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Influence of sewage sludge application on hydraulic and physical properties of a silty clay loam subsoil Kodsi, Elias G. 1987

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INFLUENCE OF SEWAGE SLUDGE APPLICATION ON HYDRAULIC AND PHYSICAL PROPERTIES OF A SILTY CLAY LOAM SUBSOIL by ELIAS G. KODSI B.Sc, American University of Beirut, 1983 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR T H E DEGREE OF MASTER OF SCIENCE in THE F A C U L T Y OF G R A D U A T E STUDIES DEPARTMENT OF BIO-RESOURCE ENGINEERING in cooperation with the DEPARTMENT OF SOIL SCIENCE We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA APRIL, 1987 • ELIAS G. KODSI, 1987 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 BIO-RESOURCE ENGINEERING in cooperation with the DEPARTMENT OF SOIL SCIENCE The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date: APRIL, 1987 ABSTRACT Turf growers have been farming the Ladner soil in the Boundary Bay area for the last decade. At each harvest, approximately a 2cm layer from the A horizon is taken out with grass. Consequently, the cultivation layer is becoming thinner year after year and the growers are already cultivating the B horizon. The possible improvement of the B horizon structure through sewage sludge application will benefit the fanners in the area. A greenhouse experiment was conducted using a Ladner subsoil. Treatments included application rates of 0, 33, and 100 t/ha of composted sewage sludge. The effect of sludge application on the soil structural stability in relation to the destructive action of water was evaluated. Soil columns were subjected to periodic 24-hour simulated ponding events. Adding sewage sludge increased the ponding tolerance of the soil. This was reflected by statistically significant differences in satiated hydraulic conductivity ('Ks') between the sludge-amended columns and the control columns. The significant decrease of 'Ks ' of the control treatment as a result of ponding was responsible for widening the gap between 'Ks' of the control columns and 'Ks ' of the sludge-treated columns. The incorporation of sewage sludge slowed down the decrease of 'Ks' but could not stop i t The most plausible explanation is that the addition of sewage sludge was effective in increasing the resistance of aggregates to breakdown when subjected to ponding. Fifty days after the last ponding event, the percent stable aggregates averaged 13.7, 26.9, and 48.1% for the 0, 33, and 100 t/ha treatments respectively. In no case was a significant difference in bulk density observed between the treatments. The soil structure deterioration as a result of ponding was not reflected by the bulk density measurements. Thus, it was concluded that hydraulic conductivity and aggregate stability are better idices of soil structural deterioration than iii bulk density. A side investigation was carried out to illustrate trends of essential nutrient and heavy metal uptake by bermuda grass. Sludge incorporation at 33 t/ha did not seem to increase nutrient and metal uptake by bermuda grass. However N , Cd, and Zn uptake appeared to increase at 100 t/ha. iv TABLE OF CONTENTS ABSTRACT iii T A B L E OF CONTENTS v LIST O F TABLES vii LIST OF FIGURES .......... ... viii A C K N O W L E D G E M E N T S x 1. INTRODUCTION 1 1.1. INTEREST IN AGRONOMIC U T I U Z A T I O N 1 1.2. T H E PROBLEM 1 1.3. OBJECTIVES 2 2. LITERATURE REVIEW 3 2.1. S L U D G E M A N A G E M E N T 3 2.1.1. Sludge production 3 2.1.2. Sludge constituents 3 2.1.3. Sludge processing 4 2.1.4. Sludge disposal options '. 7 2.2. S L U D G E AS A FERTILIZER 8 2.3. S L U D G E AS A SOIL CONDITIONER 9 2.3.1. Aggregate stability 10 2.3.2. Bulk density 12 2.3.3. Hydraulic conductivity 13 2.4. S L U D G E APPLICATION GUIDELINES FOR A G R I C U L T U R A L L A N D 15 2.4.1. Nitrogen 15 2.4.2. Pathogens 16 2.4.3. Soil pH 16 2.4.4. Heavy metals 16 2.4.5. PCBs 18 3. MATERIALS A N D METHODS 20 3.1. SOIL A N D S L U D G E CHARACTERISTICS 20 3.2. EXPERIMENTAL DESIGN 25 3.2.1. Application rates 25 3.2.1.1. Agronomic rate 25 3.2.1.2. Conditioning rate 26 3.2.1.3. Treatments 27 3.2.2. Soil Packing 27 3.2.3. Water regime 28 3.3. SOIL PHYSICAL MEASUREMENTS 29 3.3.1. Hydraulic conductivity 29 3.3.2. Bulk density 31 3.3.3. Aggregate stability 31 3.4. ESSENTIAL NUTRIENT A N D H E A V Y M E T A L U P T A K E E V A L U A T I O N ... 32 v 3.5. S T A T I S T I C A L A N A L Y S I S 33 4. R E S U L T S A N D D I S C U S S I O N 35 4.1. A P P L I C A T I O N R A T E 35 4.2. S T A T I S T I C A L D I S T R I B U T I O N 35 4.3. H Y D R A U L I C C O N D U C T I V I T Y 38 4.4. A G G R E G A T E S T A B I L I T Y 50 4.5. B U L K D E N S I T Y 60 4.6. E S S E N T I A L N U T R I E N T U P T A K E 60 4.7. H E A V Y M E T A L U P T A K E 62 5. S U M M A R Y A N D C O N C L U S I O N S 70 6. F U T U R E R E S E A R C H 72 R E F E R E N C E S 73 v i LIST OF TABLES Table I: Typical chemical composition of raw and digested sludges (Loehr et a l . , 1979) 5 Table II: Typical heavy metal content of sludge (Bastian, 1977) . . . 5 Table III: Recommended cumulative limits for metals of major concern applied to cropland (U.S. EPA, 1983) . . . . . . . . . . . 1 9 Table IV: Soil particle size distribution (Driehuyzen 1983) 21 Table V: Some physical and chemical characteristics of the s o i l (Driehuyzen, 1983) 21 Table VI: Chemical composition of the sludge . .23 Table VII: Heavy metal concentration of the sludge 24 Table VIII: Goodness of f i t of normal and log-normal distributions to the hydraulic conductivity data 36 Table IX: Goodness of f i t of the normal and log-normal distributions to the aggregate st a b i l i t y data 37 Table X: Goodness of f i t of the normal and log-normal distributions to the bulk density data 37 Table XI: Hydraulic conductivity data for the f i r s t ponding event . .43 Table XII: Hydraulic conductivity data for the second ponding event .44 • Table XIII: Hydraulic conductivity data for the third ponding event .47 Table XIV: Hydraulic conductivity data for the fourth ponding event .48 Table XV: Hydraulic conductivity data for the f i f t h ponding event . .51 Table XVI: I n i t i a l aggregate s t a b i l i t y 3.4 Table XVII: Final aggregate s t a b i l i t y (0 to 5cm depth) 36 Table XVIII: Final aggregate st a b i l i t y (5 to 10cm depth) 36 Table XIX: I n i t i a l bulk density Table XX: Final bulk density &1 Table XXI: Available metal concentration i n the s o i l M v i i LIST OF FIGURES Figure 1: Effect of sewage sludge application on water s tab i l i ty index ( Guidi et a l . , 1983) 14 Figure 2: Effect of sewage sludge application on saturated hydraulic conductivity (Epstein, 1975) 14 Figure 3: Sludge production process flow diagram . . . . . . . . . . . . . . . . . . 22 Figure 4: A simulated 24-hour ponding event 30 Figure 5: Schematic of the falling-head apparatus 30 Figure 6: Fract i le diagram of the 'Ks' data for the 33 t/ha treatment (Third ponding event) 39 Figure 7: Fract i le diagram of the ln( 'Ks') data for the 33 t/ha treatment (Third ponding event) 40 Figure 8: Effect of ponding on hydraulic conductivity 41 Figure 9: 95% confidence intervals for the means of the hydraulic conductivity data (First ponding event) 45 Figure 10: 95% confidence intervals for the means of the hydraulic conductivity data (Second ponding event) .45 Figure 11: 95% confidence intervals for the means of the hydraulic conductivity data (Third ponding event) 49 Figure 12: 95% confidence intervals for the means of the hydraulic conductivity data (Fourth ponding event) 49 Figure 13: 95% confidence intervals for the means of the hydraulic coductivity data (Fifth ponding event) 5 2 Figure 14: Effect of sewage sludge application on hydraulic conductivity J J Figure 15: 95% confidence intervals for the means of the f ina l aggregate s tab i l i ty data (0 to 5cm depth) 5 7 Figure 16: 95% confidence intervals for the means of the f ina l aggregate s tab i l i ty data (5 to 10cm depth) « 5 8 v i i i LIST OF FIGURES Figure 17: E f f e c t of sewage sludge a p p l i c a t i o n on the f i n a l aggregate s t a b i l i t y 59 Figure 18: Nitrogen concentration i n the f o l i a g e of bennuda grass ...65 Figure 19: Phosphorus concentration i n the f o l i a g e of bermuda grass ..65 Figure 20: Potassium concentration i n the foliage, of bermuda grass ..66 Figure 21: Cadmium concentration i n the f o l i a g e of bermuda grass ...66 Figure 22: Copper concentration i n the f o l i a g e of bermuda grass ....67 Figure 23: Nickel cocncentration i n the f o l i a g e of bermuda grass ....67 Figure 24: Lead concentration i n the f o l i a g e of bermuda grass 68 Figure 25: "Zinc concentration i n the f o l i a g e of bermuda grass 68 i x ACKNOWLEDGEMENTS I would like to express my gratitude to Dr. S.T. Chieng for his supervision of my M.Sc. program as well as for his advice and encouragement. Sincere appreciation is also expressed to Dr. J. de Vries for his constant advice and helpful suggestions. I would also like to thank Dr. K.V. Lo and Professor L M . Staley for serving as committee members. Special thanks are due to Mr. Neal Jackson, Mr. Jurgen Pelke, and Dr. M . Bonsu for their technical assistance. Thanks also to the graduate students of the Bio-Resource Engineering Department for their enthusiastic support and to Envirocon Company for providing the results of the heavy metal analysis of the sludge. Finally, my sincere thanks to my family in Beirut, and to Catherine for their love and patience. x 1. INTRODUCTION 1.1. INTEREST IN AGRONOMIC UTILIZATION In the past decade strict limitations have been imposed on the disposal of sewage sludge by incineration, fresh water dilution, and ocean dumping. These methods can adversely affect the environment without providing the potential benefit of resource and energy conservation. Recently, interest in the agronomic utilization of municipal sewage sludge has increased. There is a growing consensus that well-managed sludge application systems to land can be environmentally acceptable if properly designed and operated. Guidelines have been developed to enable the safe use of sewage sludge in land reclamation and biomass production. The agricultural virtues of sewage sludge can be summarized as follows (Menzies, 1973): "It is a low-analysis, slow-release organic fertilizer valued mainly as a soil conditioner. Beyond this, and perhaps more important in the long run, the waste is recycled in a useful way back to the land from which it came." 1.2. T H E P R O B L E M Due to the nature and frequency of fall and winter rainfall events in the Boundary Bay area, and the inherent characteristics of the Ladner series soil, it is not physically possible to meet the infiltration requirement for all rainfall events assuming a working subsurface drainage system is in place. Consequently, special management practices are needed to enhance the physical and hydraulic properties of this poorly drained soil. These practices include: i) soil conditioning, ii) use of cover crop, and iii) subsoiling (de Vries, 1983). 1 INTRODUCTION / 2 Turf growers have been farming for the last decade in the Boundary' Bay area. At each harvest, approximately a 2cm layer from the A horizon is taken out with the grass. Consequently, the cultivation layer is becoming thinner year after year and the growers are already farming the B horizon. The mixing of comparted B horizon clods in the cultivation layer is also another problem faced by the farmers in the area. The mixing results from using a chisel plough rather than a paraplough for subsoiling. The chisel plough is inappropriate for the Ladner soil because it tends to pull compacted subsoil clods into the cultivation layer. The possible improvement of the B horizon structure through sewage sludge application will benefit the fanners. This applies mostly to the turf growers and other non-food-chain crop farmers who can use sewage sludge with less restrictions than edible food growers. 1.3. OBJECTIVES The main objectives of this study are: 1. to determine the effects three rates of sewage sludge application on the soil structural stability in relation to the destructive action of water by: a. monitoring the soil response to periodically simulated ponding events using hydraulic conductivity as an index for ponding tolerance. b. determining aggregate stability in water at the beginning and at the end of the experiment 2. to determine the response of soil bulk density to sewage sludge treatment. 3. to determine the impacts of sewage sludge application on heavy metal and essential nutrient uptake by a commercially grown turfgrass. 2. LITERATURE REVIEW 2.1. S L U D G E M A N A G E M E N T Sludge management refers to the processing and disposal of sludge produced at wastewater treatment plants. 2.1.1. Sludge production The increasing population densities have resulted in a tremendous increase in sludge production. For example, experts have predicted that the tonnage accumulated in New York State will double between 1975 and 1985 (Rajagopal et a l , 1981). In the case of India, it has been estimated that if the entire domestic wastes of all the towns of India are utilized, it can irrigate more than 200,000 hectares of land. In 1977, Bangkok's production of sewage sludge from cesspools and septic tanks was evaluated to be around 150,000 cubic meters. This volume does not include the sludge from central treatment plants. Thus it can be seen that the potential sludge problem is omnipresent. Urbanization trends and tougher pollution control legislation suggest that sludge disposal is one of the most important problems facing wastewater treatment engineers. 2.1.2. Sludge constituents To establish an effective sludge management plan, it is important to know the composition of the sludge. The constituents vary depending on the origin of the sludge, the processing to which it has been subjected, and the amount of aging that has taken place (Metcalf and Eddie, 1979). Since sludge is a product of the food we eat, it contains many of the 3 U T E R A T U R E REVIEW / 4 elements present in our food: nitrogen, phosphorous, potassium, calcium, iron, and others. Typical data on the chemical composition of untreated and digested sludges are shown in table I. Sludge contains harmful contaminants removed from wastewater by physical, biological, and chemical treatments (Dean and Smith, 1973). These contaminants include pathogenic microorganisms, heavy metals, and toxic chemicals. Untreated sludges contain high concentrations of fecal coliforms, especially Escherichia coli. It also contains smaller quantities of intestinal and respiratory tract organisms, many of which may be disease causing. The human population is not the only contributor of contaminants to the sewage stream (Rajagopal et al., 1981). Industries and commercial establishments contribute to the supply of of toxic chemicals and hazardous metals to the wastewater system. Stormwater runoff discharging in combined sewers contains zinc and cadmium from tire wear, lead from gasoline, metals from gutters, and corrosion from other metal objects. Table II reports typical values for metals in sludges. 2.1.3. Sludge processing Whatever disposal option is selected by a municipality, the sludge should be processed to: 1. minimize environmental impacts and meet disposal standards established by regulatory agencies. 2. reduce its volume as much as possible in order to decrease the cost of subsequent disposal steps. Sludge processing is achieved by stabilization and dewatering techniques. Sludge stabilization processes are aimed at converting raw (untreated) sludges into a less offensive form with regard to odor, putrescibility rate, and pathogenic organism content LTTERATURE REVIEW / 5 Table I: Typical chemical composition of raw and digested sludges (Loehr et a l . , 1979). RAW DIGESTED ITEM* RANGE TYPICAL RANGE TYPICAL T 5 k * ( % ) 2.0-7.0 4.0 6.0-12.0 10.0 vs** 60.0-80.0 65.0 30.0-60.0 40.0 L i p i d s 6.0-30.0 - 5.0-20.0 P r o t e i n 20.0-30.0 25.0 15.0-20.0 18.0 N i t r o g e n 1.5-4.0 2.5 1.6-5.0 3.0 P a O , 0.8-2.8 1.6 1.5-4.0 2.5 K 2 0 0-1.0 0.4 0-3.0 1.0 C e l l u l o s e 8.0-15.0 10.0 8.0-15.0 10.0 S i 0 2 15.0-20.0 - 10.0-20.0 pH 5.0-8.0 6.0 6.5-7.5 7.0 * Expressed as X of total solids (TS). * * VS= v o l a t i l e solids. Table II: Typical heavy metal content of sludge (Bastian, 1977). METAL* RANGE MEAN MEDIAN 225 90 • 9 8 430 350 1,460 1,300 87 20 350 100 1,800 600 1,250 700 7 4 1,190 400 410 100 1,940 600 26 20 3,483 1,800 S i l v e r nd-960 A r s e n i c 10-50 Boron 200-1 ,430 B a r i u m n d - 3 , 0 0 0 Cadmium nd-1 ,100 C o b a l t nd-800 Chromium 22-30,000 Copper 45-16,030 M e r c u r y 0 . 1 -89 Manganese 100-8,800 N i c k e l nd -2 ,800 L e a d 80-26 ,000 S e l e n i u m 10-180 Z i n c 51-28,360 * Expressed In ppm. ** nd« not detected. U T E R A T U R E REVIEW / 6 (U.S. Environmental Protection Agency (U.S. EPA), 1974). Raw and stabilized sludges may contain up to 90 to 95% water. Dewatering is a physical process to reduce the water content to improve handling, processing, transportation, and disposal cost of sludges. The methods available for sludge stabilization include: 1. Anaerobic digestion 2. Aerobic digestion 3. Composting 4. Chlorine oxidation 5. Lime stabilization 6. Heat treatment The sludge used in this study was anaerobically digested, dewatered, and then composted. Consequently only anaerobic digestion and composting are discussed here. Anaerobic digestion involves the biological degradation of sewage sludge in the absence of molecular oxygen. The process is carried in a closed tank with an airtight cover. The stabilized sludge is non-putrescible, and its pathogen content is greatly reduced. Anaerobic digestion is a two-phase process (Peavy et al., 1985). In the first phase, acid formers which consist of facultative and anaerobic bacteria ferment the complex organics to acids and alcohols of lower molecular weight. In the second phase, anaerobic methane formers convert the acids and alcohols primarily to methane and carbon dioxide. About 50 to 60% of the the organic substrate is metabolized, with less than 10% being converted to biomass. The residual organic material consists of a mixture of microbial tissues, lignin, cellulose, organic nitrogen compounds. Composting is defined as the aerobic thermophilic decomposition of organic solids to a relatively stable humus like material (U.S. EPA, 1978). Sludge compost is a U T E R A T U R E REVIEW / 7 natural organic product with high humus content similar to peat It has a slight musty odor, is moist and dark in color, can be loaded in trucks, and bears little resemblance to the original material. The processes that have shown successful capabilities for dewatering sludges are (J.M. Montgomery, Consulting Engineers, 1985): 1. Drying beds or lagoons 2. Vacuum filtration 3. Pressure filter press 4. Belt filter press 5. Centrifugation Drying beds or lagoons rely on natural evaporation and percolation to dewater the sludge. The other dewatering devices listed above rely on mechanically assisted physical means to dewater the solids more quickly. For smaller plants where land availabilty is not a problem, drying beds are generally chosen. 2.1.4. Sludge disposal options Sludge disposal is the process of transferring the sludge to the environment so that no additional handling or processing is required. Disposal options fall into two general categories: a. Utilization disposal options b. Non-utilization disposal options Utilization refers to the beneficial use of the sludge or sludge by-products (i.e., soil amendment). However, wastewater sludge may not be always used as a resource because it contains high levels of metals and other toxic substances. In this case, U T E R A T U R E REVIEW / 8 sludge options that do not involve beneficial use can be adopted. These options include: incineration, landfilling, and dedicated land disposal. The concept of utilizing or recycling sludge nutrients on agricultural land is not only feasible but, in light of the present need for resource and energy conservation, this approach is also desirable. In the United States, recent laws encourage agricultural utilization (U.S. EPA, 1979). The Clean Water Act requires the establishment of industrial waste pretreatment programs with the objective of reducing toxic pollutant loading to municipal treatment facilities. The implementation of pretreatment programs will make more municipal solids suitable for land application. The sludge utilization trend was given a boost by the Resources Conservation and Recovery Act, which authorized the U.S. Environmental Protection Agency to develop treatment and application rate criteria for sludge application to cropland. The beneficial usage of sewage sludge in agriculture is associated with its value as a fertilizer and as a soil conditioner. These virtues are discussed seperately in this review. However, due to the scope of the thesis more emphasis is put on the value of sludge as a soil conditioner. 2.2. S L U D G E AS A FERTILIZER Information on the response of crops to sludge addition has been widely published. A few findings are discussed here. Composted sludge was applied at four rates (0 to 134 t/ha) to tall fescue growing on two different soils (loamy sand and silt loam) (Sikora et al., 1980). The results indicated a positive linear relationship between crop yield and sludge application rate for both soils. Day et al (1982) compared the effects of dried sewage sludge and inorganic LITERATURE REVIEW / 9 fertilizers on the yield and quality of hay from Harlem barley. The data showed that dried sewage sludge may be used as an alternative source for fertilizer. The researchers did not find any concern regarding heavy metal toxicity to plants when sludge is applied at a carefully planned rate. Field studies with ariaerobically digested sludge were conducted near Guelph, Ontario, using corn and bromegrass as experimental crops (Soon et al., 1978, I). The rates of application supplied 200, 400, 800, and 1600 Kg N per hectare per year for 3 years. Bromegrass yields were increaesed by sludge application supplying up to 800 Kg N per hectare. On loam and clay loam soils, there was no further increase in the yield of corn with rates in excess of 200 Kg N per hectare. Nitrate concentration in corn stover was increased at rates of 800 Kg N per hectare and above (Soon et al., 1978, II). Phosphorus concentration in corn grain and stover was unaffected by sludge treatment, however it did increase in bromegrass with increasing sludge rates. The crops exhibited similar responses to large amounts of metal in sludge. Analysis of leachates from the lysimeter experiments indicated nitrate movement through soils which received sludge at rates in excess of 200 kg N per hectare. However there was little, if any, movement of phosphorus to the groundwater. 2.3. S L U D G E AS A SOIL CONDITIONER Soil conditioning implies the improvement of the soil's physical properties by treatment with chemical materials (Schamp et al., 1975). The chemical materials used are either inorganic salts, mainly calcium salts, or high molecular mass organic chemicals. The organic compounds range from well-defined synthetic polymers to UTERATURE REVIEW / 10 complex products whose properties are less clearly understood, frequently waste products. Organic matter stabilizes soil structure through the bonding of organic polymers to clay surfaces by cation bridges, hydrogen bonding, Vander Waals forces, and sesquioxides-humus complexes (Baver et al., 1972). The drying of organic polymers results in the formation of ah insoluble irreversible matrix. Thus the adhesive bonds formed are not expected to dissolve or break down upon wetting. Since these binding substances are susceptible to microbial decomposition, organic matter must be replenished and supplied continually if aggregate stability is to be maintained in the long run (Hillel, 1980). This part of the review deals with physical processes in the soil with special reference to sewage sludge application. While the fertilizer values of sludges are now well assessed, studies on the influence of sludge organic matter on the physical properties of soil are limited (Guidi and Hall, 1983). European experiences of wastewater sludge as a soil conditioner have been recently published (Catroux et al., 1983). This and other work have shown that sludge can be effective in improving structural and hydraulic properties of soils. The physical properties discussed here are: aggregate stability, bulk density, and hydraulic conductivity. 2.3.1. Aggregate stability The enhancement of soil aggregation is of paramount importance for soil productivity. This is especially true for those soils under intensive crop production where the workability, a low tendency to surface crusting, and the resistance to the destructive actions of water and agricultural machinery are essential to obtain high yields. A one year study was initiated on 3 Indiana soil types: a Celina Blount silt I JTERATURE REVIEW / 11 loam, a Blount silt loam, and a Tracy sandy loam (Kladivko and Nelson, 1979). Anaerobic sludge applied at 56 t/ha increased the mean weight diameter of water-stable aggregates in the top 5cm of a soil as much as 4 times over that of the control samples. The data also shows that aggregate stability decreased over the winter months in both sludge-amended and control plots, but the sludge-treated plots continued to exhibit more aggregation than their respective controls. A field study was established in Italy on a sandy loam soil (Guidi et al., 1983). A stability index (WSI) was used to quantify the stability of soil aggregates in water. WSI is defined as WSI= 100x(A/B), where A and B are the weights of aggregates passing through a 0.25 mm mesh sieve after 5 and 60 minutes of wet-sieving, respectively. According to this method, the index increases as the stability of aggregates increases. The WSI of the control plots tended to be lower, but not always significantly, than that of the sludge-treated plots (Figure 1). The aggregate stability of both treated and control plots dropped sharply after some months. A similar behavior has been been observed in Kladivko and Nelson's experiments (1979). The decay of aggregate stability over the fall and winter months has been mainly attributed to: i) the lower biological activity, ii) the decomposition of organic matter during spring and summer, and iii) the destructive action of water. Furrer and Stauffer (1983) reported the results of a field experiment in Switzerland on a heavy soil. Sewage sludge was applied to meadow plots for five consecutive years at 6 and 24 t/ha. There was no significant difference in aggregation between the plots fertilized with sewage sludge and mineral fertilizers. The organic matter loading was not high enough to trigger a significant increase in aggregate stability. U T E R A T U R E REVIEW / 12 2.3.2. Bulk density Several studies indicate a decrease in bulk density in soils treated with sewage sludge. The decrease in bulk density is caused by the mixing of organic matter with the mineral soil (Khaleel et al., 1981). Dried sludge was applied to a Hubbard sand soil (Gupta et al.,' 1977). Addition of 450 t/ha annually decreased the bulk density of the sandy soil by 28% in 2 consecutive years. Hall and Coker (1983) reported significant reductions in the bulk density of 3 arable soils as a result of the addition of digested sludge at rates between 100 and 500 t/ha. While Gupta et al. (1977) and Hall and Cocker (1983) used extremely high rates of sewage sludge, Kladivko and Nelson (1979) applied the sludge at moderate rates that can be used in normal agricultural operations (i.e., 56 and 90 t/ha). Core samples were taken from the 0 to 5cm depth of the soil. Plots where sludge was disked-in exhibited a significant decrease in bulk density because most of the sludge applied was incorporated in the top 5cm of the soil. However, the incorporation of sludge by rototilling did not promote a significant decrease in bulk density because of the dilution effect of mixing the sludge in the upper 15cm rather than in the upper 5cm of the soil. Furrer and Stauffer (1983) conducted field and lysimeter experiments using low application rates (i.e., between 4 and 12 t/ha). In no case was a significant influence of sewage sludge application on bulk density reported. 1ITERATURE REVIEW / 13 2.3.3. Hydraulic conductivity The limited data available showed that saturated hydraulic conductivity (Ks) increased in sludge-treated soils, provided that sufficient organic material had been used. The addition of anaerobic sludge at 450 t/ha for 2 consecutive years increased Ks of a Hubbard sand soil by 17% from 3.0x10"4 to 3.5x10" 4 m/s (Gupta et al., 1977). In a pot experiment, sewage sludge was incorporated into a Beltsville silt loam subsoil at the rate of 5% on a dry weight basis (Epstein, 1975). The author found that Ks increased after the application time, reached a maximum, and then dropped to that of the control (figure 2). This decrease appears to be due to the: i) breakdown of soil aggregates. ii) clogging of soil pores by microbial decomposition products. Though the literature related to the influence of sludge application on physical properties of soil is limited, there is an evidence that structure and hydraulic characteristics can be improved by sludge treatment. However, most of the significant effects have been found in studies using high rates of sludge application (i.e., Gupta et al., 1977, Hall and Coker, 1983). Those rates will ultimately result in heavy metal contamination of the soil and groudwater pollution as a result of overfertilization. The challenge is to apply the sludge at rates high enough to enhance the soil structure without causing deterioration of the quality of the environment (Kladivko and Nelson, 1979). UTERATURE REVIEW / 14 to-rn to LJ I 5-i i i i i i i—i—i—i—i—i—i—i—i—i—r i i i i Legend o c A CANS + ANS TIME Figure 1: E f f e c t of sewage sludge a p p l i c a t i o n at 38 t/ha on water s t a b i l i t y index. C= con t r o l , CANS= composted anaerobic sludge, and ANS= anaerobic sludge (Guidi et a l . , 1983). E >-> c_> => o 2 o o o _ l < CC o >-X 100 120 TIME (days) i 180 Legend O CONTROL A *>7. SLUDGE F i g u r e 2: E f f e c t o f sewage s l u d g e a p p l i c a t i o n on s a t u r a t e d h y d r a u l i c c o n d u c t i v i t y ( E p s t e i n , 1975) . U T E R A T U R E REVIEW / 15 2.4. S L U D G E APPLICATION GUIDELINES FOR AGRICULTURAL L A N D The agricultural utilization option assumes that sludge is added at "agronomic rates", defined as the annual rate at which the nitrogen supplied by sludge and available to the crop does not exceed the nitrogen requirement of the crop (U.S. EPA, 1983). In addition, the application rate must take into consideration existing federal, provincial, and local regulations relative to pathogens, metals, and organics contained in the sludge. Sludge may also be used as a soil conditioner if added at rates greater than agronomic rates. In this case, increased monitoring will usually be required for potential nitrate movement into drinking water aquifers. Exceeding the allowable limits for cadmium may result in restrictions on crop use (i.e., only non-food-chain crops can be grown). Guidelines for sludge application on cropland have been developed by the U.S Environmental Protection Agency (U.S. EPA, 1979). The criteria used are based on a management rather than a performance approach to minimize potential problems associated with applying sludge on cropland. The guidelines address mainly nitrogen, pathogens, heavy metals, and polychlorinated biphenyls (PCB's) contained in sludges. The following discussion emphasizes these guidelines. 2.4.1. Nitrogen A major concern with the application of sludge on land is nitrogen management. Following sludge application, nitrate is formed by nitrification of the ammonium either added in the sludge or released during the mineralization of organic nitrogen. Nitrate is a water-soluble anion that will move downward readily in the soil profile. High nitrate concentration in drinking water may result in health problems for both infants and livestock. The maximum allowable nitrate concentration in groundwater U T E R A T U R E REVIEW / 16 has been established at 45 mg/1. Nitrate pollution can be solved by adding the amount of nitrogen from the sludge that is removed by the crop, plus whatever is volatilized into the atmosphere or is lost due to denitrification, or considered an allowable concentration in the groundwater (Vesilind, 1979). 2.4.2. Pathogens Untreated raw sludges contain a variety of pathogens. Any sludge applied to food-chain crops must be treated by a process to significantly reduce pathogens. Typical treatment processes have been discussed in section 2.1.3 . Pathogenic organisms do not enter plant tissues, but problems can result from contamination of the plant surfaces. Root crops and crops which will be eaten raw may not be grown for 18 months after the time of application, unless there is no contact between crop and sludge. Animals should not be grazed on the site for one month after sludge application if the animal product will be consumed by humans. 2.4.3. Soil pH Food-chain crops can be safely grown if the soil pH is 6.5 or greater at the time of planting. The tendency of crops to accumulate heavy metals is significantly reduced as the soil pH increases above 6.5. If the soil pH is less than 6.5, limestone should be added to adjust it to pH 6.5. 2.4.4. Heavy metals From a human health standpoint, cadmium is the sludge-borne metal that has received the greatest attention. Although Cd is not usually phytotoxic, it is readily absorbed by plants, can accumulate in edible parts, and enter the food chain (Naylor U T E R A T U R E REVIEW / 17 and Loehr, 1980). Cd tends to accumulate in the kidneys, and may cause a chronic disease called proteinuria (i.e., increased excretion of protein in the urine). The annual application rate of Cd should not exceed 0.5 Kg/ha on land used for the production of food-chain crops. For soils with a background pH of 6.5 or greater, the cumulative Cd loading should not exceed the levels given in table III. These regulations were developed from considerations of allowable increases in dietary Cd for a worst case situation, e.g., a vegetarian growing 100% of his food on an acid, sludge-treated soil. Non-food-chain crops can be grown on soils with a pH of less than 6.5, provided that the cumulative Cd application rate does not exceed 5 Kg/ha reguardless of the soil cation exchange capacity (CEC). The cumulative metal limits in table III are a function of soil CEC. The use of soil CEC in establishing metal limits does not imply that metals added to soils in sludge are retained by the exchange complex as an exchangeable cation. It has been shown experimentally that nearly all metals in sludge amended soils are not present as exchangeable cations (U.S. EPA, 1983). Thus, CEC was chosen as an indicator of soil properties, since it is easily measured and related to soil components that minimize plant availability of sludge-borne metals in soil. In addition to Cd, the cumulative amounts of Pb, Zn, Cu, and Ni applied to soils in sludge can be used to determine the number of years that sludge can be utilized. Limitations on the total metal additions to soils are needed to protect soil productivity and animal health. The majority of crops do not accumulate Pb, but there is concern regarding the potential ingestion of Pb and other trace elements (Cu, Se, Mo) by animals grazing on sludge-contaminated forage and indirect consumption of soil. In general, Zn, Cu, and Ni will be toxic to crops before their concentration in plant tissues reaches a level that poses a problem to human and animal health. U T E R A T U R E REVIEW / 18 The use of crops which accumulate small amounts of heavy metals is encouraged (e.g., corn, pea, beans, berry fruits, tree fruits, tomato) (Keeney et al, 1975). Sludge application for the production of non-food-chain crops has a great potential (e.g., cotton, turfgrass, and energy biomass trees) (Abron- Robinson et al., 1981). Using sludge in this manner would realize the advantages of its beneficial properties while circumventing the potential problems associated with the impacts of heavy metals on the human food chain. Sludge applications should cease when any single metal concentration limit is attained. If the soil pH is maintained at 6.5 or above, cessation of sludge application at the limits presented should enable the growth of any crop in the future without any adverse effects on yield. In addition, soil productivity will be at a level equal to, and most likely greater than, that which existed prior to initiation of sludge appliction. 2.4.5. PCBs PCB's are relatively resistant to decomposition in soils and may be of concern from a human health standpoint. The principal problem resulting from PCB's is the direct ingestion by animals grazing on forages treated with surface-applied sludge. Several studies have shown that essentially no plant uptake of PCB's occurs, although PCB's can be absorbed onto the surfaces of root crops (U.S. EPA, 1983). Sludges containing concentrations of PCB's greater than 10 mg/kg must be incorporated into the soil when applied to land used for producing animal feed. Dairy cattle are very susceptible to PCB contamination of forages, since PCB's in the diet are readily partitioned into milk fat, Since PCB's are no longer manufactured, PCB-related constraints should become less common in the near future. UTERATURE REVIEW / 19 Table III: Recommended cumulative limits for metals of major concern applied to agricultural land (U.S. EPA. 1983). Soil cation exchange capacity (meq/lOOg) 5 5 to 15 15 Metal . (kg/ha) — Lead 560 1,120 2,240 Zinc 280 560 1,120 Copper 140 280 560 Nickel 140 280 560 Cadmium 5 10 20 3. MATERIALS AND METHODS 3.1. SOIL AND SLUDGE CHARACTERISTICS The soil was collected from the top 20cm of the B horizon at the Boundary Bay experimental plots (Delta, B.C.). The basic soil mapping unit is the Ladner series (Luttmerding, 1981). This poorly drained soil has developed from fine-textured, stone-free deposits which are underlained by saline sandy materials at depths below 100cm. The material is grayish, partially leached, and contains reddish-brown mottles. Some physical and chemical characteristics are given in tables IV and V. The sludge was produced at the Iona Island Wastewater Treatment Plant (Richmond, B.C.). Figure 3 illustrates the production process flow diagram. The sludge was composted by Envirocon Company to further reduce: 1. Pathogen content 2. Water content 3. Heavy metal concentrations The chemical composition of the sludge is given in table VI. Heavy metal concentrations and maximum acceptable metal concentrations in processed sludge are reported in table VII. Heavy metal concentrations were based on 3 years of monitoring by Envirocon Company. A l l measurements were made according to procedures given in Standard Methods (American Public Health Association (APHA), 1975). 20 MATERIALS AND METHODS / 21 Table IV: S o i l particle size distribution (Driehuyzen, 1983). Particle size (mm) 2.0 1.0 0.500 0.250 0.125 0.105 0.074 0.0625 0.050 0.002 -X Passing-100 100 100 100 99.3 98.3 95.1 93.1 88.8 23.4 Table V: Some physical and chemical characteristics of the s o i l (Driehuyzen, 1983). Classification Jinlk density pH Carbon Total-N CEC (l i /cnO (CaCl 2) (2) (JO (meq/lOOg) Humic Luvic Gleysol 1.40 5.2 1.8 0.135 22.7 MATERIALS AND METHODS / 22 RAW WASTEWATER-I a -ARIF1! i PRIMARY SLUDCE BIO PRODI - CAS CTION ANAE DICE ROBIC STER SAND BEDS (DEWATERING) METHANE LIQUID DIGESTED SLUDGE WINDROW COMPOSTING OCX WITH, WOOD CHIPS) FINAL PRODUCT Figure 3: Sludge production process flow diagram. M A T E R I A L S A N D M E T H O D S / 23 Table VI: Chemical composition of the sludge. ITEM ** MEAN (%) S.D . U ) c . v . U ) RANGE(%) n TS 61.6 1.95 3.2 58.3-65.9 10 VS 14.7 1.5 10.3 11.5-17.5 10 NH j-N 0.55 0.1 18.2 0.45-0.70 10 TKN 1.15 0.14 12.2 0.95-1.31 10 TP 0.60 0.07 11.7 0.47-0.73 10 * Mean, standard dev ia t ion ( S . D . ) , c o e f f i c i e n t of v a r i a t i o n ( C . V . ) , range of da ta , and number of samples (n ) . * * Total s o l i d s ( T S ) , v o l a t i l e s o l i d s (VS) , ammonia-nitrogen (NH 3 -N) , to ta l Kjeldahl ni t rogen (TKN), and to ta l phosphorus (TP) . MATERIALS A N D METHODS / 24 Table VII: Heavy metal concentration of the sludge. CONCENTRATION1 Arsenic less than 20 75 Cadmium leu than 10 10 Cfvomlnum lets than 300 1.000 Cobalt lew than 20 150 Copper less than 750 750 Mercury less than 3 4 Molybdenum less than 20 20 Nickel less than 100 160 Lead less than 450 450 Selenium less than 5 12 Zinc less than 1,000 1,650 1. Ai l concentrations are in a dry weight basis, in ppm. 2. B.C. Ministry of Environment: Composted Sewage Sludge maximum allow-able concentration for non-restricted land application (Bertrand, 1980). Maximum Acceptable Metal -Concentration 3.2. E X P E R I M E N T A L DESIGN MATERIALS A N D METHODS / 25 3.2.1. Application rates The sludge application rates were based on the guidelines established by the U.S. Environmental Protection Agency. The rates included an agronomic rate and a conditioning rate. 3.2.1.1. Agronomic rate The agronomic rate is based on the nitrogen and cadmium contents of of the sludge and the nitrogen requirement of the crop grown. Corn was used as a reference crop to derive the agronomic rate because: 1. it, is commonly grown in the area. 2. it has a high annual nutrient utilization. 3. it accumulates very little cadmium, provided lime is added to raise the pH to 6.5 . The advantages of using a crop that has a high annual nutrient utilization are: 1. more sludge nutrients can be recycled. 2. higher levels of organic matter can be added to enhance the soil structural stability without resulting in nitrate pollution of the groundwater. Equation 3.1 was used to determine the agronomic rate based on nitrogen requirement (U.S. EPA, 1983): Np= Sx[(N03) + Kv(NH4) +F(No)]x(10) (3.1) where: Np= Plant available nitrogen from sludge application, in kg/ha. S= Sludge application rate, in t/ha (dry weight basis). MATERIALS A N D METHODS / 26 N 0 3 = Percent nitrate-N in the sludge, as percent K v = Volatilization factor; use K v = l for dewatered sludge applied in any manner. NH4= Percent ammonia-N in the sludge, as percent F = Mineralization factor for organic N in the sludge in the first year, expressed as a fraction. For composted sludge use F=0.1 . No= Percent organic N in the sludge, as percent In addition to considering the annual rate of nitrogen application, the rate of cadmium application must be below the prevailing limit i f a food-chain crop is grown. The maximum annual sludge application rate based on cadmium was calculated using equation 3.2 (U.S. EPA, 1983): Scd= (Lcd/Ccd) (1000 kg/t) (3.2) where: Scd= Amount of sludge, in t/ha (dry weight basis), that can be applied based on Cd limitation. Lcd= Cd limitation; use Lcd= 0.5 kg/ha/year, (i.e., U.S. EPA standard as of 1/1/87) Ccd= Concentration, in mg/kg, of Cd in the sludge. Note that the lowest of the 2 rates, S and Scd. was applied. 3.2.1.2. Conditioning rate The conditioning rate is defined as a rate of sludge application in excess of the agronomic rate and where the improvement of the soil's physical properties is the main objective. In this study, the conditioning rate was arbitrary chosen to be 3 times larger than the agronomic rate. MATERIALS A N D METHODS / 27 3.2.1.3. Treatments Three treatments were used in this study: 1. Treatment A: no sludge application or control .2. Treatment, B: sludge application at the agronomic rate 3. Treatment C: sludge application at the conditioning rate Each treatment was replicated 12 times to account for anticipated deviations in hydraulic conductivity measurements. 3.2.2. Soil Packing The soil was packed in 4-liter paint pails. The pails were painted with latex paint to prevent rusting. Drainage holes were drilled and plastic screening was installed at the bottom of each pail. The soil columns were prepared in 4 steps: 1. Aggregate preparation: The soil collected was spread on plywood boards and allowed to air-dry for 48 hours at room temperature. Big aggregates were broken down to pea size lumps using a flat shovel. The soil was then raked to insure aggregate size uniformity. 2. Mixing: The total volume of raked soil was mixed half a dozen times to obtain a homogeneous source for packing. 3. Sludge addition: Soil samples of equal weight (i.e., 4000g dry weight) were taken prior to packing. For treatments B and C the sludge was thoroughly mixed with the soil samples. 4. Packing: MATERIALS A N D METHODS / 28 The soil was packed in layers of 3cm each. Each layer was tamped by dropping on its surface, from a constant height, a 5cm x 5cm wood stick. Thus using the repeated action of gravity to achieve a realistic, uniform, and reproducible packing. Then, each layer was gently scratched with a wire brush to prevent the formation of low conductivity layers as a result of the packing technique. Bulk density was used as an index for packing uniformity. 3.2.3. Water regime The soil columns were incubated in a greenhouse for 9 months. The average temperature at 10 A M . for that period was 21° C and the temperature range was between 17 ° C and 28 0 C. The experiment consisted of 2 phases during which the treatments were subjected to the same water regime: phase 1: infiltration requirement was always met phase 2: infiltration requirement was not always met A soil's infiltration requirement is met when rainfall does not result in ponding. This implies that the soil's infiltrability is larger than the rainfall rate. The soil columns were subjected to wetting and drying cycles. Whenever water was applied, the soil surface was protected with cheeze cloth material to reduce the impact of water drops. Phase 1: During that period which lasted 3 months, the soil's infiltration requirement was always met (i.e., 4.4x10"^ m/s based on 2 years return period). Spring and summer rainfall events in the Boundary Bay area were simulated (Atmospheric Environment Service, 1982). Water was applied carefully with a squeeze bottle twice a week. MATERIALS A N D METHODS / 29 Phase 2: During this period which lasted approximately 6 months, the soil's infiltration requirement was not always met. Ponding, a major lowland soil problem, was simulated monthly. Water was applied to the soil columns using a squeeze bottle. Once a thin ponding layer was gradually established, water was then applied continuously for 24 hours using 5mm tubing. A ponding layer of a constant depth was maintained. Figure 4 illustrates the process. The ponding tolerance of the soil columns is defined within the context of this study as the ability of the soil columns to withstand the destructive actions of surface free water. 3.3. SOIL PHYSICAL M E A S U R E M E N T S 3.3.1. Hydraulic conductivity The ponding tolerance of the soil columns was evaluated by measuring their satiated hydraulic conductivity ('Ks') at the end of each ponding event The term satiated hydraulic conductivity is used rather than saturated hydraulic conductivity to recognize that there was air entrapment upon ponding of the soil columns. The measurements were made using the falling-head method (Klute, 1965). A schematic of the falling-head apparatus used in this study is shown in figure 5. A 1cm thick plexiglass plate was lined with a soft rubber gasket The plate was placed on the top of the pail just before measuring 'Ks' . Then, it was connected to a constant head water supply and to a manometer using tubing. Weights were put on the top of the plate to insure a tight seal between the rubber gasket and the top of the pail, thus making the apparatus leak-proof. 'Ks ' was calculated from Darcy's formula: 'Ks '= (al/At) ln(Hi/H2) (3.3) MATERIALS AND METHODS / 30 OVERFLOW A. WATER SAMPLE c_rt"7,T»Lzr FREE DRAIKAGE WATER SOURCE TPONDING DEPTH (3-4cm) COLUMN LENGTH (12-13cm) FIGURE 4: A slsulated 24-hour ponding event. FREE DRAINAGE Hj» I n i t i a l hydraulic head H 2" Final hydraulic head Figure 5: Schematic of falling-head apparatus. MATERIALS A N D METHODS / 31 where 'Ks' is the satiated hydraulic conductivity (m/s), a is the area of the cross section of the standpipe (m^), 1 is the length of the soil sample (m), A is the cross sectional area of the sample (m^), and t is the time (s) for the hydraulic head difference to decrease from H i (m) to H2 (m). 3.3.2. Bulk density The bulk density (BD) of the soil columns was determined at the beginning and at the end of the experiment. BD is the ratio of the mass of the solids to the bulk volume of soil particles plus pore spaces in a sample (Blake, 1965). Three soil samples per column were taken to evaluate the gravimetric moisture content (Gardner, 1965). The column bulk volume was obtained from the volume of the pail occupied by soil material. The initial bulk density was used as an index for soil packing uniformity. The final bulk density was determined 50 days after the last ponding event At that time the water content of the columns was below the plastic limit thus allowing: 1. mixing of the soil material to obtain a homogeneous source for moisture determination. 2. simultaneous, non-destructive sampling at various depths for aggregate stability testing. 3.3.3. Aggregate stability The soil's initial aggregate stability was evaluated three months before the first ponding event based on 12 samples. To determine the final aggregate stability, soil samples were collected from the 0 to 5cm and 5 to 10cm depths of each column nine months after sludge incorporation (i.e., 50 days after the last ponding event). A MATERIALS A N D METHODS / 32 total of 48 samples per treatment was taken, half of which was from the 0 to 5cm depth while the other half was from the 5 to 10cm depth. The method used to determine the stability of soil aggregates in water is a modified version of the one described by Kemper (1965). Three grams of air-dried aggregates (l-2mm) were placed onto 0.25mm mesh sieves and moistened gently with a water spray device. A mechanical wet sieving machine was used to raise and lower the sieves through a distance of 2.5cm, 40 times each minute. In this manner, the action of flowing water is simulated. After 10 minutes of sieving, the sieves were removed from the water and the oven-dry weight of the aggregates left on each sieve was determined. The soil particle size distribution (table IV) and laboratory dispersion tests showed that no correction was required for particles of diameter greater than 0.25mm. The standard procedure is to express aggregate stability (AS) in %: %AS= (a/b)xl00 (3.4) where: a= oven-dry weight of aggregates left on the sieve after 10 minutes of wet sieving (g). b= oven-dry weight of aggregates before wet sieving (g). 3.4. ESSENTIAL NUTRIENT A N D HEAVY M E T A L UPTAKE EVALUATION A side investigation was carried out to illustrate trends of essential nutrient and heavy metal uptake by bermuda grass. The soil-sludge mixtures were placed in wooden containers 30cm long, 20cm wide, and 15cm deep. The containers were placed in a greenhouse along with the soil columns and were watered twice a week with a calibrated watering can. Two months after sowing, the first grass cut was performed followed by MATERIALS A N D METHODS / 33 biweekly cuts for approximately 4 months. A pair of scissors was used for cutting the grass. Composite samples consisting of 3 consecutive cuts were used to evaluate the average plant uptake of essential nutrients and heavy metals during the elapsed sampling period. Four composite samples per treatment were taken during each sampling period.The foliage was digested according to the Parkinson and Allen method (1975). The digests were used to run K, Cd, Zn, Cu, Pb, and N i on an ICP-AES and total N and P on a Technicon Autoanalyzer II (i.e., A C P - A E S = Inductively Coupled Argon Plasma - Atomic Emission Spectromter. Model: Jarrel-Ash, Atomcomp series 1110). Note that the number of samples taken did not permit validation of the trends observed through statistical analyses. Furthermore, the plant-available metal content of the soil was evaluated to assist in the interpretation of the results. The Universal Soil Extract Method was utilized (Melich, 1984). The extracts were used to run the metals on an ICP-AES. 3.5. STATISTICAL ANALYSIS Before any statistical parametric test can be carried out, it is essential to establish a statistical frequency distribution that adequately describes the data. Since soil physical properties are generally well described by either the normal or log-normal distributions (Warrick and Nielson, 1980), it was decided that only these two will be considered. The best fitting frequency distribution was determined by comparing coefficients of determination, r 2 , from linear regression of the normal deviate, Z, upon both the raw data (normal distribution) and the log-transformed data (log-normal distribution) (Lee et al., 1985). The frequency that best describes a set of data was assumed for statistical comparison. Data were analyzed using Analysis of Variance and Newman-Keuls multiple range test as described by Zar (1974). A l l statistical analyses MATERIALS A N D METHODS / 34 were conducted at the 5% significance level, except when noted. Since the equations describing the mean, coefficient of variation, and standard deviation for log-normal distributions are less well known than those for normal distributions, they are briefly discribed below. The equations are applied to 'Ks ' since the log-normal distribution was assumed only for the 'Ks' data (Section 4.2). The mean for log-normally distributed data ('Ks') may be determined using (Hastings and Peacock, 1975) 'Ks ' = exp(X) (3.5) where X is the arithmetic mean of the log-transformed 'Ks' data. The appropriate coefficient of variation (CV) expression for log-transformed data is (Hastings and Peacock, 1975), CV = [exp(s 2)-l]xl00 (3.6) where s 2 is the variance of the log-transformed 'Ks ' data, s 2 is calculated using (Warrick and Nielsen, 1980), s 2 = l / ( n - l ) Y_ [(In'Ks')i - X ] 2 (3.7) U i . i . where n is the number of 'Ks ' measurements taken. The standard deviation (SD) is defined as as (Topp et al., 1980), SD = exp(s) (3.8) where s is the standard deviation of the log-transformed 'Ks' data (i.e., s=(s2)^-^ ). Due to the log-transformation, the SD value is a multiplier/division factor of 'Ks' rather than an addition/subtraction factor as is the case for a normal distribution (Lee et al., 1985). 4. RESULTS A N D DISCUSSION 4.1. APPLICATION RATE The agronomic rate was based on a crop nitrogen requirement of 200 kg/ha. This corresponds to a sludge application rate (S) of 33 t/ha (i.e., 2.0% on dry weight basis). The maximum sludge application rate to food-chain crops based on cadmium limitation (SC(j) is 50 t/ha. Thus, sludge incorporation at 33 t/ha did not exceed the annual cadmium limit recommended for cropland by U.S. EPA. The conditioning rate (S') was arbitrary chosen to be 100 t/ha (i.e., 6.1% on dry weight basis). S' can be applied to non-food-chain crops where heavy metal uptake is a lesser concern. The use of composted sewage sludge by the turfgrass growers in the Lower Fraser Valley has a great potential. One characteristic that distinguishes sludge from chemical fertilizers is that its organic N is released and becomes available to plant growth over a relatively long period of time. This greatly reduces the frequency and/or the amount of N application to turfgTass that can reach up to 300 kg/ha (Beard and Rieke, 1969). 4.2. STATISTICAL DISTRIBUTION Tables VIII, LX, and X report the r 2 values of linear regression of the normal deviate, Z, upon the raw data and the log-transformed data. The r 2 values indicate that both the normal and log-normal frequency distributions adequately describe the soil physical properties. The normal distribution was assumed for the statistical analyses of aggregate stability and bulk density data. The r 2 values also show that although the normal distribution describes well the 'Ks ' values for some ponding events, a universally good fit for all ponding events is obtained with the log-normal distribution. 35 RESULTS A N D DISCUSSION / 36 Table VIII: Goodness of f i t of normal and log-normal distributions to the hydraulic conductivity data as described by r . PONDING EVENT TREATMENT NORMAL LOG-NORMAL FIRST A B C 0.95 0.95 0.94 0.98 0.98 0.98 SECOND A B C 0.95 0.97 0.94 0.90 0.97 0.92 THIRD A B C 0.77 0.70 0.78 0.88 0.91 0.87 FOURTH A B C 0.96 0.77 0.79 0.94 0.95 0.97 FIFTH A B C 0.90 0.97 0.97 0.91 0.97 0.98 RESULTS A N D DISCUSSION / 37 Table IX: Goodness of f i t of normal and log-normal d i s t r i b u t i o n s to the bulk density data as described by r . BULK DENSITY TREATMENT NORMAL LOG-NORMAL INITIAL A B C 0.B7 0.94 0.86 0.86 0.94 0.84 FINAL A B C 0.93 0.97 0.92 0.93 0.96 0.90 Table X: Goodness of f i t of normal and log-normal d i s t r i b u t i o n s to 2 the aggregate s t a b i l i t y data as described by r . DEPTH TREATMENT NORMAL LOG-NORMAL A 0.87 M? O t o S e . B 0.J0 0.91 A 0.97 0.97 . 0 95 0.95 5 to 10cm B 0.95 ^ RESULTS A N D DISCUSSION / 38 Conseqently, it was decided to use the log-normal distribution for the statistical tests on the 'Ks 'data. Figures 6 and 7 illustrate fractile diagrams of 'Ks ' and ln('Ks') data for the 33 t/ha treatment at the end of the fourth ponding event Figure 6 indicate that the r 2 value obtained (i.e., 0.75) using the normal distribution is due to lack of fit of the model rather than to high random scatter. Figure 7 illustrates a strong linear ralationship between Z and ln('Ks') (i.e., =0.96). Not recognizing that the data were log-normally distributed would cause the mean to be poorly estimated (Warrick and Nielsen, 1980). 4.3. HYDRAULIC CONDUCTIVITY When the soil is subjected to potentially disruptive processes such as ponding, the structure will deteriorate as the aggregates tend to break down. Ponding and the action of prolonged water flow may cause the collapse of the aggregates, as the bonding substances dissolve and weaken and as the clay swells and possibly disperses (Hillel, 1980). Rowing water also provides the energy to detach particles and transport them away. The detachement and migration of particles may result in the clogging of pores and hence a reduction in hydraulic conductivity. The surface aggregates are the most vulnerable to the destructive action of ponding. The aggregates may collapse as a result of the presence of surface free water. The underwater collapse of the surface aggregates promotes the formation of a surface seal that clogs the surface macropores and thus tends to inhibit the movement of water into the soil columns. The soil structure deterioration as a result of repeated ponding events is reflected in figure 8 by the decay of 'Ks' over time. The decrease of 'Ks ' appears to be associated with the slaking of the mineral matter fraction of the soil. This was confirmed at the end RESULTS A N D DISCUSSION / 39 Figure 6 : Fractile diagram of the 'Ks' data for the 3 3 t/ha treatment (Fourth ponding event). RESULTS A N D DISCUSSION / 40 Figure 7: Fractile diagram of the ln('Ks') data for the 33 t/ha treatment (Fourth ponding event). RESULTS A N D DISCUSSION / 41 Legend O A=0 •/ha + B=3S t/ho A C=100 t/ho RESULTS A N D DISCUSSION / 42 of the experiment by determining aggregate stability in water. Another contributing factor to the decrease of 'Ks ' over time is the gradual consolidation of the soil columns as reflected by an increase in bulk density at the end of the experiment Tables XI to X V report the number of measurements taken, mean, coefficient of variation, standard deviation, and range of 'Ks ' data observed for each treatment at the end of each ponding event Figures 9 to 13 illustrate the 95% confidence intervals for the means for each ponding event The low ponding tolerance of the control columns was obvious at the end of the third ponding event This was manifested by a sharp drop of 'Ks ' from 1.4x10"7 m/s at the end of the first ponding event to 8.1x10"9 m/s at the end of the third ponding event (Tables XI to XIII). Thus the control columns were sealed as a result of three 24-hour ponding events. Whether the soil is sealed or not depends on one's definition of the term. A soil may be considered as sealed when its hydraulic conductivity drops below 1x10"^ m/s (De Tar, 1979). This value was originally suggested by the Pennsylvania Department of Environmental Resources as a reference point to which research results can be compared. Field measurements carried out by the Department of Soil Science at the University of B.C. have indicated that ponded water in spring infiltrated at a rate of 2.0x10" ^  m/s in the presence of "a low infiltrability surface layer" or a surface seal (de Vries, 1983). Adding composted sewage sludge increased the ponding tolerance of the soil. This was reflected by statistically significant differences in hydraulic conductivity between the control columns and the sludge-amended columns. Although mentioned before, it bears repeating that the addition of organic matter enhances the formation of water-stable aggregates • through physico-chemical reactions between the organic colloids and the soil constituents especially the clay fraction. The drying of organic polymers RESULTS A N D DISCUSSION / 43 Table XI: Hydraulic conductivity data for the f i r s t ponding event. TREATMENT STATISTICS* A-0 t/ha B«33 t/ha C« 1 0 0 t/ha n 12 12 12 T - 1 5 . 7 8 a - 1 5 . 5 9 3 - 1 4 . 9 6 c •Ks' (10 - 7 m/s) 1.4 1.7 3.2 S . D . 1.64 1.44 1.38 C.V. (%) 53.0 37.7 33.2 RANGE (10- 7 m/s) 0 .6 -3 .0 0 .8-2 .7 1.7-5.7 * Number of measurements (n), means (X and 'Ks'), standard deviation (S.D.), coefficient of variation (C.V.), and range of data, a-c A different alphabetic character indicates a significantly different 'Ks' at the 5Zlevel. RESULTS A N D DISCUSSION / 44 Table XII: Hydraulic conductivity data for the second ponding event. STATISTICS* X T R E A T M E N T A»0 t/ha B»33 t/ha C-100 t/ha 12 12 12 -I7.31 a -I5.62 b -14.69 c 'Ks' (IO* 7 m/s) 0.3 1.6 4.2 S.D. 1.70 1.79 1.49 C.V. (%) 56.9 63.2 41.6 RANGE (IO" 7 m/s) 0.09-0.61 0.5-3.9 2.2-6.6 * Number of measurements (n), means (Tand 'Ks'), standard deviation (S.D.), coefficient of variation (C.V.), and range of data, a-c A different alphabetic character indicates a significantly different at the 52 level. R E S U L T S A N D DISCUSSION / Legend A Lower 9SX confidence limit • Mean V Upper 9SX confidence flmlf B TREATMENT Figure 9: 95Z confidence intervals for the means of the hydraulic conductivity data (First ponding event). Legend A Lower 93X confidence limit • Wean V Upper 9SX confidence Omit TREATMENT Figure 10: 951 confidence intervals for the means of the hydraulic conductivity data (Second- ponding event). RESULTS A N D DISCUSSION / 46 results in the formation of an insoluble irreversible matrix. Thus aggregates stabilized through clay-organic complexing are not expected to break down upon wetting. At the end of the second ponding event 'Ks ' averaged 3.0x10" ^, 1.6x10" 7 , and 4.2x10"7 m/s for the 0, 33, and 100 t/ha treatments, respectively (Table XII). Thus, without simulated rainfall and if the evaporation rate is assumed to be equal to zero for comparison purpose, ponded water 5cm deep will take around 1, 3, and 19 days to infiltrate for the 100, 33, and 0 t/ha treatments, respectively. At the end of the last ponding event, 'Ks' values for the 0, 33, and 100 t/ha were 4.4x10" ^ , 1.7x10" and 3.8x10" 8 m/s, respectively (Table XV) . Consequently, a ponding layer of 5cm depth will disappear through the sole action of infiltration in 15, 34, and 131 days for the 100, 33, and 0 t/ha treatments, respectively. These simplistic comparisons help to illustrate the increase in ponding tolerance as a result of organic matter incorporation. Note also that at the end of the last ponding event 'Ks ' of the 33 and 100 t/ha treatments plummeted around the 'Ks ' of the control columns observed at the end of the second ponding event (i.e. 3.0x10" m/s). This confirms again that the addition of organic matter reduced the vulnerability of the soil structure to ponding since the action of 3 additional ponding events was required to decay 'Ks' of the treated columns to around 3.0x10" m/s. At the end of the first ponding event there was no statistically significant difference in 'Ks ' between the control columns and the 33 t/ha columns, but the addition of sludge increased 'Ks ' by 21% from 1.4xl0~7 to 1.7xl0"7 m/s (Table XI). On the other hand, statistical significance of 'Ks' data was observed between the control treatment and the 100 t/ha treatment as 'Ks ' increased by 126% from 1.4x10"7 to 3.2x10"7 m/s. These differences are small compared to those observed at the end of subsequent ponding events. For example, at the end of the second ponding event RESULTS A N D DISCUSSION / 47 Table X I I I : Hydraulic conductivity data for the third ponding event. T R E A T M E N T S T A T I S T I C S * A=0 t/ha B«33 t/ha C-100 t/ha n 12 12 12 T -18.63 3 -16.64 b -16.10 b •Ks' (l0-« m/s) 0.81 5.9 10.0 S.D. 1.27 3.06 1.70 C.V. (%) 24.4 158.3 57.0 RANGE dO-" m/s) 0.6-1 .5 1 .5-50.0 5.8-27.0 * Number of measurements (n), means ( X and 'Ks'), standard deviation ( S . D . ) , coefficient of variation ( C . V . ) , and range of data, a-b A different alphabetic character indicates a significantly different •Ks' at the 5Z level. RESULTS A N D DISCUSSION / 48 Table XIV: Hydraulic conductivity data for the fourth ponding event. * STATISTICS TREATMENT A-0 t/ha B»33 t/ha C-100 t/ha n 12 12 12 X -I8.90 a - I 7 . 9 l b -16.86 c 'Ks' (10-" m/s) 0.62 1.7 4.8 S.D. 1.43 1.91 1.93 C.V. (%) 37.2 72.5 73.9 RANGE (10- t m/s) 0.3-1.0 0.6-6.2 1.3-17.0 * Number of measurements (n), means (X*and 'Ks'), standard deviation (S.D.), coefficient of variation (C.V.), and range of data, a-c A different alphabetic character indicates a significantly different •Ks' at the 5Z level. RESULTS A N D DISCUSSION / 49 Legend A Lower 9SX confidence limit + Mean v Upper 95X confidence limit TREATMENT Figure 11: 95 Z confidence Intervals for the Beans of the hydraulic conductivity (Third ponding event). ' a X a hi a 0>> V • A A Legend A Lower 9SX confidence •mlt • Mean v Upper 95X confidence Hmll B TREATMENT Figure 12: 95Z confidence Intervals for the means of the hydraulic conductivity data (Fourth ponding event). RESULTS A N D DISCUSSION / 50 'Ks ' of the sludge-amended columns was around an order of magnitude larger than that of the control columns. This difference was more or less sustained till the end of the experiment, being larger between the 0 and 100 t/ha treatments than between the 0 and 33 t/ha treatments. The significant decrease of 'Ks' of the control treatment as a result of ponding was responsible for widening the gap between 'Ks ' of the control columns and 'Ks ' of the sludge-amended columns. The addition of organic matter both at 33 and 100 t/ha slowed down the decay of 'Ks ' but could not stop it. The most plausible explanation is that sewage sludge incorporation was effective in increasing the resistance of aggregates to breakdown when subjected to ponding. Figure 14 shows that 'Ks' increased as the organic matter loading increased. This trend was validated for each ponding event by statistically significant increases in 'Ks' as the sludge application rate increased. The differences in 'Ks' between the 33 and 100 t/ha treatments were consistently significant except for the third ponding event due to high random scatter of the 33 t/ha data. The scatter resulted from the fact that some 33 t/ha columns maintained approximately the same 'Ks ' value they exhibited at the end of the second ponding event Figure 10 illustrates the overlap of the 95% confidence intervals for the means of the 33 and 100 t/ha treatments at the end of the third ponding event 4.4. AGGREGATE STABILITY The decrease in 'Ks' as a result of ponding was attributed to the slaking of the mineral matter fraction of the soil. To confirm this and furthermore quantify the deterioration of the soil structure, aggregate stability was determined at the begining and at the end of the experiment Soils vary in the degree to which they are vulnerable to externally imposed destructive forces (Hillel, 1980). Aggregate stability RESULTS A N D DISCUSSION / 51 Table XV: Hydraulic conductivity data for the f i f t h ponding event. TREATMENT STATISTICS* A=0 t/ha B»33 t/ha C-100 t/ha n 12 12 12 X -19.24 3 -I7.89 b -17.09 c 'Ks' (10"« m/s) 0.44 1.7 3.8 S.D. 1.58 1.55 1.62 C V . (%) 48.5 46.2 50.9 RANGE (10-* m/s) 0.2-0.78 0.77-3.2 1.7-7.8 * Number of measurements (n), means (X and 'Ks'), standard deviation (S.D.), coefficient of variation (C.V.), and range of data, a-c A_£ifferent alphabetic character Indicates a significantly different 'Ks' at the 5Z level. RESULTS A N D DISCUSSION / 52 Legend * M«on V Upper 9SX eonfManct Hmlt TREATMENT Figure 13: 95Z confidence Intervals for the means of the hydraulic conductivity data (Fifth ponding event). RESULTS A N D DISCUSSION / 53 Figure 14: Effect of sewage sludge application rate on hydraulic conductivity. R E S U L T S A N D DISCUSSION / 54 (AS) is a measure of this vulnerability. The concept of aggregate stability was applied in this study in relation to the destructive action of water. Aggregate stability of the soil averaged 54% three months before the first ponding event (Table XVI). However, the final AS of samples taken from the 0 to 5cm depth averaged 14.9, 33, and 58.6% for the 0, 33, and 100 t/ha treatments, respectively (Table XVII). The differences in final AS between the treatments were statistically significant. Figure 15 illustrates the 95% confidence intervals for the means. Note that the sludge-amended columns exhibited an average final AS as much as four times over that of the control columns. Table XVI: I n i t i a l aggregate s t a b i l i t y . MEAN (%) S . D . (%) C . V . (%) RANGE (%) n 54.0 5.0 9 . 3 47.2 - 60.8 12 * Mean, standard deviation (S.D.). coefficient of variation (C.V.). range of da ta , and number of samples ( n ) . RESULTS A N D DISCUSSION / 55 The final AS of samples taken from the 5 to 10cm depth averaged 12.4, 20.9, and 37.8% for the 0, 33, and 100 t/ha treatments, respectively (Table XVIII). The differences in final AS between the treatments were statistically significant. Figure 16 illustrates the 95% confidence intervals for the means. Note that the sludge-treated columns exhibited an average final AS as much as three times larger than that of the control columns. Samples taken from the top 5cm of the soil columns exhibited a higher final AS than samples taken from the 5 to 10cm depth. This is due to the fact that aggregates taken from the top 5cm depth dried to a lower water content As mentioned before, drying is essential for the stabilization of aggregates through clay-organic complexing. The final AS of the soil columns averaged 13.7, 26.9, and 48.1% for the 0, 33, and 100 t/ha treatments, respectively (i.e., averages of samples taken from the 0 to 5 and 5 to 10cm depths). This corresponds to an overall decrease in aggregate stability of 75, 50. and 11% for the 0, 33, and 100 t/ha treatments, respectively. The soil structure deterioration as a result of ponding is obvious. The addition of organic matter increased the resistance of aggregates to breakdown when subjected to ponding (Figure 17). An agreement was observed between the AS and 'Ks ' data as both physical properties varied in the same direction. The highest final AS corresponded to the treatment that maintained the highest 'Ks ' throughout the experiment, while the lowest final AS corresponded to the treatment which exhibited consistently the lowest 'Ks'. However, due to experimental limitations a relationship between AS and 'Ks ' could not be established as this would have involved the destruction of the soil columns at the end of each ponding event Another consideration is that sampling for the initial and final evaluations of AS was performed three months before and fifty RESULTS A N D DISCUSSION / 56 * Table XVII: Final aggregate s t a b i l i t y (0 to 5 C M depth) . TREATMENT MEAN (%) S . D . (%) C . V . (%) RANGE (%) A»0 t/ha 14.9 a 5.9 39.6 7.4 - 30.1 24 B«33 t/ha 33.0 b 7.2 21.8 23.2 - 44.9 24 O100 t/ha 58.6C 9.5 16.2 39.4 - 70.8 24 * Mean, standard deviation (S.D.), coefficient of variation (C.V.), range of da ta , and number o f samples (n ) . a-c A different alphabetic character Indicates a significantly different aggregate s t a b i l i t y at the 5Z le v e l . Table XVIII: Final aggregate s t a b i l i t y (5 to 10cm depth) . TREATMENT MEAN (%) S . D . (%) C . V . (%) RANGE (%) A-0 t/ha 12.4 a 3.4 27.4 5.9 - 19.7 24 B«33 t/ha 20.9 b 4.1 19.6 13.7 - 31.6 24 C-100 t/ha 37.B c 13.4 35.4 20.0 - 63.5 24 * Mean, standard deviation (S.D.), coefficient of variation (C.V.), range of da ta , and number of samples (n ) . a-c Adifferent alphabetic character Indicates a significantly different aggregate s t a b i l i t y at the 5Z le v e l . RESULTS A N D DISCUSSION / 57 70->-65-60-55-50-45-m 40-& </) 3 5 -£ 30-1 O LJ 25 H or o o < 20-15-10-5-0-V Legend A lower 9SX cenf Mence BmJt + liton V Upper M X confidence limit l 6 TREATMENT c Figure 15: 952 confidence Intervals for the means of the f i n a l aggregate s t a b i l i t y data (0 to 5cm depth). RESULTS A N D DISCUSSION / 58 IS >-70-65-60-55-50-45-5 40-00 35-LU o UJ 25 CC O O < 20-15-10-5-0-V + Legend A Lower 95X confldoneo ImH + Moon V tlppor 95X eonrioone* Mmlt B TREATMENT Figure 16: 95% confidence intervals for the means of the f i n a l aggregate s t a b i l i t y data (5 to 10cm depth). RESULTS A N D DISCUSSION / 59 Figure 17: Effect of aggregate sludge application rate on the f i n a l s t a b i l i t y . RESULTS A N D DISCUSSION / 60 days after the first and last 'Ks ' measurements, respectively. 4.5. B U L K DENSITY The initial bulk density (BDi) was used as an index for soil packing uniformity. The packing technique aimed at achieving a realistic, uniform, and reproducible bulk density. BDi averaged 1.21, 1.19, and 1.19 g/cm-* for the 0, 33, and 100 t/ha treatments, respectively (Table XIX). The soil packing was fairly uniform as reflected by the small coefficients of variation. The slight decrease in BDi of the sludge-amended columns may be due to mixing of the composted sludge with the mineral subsoil. The wetting and and drying cycles resulted in the gradual consolidation of the soil columns. A 23% increase in the final bulk density (BDf) of each treatment was observed (Table X X ) . The gradual consolidation of the soil columns was probably another factor contributing to the decrease of hydraulic conductivity over time. Statistical comparisons were conducted at the 1% significance level. In no case a significant difference in bulk density was observed between the treatments. The soil structure deterioration was not reflected by the bulk density measurements. Thus, hydraulic conductivity and aggregate stability are better indices of soil structure deterioration than bulk density. 4.6. ESSENTIAL NUTRIENT UPTAKE The effects of sludge application on the concentrations of nitrogen, phosphorus, and potassium in the foliage of bermuda grass were evaluated. Sludge application at 33 t/ha did not seem to affect the nitrogen content (Figure 18). However, sludge incorporation at 100 t/ha increased the level of nitrogen from 1.2 to 1.8% during the RESULTS A N D DISCUSSION / 61 * Table XIX: I n i t i a l (Packing) bulk density . TREATMENT MEAN S.D. C.V. RANGE n <g/cm») (g/cm>) (%) (g/cm>) A>0 t/ha 1.21 0.02 1.6 1.16 - 1.24 12 B-33 t/ha 1.19 0.03 2.5 1.17 - 1.23 12 C«100 t/ha 1.19 0.02 1.7 1.14 - 1.22 12 * Mean, standard dev ia t ion ( S . D . ) , c o e f f i c i e n t of v a r i a t i o n ( C . V . ) , range of da ta , and number of samples (n ) . Table X X : Final bulk density.* TREATMENT MEAN S.D. C.V. RANGE n (g/cm1) (g/cm>) (%) (g/cm>) A-0 tAa 1.49 0.02 1.3 1.47 - 1.52 12 B«33 t/ha 1.47 0.03 2.0 1.45 - 1.50 12 C-100 t/ha 1.46 0.03 2-1 1.41 - 1.49 12 * Mean , s t a n d a r d d e v i a t i o n ( S . D . ) , c o e f f i c i e n t o f v a r i a t i o n ( C . V . ) , range o f d a t a , and number o f samples ( n ) . RESULTS A N D DISCUSSION / 62 first sampling period and from 1.5 to 1.8% during the second sampling period. Initially, the phosphorus concentration appeared to increase as the sludge application rate increased (Figure 19). However, sampling performed at a later stage showed no differences between the sludge treatments and the control treatment. Also, sludge application did not seem to affect potassium levels throughout the experiment (Figure 20). 4.7. HEAVY M E T A L U P T A K E Sludge application was expected to increase the plant-available metal content of the soil because the pH was not adjusted to 6.5 or greater (i.e., lime was not added). Although mentioned before, it bears repeating that the availability of heavy metals to plants is significantly reduced as the soil pH is increased above 6.5 (U.S. EPA, 1983). Table X X I shows that except for nickel, the available metal concentration increased as the sludge application rate increased. The effects of sludge incorporation on the concentration of heavy metals in the foliage of bermuda grass were evaluated. The following results were observed: 1. Cadmium: During the first sampling period, the data exhibited an increase in cadmium concentration as the sludge application rate increased (figure 21). However, this trend was weaker during the second sampling period as the difference between the concentrations of the 0 and 33 t/ha treatments was negligible. The jump in the concentration of the control treatment between the first and second sampling periods may reflect analytical error. Figure 20 also shows an increase in cadmium concentration over time for all 3 treatments. 2. Copper: RESULTS A N D DISCUSSION / 63 Sludge application did not seem to affect copper concentration in the foliage of bermuda grass (Figure 22). The data were variable indicating no major trends. During the second sampling period, there was no difference between the concentrations of the 0 and 100 t/ha treatments. Initially, a trend of increasing nickel concentration in the foliage with increasing sludge application rate was observed (Figure 23). However, this trend faded during the second sampling period as the nickel concentrations averaged 31.1, 25.6, and 31.0 ppm for 0, 33, and 100 t/ha treatments respectively. This can be justified by the fact that sludge addition did not affect the available nickel concentration of the soil (Table XXI). Thus, the trend observed initially may be attributed to random variation. During the first sampling period there was no appreciable trend observed, only a slight increase in lead concentration was recorded at 100 t/ha (Figure 24). During the second sampling period, this increase was more visible as the concentrations averaged 5.5 and 7.3 ppm for the 0 and 100 t/ha treatments respectively. However, there was no conclusive evidence to suggest a trend of increasing lead concentration with increasing sludge application rate because the lead levels of the 33 t/ha treatment were equal to or smaller than those of the 0 t/ha treatment. Similarly, other studies have found that the increase in lead uptake with increasing sludge application rate is minimal as most plants do not accumulate lead (U.S. EPA, 1983). The concern about lead is associated with the potential ingestion of lead by grazing animals. 3. Nickel: 4. Lead: 5. Zinc: RESULTS A N D DISCUSSION / 64 Table XXI: Plant-available metal concentration i n the s o i l (ppm). TREATMENT p H ( C a C l 2 ) Cd Ni Cu Zn Pb 0 t/ha (1) 5.0 0.6 65 66 32 25 0 t/ha (2) 5.0 0.6 66 64 33 25 33 t/ha (1) 5.0 1.3 68 93 77 61 33 t/ha (2) 4.9 1.6 65 100 93 71 100 t/ha (1) 5.1 3.5 65 168 216 139 100 t/ha (2) 5.1 3.3 65 160 200 129 (1), (2) Replicates. RESULTS A N D DISCUSSION / 65 FIRST SECOND SAMPLING PERIOD Figure 18: Nitrogen concentrat ion in the f o l i a g e of bermuda grass (Dry weight b a s i s ) . 0.5 0.4-FIRST SECOND SAMPLING PERIOD Figure 19: Phosphorus concentrat ion in the f o l i a g e of bermuda grass (Dry weight b a s i s ) . RESULTS A N D DISCUSSION / 66 FIRST SECOND SAMPLING PERIOD Figure 20: Potassium concentrat ion in the f o l i a g e o f bermuda grass (Dry weight b a s i s ) . 1.6 FIRST SECOND SAMPLING PERIOD Figure 21 : Cadmium concentrat ion in the f o l i a g e of bermuda grass (Dry weight b a s i s ) . RESULTS A N D DISCUSSION / 67 15 -FIRST SECOND SAMPLING PERIOD Figure 22: Copper concentrat ion in the f o l i a g e of bermuda grass (Dry weight b a s i s ) . FIRST . SECOND SAMPLING PERIOD Figure 23: Nickel concentrat ion in the f o l i a g e of bermuda grass (Dry weight b a s i s ) . RESULTS A N D DISCUSSION / 68 FIRST SECOND SAMPLING PERIOD Figure 24: Lead concentrat ion in the f o l i a g e of bermuda grass (Dry weight b a s i s ) . FIRST SAMPLING PERIOD Figure 25: Zinc concentrat ion i i r t h e f o l i a g e o f bermuda grass (Dry weight b a s i s ) . RESULTS A N D DISCUSSION / 69 During the first sampling period, zinc concentrations averaged 19.5, 31.0, and 67.0 ppm for the 0, 33, and 100 t/ha treatments respectively (Figure 25). However, the gap between the 0 and 33 t/ha treatments was minimal during the second sampling period. The significant increase in zinc concentration at 100 t/ha was associated with a large jump in the available zinc concentration of the soil. The zinc concentration of the 100 t/ha treatment remained unchanged throughout the experimental period. 5. S U M M A R Y AND CONCLUSIONS 1. A greenhouse experiment was conducted using a Ladner silty clay loam subsoil. Composted sewage sludge was incorporated at 0, 33, and 100 t/ha. The soil-sludge mixtures were packed in 4-liter containers. Bulk density was used as an indicator for soil packing uniformity. The main purpose of the experiment was to evaluate the effect of sewage sludge application on the soil structural stability in relation to the destructive action of water. The soil columns were subjected to periodically simulated ponding events. Hydraulic conductivity and aggregate stability , two soil structural attributes relevant to the process of ponding, were used as indices for soil ponding tolerance. 2. The addition of sewage sludge increased the ponding tolerance of the soil. This was reflected by statistically significant differences in hydraulic conductivity at the 5% level between the sludge-amended columns and the control columns. At the end of the second ponding event the satiated hydraulic conductivity ('Ks') averaged 3.0x10" 8 , 1.6x10" 7 , and 4.2x10"7 m/s for the 0, 33, and 100 t/ha treatments, respectively. The soil structure deterioration as a result of repeated ponding events was reflected by the decay of 'Ks ' over time. At the end of the last ponding event the average 'Ks ' values for the 0, 33, and 100 t/ha treatments were 4.4x10"9, 1.7x10"8, and 3.8x10"8 m/s, respectively. The addition of organic matter both at 33 and 100 t/ha slowed down the decrease of 'Ks ' but could not stop i t The most plausible explanation is that sewage sludge addition was effective in increasing the resistance of aggregates to breakdown when subjected to ponding. The final aggregate stability of samples taken from the the 0 to 5cm depth averaged 14.9, 33.0, and 58.6%, for the 0, 33, and 100 t/ha treatments, respectively. On the other hand, samples taken from the 5 to 10cm depth exhibited final aggregate stability values of 12.4, 20.9, and 37.8% for the 0, 33, 70 S U M M A R Y A N D CONCLUSIONS / 71 and 100 t/ha treatments, respectively. The differences in AS between the 3 treatments were statistically significant at the 5% level. A trend of increasing hydraulic conductivity with increasing aggregate stability was observed. However, a correlation between the 2 factors could not be established due to experimental limitations. 3. In no case a significant difference in bulk density between the treatments was observed. The soil structure deterioration as a result of of ponding was not reflected by the bulk density measurements. Thus, hydraulic conductivity and aggregate stability are better indices of soil structure deterioration than bulk density. 4. A side investigation was conducted to illustrate trends of essential nutrient and heavy metal uptake by bermuda grass. The available metal concentration of the soil increased as a result of sludge application. The incorporation of sludge at the "agronomic rate" (i.e., 33 t/ha) did not seem to increase the nutrient and metal uptake by bermuda grass. However, sludge treatment at the "conditioning rate" (i.e., 100 t/ha) appeared to increase the nitrogen, cadmium, and zinc uptake by the experimental plant 6. F U T U R E RESEARCH 1. To conduct field experiments that incorporate controlled land application of sewage sludge in a comprehensive soil and water management program aimed at enhancing the hydrologic responsiveness of Lower Fraser Valley lowland soils. 2. To determine the effects of sewage sludge application at moderate conditioning rates on the groundwater quality of lowland soils. 3. To generate more information about heavy metal uptake by crops grown on Lower Fraser Valley soils treated with sewage sludge. 4. To check the feasibility of using sewage sludge as an alternative source or supplement for chemical fertilizer in the production of turfgrass. 5. To design a long-term program for the disposal of municipal sewage on land as 1 an alternative for ocean dumping and fresh water dilution in British Columbia. 72 REFERENCES Abron-Robinson, L., Lue-Hing, C , Martin, E.J. and Lake, D.W. 1981. Production of non-food-chain crops with sewage sludge. U.S. Environmental Protection Agency, Cincinnati, Ohio. 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