t NO T t ~ '—V / V © " NO G" © T t ON on 0 0 r-* ,—: ^-^ v—' © T t T t CM on 0 0 on in NO vd CM" © on ON NO ~-T t in T £ in ON _ © CM NO on 0 0 Ov in CM CN CN CM / N Tt " T t ^ « CM on on on © © © d -^^  -^^  ON on 0 0 CM T t in T t T t T t T t T t 42 42 S3 S3 S3 T t CM O O N CM O © d d ^ — ' V ) O N IT) X NO ON ON X T f T f *o _>» o o 43 "c C C C C c o o + + o Z z Z on »- cu cn cn 2 S3 k . J 3 2 & | ? l i 143 S° oxidation may be related to time since S° application and application rate (Nor and Tabatabai 1977). There were no treatment differences in exchangeable cations, which might also be expected after S° application. Available P concentration was greatest in the control, and lowest in the N-only treatment, suggesting more of an P-N than a P-S relationship. b. Mineral Soil Nutrient Concentration Differences among treatments in mineral soil total-S, HI-S, and organic-S04 concentrations were similar (Table 26a). Concentrations of these S constituents were significantly greater in the N+S° treatment than in the control and N-only treatments. Mineral soil total-S concentration in the N+S° treatment corresponded better than the forest floor with time since fertilization. Total-S concentration was greatest at the site fertilized in 1990 (110.40 /ug g\ Cluculz Creek), and lower at the sites fertilized in 1989 (86.70 and 105.50 jug g'\ Cobb Lake and Tsus Creek, respectively). Total-S, HI-S, and organic-S04 concentrations in the N+S0 4 treatment were not different from other treatments. This pattern is similar to that observed for forest floor HI-S and organic S 0 4 concentrations. There were no differences in concentrations of total inorganicS04, soluble-S04, or C-bonded-S concentrations among treatments in mineral soil. Organic-S concentration in mineral soil was significantly greater in the N+S° treatment than the other treatments. As for the forest floor, this was attributable to increased 0rganic -SO 4 concentration in this treatment. Increased organic-S in the N+S° treatment may be at least partially explained by increased microbial biomass S associated with S° oxidation and subsequent S transformations. If this were the case, it would appear that organic-S04 is a significant component of the microbial biomass S. Since fungi accumulate more organic-S04 than bacteria (Saggar et al. 1981; Castellano and Dick 1991), it is possible that fungi are involved in S° oxidation in these soils. Treatment differences in S constituents as a proportion of total-S were only evident for organic-S 0 4 (Table 26b). There were no differences in the proportions of organic-S comprised of organic-S04 or C-bonded-S (Table 26b), or in the organic-S04 or C-bonded-S ratio (Table 26c). CD to X> 4-* a <u te x >> s 'E 0 0 to ts CO n. o 03 S3 O DC •3 cu CU 6D M B .o 2 a cu u a o u B « 2 £• X B © O * «J c » u =3 & <» £3 Hi c 53 (U •S CS 93 (N CU CO i #w '3 6JD | O CO I X I <u X I c o X2 I O O CO o '3 « . ff O O CO I jo J 3 O co O CO cs .2 o c 6 0 | O G CO s CO I "3 o H 90 CO ©V ON X vo ir, vo X i C3 H cS CO G o vo vo* vo* ir, vo © , © CM © V * o VO* VO o" I O X i 93 ci ON VO* CM X i 93 X , VO r-* VO O CO X I O 0 0 CO G P ^ o o CN vq 0 0 co VO ID CM CD X) X i ab 93 (0.7) (2.0) (1.4) (11.0 © o\ VO VO CO i - H X i - H I O ID G ^ — s ID © © ' © co © P~- co ID co © * CD CN CM CN o O s CD co VO 0 0 © CM CM VO I O r-* ON © © CO o Z Z Z CD © 8 "es CO o ses. Ferei CD C4-. •a •3 G CD G to CO par tme 'to _ c cS c o <u #\ c b CO ha "S o k> CO CO CO x Q . .c CO CS licate rrors etters ex CD — CO X s_ © II anda iffere c CO Q cS o I CO CS ts CD o 93 C O G O 93 o COD •3 cu cu C O cu a CO u '3 93 O X I B 93 CO "3 o o B O CO o. 2 o 2 S a u C O 1 -93 ccj co J« B C 5 CO = 3 O CU CO O co co XI *3 c U CO s i X) VO f S ju "S 93 H CO I X CO X c o x> I u O CO 6 0 O CO I o 1 6 0 CO i X CD X c o x> I u o CO "3 93 ff o O CO X) _3 O co o 0 0 o CO 2 CO I '3 CS 6 0 o C+H o cS Ov" ID ID c i © c s CD 0 0 >D r-~ © c-~ CO VO Ov ID ON CD CD CO o P-" CS CD CM CD CO ON (N 0 0 c s vd CO © 5s /—\ CN cs" CD CD © 87.2 © CS ON 85.9 89.9 ov" CO c s Ov ^r vo 0 0 ^r VO vd VO vd ID CN >D X i X i 93 X i 93 93 I O CM vq i - H ci ci VO co i - H «s IO* <s ON f S r* CO CO CD © © CO CO CO >D Ov vd 0 0 vq CD ID cs" CN © CO CO CO 0 0 r i CO 0 0 G c s vd 0 0 (N CO vq CN CO CO ID antrol only o CO + o CO + O Z 144 CD © 8 ts co CD O G U cD •S x c u c .S g C + J CD 5 CD • - O S In » « <0 -j X a. 8 c co cS — ^ E5 2-CO CO a. CD ° e - " 8 3 ii J E c oo Q "fr C/3 O -o c/3 £> c o &o CJ C/3 C/3 z CJ o z 6 0 6 0 3. B Z 3? 05 cu CN Tt " 0 ? d d d d T t N O O N N O d d d d G (26) G (24) T t o oo o o CO CM CM CO T t T t CM CM" (I) N O N O N O CM CM* o? (0.4) O N O N o CM CM CN" i - H d T t T f d o 00 CX) o d O N O d s o U o d 90 d r o NO C 3 T f i - H O N © © c o X i S3 CM © ON C M © © O N © X i (3 CO © CM — NO NO X i S3 © ON r- ON i—t r-i T f V > © © O N " CM © " CM © — ' © © d. N O O N N O © T t O N — CM — o C/3 + z C/3 + z in © CO cu o C CU k-,cu ^3 cu c* e O . C .s 1 c 4= ^ CD 1 « •s ° CD 03 T 3 C U B « o CD ' -o 03 T 3 C 03 -+-• C/3 C cu S3 in V ) S3 © IS on T3 CD CU C A CD 3 S3 u S3 CD a S3 «T a ,2 S3 cu S3 CD DC a S3 X I u x M a. 2 cu B i NO CM 3 S3 H 6 0 6 0 3. CJ 6 0 03 CJ 6 0 + CJ Q . O tN a. O N " G in m CN T t CN CO CM oo CM r-; CM in r- © O N O N in O N © N O 0 0 N O m m Tt " © © d d N O in 0 0 0 0 0 0 r-in CM CM co co G © G © © '—-O N © © © © © O N co CN T t CM © © © © /—\ T t T t CM" cn © T t P-co © , © © d o © © © © p-0 0 ~ © 0 0 O N " T t 0 0 © O N © w C- © p-© T t T t 0 0 T t N O OO CO co co CM Tt " CN G CN CO CM CM © © © © 0 0 CO © CO T t CO CN CO T t T t T t T t 0 0 G CM CM © " CM © © © © CO 0 0 © 0 0 © 0 0 N O p~ T t T t T t T t o CJ c o O + z C/3 + z CO CO cu a. a. cu 146 Total C and N concentrations, and C:N, N:S, and C:S ratios did not differ significantly among treatments, although the C:S ratio was lower in the N+S° treatment (Table 26c). Extractable N concentrations were significantly greater in the N-only treatment than in the control, indicating that one or two years after fertilization N had accumulated in the surface mineral soil. There was no change in mineral soil pH in the fertilizer treatments (Table 26d), nor were there significant treatment differences in mineral soil exchangeable cations or available P. c. Seedling Nutrient Status Nutrient concentrations in foliage were not significantly affected by fertilizer treatment (Table 27). Nitrogen and K were the only nutrients approaching deficiency levels, with both N and K concentrations indicating slight to moderate deficiencies (Ballard and Carter 1985). Sulphur, P, Ca, Mg, and boron concentrations were at or slightly above sufficiency levels, and N:S ratios were well below critical values (Ballard and Carter 1985; Brockley 1990). Foliar S and SCyS concentrations in bioassay seedlings were greater than in current-year foliage of trees under the same treatments in the fertilization trial (Brockley and Sheran 1994). Seedling foliar SCyS concentrations were high in all treatments (476 to 514 pig g"1), but are still within the literature range for unfertilized trees (up to 700 pig g"1). Sulphur and SCyS concentrations in unfertilized seedlings were 39% and 82% greater than in unfertilized trees, respectively. Sulphate-S accounted for a greater proportion of the total foliar S in unfertilized seedlings (34%) than in unfertilized trees (7%). These differences are likely due to 1) differences in internal S distribution between seedlings and trees, and 2) promotion of S availability by environmental conditions other than substrate S levels in the bioassay study. In the field fertilization trials, addition of S 0 4 increased first-year foliar S and SCyS concentrations more than similar rates of S° (Brockley and Sheran 1994). This was attributed to the immediate availability of the S 0 4 fertilizer, in contrast to the more slowly available S° In this study, there was no difference in foliar S or SCyS concentration between the two forms of added S. Mineral soil soluble-S04 concentrations in the N+S0 4 treatment were similar to the low levels in the control treatment, co z t>0 cS u cs e cu w s o cu cm c •3 cu v a — "3 a. CU 6X) •a o C M 9i S cs H co c cu cd CD /—\ cn CN i n © d d d ^— / CN 00 — 00 00 00 Ov m CD cn CN" o o © © d d d d s — ' 00 o 00 VO d d d d /—V /—V 00 G" o 5-" o o o o o o o d d d d s —' —' s —' ^—' vo VO i n »—' d d d d m CN* CN" o o o o d d d d -^^  CN <N cn CN i n i n i n i n d d d d ^ " c o i n CN" o o o o O o o d d d d -^^  -^^  r - as 00 d d d d CN" in" o Ov" o o o o o © o d d d d v — ' -^^  c n i n i n •—i .—> •—1 •—i d d d d —V CN G oo" o o o o d d d ^—' v —' N —' N —' r - ON 00 r -CN cn CN cn c o * 8 o + Z Z o J O . CO bO _C "3 <u u cn CO CD O CD -4-t 't/3 o O-E o o CO CO CJ CD O +3 c« C CD c c o co cn hi S 8 a, 5 CO CO g c a. -a CD >-i - cS II B C CO "w cu B o ( J cs — 3 cs H CQ r -ON ON Ov d i n S—' CN 00 ON ON r o 00 OS ON 00 Ov CM O d ON 00 c o ON i n 00 CM — ON CM' CO d CM oo VO oo Os O v o /—s /—V r—s CN cn i n i n vo S ^ s — ' CN CN m VO 00 vo vo cn cn cn m 1 1 ^ ™ r - o CM vq CN ON vd CM 00 vq o 00 i n vd i n m cn cn m CM vo d CM' d d s —' -^^  r - m ON i n vd i n i n *-" 1—1 i n 00 m vd m -^^  00 o CO ON vd r o O r - O m i n •vi- i n o is c o O c o O o CO CO + Z 147 148 indicating that by the time of sampling, any added soluble-S in the N+S0 4 treatment had already been utilized or removed. Foliar S and S0 4-S concentrations were no greater in this treatment than the others, suggesting that S 0 4 was removed from the soil in the year or two years following fertilization. This most likely occurred by leaching. Micronutrient cation concentrations in all treatments were much higher than published values of sufficient levels for conifer foliage. This was particularly true for copper (Cu), where concentrations over 1000 pig g"1 were observed (Table 27). A foliar concentration of 4 pig g"1 is the threshold for Cu deficiency in lodgepole pine (Majid and Ballard 1990). Sufficiency concentrations of other micronutrients measured in this study are: 25 to 50yug g"1 Fe, 25 pig g"1 Mn, and 10 to 15 pig g"1 Zn (Stone 1968; Ballard and Carter 1985). These values are not species specific. Two internal reference samples analyzed at the same time as these samples had much lower Cu concentrations than the bioassay tissue (Meadow Lake site foliage 3.1 pig g"1; T. Ballard reference sample 3.4 pig g"1). Iron, Mn, and Zn concentrations in reference samples were somewhat lower than in the bioassay seedlings, but did not differ as widely as Cu. Moreover, other foliage (resorption, foliar nutrient distribution by age class) analyzed using the same methods and lab indicate more typical Cu concentrations (80% of samples < 10 pig g"' Cu; n = 520). It appears that the seedlings grown in this study were subject to high micronutrient inputs. The most likely source of inputs is greenhouse tap water. Foliar Cu concentrations of 17 to 20 pig g"1 are approaching toxic levels (Stone 1968; Majid and Ballard 1990); however, concentrations greater than 700 pig g"1 have been observed in conifer foliage on Cu rich sites (Dykeman and de Sousa 1966). Although there did not appear to be visible symptoms of Cu toxicity in the seedlings in this study (Stone 1968), the effects of such high Cu concentrations on growth and metabolism are not known. d. Seedling Biomass There were no differences in seedling root, shoot, green needle, or total seedling biomass among fertilizer treatments (Table 28). This reflects the similarities in tissue nutrient status under different 149 fertilizer treatments. In the field fertilization trials, first-year 100-needle weight was increased in SO> containing treatments more than in S° treatments, which is the same trend observed for foliar S and S0 4-S concentrations (Brockley and Sheran 1994). In this study, there were no differences in total green needle biomass between S forms in the bioassay seedlings. The seedlings were not S-stressed in any treatment, as indicated by foliar S status. Micronutrient concentrations were likely excessive, but affected all treatments similarly. Table 28. Biomass of seedlings in bioassay (g oven dry weight). Treatment Root Shoot Green needles Total seedling control 2.96(0.36) 4.66(0.53) 2.17(0.12) 7.62(0.87) N-only 2.86(0.52) 4.62(1.14) 3.13 (0.72) 7.41 (1.68) N + S 0 4 3.08(0.68) 5.39(1.16) 3.70(0.66) . 8.48(1.84) N + S° 3.09(0.59) 5.09(1.13) 2.87(0.30) 8.18(1.72) n = 10 replicates per site; 3 sites. Each replicate is a composite of three seedlings/pot. Standard errors are shown in parentheses. 5. Summary and Conclusions Total-S, organic-S, HI-S, and organic-S04 were greater in forest floor and mineral soils under N+S° treatment than in unfertilized soils or soils treated with N-only. With the exception of forest floor total-S and organic-S concentrations, differences were statistically significant. Soil S concentrations in the N+S0 4 treatment were intermediate to unfertilized and N+S° treated soils. Increased soil organic-S04 concentrations in the N+S° treatment are of particular interest, as the role of organic-S04 in S availability has been identified. However, in this study, the effect of the greater soil organic-S04 concentrations in the N+S° treatment was not reflected in foliar S status or seedling biomass. In the field trial, SOycontaining fertilizer treatments had a greater effect on first foliar S status and needle biomass than S° treatments. Soil analyses in this study show that effects of the N+S0 4 application on soil S constituents are shorter-lived than in the N+S° treatment. Two possible scenarios arise from this observation. The first is that fertilizer S 0 4 available in the first growing season after application may be sufficient to ameliorate S deficiencies, maintain a suitable N:S balance in the foliage, and sustain increased growth rates. Alternatively, the initial flush of available S may stimulate growth beyond what can be sustained after the first growing season, and growth will again be S limited in relation to N . It is not known which result will emerge on the basis of the first-year field study results. It is possible that growth response to N+S° may be better than N+S0 4 in subsequent years through changes in soil organic-S04. It would be interesting to know if organic-S04 concentrations were associated with soil microbial S. Treatment differences in soil S properties in this study did not result in differences in seedling tissue chemistry or biomass. As much information was obtained from analysis of the field-fertilized soils as from the use of seedlings as a bioassay, as performed in this study. D. NUTRIENT DISTRIBUTION B Y FOLIAR A G E CLASS 1. Foliar Sampling Nutrient concentrations in different age class needles were measured by sampling needles from each age class remaining on the branches in October 1992. Three sites in the Prince George Region (Gregg Creek, Cluculz Creek, Cobb Lake) and one site in the Nelson Region (Upper Gold Creek) were sampled. The same fertilizer treatments had been applied to all sites in 1988 (Gregg Creek), 1989 (Cobb Lake, Upper Gold Creek), or 1990 (Cluculz Creek). Trees were sampled from plots in the following treatments: 1) control (unfertilized) 2) 200 kg ha 1 N (as urea and NH 4C1): N-only 3) 200 kg ha 1 N plus 50 kg ha 1 S (as urea and (NH 4 ) 2 S0 4 ): N+S At each site five plots of each treatment were randomly selected. In each plot, one branch from each of three trees was removed with a pole pruner from approximately halfway up the live crown. Needles of each age class were removed from the branches and bulked to provide one composite sample of each age class per plot. Samples were kept cool in plastic bags until oven-drying at 70° for 24 hr. Oven-dried 151 tissue was ground in a Waring blender prior to chemical analysis. Foliar analysis is described in (IIC. Methods, 5). Mean needle retention time was determined from the ages of the oldest remaining needles on the sampled trees. Trends in nutrient concentration with increasing needle age were plotted by site and by treatment. No statistical analyses were conducted. 2. Results and Discussion Mean needle retention time in each fertilization treatment was usually 5 to 6 years (Figure 17). Trees at the Upper Gold Creek (Nelson) site retained needles for two to seven years longer than the Prince George sites. There did not appear to be a consistent trend in needle retention time with fertilizer treatments at any site. Regressions between unfertilized current-year foliar N , S, and S0 4-S concentrations and years of needle retention indicated weak, negative relationships (r2 = 0.35, 0.52, and 0.01, respectively). An inverse relationship between nutrient availability and needle retention has been observed elsewhere (Edmonds et al. 1990). Foliar nutrition results from the Upper Gold Creek site must be interpreted with caution, due to fungal and insect damage. Current-year needles were stunted and chlorotic, and there were very few 1991 (current + one year) needles remaining on the branches. These observations were consistent across fertilization treatments. This site was badly affected by pine needle cast fungus the previous year (Lophodermella concolor; Forest Health Officer, Cranbrook Forest District). In addition, there was an infestation of tussock moth (Orgya antiqud) at this site. Chemical analyses were done on the affected foliage but it is not known if these samples are good indicators of nutritional status. Needle cast was also observed to a lesser extent at the Cobb Lake site. 152 1 4 12 4 TD CD CD £Z -4—I CO O o CO CO 10 H 8 H 6 H I T control N-only N+S treatment Cluculz Creek (Prince George) i Cobb Lake (Prince George) Gregg Creek (Prince George) Upper Gold Creek (Nelson) Figure 17. Age of oldest needles remaining on trees under fertilizer treatments (n = 5). 153 Trends in nutrient concentration with needle age are shown in Figure 18a-c. Foliar N concentrations generally decreased with increasing needle age in unfertilized trees (Figure 18a). Concentrations of N (as well as S and SCyS) at the Upper Gold Creek site decreased sharply after 1990, probably in relation to the needle cast (Figure 18a,b,c). There was an obvious effect of N-only fertilization on foliar N concentrations at the only Cobb Lake site. Nitrogen concentrations were substantially greater in needles formed one and two years post-fertilization than in previous or successive needles, although N concentrations had returned to pre-fertilization levels within three years. Slight increases in N concentration occurred in post-fertilization foliage at the other sites. A decrease in foliar N might be expected to occur after N+S addition if added S was large relative to N . The fairly consistent, gradual decrease in foliar N concentration with needle age does not appear to have been interrupted by N+S fertilization, indicating that balanced amounts of N and S were applied (Figure 18a). Foliar S concentration also gradually decreased with needle age in unfertilized trees (Figure 18b). Foliar S concentration would be expected to decrease following N-only fertilization, as S supplies were drawn on. This was not evident at any site. Foliar S concentrations were generally low (< 0.10%), likely limiting any further decrease with N addition. However, this furthers the expectation that N concentrations would be elevated in foliage formed after N-only fertilization, which was obvious at one site only. Foliar S concentration increased somewhat following N+S fertilization at the three Prince George sites (Cluculz Creek, Cobb Lake, Gregg Creek) and decreased at the Upper Gold Creek site. The latter was possibly due to the effects of needle cast on the foliage. Increased foliar S concentrations in the three to five years following fertilization suggests that the added S has remained available for foliage production through internal redistribution. Foliar S0 4-S concentrations were less consistent than N or S concentrations in unfertilized trees both among sites, and among age classes within a site (Figure 18c). There was as much as 50 to 75 pig g"1 variation in SCyS concentration among different age classes on unfertilized trees within a site. At the 154 1.35 1.25 Co 1.15 H 2 1.05 CO o 0.95 0.85 0.75 1.95 1.75 Co 1.55 o^ 2 1.35 CD O 1.15 0.95 0.75 1.35 1.25 Co 1.15 o*-Z 1.05 CO o 0.95 0.85 0.75 O. unfertilized CC V • o- CL GC • —v UGC 1992 1990 1988 1986 1984 1982 o-O. F N-only (note different Y axis scale) a o • cc O CL GC UGC -v- v—. 1992 1990 1988 1986 1984 1982 O. N+S — • - - CC • o- CL — • - - GC —v UGC •-v.. Y 1992 1990 1988 1986 1984 1982 Figure 18a. Foliar N concentration of all remaining age classes on unfertilized and fertilized trees (n = 5). X axis indicates year of needle origin. Year of fertilization is indicated by F. 155 0.11 0.10 — 0.09 CO CO = 0.08 0.07 0.06 0.11 0.10 ^ 0.09 H CO M 0.08 H 0.07 , 0.06 0.11 0.10 ^ 0.09 CO •J 0.08 a 0.07 0.06 unfertilized CC • o- CL GC • —v UGC N 7 1992 1990 1988 1986 1984 1982 N-only - • - cc • O • CL - r — GC - V •• UGC • • V 1992 1990 1988 — i 1 1986 1984 1982 O. N+S - • - - CC • o- CL — • GC —v- UGC -v-1992 1990 1988 1986 ^ . . . 1984 1982 Figure 18b. Foliar S concentration of all remaining age classes on unfertilized and fertilized trees (n = 5). X axis indicates year of needle origin. Year of fertilization is indicated by F. 156 cn Oi CO I O CO 200 150 100 =S 50 200 0 5 150 cn CO I o CO t— CD .o 100 50 cn 3 . CO I o CO .55 o 200 150 100 H 50 -\ unfertilized 1992 1990 1988 1986 N-only 1992 1990 1988 1986 N+S — ^ - v 1992 1990 1988 1986 CC O CL GC UGC 1984 1982 CC O CL •v— GC UGC • - V - -1984 1982 CC • o- CL GC T UGC - v " 1984 1982 Figure 18c. Foliar S0 4 -S concentration of all remaining age classes on unfertilized and fertilized trees (n = 5) X axis indicates year of needle origin. Year of fertilization is indicated by F. 157 Cobb Lake site, foliar S0 4-S concentrations were particularly low in all age classes of needles. Foliar N concentrations (unfertilized) were relatively high at this site (Figure 18a), indicating that low S0 4-S levels resulted in N accumulation. Without the influence of the needle cast, it appears that there would have been a gradual decrease in S0 4-S concentration with increasing needle age at the Upper Gold Creek site. Reasons for variations in S0 4-S concentration in unfertilized trees at the other two sites are not known. The expected decrease in foliar S status with N-only fertilization is evident in S0 4-S concentration at the Gregg Creek site. Sulphate-S concentrations in needles formed two years after fertilization had recovered to pre-fertilization levels, suggesting that S availability is not as limited on this site as others. There was no change in S0 4-S concentration following fertilization at the other sites. Below about 50 to 60 £tg g"1, foliar S0 4-S concentration appears to be unaffected by N dynamics or internal redistribution. The trend of increased foliar S concentration following N+S fertilization is also evident for S0 4-S concentration at the Gregg Creek site. A foliar S0 4-S concentration of about 50 /ig g'1 again appears to be the threshold for S0 4-S changes with fertilization. Knowledge of whether trends in nutrient resorption changed following fertilization would provide some insight into the relationship between nutrient availability and internal recycling for lodgepole pine on these sites. 3. Summary In unfertilized trees, foliar N and S concentrations decreased consistently with increasing needle age, while foliar S0 4-S concentration was more variable. Expected changes in the nutrient status of post-fertilization foliage did not occur consistently, and site-to-site variation in foliar nutrition became more pronounced under fertilization. Different patterns may have been observed if successive years foliage had been sampled in the year of formation, rather than at one time. Gradually increasing foliar S concentration in foliage produced after N+S fertilization suggests that S was retained and internally cycled. At concentrations below 50 iug g'1, foliar S0 4-S appears to be unaffected by N dynamics. There may be an inverse relationship between nutrient availability and needle retention on these sites, which in turn may be related to other aspects of production physiology. It should be recognized that stands sampled in this study 158 were not of identical density, and interpretation of the results based on retention of older needle classes must be made accordingly. E. DISCUSSION A N D CONCLUSIONS The fate of fertilizer S could be more thoroughly addressed in detailed studies using radioactive tracers or stable S isotopes. However, some information about the availability of fertilizer S was obtained from data collected from the existing field trials. Fertilization with N+S° significantly increased soil organic-S and orgaftic-S04 concentrations compared to unfertilized soil. Soil S concentrations in the N+S0 4 treatment were intermediate to unfertilized and N+S° treated soils. In trees on fertilized soils, foliar S nutrition and growth was initially improved more in the N+S0 4 treatment than in the N+S° treatment. There was no effect of fertilizer treatment on seedling nutrition or biomass. The duration of response in foliar nutrition and growth in the field trial to the N+S0 4 treatment is not known. Soil S concentrations had decreased one or two years following fertilization. Greater foliar S concentrations in foliage produced in years subsequent to N+S fertilization suggests that at least some of the assimilated S remained in the tree and was incorporated into new foliage. Whether or not fertilizer S° becomes more available over time and results in a comparable growth response remains an important question. 159 CHAPTER IV. PREDICTORS OF LODGEPOLE PINE GROWTH RESPONSE TO N FERTILIZATION Soil and foliar properties related to S availability on these sites have been identified. In this section, soil and foliar data were used in conjunction with growth response data from the B.C. Ministry of Forests fertilization trials. The objective was to determine which properties are useful in predicting stand responsiveness to N fertilization, as indicated by regressions between soil and/or foliar properties and growth response. Data for first-, third-, and sixth- year growth response to 200 kg N ha"1 (78% urea, 22% NH 4C1) were provided by R. Brockley, B.C. Ministry of Forests. First-year response was hundred-needle weight, and third- and sixth- year responses were dbh increment. Regressions were done between growth response at each measurement interval and site means of B horizon soil and foliar nutrition variables (n = 10). Soil and foliar properties selected as independent variables in regression equations met the following criteria: 1. significant differences between Prince George and Nelson regions 2. significant regression of single soil variables with foliar S0 4-S concentration. The variables selected for consideration on this basis were: a. B horizon soil properties: organic-S04, soluble-S04 and organic C concentrations (statistically significant differences in organic-S04 concentration between regions were not demonstrated due to analytical problems) b. foliar nutrition properties: foliar N and S0 4-S concentrations at time of trial establishment, litter S concentration, and foliar S resorption. Since both concentration and content of some soil S constituents were significantly correlated with foliar S0 4-S, selected nutrient contents were used as independent variables in regressions with growth response for comparison with nutrient concentrations. Simple linear regression equations were done with individual soil and foliar properties as independent variables, and one-, three-, or six-year growth response as dependent variables. 160 Variables were then combined in multiple linear regressions, with variables added manually. (SPSS Inc. 1996). Soil and foliar variables were considered both separately and in combination. The r2 values for each regression are plotted in Figure 19a-d. Significance of the regression equations is also indicated in Figure 19. The r 2 values for regressions of soil properties with growth response are shown in Figure 19a. Relationships were weak between individual soil properties and growth response to N fertilization. Regressions of soil organic-S04, soluble-S04 or organic C concentrations with growth response at one, three and six years had r 2 values of less than 0.10. Combining two soil constituent concentrations (organic C and organic-S04, soluble-S04 and organic-S04, organic C and soluble-S04) improved the regressions somewhat (r2 < 0.30). Combining the three variables further improved the regression, with r2 values of 0.46 and 0.40 for three- and six-year growth response, respectively. None of the regressions using only soil constituents were significant at « = 0.05. Relationships were weak between the quantity of individual soil constituents and growth response at any measurement interval (r2 ^ 0.14). The maximum r2 value for soil nutrient contents was 0.39 for soluble-S04 and organic C considered together. Results of regressions with foliar nutrient properties are shown in Figure 19b. The highest r2 values were obtained with the regression model containing foliar N and S0 4-S concentrations (r2 = 0.45, 0.80, and 0.79 for one-, three-, and six-year growth response). This is the model currently used by the B.C. Ministry of Forests for predicting lodgepole pine response to N fertilization (Brockley 1996). Foliar N concentration alone was inconsistent as a predictor over six years. The r2 values for regressions between litter S or foliar S0 4-S concentrations and growth response were comparable at three and six years. A l l regressions with foliar nutrition and three- and six-year response data were significant with the exception of foliar N concentration at six years (<* = 0.05). The r2 values for some combinations of soil and foliar properties are shown in Figure 19c. A regression model with foliar S0 4-S and soil organic C concentration had the highest r2 value at three and six years for a model containing one foliar and one soil variable (0.75 and 0.84, respectively). The r2 values were increased when foliar N was added, and the combination of foliar N , foliar SCyS, and soil organic C r2 year of growth response O organic C + organic-S04 - F 3 - soluble-SC\ i—i 4 — y - organic C and organic-S04 A soluble-S04 and organic-S04 organic C and soluble-S04 -<$>- organic C, organic-S04, and soluble-S04 Figure 19a. Predictors of lodgepole pine growth response to 200 kg ha"1 N fertilization: B horizon soil properties. 162 r2 year of growth response —0— initial foliar N concentration — • — litter S concentration — • - foliar S resorption initial foliar S0 4-S concentration A initial foliar N and S0 4-S concentrations Figure 19b. Predictors of lodgepole pine growth response to 200 kg ha" 1 N fertilization: foliar nutrient properties. 163 r2 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 H 0.1 0.0 ns ^ " ns ** nf / / / / / / Regressions are significant at a = 0.05* and a = 0.01** T 6 year of growth response -©— foliar S0 4-S and soil organic C concentrations - • — foliar N and S04-S and soil organic C concentra -Eh- foliar N and S04-S and soil organic-S04, solubl Figure 19c. Predictors of lodgepole pine growth response to 200 kg ha"1 N fertilization: selected soil and foliar properties. 164 Regression equations for six-year growth response: soil soluble-S0 4, organic-S0 4, and organic C concentrations y = 39.77 + (30.82 soluble S 0 4 ) + (0.53 organic S 0 4 ) - (79.62 organic C) - • — foliar N and S0 4 -S concentrations y = 42.55 - (41.23 foliar N) + (0.38 foliar SCyS) y foliar N and S0 4 -S and soil organic C concentrations y = 32.80 - (27.34 foliar N) + (0.48 foliar SCyS) - (16.74 organic C) Figure 19d. Predictors of lodgepole pine growth response to 200 kg ha"1 N fertilization: best predictors from each group. 165 concentration had the highest r2 values for any model with foliar nutrients and one soil variable (r2 = 0.88 for six-year growth response). The r2 values were not increased by adding a second soil concentration variable to this equation. Substitution of organic C content for organic C concentration in the model resulted in lower r2 values and non-significant regressions at all measurement intervals (r2 <. 0.55). When foliar N and S0 4-S, and the soil properties organic-S04, soluble-S04, and organic C concentration were all considered in the model, r2 values were increased slightly. However, the regressions containing all variables were not significant, and inclusion of all variables did not improve the model over that of the foliar N , foliar S0 4-S, and soil organic C model. For comparison, a backward regression was also applied to the total set of five variables (SPSS Inc. 1996). For three-year response, the backward procedure resulted in selection of foliar N and foliar S0 4-S concentrations as independent variables. For six-year response, the model containing foliar SCyS and organic C concentrations was selected. The selection of soil organic C as a variable in both forward and backward regressions with six-year growth response is notable. The best predictors of each group of variables (soil only, foliar only, soil and foliar) are plotted in Figure 19d. Regression equations for six-year growth response are shown in Figure 19d. The best overall regression equation contains foliar N and SCyS, and soil organic C concentrations as independent variables. In this equation, signs for the independent variables foliar N and foliar SCyS concentrations are negative and positive, respectively (Figure 19d). This indicates greater growth response to N fertilization where foliar N is lower, and foliar SCyS is higher, as expected. However, the sign for soil organic C is also negative, indicating a greater growth response to N fertilization where organic C is lower. This would appear to contradict the previous suggestion that soil organic C has a positive effect on S availability. There are several possible explanations for this result. The first is that the balance between S and C limitations to the microbial biomass is altered by the addition of fertilizer N . If it is assumed that S, N , and C are all limiting to the microbial biomass, addition of N should result in N immobilization and intensify the S limitation with respect to available C. This should stimulate mineralization of organic-S04, and result in greater growth response to added N than if C and S were comparably limiting. 166 A second explanation for the inverse relationship between organic C and growth response is that organic C may not approximate readily available C. The biological significance of organic C to N fertilization response may not be direct. Characterization of the actively cycling C, and its relationship to total organic C, may strengthen this relationship as a predictor. Finally, it is possible that organic C may also be involved in response to fertilization through physical properties such as the moisture holding capacity of soil organic matter. The role of biological, chemical, and physical factors in the relationship between soil organic C and lodgepole pine response to fertilization requires further investigation. The ultimate difference in the predictive value of models containing only foliar N and S0 4-S, or foliar N and S0 4-S with soil organic C is not known at this time. This comparison must be further addressed in field trials. Two arguments can be made for further evaluation of the model containing soil organic C. First, it appears from Figure 19d that the model containing foliar N , foliar SCyS, and soil organic C will continue to be a useful predictor of growth response at subsequent remeasurement intervals. The r 2 value for the equation containing only foliar N and SCyS concentrations had declined slightly at six years, and it is not clear whether this trend will continue. Secondly, the model containing only foliar variables does not address processes contributing to S availability and the underlying reasons for low S availability on the S-deficient sites. Soil organic C appears to have a pivotal role in S cycling and S availability on these sites. Further evaluation of a fertilization response model containing organic C would help define the role of soil organic matter in nutrient dynamics and productivity of these sites. None of the relationships between soil and foliar properties and first-year growth response were significant, reinforcing the need for long-term measurements. Results of field trials testing the predictive equations identified here could be applied to fertilization planning in the B.C. interior for developing and implementing effective fertilizer prescriptions for lodgepole pine sites. CHAPTER V . CONCLUSIONS 167 Examination of S properties of unfertilized soils and foliage from S-deficient and S-sufficient sites revealed that cycling of soluble-S04 through organic-S04 is the process limiting S availability on S-deficient sites. This is evident from: • differences in mineral soil soluble and organic-S04 concentrations at S-deficient and S-sufficient sites • correlation between mineral soil soluble-S04 and organic-S04 • correlation between mineral soil soluble-S04 and foliar S0 4-S • correlation between mineral soil organic-S04 and foliar S0 4-S • correlation between forest floor mineralizable-S04 and organic-S04 These results support the suggestion that organic-S04 is more actively cycling in soils and contributes more to S uptake than C-bonded-S. Total soil S concentrations did not differ between S-deficient and S-sufficient sites. The accuracy of total-S determinations at low concentrations by the method used here is uncertain; nonetheless, total-S soil concentration does not appear to be a good indicator of soil S availability. Measurement errors in total-S resulted in the elimination of data for other soil S constituents. Additional information about the S constituents of these soils could have been obtained by determination of the mineral S 0 4 and reduced S components of HI-S, and of adsorbed S0 4 . As well, determination of the organic and inorganic components of foliar S0 4-S would provide more information about the nature of organic-S04 inputs to soil organic matter and the internal cycling of foliar S. Separate pathways of organic-S04 and C-bonded-S cycling in soil are supported by differences in the organic-S04:C-bonded-S ratio in mineral soil, differences in patterns of organic-S04 and C-bonded-S with profile depth, and poor correlation between mineral soil organic-S04 and C-bonded-S. In addition, application of fertilizer S resulted in increased soil organic-S04 concentration, with no change in C-bonded-S concentration. Although it is evident that organic-S04 is more related to S availability than C-168 bonded-S, the proportional contributions of these constituents is not known. This information is likely to be obtained only by following S mineralization and uptake using S tracers. The role of soil organic C in the cycling of organic-S04 and S availability is supported by correlation of organic C with both soluble-S04 and foliar S0 4-S. Inclusion of soil organic C strengthened predictive relationships of lodgepole pine response to N fertilization, although the nature of the interaction of C with S and N is not clear. Identification of C fractions involved in active S cycling may provide more insight into the cycling of S through soil organic matter. Relationships between soil and foliar nutrition were consistently stronger for soil nutrient concentrations than contents. Soil organic matter has been suggested as an indicator of soil quality, although attempts to link soil organic matter and forest productivity have not always been successful. In this study, the role of soil organic matter in soil S cycling, S availability, and lodgepole pine productivity has been identified. Organic matter loss in fire over the history of these stands is proposed as the reason for low levels of soil organic C on the S-deficient sites. The comprehensive effects of management practices on S dynamics on these sites are not known and should be further investigated. In particular, losses of S and C due to fire and harvesting, and the effects of these processes on S mineralization and mobilization should be determined. Interior lodgepole pine sites vary in their susceptibility to S deficiencies. Pedogenetic processes favouring S removal, such as weathering of fine-textured S minerals and translocation of soluble organic-S are operating at both locations. The nature of the primary S minerals in these soils and their weathering attributes would provide further insight into soil S dynamics. Soils undergoing luvisolic processes may be more predisposed to S deficiencies, especially where soil organic matter content is low. On these sites, S and organic matter losses to fire or other removal should be minimized. Soils on the Prince George sites are more developed than those on the Nelson sites, and it is likely that S-removing processes are more advanced and more evident. Although inorganic-S04 was retained in the most developed (podzolic) profiles, it apparently supplied inadequate S for lodgepole pine. Sulphur is clearly important to the productivity of lodgepole pine on certain sites in the B.C. interior. Further information is required regarding approaches to S conservation, for example, in relation to 169 fire and harvesting losses. Sulphur deficiencies can be alleviated with fertilizer S additions, as evidenced by improved foliar nutrition and first-year growth response in the B.C. Ministry of Forests field trial. Response to fertilization may result through immediate uptake of readily available S 0 4 fertilizers, or through changes in soil organic-S under S° application. Fertilizer S 0 4 appears to be internally cycled and incorporated into new foliage for at least several years following fertilization. Availability of fertilizer S°, including its micobial oxidation and its effect on soil organic-S04 pools should be determined. Interactions between S availability, fertilizer N additions, and the cycling of these nutrients through microbial biomass and soil organic matter are a key component of nutrient management on these sites. 170 VI. LITERATURE CITED Adams, F. and Z. Rawajfih. 1977. Basaluminite and alunite: a possible cause of sulfate retention by forest soils. Soil Sci. Soc. Am. J. 41: 686-692. Adams, T .M. and P.W. Lane. 1984. A comparison of four methods of analysing aqueous soil extracts for sulphate. J. Sci. Food Agric. 35: 740-744. Agee, J.K. 1993. 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L 198 APPENDIX I CRITERIA FOR SITE SELECTION Sites Prince George first-year needle three-year diameter foliar S foliar S0 4-S foliar Region weight responseb,c responseb'c (%) (/ug g"1) N:S N N+S N N+S M L 20 31* 0.088 46 12 TC 13 41* .0.092 48 13 GC 18 41* 0.081 59 16 CC 24 50* 0.095 43 12 C L -4 51* 0.091 39 13 B 29 32 20d 40* 0.095 57 15 Nelson Region G 17 27 23 34 0.089 60 13 UGC 24 31 0.093 136 10 L G C 40 52 69 78 0.089 115 11 C F e 23 55 0.100 n.d.f 10 a Based on growth response data available in 1991 and foliar nutrient concentrations at time of trial establishment b response to: 200 kg ha 1 N (as urea and NH4C1) 200 kg ha 1 N plus 50 kg ha"1 S (as urea and NH 4 S0 4 ) c percent response relative to control d three-year growth response in adjacent stand (EP 886.01 #15) e N-only treatments applied at this site f not determined * statistically significant difference (<* = 0.05) between N and N+S treatments 199 APPENDIX 2 SOIL PROFILE DESCRIPTIONS" b c PRINCE GEORGE REGION Meadow Lake pit 1 * Depth (cm) Brunisolic Grey Luvisol Horizon L F Aej Bfjl Bfj2 Bml Bm2 Bm3 C IIC 7-1 1-0 0- 1 1- 15 15-29 29-43 43-58 58-91 91-114 114-139 Meadow Lake pit 2* Horizon Depth (cm) L F Aej Bf Bml Bm2 Bm3 C IIC 7-2 2-0 1-0 1-18 18-27 27-57 57-68 68-92 92-117 Weakly developed 10YR 4/4; SCL; 10% coarse fragments; moderate, fine subangular blocky; abundant very fine roots 10YR 5/4; SC; 20% coarse fragments; moderate, very fine, subangular blocky; abundant very fine roots 10YR 5/3; L ; 30% coarse fragments; moderate to strong, coarse, subangular blocky; plentiful very fine roots 10YR 4/4; SCL; 65% coarse fragments; moderate, fine, subangular blocky; plentiful very fine roots 10YR 3/3; SC; 80% coarse fragments; strong, medium, subangular blocky; few fine roots 10YR 4/2; SCL; 85% coarse fragments; strong, fine, subangular blocky; no roots Fine gravel; coatings on gravel 10 Y R 3/3; no roots Podzolic Grey Luvisol Weakly developed 10YR 5/4; SL; 20% coarse fragments; weak, fine, granular; abundant fine roots 2.5Y 6/2; SL; 50% coarse fragments; moderate, fine, subangular blocky; plentiful very fine roots 10YR 4/3; SCL; 75% coarse fragments; strong, medium, subangular blocky; plentiful very fine roots 10YR 4/3; C L ; 85% coarse fragments; strong, medium, angular blocky; few very fine roots 2.5YR 3/2; SC; 80% coarse fragments; strong, medium, subangular blocky; no roots 10YR 3/2; LS; 70% coarse fragments; moderate to strong, fine, granular; no roots 200 Appendix 2. (Continued) Meadow Lake pit 3 * Horizon Depth (cm) F Ahj B f Bf) Bml Bm2 BC1 BC2 2-0 0- 1 1- 6 6-14 14-24 24-52 52-80 80-105 Eutric Brunisol 5Y 4/2; 30% coarse fragments; weak, very fine, granular; plentiful coarse roots 10YR 5/4; LS; 30% coarse fragments; weak, very fine, granular; plentiful coarse roots 10YR 6/3; SL; 50% coarse fragments; weak, very fine, granular; plentiful medium roots 10YR 6/3; SiS; 50% coarse fragments; weak to moderate, medium, subangular blocky; few medium roots 10YR 3/3; LS; 30% coarse fragments; moderate, medium, subangular blocky; plentiful fine roots 2.5Y 4/2; S; 40% coarse fragments; weak to moderate, medium granular; plentiful very fine roots 2.5Y 3/2; S; 30% coarse fragments; moderate, medium, subangular blocky; no roots Tsus Creek pit 1 Orthic Humo-Ferric Podzol Horizon Depth (cm) L 6-1 F 1-0 Ae 0-3 10YR 7/1; LS; 5% coarse fragments; weak, fine, subangular blocky; plentiful medium roots Bf 3-13 10YR 5/6; LS; 10% coarse fragments; weak, fine, subangular blocky; plentiful coarse roots Bml 13-23 10YR 4/6; LS, 10% coarse fragments; weak, medium, subangular blocky, plentiful coarse roots Bm2 23-41 10YR 3/6; S; 80% coarse fragments; single grain; abundant fine roots B C 41-60 10YR 3/2; S; 80% coarse fragments; single grain; plentiful fine roots C 60-85 10YR 2/2; S; 80% coarse fragments; single grain; plentiful very fine roots 201 Appendix 2. (Continued) Tsus Creek pit 2 Horizon Depth (cm) Orthic Humo-Ferric Podzol L F Ae B f Bm BC C 6-1 1-0 1-10 10-24 24-66 66-92 92-120 10YR 8/1; SL; 30% coarse fragments; moderate to strong, medium, subangular blocky; plentiful fine roots 10YR 5/8; LS; 40% coarse fragments; weak, fine, subangular blocky; plentiful very fine roots 10YR 5/6; S; 80% coarse fragments; very weak, very fine, subangular blocky; plentiful very fine roots 2.5Y 5/4; S; 90% coarse fragments; single grain; few, very fine roots 2.5Y 4/4: S; 65% coarse fragments; single grain; no roots Tsus Creek pit 3 Horizon Depth (cm) Orthic Humo-Ferric Podzol L F Ae B f Bml Bm2 BC 5-1 1-0 0-5 5-17 17-30 30-54 54-86 86-105 5YR 8/1; SL; 30% coarse fragments; weak, fine, subangular blocky; plentiful fine roots 7.5YR 5/8; S; 60% coarse fragments; single grain; plentiful fine roots 10YR 5/8; S; 60% coarse fragments; very weak, fine, subangular blocky; few fine roots 10YR 5/6; S; 80% coarse fragments; single grain; plentiful very fine roots 10YR 6/6; S; 80% coarse fragments; single grain; plentiful very fine roots 2.5Y 4/4; S; 80% coarse fragments; single grain; no roots Gregg Creek pit 1 Horizon Depth (cm) Orthic Humo-Ferric Podzol L F Ae B f Bml Bm2 5-1 1-0 0-4 4-14 14-25 25-37 37-62 5YR 6/2; SCL; 10% coarse fragments; moderate, fine, subangular blocky; plentiful very fine roots 10YR 5/4; SL; 25% coarse fragments; weak, very fine, subangular blocky; plentiful fine roots 2.5Y 7/2; SiCL; 40% coarse fragments; strong, medium, angular blocky; few, very fine roots 10YR 6/2; L; 50% coarse fragments; strong, medium, subangular blocky; few, very fine roots 10YR 6/2; SCL; 40% coarse fragments; medium, fine, subangular blocky; no roots; few fine mottles, 7.5YR 5/3 202 Appendix 2. (Continued) Gregg Creek pit 2* Horizon Depth (cm) Brunisolic Grey Luvisol F Ahe B m l Bm2 Bm3 BCgj Cgj 6-0 0-2 2-6 6-18 18-29 29-46 46-71 10YR 4/2; L ; 15% coarse fragments; weak, fine, subangular blocky; abundant very fine roots 10YR 6/2; SiL; 15% coarse fragments; medium, fine, subangular blocky; abundant very fine roots 10YR 3/3; SCL; 60% coarse fragments; moderate, medium, subangular blocky; plentiful very fine roots 2.5Y 5/2; SCL; 40% coarse fragments; moderate, medium, subangular blocky; few fine roots; common medium mottles, 10YR 4/6 5Y 4/2; SCL; 30% coarse fragments; strong, coarse, subangular blocky; no roots; common medium mottles, 10YR 3/6 Gregg Creek pit 3 Horizon Depth (cm) Gleyed Humo-Ferric Podzol L F Ae B f Bml Bm2 Cg 4-1 1-0 0-8 8-19 19-26 26-35 35-60 10YR 6/2; SCL; 40% coarse fragments; weak, fine, platey; plentiful very fine roots 10YR 4/6; L S ; 40% coarse fragments; weak, fine, granular; plentiful very fine roots 10YR 6/2; SL; 50% coarse fragments; weak to very weak, fine, subangular blocky; plentiful very fine roots 10YR 5/2; S; 60% coarse fragments; weak to moderate, fine, subangular blocky; few fine roots 10YR 7/1; SL; 40% coarse fragments; moderate to strong, coarse, angular blocky; few fine roots; many fine mottles, 10YR 5/4 203 Appendix 2. (Continued) Cluculz Creek pit 1* Horizon Depth (cm) Brunisolic Grey Luvisol L F Ahe Bml Bm2 Bm3 Cgj 8-5 5-0 0-5 5-19 19-37 37-57 57-82 10YR 4/4; LS; 5% coarse fragments; weak, very fine, subangular blocky; few fine roots 10YR 6/3; SL; 30% coarse fragments; weak to moderate, fine, subangular blocky; plentiful fine roots 7.5YR 7/2; SCL; 50% coarse fragments; moderate, very fine, subangular blocky; plentiful very fine roots 10YR 5/3; LS; 60% coarse fragments; strong, fine, subangular blocky; plentiful very fine roots 10YR 4/2; C L ; 5% coarse fragments; strong, medium, subangular blocky; plentiful medium roots; common fine mottles, 10YR 5/4 Cluculz Creek pit 2 * Horizon Depth (cm) L F H Ae Bmgjl Bmgj2 Bmgj3 BCgj 8-3 3-2 2-0 0-2 2-13 13-17 17-28 28-48 Brunisolic Grey Luvisol Plentiful fine roots Plentiful fine roots Plentiful fine roots 2.5 Y R 6/2; SL; 30% coarse fragments; moderate, very fine, subangular blocky; plentiful very fine roots 10YR 5/3; L ; 50% coarse fragments; weak to moderate, fine, platy; plentiful very fine roots; common coarse mottles, 10YR 6/6 10YR 6/2; SCL; 40% coarse fragments; moderate, very fine, subangular blocky; few very fine roots; few fine mottles, 10YR 5/4 10YR 6/2; SCL; 30% coarse fragments; weak to moderate, very fine, subangular blocky; few very fine roots; common fine mottles, 10YR 4/4 10YR 5/2; SCL; 10% coarse fragments; weak to moderate, fine, platey; few very fine roots; common medium mottles 10YR 4/4 204 Appendix 2. (Continued) Cluculz Creek pit 3 * Horizon Depth (cm) Brunisolic Grey Luvisol LF H Aej Bml Bm2 BC 4- 1 1-0 0-5 5- 22 22-32 32-46 46-71 10YR 5/3; SCL; 30% coarse fragments; weak, fine, platey; plentiful very fine roots 10YR 4/2; SCL; 50% coarse fragments; weak to moderate, fine, subangular blocky; abundant very fine roots 10YR 5/2; SCL; 40% coarse fragments; moderate, medium, subangular blocky; abundant very fine roots 7.5YR 5/2; SCL; 20% coarse fragments; moderate, medium, subangular blocky; plentiful very fine roots 10YR 3/3; SC; 10% coarse fragments; strong, coarse, subangular blocky; few very fine roots Cobb Lake pit 1 Eluviated Dystric Brunisol Horizon L F Ae Bfj Bm BC Depth (cm) 4-1 1- 0 0-2 2- 16 16-42 42-80 80-105 10YR 5/2; no coarse fragments 10YR 5/6; SL; 15% coarse fragments; weak, medium, platey; plentiful very fine roots 2.5Y 6/4; SL; 40% coarse fragments; weak, medium, platey; few very fine roots 10YR 3/3; SL; 30% coarse fragments; moderate, very fine, subangular blocky; no roots; few fine mottles, 10YR 4/4 10YR 4/2; LS; 15% coarse fragments; weak to moderate, very fine, subangular blocky; no roots 205 Appendix 2. (Continued) Cobb Lake pit 2 * Horizon Depth (cm) Eluviated Dystric Brunisol L H Ahe Ae Bfj Bml Bml Bm3 7-4 4-0 0-4 4-10 10-30 30-45 45-59 59-71 71-96 5YR 5/3; SiL; 5% coarse fragments; weak, fine, platey; plentiful very fine roots 10YR 5/6; L ; 5% coarse fragments; moderate, medium, subangular blocky; plentiful very fine roots 10YR 3/4; SL; 30% coarse fragments; moderate to strong, coarse, subangular blocky; few fine roots 2.5Y 5/2; LS; 60% coarse fragments; weak, fine, subangular blocky; few fine roots 10YR 4/3; LS; 80% coarse fragments; weak, fine, subangular blocky; few very fine roots 2.5Y 4/2; LS; 20% coarse fragments; weak, very fine subangular blocky; no roots Cobb Lake pit 3 Orthic Gleysol Horizon Depth (cm) L 8-3 F 3-1 H 1-0 Ae 0-1 2.5Y 7/2; 5% coarse fragments; single grain; plentiful fine roots Bgl 1-10 10YR 7/2; SL; 50% coarse fragments; moderate, medium, platey; few fine roots; mottles 10YR 6/8 Bg2 10-30 10YR 6/2; SL; 40% coarse fragments; weak to moderate, fine, platey; few fine roots; mottles 10YR 4/6 BCg 30-50 10YR 6/2; LS; no coarse fragments; moderate to strong, medium, platey; no roots 206 Appendix 2. (Continued) Bowron pit 1 Orthic Humo-Ferric Podzol Horizon Depth (cm) F 6-0 Ae 0-8 1OYR 6/2; SCL; 20% coarse fragments; weak to moderate, very fine, subangular blocky; plentiful fine roots B f 8-30 5YR 5/8; LS; 35% coarse fragments; weak, very fine, subangular blocky; few fine roots Bml 30-56 2.5Y 5/6; LS; 45% coarse fragments; very weak, very fine, subangular blocky; few fine roots Bm2 56-73 2.5Y 5/6; S; 60% coarse fragments; very weak, very fine, subangular blocky; few fine roots Bm3 73-94 2.5Y 4/4; S; 75% coarse fragments; single grain; few fine roots BC 94-126 2.5Y 4/4; S; 80% coarse fragments; single grain; few fine roots C 126-146 2.5Y 5/4; S; 30% coarse fragments; single grain; no roots Bowron pit 2 Orthic Humo-Ferric Podzol Horizon Depth (cm) L 4-1 F 1-0 Ah 0-1 Ae 1-10 1 OYR 7/1; SL; 30% coarse fragments; moderate, medium, subangular blocky; plentiful medium roots Aej 10-12 B f 12-25 1 OYR 5/8; LS; 60% coarse fragments; weak to moderate, fine, subangular blocky; few fine roots B m l 25-43 1 OYR 5/6; S; 60% coarse fragments; very weak, very fine, subangular blocky; few very fine roots Bm2 43-68 10YR 7/6; S; 50% coarse fragments; single grain; plentiful very fine roots BC 68-112 5Y 6/3; S; 90% coarse fragments; single grain; plentiful very fine roots C 112-140 5Y 5/2; S; 80% coarse fragments; single grain; no roots 207 Appendix 2. (Continued) Bowron pit 3 Orthic Humo-Ferric Podzol Horizon Depth (cm) L 5-3 F 3-0 Ae 0-5 10YR 6/2; SL; 30% coarse fragments; weak to moderate, very fine, subangular blocky; plentiful fine roots Bf 5-30 7.5YR 5/8; LS; 20% coarse fragments; weak, very fine, subangular blocky; plentiful very fine roots Bml 30-53 10YR 4/6; S; 60% coarse fragments; weak, fine, subangular blocky; few fine roots Bm2 53-71 10YR 4/6; LS; 45% coarse fragments; very weak, very fine subangular blocky; few fine roots Bm3 71-92 2.5Y 4/4; S; 90% coarse fragments; single grain; few fine roots BC 92-120 5Y 4/3; S; 60% coarse fragments; single grain; few fine roots C 120-145 2.5Y 5/4; S; 30% coarse fragments; single grain; no roots NELSON REGION Golden pit 1 Orthic Humic Podzol Horizon Depth (cm) L 3-1 F 1-0 Ae 0-2 Bh 2-24 10YR 5/8; SL; 20% coarse fragments; very weak, fine, subangular blocky; plentiful fine roots Bm 24-33 10YR 6/4; SCL; 70% coarse fragments; moderate, fine, subangular blocky; plentiful fine roots Bmk 33-58 10YR 3/3; SL; 90% coarse fragments; single grain; plentiful very fine roots BCk 58-65 10YR 5/3; LS; 90% coarse fragments; single grain; few fine roots Ck 65-95 10YR 4/2; LS; 90% coarse fragments; single grain; no roots 208 Appendix 2. (Continued) Golden pit 2 Horizon L F Bm Bmkl Bmk2 Bmk3 Bmk4 Bmk5 Bmk6 BCk Ck Orthic Eutric Brunisol Depth (cm) 2-1 1-0 0-12 12-22 22-26 26-46 46-67 67-84 84-110 110-130 130-155 7.5YR 6/6; SiL; 10% coarse fragments; weak, very fine, subangular blocky; few coarse roots 1 OYR 7/3; L ; 70% coarse fragments; weak, very fine, subangular blocky; plentiful fine roots 10YR 5/3; SCL; 70% coarse fragments; weak, fine, subangular blocky; plentiful fine roots 10YR 7/3; SL; 80% coarse fragments; weak to moderate, medium, subangular blocky; plentiful fine roots 10YR 6/3; L ; 90% coarse fragments; weak, fine, subangular blocky; few fine roots 1 OYR 6/2; SiL; 90% coarse fragments; weak, fine, subangular blocky; few very fine roots 10YR 6/3; SL; 90% coarse fragments; weak, fine, subangular blocky; few very fine roots 10YR 5/2; SCL; 90% coarse fragments; weak, fine, subangular blocky; no roots 10YR 5/1; C L ; 90% coarse fragments; weak, fine, subangular blocky; no roots Golden pit 3 Orthic Humic Podzol Horizon Depth (cm) L 1-0 Bh 0-10 1 OYR 6/6; SL; 30% coarse fragments; moderate, fine, subangular blocky; plentiful fine roots Bm 10-16 1 OYR 6/3; L ; 40% coarse fragments; moderate, very fine, subangular blocky; plentiful fine roots Bmkl 16-30 1 OYR 5/2; SL; 70% coarse fragments; weak to moderate, very fine, subangular blocky; plentiful very fine roots Bmk2 30-42 1 OYR 4/3; LS; 80% coarse fragments; weak, very fine, subangular blocky; plentiful very fine roots BCk 42-60 1 OYR 5/3; 80% coarse fragments; plentiful very fine roots Ck 60-90 1 OYR 4/2; 85% coarse fragments; few very fine roots 209 Appendix 2. (Continued) Upper Gold Creek pit 1* Horizon Depth (cm) Brunisolic Grey Luvisol L F Ae B f Bml Bm2 Bm3 B C 2-1 1-0 0-5 5-9 9-32 32-45 45-57 57-85 5YR 6/1; SiCL; 40% coarse fragments; weak to moderate, fine, subangular blocky; abundant very fine roots 10YR 5/6; L ; 70% coarse fragments; weak, very fine, subangular blocky; plentiful coarse roots 10YR 7/2; SiCL; 70% coarse fragments; weak to moderate, very fine, subangular blocky; abundant fine roots 10YR 5/4; LS; 80% coarse fragments; weak to moderate, fine, subangular blocky; abundant fine roots 10YR 5/6; SL; 80% coarse fragments; moderate, fine, subangular blocky; plentiful medium roots 10YR 5/2; SiCL; 50% coarse fragments; strong, very coarse platey; plentiful very fine roots Upper Gold Creek pit 2 Orthic Dystric Brunisol Horizon Depth (cm) F 4-3 H 3-0 Ah 0-3 Bfj 3-12 10YR 3/4; L, 20% coarse fragments; weak, fine, subangular blocky; plentiful very fine roots Bml 12-28 10YR 6/6; L ; 45% coarse fragments; moderate to strong, fine, subangular blocky; abundant fine roots Bm2 28-42 10YR 6/4; SiL; 60% coarse fragments; very strong, coarse, subangular blocky; plentiful very fine roots BC1 42-74 10YR 5/4; SiCL; 80% coarse fragments; strong, medium, subangular blocky; plentiful very fine roots BC2 74-102 10YR 6/3; SL; 85% coarse fragments; strong, medium, subangular blocky; few very fine roots 210 Appendix 2. (Continued) Upper Gold Creek pit 3 Orthic Dystric Brunisol Horizon Depth (cm) L 2-1 F 1-0 Bfi 0-8 1 OYR 4/3; SL; 30% coarse fragments; weak to moderate, very fine, subangular blocky; plentiful very fine roots Bm 1 8-28 1 OYR 4/6; L ; 30% coarse fragments; weak to moderate, very fine, subangular blocky; abundant medium roots Bm2 28-45 10YR 6/3; SCL; 40% coarse fragments; strong, medium to coarse, subangular to angular blocky; plentiful medium roots Bm3 45-70 10YR 5/3; SL; 80% coarse fragments; moderate, fine, subangular blocky; plentiful medium roots IC 70-105 10YR 7/3; SiL; 80% coarse fragments; single grain; few fine roots IIC 105+ Large angular colluvial boulders Lower Gold Creek pit 1 Orthic Dystric Brunisol Horizon Depth (cm) L 4-1 F 1-0 Ahe 0-2 Ae 2-3 10YR 5/2; SCL; 10% coarse fragments; moderate to strong, fine, subangular blocky; plentiful fine roots Bml 3-26 10YR 4/6; SL; 20% coarse fragments; strong, medium, subangular blocky; plentiful fine roots Bm2 26-40 1 OYR 5/4; LS; 40% coarse fragments; weak to moderate, fine, subangular blocky; plentiful very fine roots Bm3 40-85 10YR 5/3; S; 60% coarse fragments; single grain; plentiful, very fine roots BC 85-122 1 OYR 5/6; S; 60% coarse fragments; single grain; few fine roots Ck 122-162 2.5Y 4/4; S; 50% coarse fragments; single grain; few fine roots 211 Appendix 2. (Continued) Lower Gold Creek pit 2 Horizon Depth (cm) Orthic Humic Podzol L F Ae Bh Bml Bm2 Bm3 Bm4 Bm5 ICkl HCkl ICk2 IICk2 3-2 2-0 0-2 2-19 19-42 42-58 59-72 72-92 92-109 109-122 122-133 133-143 143-152 10YR 4/1; SiCL; no coarse fragments 7.5YR 4/4; SL; 10% coarse fragments; weak to moderate, coarse, subangular blocky; few medium roots 10YR 4/3; SC; 20% coarse fragments; moderate, fine, subangular blocky; few fine roots 10YR 4/2; SL; 30% coarse fragments; moderate, fine, subangular blocky; few fine root 2.5Y 5/4; SiC; 5% coarse fragments; moderate, coarse, subangular blocky; few fine roots 2.5Y 6/4; SCL; 50% coarse fragments; moderate, fine, subangular blocky; few fine roots 2.5Y 6/4; SiC; 5% coarse fragments; weak to moderate, medium, subangular blocky; few fine roots 2.5Y 5/4; S; 70% coarse fragments; single grain; no roots 2.5Y 4/4; SiCL; 30% coarse fragments; weak, medium, subangular blocky; no roots 2.5Y 5/4; S; 70% coarse fragments; single grain; no roots 2.5Y 4/4; C L ; 5% coarse fragments; weak, coarse, subangular blocky; few fine roots 212 Appendix 2. (Continued) Lower Gold Creek pit 3 Horizon Depth (cm) Gleyed Eluviated Dystric Brunisol L F Ahe Ae Bfj Bml Bm2 Bm3 BCgj ICgj IIC 6-2 2-0 0- 1 1- 4 4-19 19-39 39-69 69-82 82-115 115-137 137-162 1 OR 6/1; SiL; no coarse fragments; moderate, fine, platey; few very fine roots 1 OYR 4/6; SiL; no coarse fragments; strong, coarse, subangular blocky; plentiful fine roots 10YR 6/3; SiCL; no coarse fragments; strong, coarse, subangular blocky; few very fine roots 10YR 7/2; SiL; no coarse fragments; strong, coarse, subangular blocky; few fine roots 2.5Y 6/2; Si to SiL; no coarse fragments; strong, medium, subangular blocky; few fine roots 2.5Y 6/2; SiL; no coarse fragments; very strong, very coarse, subangular to angular blocky; few fine roots; common coarse mottles, 2.5YR 4/8 2.5Y 5/2; SiCL; no coarse fragments; very strong, very coarse, subangular to angular blocky; few very fine roots; common coarse mottles, 5YR 5/8 7.5YR 4/2; S; 10% coarse fragments; single grain; no roots Canal Flats pit 1 Horizon Depth (cm) F Ae Bh Bmkl Bmk2 BCk Ck 3-0 0-2 2-16 16-25 25-41 41-65 65-77 Orthic Humic Podzol 10YR 6/3; SiL; no coarse fragments; weak to moderate, medium, subangular blocky; few fine roots 10YR 5/8; SL; 10% coarse fragments; weak, medium, subangular blocky; plentiful very fine roots 10YR 5/6; SCL; 20% coarse fragments; moderate, medium, subangular blocky; plentiful very fine roots 1 OYR 4/4; SCL; 40% coarse fragments; strong, fine, subangular blocky; plentiful fine roots 2.5Y 5/4; C L ; 50% coarse fragments; strong, fine, subangular blocky; plentiful fine roots 2.5Y 6/4; SiC; 60% coarse fragments; very strong, medium, subangular blocky; few fine roots 213 Appendix 2. (Continued) Canal Flats pit 2 Horizon Depth (cm) F Aej Bm Bmkl Bmk2 BCk Ck 1-0 0-3 3-17 17-28 28-44 44-62 62-78 Eluviated Eutric Brunisol 10YR 5/2; L; no coarse fragments; strong, fine, subangular blocky; few fine roots 7.5YR 5/6; L; 5% coarse fragments; strong, medium, subangular blocky; plentiful very fine roots 1OYR 5/6; C L ; 20% coarse fragments; strong, medium, subangular blocky; plentiful very fine roots 10YR 5/4; C L ; 50% coarse fragments; moderate to strong, subangular blocky; few very fine roots 2.5Y 4/4; SiL; 50% coarse fragments; strong, medium, subangular blocky; no roots 2.5Y 6/4; SiL; 60% coarse fragments; very strong, coarse, subangular blocky; no roots Canal Flats pit 3 Horizon Depth (cm) Orthic Humic Podzol F H Ahe Ae Bh Bmkl Bmk2 B C k l BCk2 4-1 1-0 0- 1 1- 3 3-14 14-26 26-38 38-54 54-76 10YR 6/2; SiL, no coarse fragments; moderate to strong, medium, subangular blocky; plentiful medium roots 1 OYR 5/8; SiL; 5% coarse fragments; moderate, medium, subangular blocky; abundant very fine roots 1 OYR 5/6; SiCL; 40% coarse fragments; moderate, coarse, subangular blocky; plentiful very fine roots 1 OYR 4/4; SiCL; 50% coarse fragments; moderate, medium, subangular blocky; plentiful very fine roots 10YR 5/4; SCL; 60% coarse fragments; weak, fine, subangular blocky; plentiful very fine roots 1 OYR 5/4; SCL; 70% coarse fragments; moderate to strong, fine, subangular blocky; few very fine roots 3 Soil descriptions following B.C. Ministries of Environment and Forests 1990. b Moist colors. 0 Bfj horizons have greater than or equal to 0.35% pyrophosphate extractable Fe+Al in L and finer textures. * Classifications are tentative. C/3 i IS _3 O C/3 C/3 i o '1 C/3 i T 3 CU -o C o I O O C/3 eS 60 o o l £ 1 C/3 C/3 ccj s° a jo 'El cu as cu M i_ o cu o cu cu a OH t-- CO —^v —^v _*| co r~ C~- CN CN 1—1 CO 00 -^^  N—' s —' s —' —' N O — oo Tt r~ N O N O Tt Tt d CO N O N O Tt m Tt Tt 00 Tt O N d CN O N 00 N O CN o o O N O co CO CO ^—' —' -^^  co O N Tt CN in O — 00 Tt d Tt ON N O CO Tt IT) co O N ON OO r~ r-~ oo CN ^ ^ /—\ IT) in CO *—< CN Tt d CO Tt 00 CN 00 CO 00 CN N O T T w N ' o o CO CO m o O N CN d d ON CO o CN in N O CN m 00 OO O N N O in / s O N N O 00 O N N O r~ O N 00 oo 00 CN CN in Tt CO T—1 v—' s —' CO O N — O N o o CN N O Tt O N in N O O Tt o CN 00 '—1 O N CN (13.6) (67.5) (82.0) (8.7) (137.4 (10.1) C O o r- o in Tt C O 00 O N 1049. 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E E £ CJ 53 CJ < < f f l f f l f l 5 D 3 f f l U S I I I I t I I I I r n c o c o r o c o r o < ^ c o c o i i i i i i i i i C J C J O C J C J C J C J C J O o o o o o o o o o 237 o 0 0 O c o VO 0 0 CM vo i n CO T t vo i n CM i n 0 0 0 0 CO CO i n r -T t vo o VO r - -i n r -c o c o vb vb vb i n vb p ~ r-° T f i n vb vb vb 0 0 — T t OS co r-~ m i n o o T t vo c-~- 0 0 0 0 f-vo os o T t i n CO OS O i n r -0 0 i n SO i n 0 0 T t O s o o O s o o T t CM P ^ so i n 0 0 r -O s CO 0 0 CN OS CM Os i n CO so T t O s Os co co d i n O s r ~ vb co SO CM CO co CM 0 0 o o SO co o T t 0 0 T t o so o CM co CO co 0 0 CN Os o so o d d d d d d d d d d d d d d d d d d 0 0 CO r - ; r~ T t 0 0 SO O s CM O s CM SO T t O s o OS o O s T t 0 0 T t r-0 0 T t CN T t CN c o c o T t CO CN c o T t T t T t CN CN CN T-H' T t T t T t c o VO O T t o p CO O O s P -SO CO c o 0 0 SO SO i n 0 0 O s CO CM O s O s 0 0 CN CO CM SO o o d CO CO CO Os r-; os sq CM o SO 0 0 CM 0 0 0 0 CM i n CO OS r-° r-° sb — i — i « » 5 / 3 0 0 ooP oo , , J J J J • J J O O w w - J — i r> r> J - J s cj U o U 5 / 3 ^ &o oo oo oo CM VO m CN T t m vq r - CO 0 0 CN T t T t CN VO 0 0 C--O CM vo m CN T t i n SO o c o 0 0 CN T t T t CN SO m r - CM m CN c o m CO i n CN r — CN c o m 'E B lu < 2 ^ XJ E £ O CQ CQ CQ CQ CJ u. u_ u. u_ u. u. CJ cj o cj u o £ £ 3 2 • E CJ CQ CQ CQ CQ U CN CN CM CM CN CN U- u. u. u. U CJ CJ CJ O CJ < ^ 2 js E £ U CJ CQ CQ CQ CQ CQ CO CO CO CO CO CO I I I I I I U . U . U - U_ t u U . u cj o u a cj cd | Z 0 0 c I f a .3 238 APPENDIX 7 EXCHANGEABLE CATIONS, CEC, AND PARTIAL BASE SATURATION IN B HORIZON SOILS Prince George Region Nelson Region Exchangeable Ca (cmol(+)kg"') 3.39 (1.12) 15.36 (5.34) Exchangeable M g (cmol(+)kg1) 1.76 (0.59) 1.21 (0.58) Exchangeable K (cmol(+)kg"1) 0.12 (0.03) 0.05 (0.02) CEC (cmol(+)kg-') 6.22 (1.45) 3.28 (0.39) Partial base saturation (%)a 70.03 (14.38) 60.87 (13.03)b a Excluding Na. b Data from one site only (Upper Gold Creek). Prince George Region: n = 54 (weighted average of first 3 B horizons per pit; 3 pits per site; 6 sites). Nelson Region: n = 36 (weighted average of first 3 B horizons per pit; 3 pits per site; 4 sites). Standard errors are shown in parentheses. 239 Q r* = 0.29 n = 32 8 -CN o CO O X Q. 7 -c * V • • • • • o i 0 1 2 3 inorganic C (%) 4 J Appendix 8. Relationship between mineral soil inorganic C concentration and pH. 240 APPENDIX 9 NUTRIENT CONTENT OF FOREST FLOORS Nutrient (kg ha"1) Prince George Region Nelson Region Total-S 63 (17) 36 (3) HI-S 12 (7) 4 (1) Forest floor soluble-S04 3 (1) 2 (0.4) Organic-S04 9 (6) 3 (1) C-bonded-S 47 (11) 32 (3) Organic-S 56 (17) 35 (3) Soluble-S 4 (1) 2 (0.5) C (1000 kg ha 1) 26 (4) 19 (3) N 581 (94) 458 (21) P 59 (1) 5 (1) Exchangeable cations3 260 (53) 309 (55) a Sum of exchangeable Ca, Mg, and K . Prince George Region: n = 18 (3 pits per site; 6 sites). Nelson Region: n = 12 (3 pits per site; 4 sites). Standard errors are shown in parentheses. 

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