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Some aspects of buffering of acid soils of the Lower Fraser Valley Wiens, John H. 1970

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SOME ASPECTS OF BUFFERING OF ACID SOILS OF THE LOWER FRASER VALLEY by JOHN H. WIENS B.S.A., University of B r i t i s h Columbia, 1968 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of S o i l Science We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA September, 197 0 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available f o r reference and study. I further agree that permission f o r extensive copyong of t h i s thesis f o r scholarly purposes may be granted by the Head of my Department or by his representatives. I t i s understood that copying or duplication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission Department of S o i l Science The University of B r i t i s h Columbia Vancouver 8, Canada. ABSTRACT A study was made to: i ) determine the nature of ac i d i t y and buffering i n acid s o i l s of the Lower Fraser Valley of B r i t i s h Columbia, i i ) evaluate and develop methods of predicting buffer capacities of these s o i l s . Results of thi s study are described i n a series of four papers, each describing d i f f e r e n t phases of t h i s study. The Woodruff and Shoemaker, McLean and Pratt buffer methods proved to be unsuitable f o r use with these s o i l s when compared to CaCOH)^ t i t r a t i o n because the buffer pH depression was too small per unit lime requirement and there was considerable scatter about the regression c a l i b r a t i o n lime. Measurements of lime p o t e n t i a l and corrected lime po t e n t i a l as well as pH were found to be s i g n i f i c a n t l y correlated with measures of exchangeable a c i d i t y but not with measures of pH-dependent a c i d i t y . The pH-dependent component of p o t e n t i a l a c i d i t y was found to be highest for horizons highest i n organic matter and i n acid ammonium oxalate extractable A l and Fe. Regression equations derived f o r predicting buffer capacities explained the largest degree of v a r i a t i o n of t i t r a b l e a c i d i t y i n the pH ranges below pH 5 and above pH 6. The model developed, combining these equations for prediction of buffer capacities to selected end pH values predicted buffer capacities as determined by a Ca(OH) 2 t i t r a t i o n reasonably well. i v Comparison of NaOCl with ^2^2 ^ o r oxidation °f organic matter p r i o r to acid ammonium oxalate extraction showed the former to be less destructive to sesquioxides, while at the same time as good or better f o r the oxidation of organic matter. Results of t i t r a t i o n s of s o i l s before and a f t e r oxalate extraction following treatment with NaOCl gave inconclusive r e s u l t s with respect to a c i d i t y due to the oxalate extractable component. This was due not to the method of removal of organic matter, however, but to uncertainties with respect to the nature of the exchange phase. V ACKNOWLEDGEMENTS The author wishes to express his sincere appreciation to Dr. L.M. Lavkulich, Department of S o i l Science, for his i n t e r e s t , d i r e c t i o n and assistance throughout the project and i n the preparation of t h i s t h e s i s . Appreciation i s also expressed to Miss Pat Dairon, Mr. B. von Spindler, Mr. Barry Given, Mr. Mark Walmsley and p a r t i c u l a r l y Miss Anne Harris for assistance with laboratory work during various stages of the study, and to Miss Beth Loughran for assistance with laboratory work and the draughting of figures for t h i s t h e s i s . F i n a n c i a l assistance from the B r i t i s h Columbia Department of Agriculture i s also g r a t e f u l l y acknowledged. v i TABLE OF CONTENTS Page INTRODUCTION 1 COMPARISON OF METHODS FOR EVALUATING LIME REQUIREMENT OF SELECTED BRITISH COLUMBIA SOILS 4 Abstract 4 Introduction 5 Materials and Methods 7 Results and Discussion 9 Lime requirements from titration curves 9 Buffer methods 13 Literature cited 2 3 EVALUATING ACIDITY OF SELECTED ACID SOILS OF BRITISH COLUMBIA 24 Abstract 24 Introduction 2 5 Materials and Methods 2 9 Results and Discussion 31 Literature^Cited 42 FACTORS AFFECTING THE BUFFERING CAPACITY OF SOILS AND A MODEL FOR CALCULATING THE BUFFERING CAPACITY TO SELECTED pH VALUES 45 Abstract 45 Introduction 46 Materials and Methods 5 0 Soils 50 Lime requirements 5 0 Soil properties 5 0 Sta t i s t i c a l analysis 52 Results and Discussion 52 Relation between s o i l properties and LR 5 3 Derivation of relationships between s o i l properties and LR 55 v i i Development and testing of a model incorporating functional relationships 5 9 Literature Cited 6 3 COMPARISON OF ORGANIC MATTER DESTRUCTION BY HYDROGEN PEROXIDE AND SODIUM HYPOCHLORITE AND ITS EFFECTS ON SELECTED MINERAL CONSTITUENTS 65 Abstract 6 5 Introduction 6 6 Materials and Methods 6.8 Results and Discussion 72 Literature Cited 8 3 SUMMARY 84 APPENDIX I: Chemical properties of soils incubated with reagent grade CaCO^ for a period of fifteen and one-half months 8 8 APPENDIX II: Discontinuous Ca(0H)_ titration curves of soils used in the present study 92 v i i i LIST OF TABLES Table Page 1. Selected properties of the soils 10 2. Lime requirements of the soils as determined by titr a t i o n and incubation to pH 6 and 6.5 11 3. Lime required to bring s o i l to indicated pH as determined by two different calibrations of pH buffer solution pH depression 20 I I - l . Selected properties of soils 32 2. Extractable components of soils 3 4 3. Correlation coefficients between pH, LP and CLP and measures of components of potential acidity 3 6 4. Titrable acidity (CaCO^ incubation) to pH 5.0, 5.5, 6.0 and measures of potential acidity 3 8 5. Measures of pH-dependent acidity 4 0 III - 1. Correlation coefficients between selected s o i l properties and Ca(0H)_ titrable acidity in a number of pH Buffer ranges 54 2. I n i t i a l and f i n a l equations calculated by simple and stepwise multiple regression analysis - Series I 56 3. I n i t i a l and fi n a l regression equations calculated by stepwise multiple regression analysis - Series II 58 4. Summary of comparison of Ca(0H)2 t i t r a t i o n LR values and values predicted by the model 61 C l a s s i f i c a t i o n and selected c h a r a c t e r i s t i c s of s o i l s Organic carbon i n s o i l and remaining i n residue a f t e r treatments Oxalate extractable S i 0 2 , Mn, Fe and Al i n residues af t e r treatment Si02, Mn, Fe and A l i n extracts a f t e r treatments 0.5 N NaOH extractable S i 0 2 and Al^O^ i n s o i l and i n residue a f t e r treatments S t a t i s t i c a l l y s i g n i f i c a n t differences between residue, residues and s o i l s and extracts of treatments Reagents, extract and Whatcom Ap residue c h a r a c t e r i s t i c s at various pH values X LIST OF FIGURES Figure Page I - 1. S o i l buffer curves determined by CaCOg incubation and CaCOH^ t i t r a t i o n 12 2. Buffer c a l i b r a t i o n curves for LR to pH 6.0 14 3. Buffer c a l i b r a t i o n curves for LR to pH 6.4 15 4. Buffer c a l i b r a t i o n curves for LR to pH 6.8 16 5. Buffer c a l i b r a t i o n curves as reported for Ohio s o i l s by Shoemaker et a l . and curves calculated for s o i l s used i n the present study 19 III - 1. Flowchart of the procedure for ca l c u l a t i n g lime requirements to selected pH values 60 IV - 1. % carbon remaining i n s o i l following successive treatment with NaOCl 81 INTRODUCTION Problems related to liming of acid s o i l s i n the Lower Fraser Valley of B r i t i s h Columbia have been known to exist f or some time. A study was undertaken with the objectives of elucidating some of the components of a c i d i t y i n these s o i l s and developing laboratory determinations which could r e l i a b l y predict buffering. In thi s study, crop response to additions of liming materials was not tested. It was understood that t h i s phase of the study of acid s o i l s of the Lower Fraser Valley of B r i t i s h Columbia was to be undertaken elsewhere and that duplication of e f f o r t was to be avoided. Incubation, t i t r a t i o n and buffer methods are often used to estimate the amounts of liming materials required to neutralize acid s o i l s to various pH values. Because the incubation and t i t r a t i o n methods are too laborious, buffer methods are widely used i n many laboratories for routine determinations of s o i l buffering capacity. No universal buffer method has been developed because buffers developed for one region are very often not suitable f o r s o i l s of another region. Shoemaker, McLean and Pratt i n 1961 described a new buffer method found to be suitable for Ohio s o i l s which had been found to show variable response to liming and to be f a i r l y high i n extractable A l . This method was a 2 modification of the established Woodruff buffer method. Because no one method i s used for prediction of lime requirement of s o i l s of the Lower Fraser Valley and these ex i s t i n g methods had not been evaluated for use with these s o i l s , such an evaluation was made. The r e s u l t s of such a study are given i n the paper e n t i t l e d : Comparison of methods for evaluating lime requirement of selected B r i t i s h Columbia s o i l s . To investigate the nature of a c i d i t y of s o i l s of the region, measurements of active and pot e n t i a l a c i d i t y were made. The re s u l t s of t h i s phase of the study are found i n the paper e n t i t l e d : Evaluating a c i d i t y of selected B r i t i s h Columbia s o i l s . Individual and combinations of s o i l properties such as % carbon, clay content and cation exchange cap a c i t i e s , either by use of regression equations or by the experience of the agronomist concerned have been used to make recommend-ations for liming acid s o i l s . Generally a single equation i s used for predicting lime requirement. It was thought that for widely varying s o i l s a series of equations for predicting lime requirement i n various buffer ranges would r e s u l t i n better predictions. The paper e n t i t l e d : Factors a f f e c t i n g buffering capacity of s o i l s and a model fo r c a l c u l a t i o n of the buffer capacity to selected pH values, describes 3 derivation of such a series of equations and a model for combining these equations for predicting lime requirement to selected pH end points. These equations and model were an attempt to incorporate factors a f f e c t i n g a c i d i t y into lime requirement determinations i n a quantitative way. One s p e c i f i c objective of the investigation into the components of a c i d i t y was determination of the role played by amorphous inorganic material i n buffering s o i l s . To do t h i s , i t was thought that i f organic matter was removed s e l e c t i v e l y and the s o i l s t i t r a t e d before and a f t e r removal of amorphous materials, the r o l e of these constituents could be determined. A method fo r removal of organic matter using NaOCl had been proposed e a r l i e r and i t was suggested to be r e l a t i v e l y non-destructive to sesquioxides. L i t t l e evidence for t h i s l a t t e r suggestion was given. It was therefore decided to compare hydrogen peroxide with NaOCl oxidation to see i f the l a t t e r method was i n fact superior with respect to removal of organic matter with a minimum of destruction of sesquioxides. The paper reporting t h i s study i s e n t i t l e d : Comparison of organic matter destruction by hydrogen peroxide and sodium hypochlorite and i t s e f f e c t s on selected mineral constituents. COMPARISON OF METHODS FOR EVALUATING LIME REQUIREMENT OF SELECTED BRITISH COLUMBIA SOILS ABSTRACT Lime requirements (LR) of a number of Lower Fraser Valley s o i l s were determined by CaCOg incubation and by Ca(OH) 2 t i t r a t i o n methods. Values obtained by the Ca(0H)2 t i t r a t i o n method were used as standards of comparison i n evaluating the Woodruff and the Shoemaker, McLean and Pratt (SMP) buffer methods. It was found that the lime requirement as determined by the CaCO^ incubation method was underestimated f o r most s o i l s by Ca(OH) 2 t i t r a t i o n . This was attributed largely to the suspension e f f e c t . It appeared that the SMP and the Woodruff buffer methods were unsuitable for use with the s o i l s studied because the depression of the buffer solution pH was too small and the scatter of i n d i v i d u a l points around the regression c a l i b r a t i o n l i n e was too large. The co r r e l a t i o n between LR values predicted from the present c a l i b r a t i o n of the buffer depression and standard LR values was, however, better than c o r r e l a t i o n between LR values predicted from a c a l i b r a t i o n table given by Shoemaker et a l . and standard values. 5, INTRODUCTION Determination of the buffer capacity of acid s o i l s can be made by several procedures. These can be grouped as follows: ( i ) incubation methods ( i i ) t i t r a t i o n methods ( i i i ) buffer methods, and (iv) predictions based on equations r e l a t i n g i n d i v i d u a l or combinations of measured s o i l parameters with lime requirement. Incubation methods involve e q u i l i b r a t i n g increments of liming material with moist s o i l samples i n the laboratory or greenhouse for enough time that no additional change i n s o i l pH occurs. Pionke et a l . (1968), Keeny and Corey (1963) and Shoemaker et a l . (1961) used e q u i l i b r a t i o n times of 9, 12 and 17 months, respectively. These methods, although probably most c l o s e l y approximating f i e l d conditions, are time consuming and laborious. Consequently, they have not proved as suitable methods f o r routine t e s t i n g but are often used as a standard for comparison for other more rapid methods. Although t i t r a t i o n methods are somewhat f a s t e r , they are s t i l l unsatisfactory for routine applications because of amounts of s o i l required and problems i n r e l a t i n g values for lime requirement (LR) to incubation methods and f i e l d conditions. Discontinuous t i t r a t i o n s are superior to continuous t i t r a t i o n s as the l a t t e r do not allow s u f f i c i e n t time for e q u i l i b r a t i o n 6 to occur. BradfieId's (1942) method i s a commonly used t i t r a t i o n method. It involves e q u i l i b r a t i n g a series of s o i l samples with increments of Ca(OH) 2 and p r e c i p i t a t i n g excess Ca(OH) 2 as CaCOg. Buffer.methods are probably the most popular means of determination of LR due to t h e i r speed and the small amount of s o i l sample required. B a s i c a l l y the method involves e q u i l i b r a t i n g a buffered a l k a l i n e solution with a s o i l sample and measuring the pH depression of the buffer. This i s taken as a measure of the s o i l buffer capacity or LR. Different buffer solutions react with various a c i d i c s o i l components to d i f f e r e n t degrees, thus a universal buffer method has not been developed. One method may predict the LR of s o i l s of one region but be unsuitable for other s o i l s . Woodruff (1947, 1948) developed and calibrated a buffer solution which was found s a t i s f a c t o r y for Missouri s o i l s . McLean et a l . (1958), however, found i t to be unsuitable for some Ohio s o i l s . Shoemaker et a l . (1961) subsequently described a new method which was found to be more suitable for Ohio s o i l s . A modification of the Woodruff method has been made and used i n Iowa (Keeny and Corey, 1963). The use of regression equations i s discussed b r i e f l y on pages 48 to 49 i n t h i s t h e s i s . D i f f e r e n t i a l response to liming of s o i l s i n the Lower Fraser Valley of B r i t i s h Columbia have been observed (Hughes, 7 1965). Available methods for determining lime requirement have not been evaluated for soils of this region. Therefore the objectives of the study described in this paper were: (i) to compare CaC03 incubation LR values with Ca(0H)2 titration LR values to several end points as measures of LR and to arrive at some statement about the relationship with regard to soils with different characteristics, and ( i i ) to compare the Shoemaker et a l . and Woodruff buffer methods with CaCO incubation and Ca(OH)2 t i t r a t i o n and to each other in order to evaluate their relative merits and usefulness for routine use in testing soils for LR. MATERIALS AND METHODS Soils used in this study were surface and subsurface samples of 10 s o i l series in the Lower Fraser Valley of B.C. The soils were air-dried and crushed to pass a 2 mm sieve. Selected properties of the soils are given in Table 1. For the CaC03 equilibration study, only the A horizon samples were used. A series of duplicate samples of each of the soils were weighed and placed in plastic beakers. To each of the duplicates of each s o i l was added reagent grade CaCOg, equivalent to 0, 2, 4, 6, 8, 10, 12, 14 and for 2 s o i l s , 16 and 18 tons per acre calculated on the basis of 2,000,000 pounds of s o i l per acre. The soils were wetted with d i s t i l l e d water and the beakers were covered with one thickness of parafilm to allow 8 some aeration but prevent evaporation. During the period of 16 months e q u i l i b r a t i o n the samples were uncovered, allowed to dry out, rewetted and recovered several times. At the end of the e q u i l i b r a t i o n time, pH values were read i n water (1:2 s o i l to water). Discontinuous Ca(0H) 2 t i t r a t i o n s were carried out for a l l s o i l samples by adding varying increments of standardized, saturated or nearly saturated Ca(0H) 2 to flasks containing 5.0 g of a i r dry s o i l and enough water to make a t o t a l volume of 100 ml. The increments varied, based on the previously measured CEC values. The flasks were stoppered and placed on a wrist action shaker for 15 hours. After t h i s time, C0 2 was bubbled through the suspensions for 3 minutes followed by a i r f o r approximately 3 0 minutes. Fifteen hours shaking time was chosen as convenient based on the res u l t s published by Dunn (1943) showing that equilibrium was reached i n four days without shaking but i n 8 hours with shaking. Also, shaking while maintaining a posit i v e N 2 pressure above the suspension was found to have no e f f e c t on the r e s u l t i n g t i t r a t i o n curve. Following s e t t l i n g of the suspension for 1 hour, pH measurements were made by placing the glass electrode i n the suspension and keeping the reference junction i n the supernatant solution. Lime requirement determinations were made using the Woodruff buffer method described by Woodruff (1947, 1948) and 9 Keeny and Corey (1963) and the SMP method as described by Shoemaker et a l . (1961). Other s o i l properties were determined as described by Wiens (1970). S t a t i s t i c a l analyses were carried out using the IBM 360-67 computer and exi s t i n g c o r r e l a t i o n and regression routines in the University of B r i t i s h Columbia Computing Centre program l i b r a r y . RESULTS AND DISCUSSION Characteristics of s o i l s used i n t h i s study are given i n Table 1. Organic carbon ranged between 0.12% and 8.88%, pH ranged from 4.0 to 8.6 and clay content ranged from 1.0 to 5 0.0%. Based saturation values, by subtracting sums of Ca, Mg, Na and K from CEC by NH^OAC varied from 1.7 to 66.3%. Lime requirements from t i t r a t i o n curves Table 2 shows how Ca(0H) 2 t i t r a t i o n LR values compare with LR values determined by the standard method, CaCO^ incubation.- These re s u l t s were determined from curves such as those presented i n Figure 1. It can be seen that the mean LR by Ca(0H) 2 t i t r a t i o n i s only 53.4% and 72.8% respectively of that determined by CaC0 3 incubation. Shoemaker (1959) reported a value of 65.6% when considering LR to pH 6.8. It can be seen, however, that underestimation of LR by Ca(0H) 2 t i t r a t i o n increases as % C increases. The curves i n Figure 1 show that for s o i l s having a high C content the CaC0„ curves are lower 10 T a b l e 1. S e l e c t e d p r o p e r t i e s o f t he s o i l s NH^OAc o . S o i l S e r i e s H o r i z o n Depth pH ( H 2 0 ) C C l a y CEC B . S. cm % % meq/lOOg % 1 A b b o t s f o r d Ap 0 - 1 7 . 8 5.35 2 .42 2 .5 16 .22 39 . 32 2 B f ( i r ) 1 7 . 8 - 3 5 . 6 5 .18 0.84 1.0 11 .64 38 . 83 3 I I C 35.6 + 5 .65 0.16 1.25 5.51 10 . 36 4 A l o u e t t e Bg 2 2 . 9 - 4 5 . 7 4 .44 4 .56 9.6 23 .43 32 . 01 5 Cg 45 .7 + 5 .31 1.32 7 .0 12 .26 64 . 86 6 C l o v e r d a l e Ap 0 - 1 7 . 8 5.90 4 .88 13 .6 31 .31 8. 73 7 Ae 1 7 . 8 - 3 3 6.95 0 .64 25 .9 19 .98 63 . 12 8 Bt 1 7 . 8 - 6 1 7 .60 0.24 50 .0 47 .07 60 . 81 9 C 61 + 8.60 0 .20 43 .2 46 .56 42 . 43 0 L a n g l e y Ap 0 - 2 2 . 9 5.30 8.88 8.3 66 .25 25 . 13 1 Bt 3 5 . 6 - 5 0 . 8 5 . 80 0.22 1 9 . 5 33 .68 63 . 48 2 C 50 . 8 + 6.70 0 .20 4 3 . 2 32 .97 66 . 33 3 Monroe Ap 0-25 5 .50 3 .42 7 .0 39 .32 17 . 80 4 C 2 5 + 5 .60 0 .84 6.8 33 .06 66 . 31 5 M i l n e r B f 0 - 2 5 . 4 5.55 2 .75 1 6 . 1 24 .00 42 . 08 6 C 38 .1 + 5.40 0 .12 33 .5 14 .20 34 . 92 7 Ryder Ap 0 - 1 7 . 5 5 . 80 3 .60 4 . 1 28 .33 65 . 88 8 B f 1 7 . 5 - 4 2 5.68 2 . 32 3.7 26 .18 26 . 90 9 I I C 75 + 5 .45 0 .72 3.2 17 .51 13 . 30 0 S u n s h i n e B f 0 - 2 5 . 4 5 .45 3.64 2 .0 29 .14 8 . 36 1 B f o 2 5 . 4 - 6 8 . 6 5.45 2 .40 1.25 1 1 . 54 8. 02 2 I I C 76 .2 + 5 .65 0.68 1.0 24 .36 1. 69 3 S p e t i f o r e Ap 0 - 1 7 . 8 4 .00 5.33 13 .6 27 .91 9 . 89 4 Cg 1 7 . 8 - 4 0 . 6 4 .25 1.32 15 .0 20 .29 27 . 33 5 C g 2 40 .6 + 4 .25 1.00 3.5 14 .99 30 . 80 6 Whatcom Ap 0 -17 .5 5.25 6 .90 7 .0 42 .13 26 . 64 7 B f 1 7 . 5 - 7 5 5 . 80 2 .60 2.0 24 .82 15 . 10 8 C 75 + 5 .50 0 .16 20 .0 24 .11 45 . 52 11 Table 2. Lime requirements of the soils as determined by ti t r a t i o n and incubation to pH 6 and 6.5 Ca(OH). Titration CaC0„ Incubation m P H  Soil 6.0 6.5 6.0 6.5 meq/100 T/A meq/100 T/A meq/100 T/A meq/100 T/A Abbotsford 13. .5 6, .75 18, .5 9, , 25 8. .0 4, .0 11. , 5 5, ,75 Cloverdale 9, .0 4, ."50 17 , . 0 8, .5 20, .5 10, .25 28. ,0 14, .0 Langley 3 , .0 1, .5 16. .0 8, .0 21, .0 10, .5 32, .0 ' 16, .0 Monroe 5, .0 2 , .50 10, .5 5, .25 8 , .0 4, .0 11, .5 5, .75 Ryder 9 . 5 4. .75 20, .0 10, .0 6, ,5 3. .25 11, ,0 5, ,50 Spetifore 16 . 5 8 , .25 20, .7 10, . 35 22 , .5 11, .25 28. ,0 14, .0 Whatcom 1. .4 0, .7 6, .6 3 , .3 22, .0 11, .0 28 , .0 14, .0 Mean 8, .27 4 , .14 15, .61 7 , .80 15. .5 7, .75 21. .43 10, .71 % of CaC03 LR 53 .4% 72 . 8% T/A - tons/acre 12 o o CaC0 3 incubation (|:|) o o discontinuous CaCOHjg titrations (|:20) Cloverdale Ap -j 1 1 1 i i i_ Langley Ap -i 1 1 1 1 • ' -I 1 I L. 12 16 0 4 8 C a C O j added (tons/acre) Whatcom Ap Spetifore Ap J i i i 12 16 Figure 1. S o i l buffer curves determined by CaCO„ incubation and Ca(OH) t i t r a t i o n , ^ 2 13 than the Ca(OH)2 curves but these curves parallel each other very closely. Measurements of pH for the Ca(0H)2 titrations were made in a 1:20 s o i l to solution ratio whereas the pH values of the incubation samples were made in a 1:2 s o i l to water ratio. Suspension effects, therefore, could explain at least some of this difference. However, i t was also found that the no-lime incubation sample pH values after equilibration were lower by an average of 0.55 pH units than the 1:1 soil/water pH measurements of soils without incubation. Hydrolysis or some other reaction responsible for liberating acidity therefore appears to have taken place. In the case of the Abbotsford and the Ryder soils LR was overestimated by CaCOH)^ ti t r a t i o n . The slopes of the CaC03 curves were steeper for these soils. This suggests the presence of acidic s o i l components neutralized by Ca(0H)2 but not by CaCO^ or neutralized much more slowly by CaCOg. This underestimation was lower at pH 6.5 than at 6.0. The two t i t r a t i o n curves for the Monroe s o i l were very similar. Reasons for the variation of relationship between CaCO^ and Ca(0H)2 titrations for different soils requires further elucidation using a larger number of samples. Buffer methods Results of equilibrating the SMP buffer and the Woodruff buffer with soils are shown in Figures 2, 3 and 4 by scattergrams, and statistics calculated by regression analysis. It should be noted that the regression of equilibrium buffer pH on LR was significant at the 1% level at a l l pH values for both buffers. 7.51 SMP BUFFER Y= 6.72-0.053 X r2 = 0.278 SEJ = 0.44 3 CT LU WOODRUFF BUFFER Y= 6.533-0.037 X r2= 0.404 SEJ = 0.23 5.6 H meq. Ca(0H)2 /lOOg. soil Figure 2. Buffer c a l i b r a t i o n curve f o r LR to pH SMP BUFFER Y= 6.82- 0.048 X r2 = 0.43 SEJ- = 0.39 x C L cr LU 6.8ir-6.4 6.0-5.6-T 1 1 i — 1 1 1 1 8 12 16 20 WOODRUFF BUFFER Y= 6 .57 -0 .029X r 2 = 0.48 SEJ = 0.22 16 20 meq. CaCOH)^  /I00 g. soil Figure 3. Buffer c a l i b r a t i o n curve f o r LR to pH 6.4 16 7.5 i SMP BUFFER Y = 6.93- 0.042 X r2= 0.609 SE} = 0.32 x CD ««— CD E 3 3 C T 7.21 6.8 6.4-6.0 -5.6 -WOODRUFF BUFFER Y = 6 . 6 3 - 0.0236 X r2= 0.58 SE} = 0.19 0 5 10 15 20 25 30 meq. Ca(0H)2 /100 g. soil Figure 4. Buffer calibration curve for LR to pH 6.8 17 From the regression c o e f f i c i e n t s i t can be seen that the SMP buffer pH changes are 0.053, 0.049. and 0.042 pH units per 1 m i l l i e q u i v a l e n t Ca per 100 g' for predicting LR to pH 6.0, 6.4 and 6.8, respectively. This i s equivalent to saying that each 0.10 6, 0.097 and 0.0 84 pH unit change c a l l s for an additional one ton of CaCO^, or equivalent, per acre (2,000,000 lb) when liming to pH 6.0, 6.4 and 6.8 respectively. For the Woodruff buffer, the buffer changes are 0 . 037, 0 . 0.3,0. and 0.024 . pH units per 1 mi l l i e q u i v a l e n t of Ca per 100 g s o i l for LR to pH 6.0, 6.4 and 6.8, respectively. Shoemaker (195 9) i n developing the new buffer had the objective of formulating a buffer of such a strength that 0.1 pH unit change would indicate a LR of 1 m i l l i e q u i v a l e n t Ca per 100 g s o i l or 1,000 lb pure CaCO^ per acre for the s o i l s he was using. The f i n a l buffer i n fact required 0.116, 0.102 and 0.086, pH unit depressions for liming to pH 6.0, 6.4 and 6.8, respectively. On the average, therefore, f o r s o i l s used i n t h i s study a larger LR i s predicted per unit buffer pH change than was predicted f o r the Ohio s o i l s used by Shoemaker. A smaller f r a c t i o n of s o i l a c i d i t y requiring n e u t r a l i z i n g was e f f e c t i v e i n n e u t r a l i z i n g the buffer than was found by Shoemaker. So i l s used i n th i s study therefore, appeared to have larger quantities of weak but t i t r a b l e or pH-dependent a c i d i t y . Shoemaker et a l . (19 61) presented a table for i n t e r -preting the equilibrium buffer pH i n terms of CaCO- i n tons 18 per acre required to increase s o i l pH to 6.0, 6.4 and 6.8. Relation between t h e i r c a l i b r a t i o n of the equilibrium buffer pH for Ohio s o i l s and c a l i b r a t i o n for s o i l s used i n t h i s study can be seen from Figure 5 and Table 3. For s o i l s i n t h i s study, the c o r r e l a t i o n c o e f f i c i e n t s between the CaCOH^ t i t r a t i o n LR to pH 6.0, 6.4 and 6.8 and the LR as determined from the table given by Shoemaker et a l . (1961) were 0.4911, 0.6230 and 0.7557, respectively. Using the LR values as determined from the newly calculated c a l i b r a t i o n l i n e resulted i n c o r r e l a t i o n c o e f f i c i e n t s of 0.5277, 0.6588 and 0.7809. Similar observations to those made for the SMP buffer can be made for the Woodruff buffer. Depression of the pH using t h i s buffer was even smaller per unit LR for the same reason as above i n addition to the fact that t h i s buffer i s even stronger. Changes i n pH of t h i s buffer to predict 1 m i l l i e q u i -valent Ca per 100 g were 0,0369, 0.0295 and 0.0237 pH units f o r LR to pH 6.0, 6.4 and 6.8. Keeny and Corey (1963), using the same s o i l / b u f f e r quantity r a t i o for Iowa s o i l s used a buffer depression of 0.1 pH units to indicate a LR of 1 m i l l i e q u i v a l e n t Ca per 100 g. Using t h i s interpretation of the Woodruff buffer pH depression to predict LR for s o i l s i n the present study, the c o r r e l a t i o n c o e f f i c i e n t between predicted LR values and LR by Ca(0H)2 t i t r a t i o n to pH 6.8 was 0.6879. Between the LR values predicted from the newly calculated c a l i b r a t i o n curve and the LR values by Ca(0H)2 t i t r a t i o n , the c o r r e l a t i o n c o e f f i c i e n t was 0.76 23. 7.0 i x Q. Q> «*— CO E 3 3 cr LU 5.0-8 12 14 18 Lime requirements (tons CaC03/acre). Figure 5» Buffer c a l i b r a t i o n curves as reported f o r Ohio s o i l s by Shoemaker et a l . and curves calculated f o r s o i l s used i n the present study vo 20 Table 3. Lime required to bring s o i l to indicated pH as determined by two different calibrations of buffer solution pH depression Soil buffer Shoemaker et a l . (1961) Present Study pH pH 6.8 pH 6.4 pH 6.0 pH 6.0 pH 6.4 pH 6.8 tons/acre tons/acre 7.0 6.9 0 . 8 6.8 0.4 3.2 6.7 1.4 1.2 1.0 0.3 2.4 5.6 6.6 1.9 1.7 1.4 2.2 4.5 8.0 6.5 . 2.5 2.2 1.8 4.2 6.5 10.4 6.4 3.1 2.7 2.3 6.1 8.6 12 .8 6.3 3.7 3.2 2.7 8.0 10.6 15.2 6.2 4.2 3.7 3.1 9.9 12 .7 . 17.5 6.1 4.8 4.2 3.5 11.8 14.7 19 .9 6.0 5.4 4.7 3 . 9 13.7 16.8 22 . 3 5.9 6.0 5.2 4.4 15.6 18.9 24.7 5.8 6.5 5.7 4.8 17.5 20.9 5.7 7.1 6.2 5.2 19.4 23.0 5.6 7.7 6.7 5.6 21.3 5.5 8.3 7.2 6.0 23.2 5.4 8.9 7.7 6.5 5.3 9.4 8.2 6.9 5.2 10.0 8.6 7.4 5.1 10 .6 9.1 7.8 5.0 11.2 9.6 8.2 4.9 11.8 10.1 8.6 4.8 12.4 10.6 9.1 21 Standard error estimates (SEy) and c o e f f i c i e n t s of 2 determination (R ) given i n Figures 2, 3 and 4 give measures of the scatter of points about the buffer c a l i b r a t i o n regression l i n e s . It can be seen that for both buffer methods, SE$ i s large. Prediction of accurate LR values from depression of the pH of the buffer solutions therefore appears to be d i f f i c u l t for s o i l s s i m i l a r to those of the present study. According to 2 the R values, only 27.8%, 43.4% and 61% of the v a r i a t i o n of the LR to pH 6.0, 6.4 and 6.8 respectively i s accounted for by regression of equilibrium SMP buffer pH on LR. In the case of the Woodruff buffer, 40.4%, 47.7% and 58.1% of LR v a r i a t i o n i s explained. It would appear i n i t i a l l y that an even weaker buffer than the SMP should be developed so that a greater pH depression per unit LR occurs. This, however, would r e s u l t i n an even smaller portion of the t o t a l a c i d i t y being neutralized by the buffer and therefore being e f f e c t i v e i n indicating LR. The end point pH would be lower and the r e l a t i v e l y strongly a c i d i c (low pH) components would be predominantly measured. LR for s o i l s high i n pH dependent a c i d i t y and low i n exchange a c i d i t y would be underestimated and those high i n exchange a c i d i t y would be overestimated. Use of such a buffer would r e s u l t i n more scatter about the regression c a l i b r a t i o n l i n e of equilibrium buffer pH on LR and i n reduced accuracy of predicting LR. This p o s s i b i l i t y therefore must be ruled out. Shoemaker (19 59) i n fact makes the observation that the s o i l s he used had 22 appreciable buffer capacity r e l a t i v e to the buffer solution and for t h i s reason there was considerable scatter about the best f i t c a l i b r a t i o n l i n e . He believed a buffer should not be any weaker than the buffer he formulated. To predict LR to pH 6.8 for s o i l s high i n pH dependent . 'acidity i t appears that a buffer strongly buffered i n the range pH 6.5 to 7.0 i s required. T i t r a t i o n of aliquots of the o r i g i n a l buffer and of the equilibrated solution might then be required to determine s o i l a c i d i t y neutralized as pH depression would be tob small and could not be measured accurately. The SMP and Woodruff buffer methods as they have been proposed and calibrated by Shoemaker et a l . (1961) and Woodruff (1947, 1948) respectively appear to be unsuitable for routine application to s o i l s s i m i l a r to those of the present study. The depression of the buffer pH i s too small per unit LR and the SEy i s too large, both i n d i c a t i n g the p o s s i b i l i t y of large errors i n predicting LR. It may be suggested that i f n e u t r a l i z a t i o n of neutral s a l t exchangeable a c i d i t y i n s o i l i s found to correlate with increased productivity, weak buffers such as the SMP buffer might be calibrated against neutral s a l t exchangeable a c i d i t y d i r e c t l y . The depression and r e s u l t i n g predicted LR would then be expected to correlate with response to lime applied. LITERATURE CITED Bradfield, R. 1942. Calcium i n s o i l : I. Physico-chemical r e l a t i o n s . S o i l S c i . Soc. Amer. Proc. 6: 8-15 Dunn, L.E. 194 3. Lime requirement determinations of s o i l s by means of t i t r a t i o n curves. S o i l S c i . 56: 341-351. Hughes, E.C. 1965. Lime use i n B r i t i s h Columbia. In Report of 3rd Ann. B r i t i s h Columbia S o i l S c i . Workshop. B.C. Dept. Agriculture, Cloverdale, B.C. Kenney, D.R. and R.B. Corey. 196 3. Factors a f f e c t i n g lime requirements of Wisconsin s o i l s . S o i l S c i . Soc. Amer. Proc. 27: 1-10. Pionke, H.B., R.B. Corey and E.E. Schulte. 1968. Contributions of s o i l factors to lime requirement t e s t s . S o i l S c i . Soc. Amer. Proc. 32: 113-117. Shoemaker, Harold E. 19 59. The determination of a c i d i t y i n Ohio s o i l s by using lime addition, and buffer e q u i l i b r a t i o n methods. Ph.D. Thesis. Ohio State University (Library Congr. Card No. Misc. 60-1213) 101 p. Univ. Microfilms. Ann> Arbour, Mich. Shoemaker, H.E., E.O. McLean and P.F. Pratt. 1961. Buffer methods for determining lime requirement of s o i l s with appreciable amounts of exchangeable aluminum. S o i l S c i . Soc. Amer. Proc. 25: 274-277. Wiens, J.H. Evaluating a c i d i t y of selected B r i t i s h Columbia s o i l s . Unpublished. Woodruff, CM. 1947. Determination of exchangeable hydrogen and lime requirement by means of the glass electrode and a buffered solution. S o i l S c i . Soc. Amer. Proc. 12: 141-142. Woodruff, CM. 1948. Testing s o i l s for lime requirement by means of a buffered solution and the glass electrode. S o i l S c i . 66: 53-63. EVALUATING ACIDITY OF SELECTED ACID SOILS OF BRITISH COLUMBIA ABSTRACT M a s t e r h o r i z o n s o f t e n a c i d s o i l s o f t h e Lower F r a s e r V a l l e y o f B r i t i s h C o l u m b i a , d e v e l o p e d on s e v e r a l p a r e n t m a t e r i a l s were e v a l u a t e d w i t h r e s p e c t t o a c i d i t y r e l a t e d p r o p e r t i e s . These i n c l u d e d measurements o f pH, l i m e p o t e n t i a l , c o r r e c t e d l i m e p o t e n t i a l and exchangeable and e x t r a c t a b l e components o f p o t e n t i a l a c i d i t y . Measures o f pH, l i m e p o t e n t i a l and c o r r e c t e d l i m e p o t e n t i a l c o r r e l a t e d w e l l w i t h exchangeable a c i d i t y but not w i t h measures o f pH-dependent a c i d i t y . The amounts o f 1 N KC1 exchangeable A l and Al+Fe d i d not acc o u n t f o r a l l a c i d i t y t i t r a b l e t o pH 5. The amounts o f A l and Al+Fe e x t r a c t a b l e w i t h NH^OAc b u f f e r e d a t pH 4.8 were g e n e r a l l y more t h a n were exchange-a b l e w i t h 1' N KC1 but no c o n s i s t e n t t r e n d was n o t i c e d i n w h i c h t h i s component was r e l a t e d t o t i t r a b l e a c i d i t y t o a p a r t i c u l a r pH end p o i n t . As e x p e c t e d , pH-dependent a c i d i t y was g r e a t e s t f o r t h e s u r f a c e h o r i z o n s , due l a r g e l y t o t h e p r e s e n c e o f o r g a n i c m a t t e r . A c i d ammonium o x a l a t e e x t r a c t a b l e A l and Fe was g r e a t e r t h a n t h a t e x t r a c t a b l e w i t h 0.1 M pyrophosphate and was l a r g e s t , f o r t h e s u r f a c e and p o d z o l i c B h o r i z o n s . 25 INTRODUCTION. Various methods have been devised to measure acidic properties of soils. Some attempt to measure active acidity or the condition of the s o i l solution. Generally these same measures also reflect the condition of a part of the exchange phase of so i l s . Other methods determine the magnitude of the various components of potential acidity. Although not a l l aspects of pH measurements are understood completely, they are useful and probably the most widely used empirical indices of s o i l acidity. pH is measured at various ratios of s o i l to water. It is also measured in 0.01 M CaCl2 and in 1 N KC1, mainly to avoid uncertainties with respect to junction potentials. The lime potential (LP) expressed as pH-^pCa or pH-%p (Ca+Mg) has been proposed by Schofield (1952). It is measured in the supernatant solution after equilibration of a clay or s o i l sample with 0.01 M CaC^ in order to avoid uncertainties with respect to the suspension effect. This method has been found to be relatively constant for a system with varying electrolyte concentration (Schofield and Taylor, 1955; Turner and Nichol, 1962). LP should be a good reflection of the degree of base saturation of the exchange phase because the activity ratio of two ions on the exchange phase should equal the activity ratio of these two ions in the solution phase (Low, 1951). Correlations between LP and degree of base 26 saturation have been made and found to be slightly better than between pH and degree of base saturation (Webster and Harward, 1959). It has been proposed that in acid s o i l neutralization, two'reactions take place. 2A1X3 + 3Ca -»• 3CaX2 + 2A1 Al + 30H + A1(0H)3 Combining the solubility product and ion exchange expressions has resulted in an expression of LP as a function of base saturation where base saturation is defined as the degree of Ca+Mg saturation of electrostatic charges (Turner et a l . , 1963). The solubility product (pK^) of AKOH)^ has been found to be variable for soils (Lindsay et a l . , 1959; Turner and Clark, 1965.) and therefore a modification of the LP expression was made to eliminate the effect of this v a r i a b i l i t y (Turner and Clark, 1965). This modified expression pH-Jgp (Ca+Mg) - 1/3 (33.8-pK"2), was proposed as an improved measure of LP and called the corrected lime potential (CLP). Experimental values of this expression for 31 soils corresponded f a i r l y closely to the calculated curve for bentonite clay. Also, in a later study (Turner and Clark, 1966) a very good agreement between CLP and %BS for a wide variety of soils was reported. Normal KC1 exchangeable Al is commonly used as a measure of the potential acidity at the pH of the s o i l . 27 Exchangeable Fe has been v i r t u a l l y ruled out as a component of exchange a c i d i t y but has been used as a saturating cation i n studies of acid clays. Substantial amounts of KC1 A l have been found i n some acid s o i l s of southeastern United States (Dewan and Rich, 1970; Coleman et a l . , 1958) but considerably smaller amounts are reported elsewhere. It has also been found i n working with a c i d i f i e d clays, that the extractable amounts of Al by t h i s method increase when these clays are aged (Chernov, 1959). Normal KC1 A l has been related to low pH buffering capacity and has been proposed as the c r i t e r i a f or liming of some s o i l s (Kamprath, 1970). McLean (1958) has proposed using a buffered s a l t s olution, NH^OAc a c i d i f i e d to pH 4.8, for extraction of A l . For some s o i l s t h i s method has been found to extract more than 1 N KC1 and for others, e s p e c i a l l y highly a c i d i c s o i l s , the amount extracted i s le s s . Ammonium acetate i s generally considered to measure some A l which i s not s t r i c t l y exchangeable but i s nevertheless a c i d i c . McLean (196 5) also indicated i t may be an index of the degree of weathering of some kinds of s o i l s . Higher pH a c i d i t y or pH-dependent a c i d i t y has been variously characterized. The modified Mehlich (Peech, 1965) method employing BaCl^ and triethanolamine (BaC^-TEA) buffered at pH 8.0 or 8.2 i s one measure of " t o t a l exchange a c i d i t y " or more c o r r e c t l y , t i t r a b l e acidity.. This measure corresponds 28 to acidity requiring neutralization to bring a s o i l to the point of being f u l l y base saturated according to Allison and Bradfield's (1933) concept of a s o i l in equilibrium with CaCO^ at the partial pressure of CO^  in the atmosphere. For some soils especially those high in organic matter, the difference between CEC to pH 7 ( I N NH^OAc) and the sum of exchangeable bases is a good measure of pH dependent acidity. The quantity of acidity measured is generally less than is measured with BaC^-TEA to pH 8 but almost always greater than the difference between CEC by extraction with neutral salt and the sum of exchangeable bases. Hydroxy Al and Fe coatings on s o i l particles as well as in interlayer spaces of layer silicates are the cause of several characteristics of soils and clays. These include reduced neutral salt exchange acidity, blocked exchange sites and increased buffering in the pH range 5 to 8 (Clark, 1963; Clark, 1964; Coleman and Thomas, 1964; Rich, 1960). Hydroxy Fe and Al in soils have therefore come to be considered pH-dependent acidic components. Organic matter has been well demonstrated to be an important component in buffering s o i l s , although causitive properties s t i l l require investigation. Evidence indicates that complexed multivalent ions may be a cause (Martin, 196 0; Martin and Reeve, 1960; Schnitzer and Wright, 1960). Direct 29 deprotonation of functional groups .such as carboxyls, phenols, enols, etc. has also been cited as a cause (Broadbent and Bradford, 1952). Methods and extractants have been devised to extract specifically amorphous and organic matter associated Al and Fe. Na and K pyrophosphate have been used to extract the illuviated portion from podzol (spodic) B horizons (McKeague, 1967) which are believed to consist primarily of amorphous or organically complexed Al and Fe. Acid ammonium oxalate (McKeague and Day, 1966) as well as Na pyrophosphate dithionite (Franzmier, 1965) have also been used for the same purpose. The purpose of the study described in this paper was to evaluate acid soils with respect to measures of acidity described above. These included measures of active, as well as exchangeable and pH-dependent components of potential acidity. MATERIALS AND METHODS Soils used in this study included 8 surface and 21 subsurface samples of 10 common soils found in the Lower Fraser Valley of British Columbia. Sample preparation involved air drying, crushing and sieving the soils to pass a 2 mm mesh sieve. Measurements of pH were made in ratios of 1:1 s o i l to water and 1:2 s o i l to 0.01 M CaCl-. •3 0 Carbon was determined by dry combustion (Laboratory Equipment Corporation, 1959). LP and CLP were determined by measuring Ca, Mg and Al in supernatant solutions after equilibrating 10 g samples in 50 ml of 0.01 M CaC^ with shaking and aeration for 5 days (Clark, 1965). Concentrations of Ca, Mg and Al were corrected for activity. This was done by calculating ionic strength using concentration of Ca and Mg and assuming anions were monovalent and at a concentration for electronic neutrality. The activity coefficient for Ca and Mg were then calculated using the second approximation of the Debye-Huckel equation as given by Schofield and Taylor (1955). The activity coefficient for Al was calculated as suggested by Lindsay et a l . (1959) and Frink and Peech (1962). Exchangeable Al and extractable Al were determined by extraction as described by McLean (1965). These solutions were also analyzed for Fe and Mn. Total titrable acidity was determined by the modified BaCl2-TEA method as described by Peech (1965). CEC was determined by the NH^ OAc pH 7.0 and by the method of Clark (1965) where CEC is defined as the sum of Ca+Mg+Al exchangeable with 2 N NaCl. Base saturation values were determined by dividing the sums of Ca+Mg+Na+K by CEC (NH^OAc pH '7.0) and by the method of Clark where %BS = (Ca+Mg/Ca+Mg+Al) x 100. Al and Fe were also extracted with acid ammonium oxalate (McKeague and Day, 1966), Na pyrophosphate and Na pyrophosphate dithionite (Franzmier et a l . , 1965). 31 Elemental analyses were made using a Perkin Elmer model 303 atomic absorption spectrophotometer, except Al in Clark's method for CEC where the Eriochrome cyanine R.A. method (Jones and Thurman, 1957) was used. St a t i s t i c a l analysis was carried out using existing routines in the U.B.C. computing centre library and the IBM 360/67 computer at the centre. RESULTS AND DISCUSSION Results of chemical analysis of soils are given in tables 1 and 2. Only the subsurface samples of the Cloverdale s o i l were non acidic. The Alouette and Spetifore soils were very acidic as can be seen from the pH values in water of 3.84 and 4.44 from the Ap and Bg respectively of the Alouette, and 4.00 and 4.25 for the Ap and subsurface horizons of the Spetifore s o i l . The corresponding pH, in 0.01 M CaCl^ were 3.41 and 3.89 for Alouette and 3.95 and 3.90 for Spetifore. The overall mean of pH values in 0.01 M CaC^ was 0.4 5 units lower than the mean of pH values in water. Organic C ranged from 3.42 to 28.81% for surface master horizons and from 0.16 to 4.56% for subsurface horizon samples. Corresponding % clay values ranged from 2.5 to 13.6% and 1.0 to 50%. •It can be seen from table 3 that the difference between CEC measured by the NH^ OAc pH 7 and CEC measured by the method of Clark i s substantial for most soils. The mean for CEC by the former method is 25.5 me/100 g whereas by the latter i t is 32 Table 1. Selected properties of the soils Class- £2 -Soil series i f i c a t i o n Horizon Depth H_0 CaCl- Carbon Clay cm Abbotsford MHFP Ap 0-17. , 8 5. . 35 5. .25 2. .42 2. , 5 Bf 17 . 8-35. ,6 5. ,18 5. ,05 0. , 84 1. , 0 IIC 35 .6 + 5. , 65 5. ,45 0. ,16 1. , 3 Alouette OG Ap 0-22. ,9 3. , 84 3. ,41 28 . , 88 Bg 22 .9-45. , 7 4. ,44 3. , 89 4. ,56 9. ,6 Cg 45 .7 + 5. ,31 4. ,61 1. , 32 7. ,0 Cloverdale HEG Ap 0-17. , 8 5. .90 4. ,70 4. . 85 13. ,6 Ae 17 . 8-33 ,6. 95 5. ,45 0. ,64 25. ,9 Bt 33 .0-61 7. ,60 6 . . 85 0. ,24 50. , 0 C 61 . 0 + 8. ,60 7. , 35 0. ,20 43 . , 2 Langley HEG Ap 0-22. ,9 5. , 30 5 . 45 8. , 80 8. , 3 Bt 35 .6-50. , 8 5 , . 80 5. ,45 0. .22 19. .5 C 50 . 8 + 6 . 70 6. .05 0. .20 43. ,2 Monroe DEB Ap 0-25 5. , 50 5. .05 3. ,42 7 . , 0 C 25 + 5. .60 5, .10 0. .84 6. . 8 Milner BMHFP Bf 0-25. .4 5. , 55 5. .00 2. .75 16. ,1 C 38 .1+ 5. .40 5. .10 0. .12 33. , 5 Ryder MHFP Ap 0-17. . 5 5, . 80 5. .45 3 , .60 4 , .1 Bf 17 .5-42 5. .68 5, .65 2, . 32 3. .7 IIC 7 5 + 5, .45 4, . 80 0, .72 3 . 2 Sunshine MHFP Bf_ 0-25. .4 5 , .45 5, . 25 3, .64 2. .0 Bf 2 25 .4-68, .6 5, .45 5, .25 2 . 40 1. , 3 C 72 .6 + Spetifore SRHG Ap 0-17. . 8 4 , .00 3 , .95 5, .33 13. .6 Cgl 17 . 8-40, .6 4, .25 3 , .95 1, . 32 15, .0 Cg2 40 .6 + 4, .25 3 , .90 1, .00 3 , . 5 Whatcom BMHFP Ap 0-17, .5 5, .25 4, .90 6. .90 7. . 0 Bf 17 . 5-75 5, . 80 5 , .25 2, .60 2 , . 0 C 75 + 5, .50 0, .'2 0 0, .16 20, .0 Mean Range 5, 3 , 8, . 56 . 84-.60 5, 3, 7, .11 .45-. 35 3 , 0, 28 , .05 .12-.88 13, 1, 50, .03 .0-.0 MHFP—mini humo-ferric podzol BMHFP—bisequa mini humo-ferric 0G--orthic gleysol podzol HEG--humic illuviated gleysol SRHG--saline rego-humic gleysol DEB—degraded eutric brunisol Table 1 (continued) 33; NH.OAC 4 CEC BS CaCl 2+NaCl CEC BS LP CLP KC1 A l KC1 Fe meq/lOOg 16.2 11.64 5.51 % 39.32 38.83 10.36 meq/lOOg 0.56 0.70 1.09 % 77.56 62.35 76.99 4.60 3.87 4.13 4.78 4.45 4.85 meq/lOOg .56 .74 .40 0.05 0.07 0.05 88.32 23.43 12.26 10.48 32.01 64.86 1.53 5.43 6.41 68.18 38.00 95.62 2.54 3.04 3.77 3.51 4.25 4.67 11 4 23 84 1.19 0.26 0.16 0.06 31.31 19.98 47.07 46.56 8.73 63.12 10.81 42.43 6.88 11.22 27.99 26.10 78.99 97.50 99.35 99.15 3.37 4.25 5.40 5.97 4.13 4.85 4.89 5.01 3.45 1.19 0.0 0.0 0.07 0.10 0.05 0.06 66.25 33.68 32.97 25.13 63.48 66.33 13.23 14.34 19.70 99.69 99.79 97.93 4.38 4.40 5.21 4.65 4.54 4.34 1.07 1.78 2.37 0.06 0.07 0.07 39.32 33.06 11.80 66.31 9.97 5.48 99.68 96.99 4.19 4.07 68 42 1.11 3.08 0.05 0.05 24.00 14.20 42.08 34.92 6.02 18.33 89.14 99.54 3.90 4.06 4.39 4.55 6.16 0.31 0.05 0.06 28.33 26.18 17.51 65.88 26.90 13.30 5.78 2.90 6.00 99.45 90.42 91.31 32 10 85 4.85 4.42 4.16 0.76 3.84 1.61 0.06 0.07 0.07 29.14 11.54 24.36 8.36 8.02 1.69 3.77 0.52 0.23 92.88 87.91 95.72 3.85 4.06 4.24 4.20 4.34 4.45 6.09 1.56 2.89 0.06 0.07 0.07 27.91 20.29 14.99 19.89 27.33 30.80 7.79 7.41 3.86 21.42 23.45 24.30 94 84 66 3.74 3.76 3.75 8.78 6.12 2.84 0.20 0.33 0.31 42.13 24.82 24.11 26.64 15.10 45.52 9.55 3.09 16.62 98.81 95.95 99.67 04 25 09 53 60 41 4.89 2.84 3.56 0.06 0.06 0.05 28.86 5.51-88.32 31.73 1.69-66.33 8.39 0.56-27.99 82.68 21.42-99.93 4.01 2.54 5.97 4.45 3.51 5.01 2.68 0.0-11.23 0.097 0.05-0.26 34 Table 2. Extractable components of soils Soil NH 40Ac 4. 8 oxalate extractable 0.1 M pyrophosphate extractable Al Fe Al Fe Al Fe meq/lOOg \ : 7 —— Abbotsford Ap 1. 74 0. 09 1. ,00 0. ,76 0. ,17 0. 24 Bf 2. 63 0. 07 0. .78 0, .35 0. ,10 0. 04 IIC 1. 40 0. 04 0. .50 0. ,19 0. ,04 0. 01 Alouette Ap 4. 58 0. 65 1. ,02 0. ,78 0. ,38 0. 80 Bg 4. 01 0. 39 0. , 34 0. ,44 0. ,12 0. 38 Cg 0. 56 o . 46 0. .19 0, .57 0 , 03 0. 15 Cloverdale Ap 3 . 42 0. 76 0. ,46 0. ,86 0. ,17 0. 46 Ae 0. 78 0. 06 0. ,26 0, .64 0. ,05 0. 32 Bt 8. 78 0. 03 0. ,30 0, . 39 0. .02 0. 08 C 0. 78 0. 03 0, .26 0 , .42 0, .02 0. 13 Langley Ap 5. 61 0. 31 1. .20 1, .50 0. .39 1. 29 Bt ' 1. 12 0. 04 0. . 31 0. .22 0, ,01 0. 17 C 0. 51 0. 04 0. .24 0, .44 0, .01 0. 07 Monroe Ap 7. 12 0 . 19 0. ,19 0, .63 0. .08 0. 40 C 0. 73 0. 05 0. ,19 0, , 59 0. ,05 0. 29 Milner Ap 0. 76 0. 18 0, .78 0, .70 0, . 32 0. 59 C 1. 36 0. 23 0. .36 0, .39 0. ,02 0. 07 Ryder Ap 2 . 48 0. 09 0. ,98 0. .72 0, .22 0. 38 Bf 5. 51 0. 13 1, .42 1, .00 0, .17 0. 42 IIC 5. 92 0. 15 0. . 80 0, .92 0, .16 0. 31 Sunshine Bf x 3. 93 0. 07 1. .42 0, .94 0, .25 0. 32 Bf 2 5 . 31 0. 05 2. .22 0, .99 0, .23 0. 15 C 4. 28 0 . 05 1, .42 0, .34 0 , .11 0. 01 Spetifore Ap 5. 01 0. 67 1. .42 0. .51 0, .28 0. 45 C§1 4 . 78 0. 58 0, .11 0, .53 • 0, .06 .0. 32 Cg2 1. 39 0. 18 0, .16 0, .76 0, .02 0. 27 Whatcom Ap 2. 58 0. 11 0, .67 0, .99 0, .25 0. 65 Bf 6 . 17 0. 12 1, .68 1, .20 0 , . 30 0. 45 C 6. 34 0. 06 0, .21 0, .41 0, .03 0'. 09 3.11 0.33 .674 0.664 0.115 0.255 0.51- 0.03- 0.11- 0.19- 0.01- 0.01-7.12 0.76 1.68 1.50 0.39 1.29 35 8.6 meq/100 g. Therefore pH-dependent CEC (and pH-dependent ac i d i t y ) i s a major component. The s o i l s for which pH-dependent CEC to pH 7 was the smallest f r a c t i o n of t o t a l CEC were the Ryder Bf sample and Whatcom C samples, where only 2 3.25% and 31.06% respectively was pH dependent. In addition, the pH dependent CEC of the subsurface samples of the Cloverdale and C horizon of the Langley and Alouette were less than 5 0% of the t o t a l CEC. With the exception of the Ryder Bf these samples were also those found to be highest i n % clay. The r e l a t i o n between pH, LP and CLP and measures of pot e n t i a l a c i d i t y are of i n t e r e s t . Table 3 gives calculated c o r r e l a t i o n c o e f f i c i e n t s between the values of pH, LP and CLP and the values of % BS of neutral s a l t extractable CEC and NH^OAc pH 7 CEC. It can be seen that between pH, LP and CLP values, and % BS by the former method, c o e f f i c i e n t s are highly s i g n i f i c a n t . Between these measures and % BS by the l a t t e r method, c o e f f i c i e n t s are not s i g n i f i c a n t . Between pH, LP and CLP and 1 N KC1 exchangeable A l , considered to be a measure of exchangeable a c i d i t y , the co r r e l a t i o n c o e f f i c i e n t s were a l l highly s i g n i f i c a n t . On the other hand, only pH (R^O) was correlated s i g n i f i c a n t l y with BaCl 2~TEA extractable a c i d i t y , consisting primarily of pH-dependent a c i d i t y . The closer relationships of pH, LP and CLP to exchange a c i d i t y then to pH-dependent a c i d i t y i s therefore shown. In a l l cases, LP and CLP correlated better with measures of exchangeable a c i d i t y than acid pH. Measured i n 0.01 M CaCl 2 pH also correlated better with measures of exchange a c i d i t y than did pH (H„0). Table 3. Correla t ion coeff icients between pH, LP and CLP and measures of components of potent ia l ac id i ty KC1 A l KC1 Fe 2N NaCl A l %BS1 %BS2 ExH NH.OAc A l 4 NH.OAc Fe 4 pH(H20) -0.5611** -0.5298** -0.5752** 0.6533** 0.3521 -0.4102* -0.3908* -0.2900 P H(CaCl 2 ) -0.5778** -0.6166** -0.6567** 0.6991** 0.2776 -0.3346 -0.5308** -0.6147** LP -0.6171** -0.6667** -0.6884** 0.7400** 0.3484 -0.3544 -0.3063 -0.6178* CLP -0.7412** -0.7179** -0.7486** 0.7355** 0.3637 -0.3535 -0.3341 -0.6187** * S ign i f ican t at the. 5% l e v e l . ** S ign i f ican t at the 1% l e v e l . % BS^ Base saturat ion calculated on the basis of CEC determined by the method of Clark, 1965. % BS 0 Base saturat ion calculated on the basis of CEC determined with IN NH.OAc, pH 7. KC1 A l A l exchangeable with 1 N KC1 (100 ml/100 g) 4 Fe - Fe exchangeable with 1 N KC1 (100 ml/100 g) ExH - t i t r a b l e a c i d i t y (BaCl 2-TEA, pH 8.0) NH OAc A l ~ A l extractable with 1 N NH^OAc, pH 4.8 4 Fe - Fe extractable with 1 N NH.OAc, pH 4.8 37 NH^OAc buffered at pH 4.8 extracted more A l from most s o i l s than did 1 N KC1. The exceptions were the very acid samples, Alouette Ap, Bg and Spetifore Ap, Cgl, Cg2 and the moderately acid Langley Bt, C, Monroe C, Milner Bf and Sunshine Bf. The higher KC1 exchangeable values for the very acid samples may be explained by the nature of the unbuffered KC1 solution which takes on the pH of the s o i l . The mean for NH^OAc pH 4.8 extractable Fe was also larger than was the mean for 1 N KC1 exchangeable Fe. There are several exceptions to t h i s trend but magnitudes of differences i n these can hardly be c a l l e d s i g n i f i c a n t . Table 4 shows magnitudes of a c i d i t y neutralized to several pH end points by incubation of several samples with CaCOg. Also given are values f o r exchangeable and extractable A l and Al+Fe. It can be seen that 1 N KC1 exchangeable A l and Al+Fe did not account f o r a l l a c i d i t y t i t r a b l e even below pH 5.0 for 6 of the 7 s o i l s . An average of only 55% and 56.4% was accounted f o r . Possibly one extraction was not s u f f i c i e n t to remove a l l exchangeable a c i d i t y . The trend i s not as clear with regard to A l and Fe extractable by NH^OAc pH 4.8. An average of 74.4% of t i t r a b l e a c i d i t y to pH 5.0 i s accounted f o r but no consistent trend i s evident. For the Monroe, Ryder and Langley s o i l s , NH^OAc pH 4.8 extractable A l was more than would be required to neutralize CaCO^ i n liming to pH 5.0. For the other s o i l s , i t was s u b s t a n t i a l l y less than could be accounted for by t i t r a t i o n to pH 5.0. The Monroe, Ryder and Langley Table 4. Ti t rab le ac id i ty (CaC03 incubation) to pH 5.0, 5.5, 6.0 and measures of potent ia l a c i d i t y No. S o i l Series LR 5.0 5.5 6.0 KC1 A l KC1 A l + Fe NH,0Ac A l NH,0Ac A l + Fe meq/100 g 1 Abbotsford Ap 3.0 5.5 8.0 0.56 0.61 1.73 1.82 2 Cloverdale Ap 9.5 15.5 20.5 3.45 3.52 3.41 4.27 3 Langley Ap 2 11.0 21.0 1.07 1.13 5.60 5.91 4 Monroe Ap 3 5.5 8.5 1.11 1.16 7.11 7.30 5 Ryder Ap 0.0 2.0 6.5 0.76 1.82 2.48 2.57 6 Spetifore Ap 12.0 18.5 22.5 8.78 8.98 5.0 6.67 7 Whatcom Ap 8.0 14.5 22.0 4.89 4.95 2.58 2.69 Mean 5.30 10.36 15.6 2.95 3.02 3.99 4.47 * A pos i t ive lime requirement was found for s o i l s with o r i g i n a l s o i l pH greater than 5.0. For an explanation see page 13. co oo 3 9 therefore appear to have a component of A l not exchangeable but r e l a t i v e l y e a s i l y extractable. This may correspond i n part to oxalate extractable Al for the Ryder and Langley s o i l s as these s o i l s contained large amounts of t h i s extractable component. For the Monroe, however, t h i s i s not the case. I t would appear from the above that NH^OAc at pH 4.8 varies considerably among s o i l s i n i t s effectiveness i n extracting a c i d i t y responsible for buffering i n lower pH ranges. This i s i n contrast to 1 N KC1 which appeared to be more consistent i n r e l a t i v e amounts of A l extracted and would therefore be expected to r e l a t e more c l o s e l y to buffering capacity within defined pH ranges. Some c h a r a c t e r i s t i c s of the s o i l s with regard to the pH-dependent components can be determined from the values of t i t r a b l e a c i d i t y , CEC (pH 7)-(Exchangeable bases + 1 N KC1 A l ) , and (titrable a c i d i t y ) - (l N KC1 A3). In theory the l a t t e r two should correspond to pH-dependent a c i d i t y to pH 7 and pH 8 r e s p e c t i v e l y . It can be seen from table 5 that almost without exception, these measures were largest f o r surface horizons which correspondingly had highest values of % C. Higher values of ( t i t r a b l e a c i d i t y ) - ( I N KC1 Al) than values of (CEC) -(exchangeable bases + 1 N KC1) were expected but not obtained i n a l l cases. The surface horizons of g l e y s o l i c s o i l s had the highest values of both measures of pH-dependent a c i d i t y . Also notrceably high were the podzolic B (Bf) horizons of the Milner, Ryder and Sunshine s o i l s . These horizons also had high values for acid ammonium oxalate extractable Al and Fe and 0.1 M Na 40 Table 5. Measures of pH-dependent ac id i t y S o i l series T i t r ab le CEC (pH) - T i t r ab le a c i d i t y (Exch. Bases + ac id i t y -(BaCl 2-TEA) IN KC1 Al ) IN KC1 A l meq/lOOg Abbotsford Ap 17. 82 9. 29 17. 26 Bf 11. 13 5. 39 10. 39 IIC 5. 49 4. 54 5. 09 Alouette Ap 47. 80 67. 83 36. 57 Bg 10. 19 11. 09 5. 35 Cg 8. 63 3. 13 . 7. 44 Cloverdale Ap 25. 20 20. 76 . 21. 75 Ae 11. 97 6. 18 10. 78 Bt 6. 75 18. 45 6. 75 C 5. 49 26. 80 5. 49 Langley Ap 29. 94 48. 54 28. 87 Bt 9. 57 10. 52 7. 79 C 7. 10 8. 74 4. 73 Monroe Ap 14. 79 28. 11 13. 68 C 8. 11 25. 03 5. 03 Milner Bf 20. 64 10. 84 14. 48 C 9. 67 9. 36 Ryder Ap 18. 24 8. 91 17. 48 Bf 20. 08 15. 20 16. 24 IIC 14. 08 13. 57 12. 74 Sunshine. B f l 21. 01 20. 62 14. 92 Bf2 22. 73 9. 05 21. 17 IIC 10. 19 21. 05 7. 30 Spetifore Ap 26. 38 13. 57 17. 60 Cgl 16. 98 9. 56 10. 86 Cg2 13. 58 7. 54 10. 74 Whatcom Ap ' 28. 16 28. 79 23. 27 Bf 7. 21 18. 23 4. 37 C 8. 94 5. 38 41 pyrophosphate Al and Fe. The acid ammonium oxalate extractable amounts of Al and Fe were greater than the 0.1 M pyrophosphate extractable amounts of these elements. This is in agreement with results given by McKeague (1967) for podzolic B horizon samples. The correlation coefficients between titrable acidity (BaC^-TEA) and oxalate extractable Al and Fe were 0.3696 and 0.6604 respectively. Between pyrophosphate extractable Al and Fe and titrable acidity the coefficients were 0.5136 and 0.6115 respect-ively. Values of coefficients significant at the 1% and 5% level are 0.4965 and 0.4484. It is indicated from the above trends that oxalate and pyrophosphate extractable Al and Fe are components related to some extent with higher pH (pH-dependent) buffer capacity in soi l s . Relative importance undoubtedly varies between soils and more intensive investigations into the applicability to samples other podzolic B horizons should be made. LITERATURE CITED Brad f i e l d , R. and W.H. A l l i s o n . 1933. C r i t e r i a of base saturation of s o i l s . Trans. 2nd Comm. Intern. Soc. S o i l S c i . A: 63-79. Broadbent, F.E. and G.R. Bradford. 1952. 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Dewan, H.C. and C.I. Rich. 197 0. T i t r a t i o n of acid s o i l s . S o i l S c i . Soc. Amer. Proc. 34: 38-44. Franzmier* D.P.,-B.F. Hajek and CH. Simonson. 1965. Use of amorphous material to i d e n t i f y spodic horizons. S o i l S c i . Soc. Amer. Proc. 29: 737-743. Frink, CR. and Michael Peech. 1962. The s o l u b i l i t y of gibbsite i n aqueous solutions of s o i l extracts,. S o i l S c i . Soc. Amer. Proc. 26: 346-377. Jones, L.H. and Thurman, P.A. 1957. The determination of aluminum i n s o i l ash and plant materials using E r i o -chrome cyanine R.A. Plant and S o i l 9: 131-142. Kamprath, E.J. 1970. Exchangeable aluminum as a c r i t e r i o n for liming leached mineral s o i l s . S o i l S c i . Soc. Amer. Proc. 34: 252-254. 43 15. Low, P h i l i p F. 1955. The r o l e of aluminum i n t i t r a t i o n of Bentonite. S o i l S c i . Soc. Amer. Proc. 19: 135-139. 16. Laboratory Equipment Corporation. 1959. Instruction manual for operation of LECO carbon analyzers. 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S o i l S c i . 46: 13-22. 22. McLean, E.O. 1965. Aluminum. In C.A. Black (ed.). Methods of s o i l analysis. I I . Chemical and microbiological properties. Amer. Soc. of Agronomy, Inc., Madison, Wisconsin, U.S.A. p. 978-998. 23. McLean, E.O., M.R. Heddleson, R.J. B a r t l e t t and N. Hollowaychuk. 195 8. Aluminum i n s o i l s . I. Extraction methods and magnitudes i n clays and Ohio s o i l s . S o i l S c i . Soc. Amer. Proc. 22: 382-387. 24. Peech, Michael. 1965. Exchange a c i d i t y . In C.A. Black (ed.). Methods of s o i l analysis. I I . Chemical and microbiological properties. Amer. Soc. Agron. Inc., Madison, Wise. 25. Rich, C.I. 1960. Aluminum interlayers of vermiculite. S o i l S c i . Soc. Amer. Proc. 24: 26-32. 26. Schnitzer, M. and J.R. Wright. 1960. N i t r i c acid oxidation of the organic matter of a podzol. S o i l S c i . Soc. Amer. Proc. 24: 273-277. 44 27. Schofield, R.K. 1952. S o i l c o l l o i d s . Chemistry and industry (London) 4: 476-478. 28. Schofield, R.K. and A.W. Taylor. 1955. The measurement of s o i l pH. S o i l S c i . Soc. Amer. Proc. 19: 164-167. 29. Turner, R.C. and W.E. Nichol. 1962. A study of the lime p o t e n t i a l : 1. Conditions for the lime potential to be independent of s a l t concentration i n aqueous suspensions of negatively charged clays. S o i l Science 93: 374-382. 30. Turner, R.C. and J.S. Clark. 1965. Lime potential and degree of base saturation of s o i l s . S o i l S c i . 99: 194-199. 31. Turner, R.C. and J.S. Clark. '196 6. Lime pote n t i a l i n acid clay and s o i l suspensions. Trans. 8th Int. Cong. S o i l S c i . II: 207-215. 32. Turner, R.C, W.E. Nichol and J.E. Brydon. 1963 . A study of the lime p o t e n t i a l : 3. Concerning ractions responsible for the magnitudes of the lime p o t e n t i a l . S o i l S c i . 95: 186-191. 33. Webster, G.R. and M.E. Harward. 195 9. Hydrogen and calcium ion r a t i o s i n d i l u t e equilibrium solutions as related to cation saturation. S o i l S c i . Soc. Amer. Proc. 23: 446-451. FACTORS AFFECTING THE BUFFERING CAPACITY OF SOILS AND A MODEL FOR CALCULATION OF THE BUFFERING CAPACITY TO SELECTED pH VALUES ABSTRACT Correlation c o e f f i c i e n t s were calculated between buffer capacities within s p e c i f i c pH ranges as determined by Ca(0H>2 t i t r a t i o n , and various measured s o i l properties. Variables found to be s i g n i f i c a n t l y related to LR were used as independent variables i n a f i r s t series of i n i t i a l backward stepwise regression equations. Another set of equations were calculated by including up to ten variables in i n i t i a l backward stepwise regression equations. These two series of functional relationships were tested by incorporating them into a model developed for ca l c u l a t i n g buffer capacities to selected pH end points. It was found that for 2 8 s o i l samples of widely varying properties, c o r r e l a t i o n c o e f f i c i e n t s between the standard and predicted LR values were highly s i g n i f i c a n t . Such a procedure might be used to construct buffer curves for s o i l s of varying properties. f+6 INTRODUCTION Several factors have been commonly held responsible for the buffering action of s o i l . Of these organic matter, exchangeable A l and Fe, and A l and Fe hydroxy interla y e r s and coatings have been most frequently studied and discussed. Jackson (1963) proposed f i v e components as being primarily responsible f o r buffering i n s o i l s low i n organic matter. + + These were: ( i ) exchangeable H or H^ O ( i i ) exchangeable A l ( H 2 0 ) + + + ( i i i ) p o s i t i v e hydroxy A l polymers (iv) r e s i d u a l weaker hydroxy A l polymers, and (v) aluminosilicate d i s s o l u t i o n reactions. I t has been shown that exchangeable A l i s the pre-dominant exchangeable component of aged a c i d i f i e d clays and that no s i g n i f i c a n t amounts of H 30 +-clay exists because H 30 +-clays spontaneously change to Al-clays on aging (Low, 1955, Chernov, 195 9, Coleman and Craig, 19 61). The same i s presumably true for acid s o i l s . Exchange a c i d i t y i s generally extracted with neutral s a l t (McLean, 1965). Schwertman and Jackson (1964) and Volk and Jackson (1964) distinguished the t h i r d buffer range by t i t r a t i n g a c i d i f i e d clays and s o i l s i n neutral s a l t solutions. Other studies have demonstrated p r e c i p i t a t i o n of hydroxy Al and Fe i n synthetic cation exchangers (Po Ho Hsu and Rich, 1960) and formation of interlayers and coating on aluminosilicate clays (Rich, I960; Coleman and Thomas, 1964; Coleman et a l . , 1964). Such interlayers and coatings block exchange s i t e s , reduce neutral s a l t exchange-able a c i d i t y and increase buffering i n the pH range 5 to 8. The nature and contribution of organic matter to pH dependent a c i d i t y i s s t i l l somewhat undefined. The work of Martin and Reeve (1960), Martin (1960), and Schnitzer and 3 + Wright (1960) suggested that Al and Fe ions or hydroxy Al and Fe ions were primarily responsible. Whether d i r e c t deprotonation of functional groups such as carboxyls, phenols, etc. contribute s i g n i f i c a n t l y to pH dependent a c i d i t y appears uncertain. Regardless of the nature of the contribution of organic matter the magnitude of i t s buffering e f f e c t at higher pH values i s important. McLean et a l . (1965) i n studying extractable A l , CEC and organic matter i n t e r r e l a t i o n s h i p s of several Ohio s o i l s concluded that organic matter was primarily responsible for the high pH component of s o i l a c i d i t y . Sawhney et a l . (1970) described a procedure for determining the magnitude of the contribution of the two pH-dependent CEC components of s o i l : a) weakly dissociated organic matter groups and, b) sesquioxide coatings on clay mineral surfaces or p a r t i a l l y neutralized complexes of A l and Fe i n the interla y e r s of 2:1 layer s i l i c a t e s . On the basis of r e s u l t s obtained by t h i s procedure for s o i l s having organic matter contents i n the range 0.2 to 6.6% they concluded that pH dependent CEC and therefore pH dependent a c i d i t y was a r e s u l t primarily of weakly dissociated protons of organic matter. 48 The foregoing has shown that components of d i f f e r e n t r e l a t i v e acid strengths buffer s o i l s . Therefore r e l a t i v e amounts of these components would be expected to influence the amount of liming material required to neutralize s o i l s to a prescribed pH value. For example, a s o i l low i n exchangeable Al and organic matter but with considerable amounts of hydroxy Al and Fe would require very l i t t l e liming material to neutralize exchangeable A l and the pH dependent a c i d i t y due to organic matter but r e l a t i v e l y more to neutralize the hydroxy A l and Fe. Amounts and proportions of these components vary from s o i l to s o i l . Inadequacies of the single a c i d i t y related s o i l properties, pH, CEC, per cent base saturation (%BS) and per cent base unsaturation (%BUS) for predicting lime requirement of s o i l s have been discussed by Pionke et a l . (1968). Using the ApHx%OM function proposed by Kenny and Corey (196 3) and in addition ApHx%clay, KC1 exch. A l and nonexch. A l , Pionke et a l . (1968) found an equation by multiple regression analyses for lime requirement to pH 6 as follows: LR = 0.47 + 0.97 ApHx%0M + 0.03 ApHx%clay + 1.73 exch. A l + 0.5 3 nonexch. A l In deriving such a regression equation better r e s u l t s are obtained i f regression of the dependent variable on a l l independent variables i s l i n e a r over the range to 49 which the equation applies. It would seem that such a condition would be most clo s e l y met i n the case of LR as the dependent variable when only LR for a range corresponding to the range of buffering of the included independent v a r i -ables i s being considered. Buffer curves f o r a number of samples studied were non-linear i n the range from the natural s o i l pH to pH 6, 6.5 or 6.8, etc., values often used as desired end pH values i n s o i l liming practices. This i s as would be expected i f components of d i f f e r e n t acid strengths are present. I t was thought a series of equations would be an improvement over a single equation to predict lime requirement for widely varying s o i l s and that an improved prediction could be made by adding the predicted values from a series of equations, one for each of a series of segments of a buffer curve which exists for a l l s o i l s . The study described here was conducted to ( i ) determine the buffering capacity of a number of s o i l s within a series of buffer ranges ( i i ) determine which of a number of operationally defined components singly or i n combinations, would explain to the greatest degree, v a r i a t i o n of LR within the above ranges and ( i i i ) develop a model for predicting lime requirement using the multiple regression equations which incorporate as independent variables those components found to be related to buffering i n each of the several buffer regions. 50 MATERIALS AND METHODS Soils Surface and subsurface horizons of a number of s o i l s as described by Wiens (197 0) were chosen to represent considerable v a r i a t i o n with respect to parent material, organic matter content, a c i d i t y , amorphous Fe and Al content and texture. As far as could be determined none had received lime applications f o r a number of years. Lime Requirements Discontinuous Ca(0H) 2 t i t r a t i o n s were carried out by adding varying increments of standardized, saturated or nearly saturated Ca(0H)2 to flasks containing 5.0 g of a i r dry s o i l and enough solution to make a t o t a l volume of 100 ml. The flasks were stoppered and placed on a wrist action shaker for 15 hours. C0 2 was passed through the suspensions for 3 minutes, followed by a i r for approximately 3 0 minutes. Measurements of pH were made with a calomel and glass electrode couple with the reference junction i n the supernatant solution and the glass electrode i n the suspension, following s e t t l i n g of the suspension for 1 hour. S o i l Properties S o i l pH measurements were made i n d i s t i l l e d water (1:1 s o i l to water) and 0.01M CaCl 2 (1:2 s o i l to C a C l 2 ) , suspensions. Carbon was determined by the induction furnace 51 method (Laboratory Equipment Corporation, 1959). Exchangeable Al and Fe were extracted by leaching 100 ml of 1 N KC1 through 10.0 g s o i l over a period of 2 hours and extractable A l and Fe were extracted with 1 N NH^OAc, pH 4.8 as described by McLean (1965). Acid ammonium oxalate extractable A l and Fe were extracted using the method of McKeague and Day (1966). Pyrophosphate d i t h i o n i t e and pyrophosphate extractions were carried out as described by Franzmier et a l . (1965). Cation exchange capacities (CEC) were determined by the NH^OAc pH 7.0 method (Chapman, 1965), where NH^+ adsorbed i s determined by Kjeldahl d i s t i l l a t i o n . Lime potential (LP), corrected lime potential (CLP), CEC and %BS were determined as described by Clark (1965). This procedure involved e q u i l i b r a t i n g aerated s o i l samples with 0.01 M CaCl^ f o r 5 days, determining Ca, Mg, Al on the supernatant solutions a f t e r centrifugation, washing with water and then replacing exchangeable cations with Na + using 2 N NaCl. CEC i s defined as Ca+Mg+Al replaced and %BS i s defined as one hundred times Ca+Mg/Ca+Mg+Al. A l l quantitative elemental analysis were carried out using a Perkin-Elmer 303 spectrophotometer except for A l in Clark's procedure for CEC, %BS, LP and CLP. The Eriochrome cyanine R.A. method (Jones and Thurman, 1957) was used i n thi s case. Calcium, Mg, Mn and Fe determinations were made using an acetylene-air mixture and A l determinations were made using an acetylene-N20 mixture as f u e l when the spectrophotometer was used. 52 S t a t i s t i c a l Analysis S t a t i s t i c a l analysis was carried out using an IBM 360/67 computer and e x i s t i n g c o r r e l a t i o n and simple and stepwise regression routines (INMSDC, SIMREG and STPREG respectively) of the Triangular Regression Package (TRIP) program stored i n the University of B r i t i s h Columbia Computing Centre program l i b r a r y . The stepwise regression procedure used i s commonly ca l l e d backward stepwise regression. The input for t h i s procedure was a c o r r e l a t i o n matrix inverted with respect to a l l p o t e n t i a l independent variables along with means and standard deviations. This resulted i n the i n i t i a l equation with a l l p o t e n t i a l independent variables included. Elimination of variables was continued as long as the extra regression sums of squares due to i n c l u s i o n of at least one variable present i n the equation was not s i g n i f i c a n t at the 0.05 l e v e l . RESULTS AND DISCUSSION Results of analysis of s o i l s f o r a c i d i t y related properties, and exchangeable and extractable components are given elsewhere (Wiens, 1970). It can be seen that i n general there was a considerable range i n each of the properties measured. Differences between CEC measured by neutral s a l t extraction and the NH^OAc pH 7.0 method were substantial i n most cases i n d i c a t i n g that a large portion of the exchange capacity of the s o i l s was pH-dependent. Several of the samples, however, were found to be low i n %BS when t h i s was calculated 53 as defined by Clark (1965), and therefore high i n exchangeable a c i d i t y . These s o i l s had very low pH values. Measures of the amorphous Fe and A l (acid ammonium oxalate extractable) and organic matter associated Fe and A l (pyrophosphate extractable) also ranged f a i r l y widely. Relationships between s o i l properties and LR As stated the objectives of t h i s study were i n part to determine relationships between s o i l properties and buffer capacities or LR as determined by Ca(OH) 2 t i t r a t i o n s i n a number of pH buffer ranges. Correlation c o e f f i c i e n t s were calculated between various measured properties and these LR values. These are given i n Table 1. Several trends become apparent. Correlations between pH(H 20) and pH(CaCl 2) and LR values were progressively poorer as the pH of the end point of the buffer ranges increased. The same held true f o r LP and CLP. These measures therefore could be only moderately good i n predicting LR to pH 5.0, 5.5 or 6.0 and r e l a t i v e l y poor beyond th i s point. Highly s i g n i f i c a n t c o r r e l a t i o n c o e f f i c i e n t s (1% level) were found for these measures with %BS of e f f e c t i v e neutral s a l t exchangeable CEC, as well as with KC1-A1 and KCl-Fe and non-significant correlations with %BS of NH^OAc CEC. This indicated t h e i r r e l a t i o n s h i p to neutral s a l t exchangeable a c i d i t y and lack of r e l a t i o n to pH-dependent a c i d i t y . KC1 exchangeable Fe and 2 N NaCl exchangeable A l were the two variables found to be most highly Table 1. Correlat ion coeff ic ients between selected s o i l properties and Ca(OH)2 t i t r a b l e ac id i ty i n a number of pH buffer ranges end point pH of buffer range from pH of s o i l buffer range pH l i m i t s 5.0 5.5 6.0 6.5 7.0 7.5 5.0-5.5 5.5-6.0 6.0-6.5 6.5-7.0 7.0-7.. pH(H20) -.5263 -.5578 -.5270 -.4884 -.4562 -.3591 -.4167 -.3370 -.2542 -.1945 .0084 P H(CaCl 2 ) -.5636 -.5564 -.5525 -.4774 -.4134 -.2701 -.4143 -.3881 -.1945 -.2193 .1040 LP -.5871 -.4843 -.5237 -.4429 -.3676 -.2399 -.3123 -.4209 -.1645 -.1653 .0929 CLP -.6725 -.4309 -.4588 -.3177 -.2130 -.1861 -.2026 -.3606 .0017 .0026 -.0282 CEC(CaCl 2) -.0798 -.2438 -.3098 -.3259 -.3327 -.3674 -.2653 -.3013 -.2298 -.2706 -.1773 CEC(NH40Ac) -.1397 -.0500 -.0107 .1142 .1955 .1040 -.0869 .0892 .2522 .2837 -.0904 % BS -.7881 -.7503 -.6882 -.4645 -.2895 -.0899 -.5447 -.4132 .0276 .0564 .2453 % BS -.1876 -.1593 -.1637 -.2561 -.2941 -.3545 -.1054 -.1220 -.2953 -.2907 -.2085 % C .2412 .4101 .5044 .7242 .8372 .7064 .3927 .4746 .7758 .8350 .0670 % clay .0865 .2013 -.2547 -.3675 -.4306 -.4613 -.2088 -.2466 -.3955 -.4370 -.2049 KC1 A l .5106 .3853 .4919 .3879 .3717 .3098 .2267 .4809 .0963 .2638 .0230 KC1 Fe .8295 .5671 .4786 .2855 .1343 -.0192 .2946 .2314 -.0969 -.1391 -.2198 NH.OAc A l 4 .2298 .2099 .1931 .3391 .3744 .3555 .1477 .0778 .4541 .3486 .0989 NH.OAc Fe 4 .6969 .6538 .6183 .4849 .3462 .1192 .4695 .3961 .1155 .0464 -.2732 NH.OAc Mn 4 -.1850 -.1464 .0224 .1700 .3941 .5209 .0906 .2235 .3203 .6685 .3592 Oxalate A l .2611 .1349 -.0126 .1213 .2332 .3892 -.0381 .1414 .2698 .3623 .3534 Oxalate Fe .0104 .0362 .1327 .4086 .5372 .6095 -.0402 .2130 .6565 .6262 .3147 Pyro d i th A l .1755 .3393 .4918 .5183 .5181 .0777 .5128 .5371 .3648 .4053 -.5838 Pyro d i th Fe .1283 .1261 -.0610 .0381 .1759 .3731 -.2222 .0366 .1669 .3592 .4049 Pyro d i th Mn -.2451 -.1956 -.0291 .0907 .3259 .4590 -.1221 .1840 .2300 .6334 .3461 Pyro A l .0519 .0950 .2733 .3719 .4941 .7226 .0930 .4136 .3778 .5824 .5713 Pyro Fe .2427 .1213 .2058 .3944 .5396 .7191 .0303 .2503 .5215 .6548 .5021 Pyro Mn -.1073 -.0043 .1851 .2305 .4570 .6051 .0484 .3646 .2114 .7215 .4185 Signi f icant cor re la t ion coeff ic ients are: >.4484 (5%); >.4965 (1%) 55 correlated with LR to pH 5.0. It i s also of note that c o r r e l a t i o n of %C with LR increased as the LR pH end point increased. In the pH ranges 5.0 - 5.5 and 5.5 - 6.0, pyrophosphate d i t h i o n i t e extractable components were those most highly correlated with LR. In the buffer ranges above pH 6.0, pyrophosphate extractable A l and Fe, as well as exalate extractable components were most highly correlated. Ammonium acetate pH 4.8, pyrophosphate d i t h i o n i t e and pyro-phosphate extractable Mn were s i g n i f i c a n t l y correlated with LR i n the range pH 7.0 - 7.5 Derivation of relationships between s o i l properties and LR. Simple and multiple stepwise regression analysis was used to determine functional relationships between LR i n d i f f e r e n t ranges and measured s o i l components, such that the greatest degree of v a r i a t i o n of LR was explained by measured components. Two series of regression equations were calculated. The f i r s t series of equations was calculated a f t e r choosing independent variables f o r the i n i t i a l equations on the basis of the magnitude of the c o r r e l a t i o n c o e f f i c i e n t s between buffer capacities i n various ranges and measured quantities of various a c i d i t y related s o i l properties. The i n i t i a l , as well as f i n a l equations, following stepwise regression f o r the f i r s t series are given i n Table 2. 2 Multiple c o e f f i c i e n t s of determinations (R ) gave the degree of v a r i a t i o n explained by the regression of the independent variables on LR. I t can be seen that i n the range between Table 2. I n i t i a l and f i n a l equations calculated by simple and stepwise mult iple regression analysis - series I Regression equations R 2 Y l = 0.68 - 0.02 (NaCl A l ) 0.742 * Y2 = 3.889 + 0.0056 (NH40Ac/4.8Fe) + 1.556 (PD Al) + 0.208 (%C) - 0.045 (%-B.S.) 0.496 + = 4.409 + 1.915 (PD Al ) - 0.047 (% B.S.) 0.467 Y3 -0.475 +0.0399 (KC1 Al) + 0.0308 (NH 40Ac/4.8 Fe) + 2.038 (PD Al ) 0.433 = -0.542 + 0.0497 (KC1 Al ) +• 2.077 (PD Al) 0.422 Y4 = -0.369 + 2.404 (Ox Fe) + 0.0140 (NH 40Ac/4.8 Al) + 0.895 (%C) - 0.018 (% clay) 0.649 = 0.732 + 1.202 (%C) 0.602 Y5 = 0.57 + 1.850 (OxAl) - 1.883 (Ox Fe) + 0.116 (NH 40Ac/4.8 Mn) + 1.332 (%C) 0.800 = 0.753 + 0.102 (NH 40Ac/4.8 Mn) + 1.333 (%C) 0.770 Y6 = 2.065 + 0.328 (KC1 Mn) - 8.635 (PD Al) + 6.146 (PD Fe) - 0.0602 (PD Mn) 0.686 5.42 + 0.321 (KC1 Mn) - 9.130 (PD Al) 0.669 Y l - LR to pH 5.0 NaCl A l - A l extracted with 2N NaCl. Y2 - LR to pH 5.5 NH OAc/4.8 A l - A l extracted with NILOAc buffered at pH 4.8. Y3 - LR to pH 6.0 Mn - Mn extracted with NH OAc buffered at pH 4.8. Y4 - LR to pH 6.5 Fe - Fe extracted with NH40Ac buffered at pH 4.8. Y5 - LR to pH 7.0 PD A l - A l extracted with pyrophosphate d i t h i o n i t e . Y6 - LR to pH 7.5 Mn - Mn extracted with pyrophosphate d i t h i o n i t e . Fe - Fe extracted with pyrophosphate d i t h i o n i t e ; KC1 A l - A l extracted with IN KC1 (100 ml/10 g) . Mn - Mn extracted with IN KC1 (100 ml/10 g) . Fe - Fe extracted with IN KC1 (100 ml/10 g) . Ox A l - A l extracted with acid ammonium oxalate, pH 3.0. Fe - Fe extracted with acid ammonium oxalate, pH 3.0 * I n i t i a l equation + f i n a l equation 57 pH 5 and pH 6 the degree of v a r i a t i o n explained by regression was r e l a t i v e l y smaller than i n the other ranges. It appeared that the influence of neutral s a l t extractable or low pH a c i d i t y i n buffering s o i l s was diminishing and the pH dependent a c i d i t y active i n t h i s range had not r e a l l y been measured by variables included. The pH buffer range 6.5 to 7.0 has the greatest degree of v a r i a t i o n explained by regression. The second series of equations were calculated by including as independent variables i n the i n i t i a l stepwise regression equations, up to ten measured s o i l properties expected to be a c i d i t y r e l a t e d . By the elimination stepwise regression procedure, least s i g n i f i c a n t variables were excluded. Table 3 gives the i n i t i a l and f i n a l equations. As i n series I, 2 R i s the lowest f o r both i n i t i a l and f i n a l equations calculated for the buffer ranges between pH 5.0 and 6.0. Of i n t e r e s t were the variables on which LR was found to be s i g n i f i c a n t l y regressed. Normal KC1 exchangeable Fe was included i n equations for the f i r s t two buffer ranges but exchangeable A l was not. This was unexpected as exchangeable A l i s the component which has been almost exclusively held responsible for buffering due to exchange a c i d i t y . Also to be noted i s the importance of pyrophosphate extractable A l . It was found to be a s i g n i f i c a n t contributor i n equations for a l l ranges except the pH range 6.0 - 6.5 McKeague (1967) has suggested that the pyrophosphate extraction for Fe and A l i s s p e c i f i c for that associated with organic matter. Thus i t i s suggested that organic matter associated A l was neutralized over e s s e n t i a l l y Table 3. I n i t i a l and f i n a l regression equations calculated by stepwise mul t ip le regression analysis - series I I . Regression equations R' * Y l = -0.372 - 0.322 (Ox Al) - 0.056 (Ox Fe) + 0.079 (KC1 Fe) + 0.002 (Kcl A l ) + 0.233 (%C) -0.658 (PD Fe) - 0.920 (PD Al) - 1.560 (P Fe) + 4.560 (P Al ) 0.870 + = -0.011 + 0.077 (KC1 Fe) + 0.199 (%C) - 0.766 (PD Al) 0.823 Y2 = 1.912 - 3.794 (Ox Al) + 3.058 (Ox Fe) 0.089 (KC1 Fe) - 0.053 (KC1 Al) - 4.655 (PD Fe) 2.423 (PD Al) - 6.270 (P Fe) + 25.824 (P Al) 0.528 = 0.268 + 2.330 (PD Al) 0.263 Y3 -0.445 - 3.520 (Ox Al) + 2.801 (Ox Fe) + 0.044 (KCl Fe) - 0.0014 (KCl A l ) - 0.502 (PD Fe) + 2.35 (PD Al) - 8.292 (P Fe) +27.74 (P Al ) -0.022 - 2.137 (Ox Al ) + 2.728 (PD Al) + 15.509 (P Al ) 0.584 0.501 Y4 = 1.300 - 1.876 (Ox Al) + 3.947 (Ox Fe) - 0.00028 (KCl Fe) - 0.0523 (KCl A l ) + 0.827 (%C) -3.114 (PD Fe) + 0.819 (PD Al) + 1.908 (P Fe) + 9.514 (P A l ) 0.707 = 0.732 + 1.202 (%C) 0.602 Y5 = -0760 + 2.152 (Ox Al) - 9.330 (Ox Fe) - 0.05 (KCl Fe) - 0.036 (KCl A l ) + 1.589 (%C) +7.492 (PD Fe) + 2.041 (PD Al) + 13.375 (P Fe) - 0.686 (P Al ) -0.827 - 4.956 (Ox Fe) - 0.0866 (KCl Fe) + 1.415 (%C) + 6.956 (PD Fe) + 2.079 (PD Al ) +9.262 (P Fe) 0.905 0.877 Y6 = 1.640 + 6.057 (Ox Al ) - 3.202 (Ox Fe) - 0.018 (KCl Fe) +0.031 (KCl Al ) + 0.830 (PD Fe) -10.019 (PD Al) + 13.837 (P Fe) + 23.074 (P Al ) 0.878 = 2.112 + 4.179 (Ox Al ) - 10.745 (PD Al) + 40.30 (P Al) 0.854 Ox Ox A l Fe - A l extractable with acid ammonium oxalate, pH 3.0 P Fe - pyrophosphate extractable Fe Fe extractable with acid ammonium oxalate, pH 3.0 P A l - pyrophosphate extractable A l KCl Fe - Fe extractable with IN KCl (100 ml/100 g) KCl A l - A l extractable with IN KCl (100 ml/10 g) * i n i t i a l equation % C - per cent carbon determined by dry combustion + f i n a l equation PD Fe - Fe extractable with pyrophosphate d i th ion i t e PD A l - A l extractable with pyrophosphate d i th ion i t e 59 the whole pH range to 7.5. Development and tes t i n g of a model incorporating functional  relationships To predict LR for a number of d i f f e r e n t s o i l s with varying i n i t i a l pH values using the above derived r e l a t i o n -ships a series of computations i n proper sequence must be performed. A simple procedure or model i s outlined i n the form of a flow chart given i n Figure 1. I t i s arranged for convenience of writing a FORTRAN computer program. The procedure e s s e n t i a l l y involves three parts: ( i ) c a l c u l a t i o n of predicted buffer capacities for the series of pH ranges from previously derived functional relationships between LR and measured s o i l properties, ( i i ) determination of the pH range of the i n i t i a l s o i l pH and modification of the magnitude of the predicted buffer capacity of thi s range depending on actual s o i l pH,(>arfd ( i i i ) c a l c u l a t i n g by summation the LR to various pH end points. It should be noted that although the flow chart given in figure 1 indicates LR i s calculated to pH 7.5, the procedure can be cut short i f c a l c u l a t i o n to a lower pH value i s desired. With minor modifications, c a l c u l a t i o n of LR to any desired pH between the one-half units as indicated could be made. A FORTRAN program was written to calculate LR values by t h i s procedure and res u l t s were compared to those found by Ca(OH) 9 t i t r a t i o n . Table 4 gives a summary of r e s u l t s . 60 ( S T A R T ) read values/ of variables Xa, Xb. V Y l = f ( X a , Xb...) / Y 2 = f ( X a , Xb...) / Y 3 = f ( X a , Xb.. .) \ / Y 4 = f ( X a , Xb. . .) f Y 5 = f ( X a , X b . ) Y 6 = f ( X a . X b . ) Y E S Y 4 = 0 Y E S Y 5 = 0 v NCK Y 2 = 5 . 5 - soil pH > NO-v Y 3 = 6 . 0 - s o i l pH ->© LR to pH 5 . 0 = Y l LR to pH 5.5 = LR-*o.0+Y2i LR to pH 6 . 0 = LR->5.5+Y3 3E LR to pH 6.5 = L R » 6 . 0 + Y 4 | LR to pH 7.0 = LR->6.5+Y5 LR to pH 7.5 = LR->7.0-fYS ' print LR 'values t o , /various pHs Figure 1. Flowchart of the procedure f o r c a l c u l a t i n g lime requirements to selected pH values Table 4. Summary of comparison of Ca(0H) 2 t i t r a t i o n predicted by the model LR values and LR values pH end point mean Ca(OH) LR value Series 2 pH(H20) 1 I : l + Series pH(H20) I 1:20 + Series pH(H20) I I l : l + Series I I pH(H20) 1:20 + Mean LR Corr. Coef, Mean LR Corr. Coef. Mean LR Corr. Coef. Mean LR Corr. Coef. meq/100 g meq/lOOg meq/lOOg meq/lOOg meq/lOOg 5.0 0.55 0.26 .9155 0.23 .9276 0.3711 .9187 0.3711 0.8461 5.5 1.95 1.01 .7709 1.03 .7585 0.690 .6641 0.7161 0.6138 6.0 3.62 2.25 .7498 2.13 .7708 0.9257 .5864 1.94 0.8086 6.5 6.91 5.39 .7773 5.17 .8065 4.06 .7614 4.99 0.8414 7.0 11.81 9.99 .8555 9.76 .8703 4.14 .8292 9.64 0.9076 7.5 16.15 13.96 . 7576 13.53 .7764 13.42 .8615 13.69 0.9043 + ra t ios of s o i l to water used i n measurement of i n i t i a l s o i l pH S ign i f ican t cor re la t ion coeff ic ients are: J .4484 (5%); ^>.4965 (1%) ON 62 It can be seen from the means that on the average, the model underestimated LR to a l l pH end points. Correlations to a l l end points were highly s i g n i f i c a n t (1% l e v e l ) . However, i t appears a l o g i c a l improvement could be made by incorporating the equations used i n series I to predict LR to pH 5 and 5.5 into the model instead of those calculated i n series I I . It can be seen that the degree of assoication i s closer between CaCOH^ t i t r a t i o n LR and the values predicted when pH measured in a 1:20 s o i l to solution r a t i o was used rather than pH measured i n a 1:1 s o i l to water r a t i o . The relationships were i n i t i a l l y derived from measurement i n a 1:20 r a t i o and therefore t h i s r e s u l t was anticipated. For p r a c t i c a l a p p l i c -ation a factor to account for the difference i n pH values between measurements in a 1:1 s o i l to water r a t i o and i n a 1:20 s o i l to water r a t i o might be incorporated. Had more samples been used i n deriving the i n i t i a l functional r e l a t i o n s h i p s , i t i s reasonable to assume that the r e l a t i o n s h i p between standard and predicted LR values might be even closer. Additional investigations using other l i m i t s for buffer ranges might also r e s u l t i n better regression equations. I t would seem that a model of t h i s kind can be used i n constructing buffer curves for s o i l s with widely varying properties. 63 LITERATURE CITED 1. Chapman, H.D. .1965 . Cation exchange capacity. Iri CA. Black (ed.). Methods of s o i l analysis. I I . Chemical and microbiological properties. Amer. Soc. Agron., Inc., Madison, Wise. 2. Chernov, V.A. 1959. Genesis of exchangeable aluminum i n s o i l s . Soviet S o i l S c i . 113: 25-33. 3. Clark, J.S. 1965. The extraction of exchangeable cations from s o i l s . Can. J . S o i l S c i . 45: 311-322. 4. Coleman, N.T. and Doris Craig. 19 61. The spontaneous a l t e r a t i o n of H-clay. S o i l S c i . 91: 14-18. 5. , Coleman, N.T. and G.W. Thomas. 1964. Buffer curves of acid clays as affected by the presence of f e r r i c i ron and aluminum. S o i l S c i . Soc. Amer. Proc. 28: 187-190. 6. Coleman, N.T., G.W. Thomas, F.H. leRoux and G. Bredell. 1964. Salt exchangeable and t i t r a b l e a c i d i t y i n bentonite sesquioxide mixtures. S o i l S c i . Soc. Amer. Proc. 28: 35-37. 7. Franzmier, D.B., B.F. Hajek, and CH. Simonson. 1965. Use of amorphous material to i d e n t i f y spodic horizons. S o i l S c i . Soc. Amer. Proc. 29: 737-734. 8. Jackson, M.L. 1963. Aluminum bonding i n s o i l s : A unifying p r i n c i p l e i n s o i l science. S o i l S c i . Soc. Amer. Proc. 27: 1-10. 9. Jones, L.H. and D.A. Thurman. 19 57. The determination of aluminum i n s o i l ash and plant materials using Eriochrome cyanine R.A. Plant and S o i l 9: 131-142. 10. Kenny, D.R. and C B . Corey. 1963. Factors a f f e c t i n g lime requirements of Wisconsin s o i l s . S o i l S c i . Soc. Amer. Proc. 27: 27 7-2 80. 11. Laboratory Equipment Corporation. 1959. Instruction manual f o r operation of LECO carbon determinations. St. Joseph, Mich., USA. 12. Low, P h i l i p F. 195 9. The r o l e of aluminum i n t i t r a t i o n of bentonite. S o i l S c i . Soc. Amer. Proc. 19: 135-139. 13. Martin, A.E. 1960. Chemical studies of podzolic a l l u v i a l horizons: V. Flocculation of humus by f e r r i c and ferrous iron and n i c k e l . J . S o i l S c i . 11: 382-393. 64 14. Martin, A.E. and R. Reeve. 1960. Chemical studies of podzolic a l l u v i a l horizons. IV. The f l o c c u l a t i o n of humus by aluminum. J . S o i l S c i . 11: 369-381. 15. McKeague, J.A. 1967. An evaluation of 0.1 M pyrophosphate and pyrophosphate d i t h i o n i t e i n comparison with oxalate as extractants of the accumulated products of podzols and some other s o i l s . Can. J . S o i l S c i . 47: 95-99. 16. McKeague, J.A. and J.H. Day. 1966. D i t h i o n i t e - and oxalate-extractable Fe and A l as aids i n d i f f e r e n t i a t i n g various classes of s o i l s . Can. J . S o i l S c i . 46: 13-22. 17. McLean, E.O. 1965. Aluminum. In C.A. Black (ed.). Methods of s o i l analysis. I I . Chemical and microbiological properties. Amer. Soc. Agron., Inc., Madison, Wise. 18. McLean, E.O., D.C. Reicosky and C. Lakshmanan. 1965. Aluminum i n s o i l s . VII. Interrelationships of organic matter, liming, and extractable aluminum with "permanent charge" (KC1) and pH-dependent cation exchange of surface s o i l s . 19. Pa Ho Hsu and C.I. Rich. 196 0. Aluminum f i x a t i o n i n a synthetic cation exchanger. S o i l S c i . Soc. Amer. Proc. 24: 21-25. 20. Pionke, H.B., R.B. Corey and E.E. Schulte. 1968. Contribution of s o i l factors to lime requirement t e s t s . S o i l S c i . Soc. Amer. Proc. 32: 113-117. 21. Sawhney, B.L., CR. Frink and D.E. H i l l . 1970. Components of pH-dependent cation exchange capacity. S o i l S c i . 101: 272-278. 22. Schnitzer, M. and J.R. Wright. 1960. N i t r i c acid oxidation of the organic matter of a podzol. S o i l S c i . Soc. Amer. Proc. 24: 273-277. 23. Schwertman, U. and M.L. Jackson, 1964. The influence of hydroxy aluminum ions on pH t i t r a t i o n curves of hydroxy-aluminum clays. S o i l S c i . Soc. Amer. Proc. 28: 179-183. 24. Volk, V.V. and M.L. Jackson. 1964. Inorganic pH-dependent exchange charge of s o i l s . Clays and Clay Minerals, 12th Conf. Pergamon Press, London, pp 281-295. 25. Wiens, J.W. 1970. Evaluating a c i d i t y of selected B r i t i s h Columbia s o i l s . M.Sc. Thesis. COMPARISON OF ORGANIC MATTER DESTRUCTION BY HYDROGEN PEROXIDE AND SODIUM HYPOCHLORITE AND ITS EFFECTS ON SELECTED MINERAL CONSTITUENTS ABSTRACT The destruction of organic matter from widely d i f f e r e n t s o i l s was evaluated by using hydrogen peroxide and sodium hypochlorite oxidation procedures. The amounts of extractable S i , Mn, Al and Fe were determined on the residues following treatment with the oxidizing agents by using acid ammonium oxalate and 0.5 N NaOH extraction procedures. In addition, the amount of S i , Mn, Fe and Al in the extracting solutions was also determined. It was found that NaOCl extracted more organic matter with less destruction of the oxides than procedures employing H^O^. This was substantiated s t a t i s t i c a l l y using the t-te s t as applied to paired values. Three treatments with NaOCl were concluded to be s a t i s f a c t o r y for destruction of organic matter with minimum removal of S i , Mn, Fe and A l . 66 INTRODUCTION The destruction of organic matter i n s o i l s i s a common pretreatment for s o i l s p r i o r to physical, chemical and mineralogical analyses. Methods employed have attempted to destroy organic matter completely with minimum destruction or a l t e r a t i o n of the inorganic f r a c t i o n . There have been attempts also to s e l e c t i v e l y destroy organic matter p r i o r to chemical measurements, such as cation exchange capacity, i n order to assess the ro l e that organic constituents play i n a f f e c t i n g these properties. Because of the d i v e r s i t y of objectives for the removal of organic matter no universal extractant has been developed. The extractant for maximum destruction of organic matter to f a c i l i t a t e study of inorganic components, or to attri b u t e s o i l properties to organic matter by difference, has most commonly been hydrogen peroxide (Jackson, 19 56; He l l i n g et a l . , 1964; McLean et a l . , 1965; McLean and Owen, 1969; M i t c h e l l , Farmer and McHardy, 1964). Several problems associated with the use of hydrogen peroxide as a pretreatment for s o i l s have been pointed out by various workers. Jackson (19 56) has shown that H 20 2 can cause di s s o l u t i o n of Mn02. E x f o l i a t i o n of mica can be caused by H 20 2 treatment (Drosdoff and Miles, 1938). Formation of calcium oxalate i n s o i l s by treatment with H 20 2 has been discussed by several workers (Martin, 19 54; Farmer and M i t c h e l l , 196 3; Bourget and Tanner, 19 53). Dissolution of 67 sesquioxides during peroxide treatment has been the subject of some discussion. M i t c h e l l et a l . (1964) made the point that amorphous material by i t s very nature i s subject to attack or a l t e r a t i o n by peroxide and cautioned the use of peroxide when amorphous inorganic material i s to be studied. Williams et a l . (19 58) showed that phosphate sorption was highly correlated with acid ammonium oxalate (Tamm's reagent) extractable aluminum and iro n . Removal of organic matter by peroxide appeared to s o l u b i l i z e large amounts of iron and aluminum and the residue remaining l o s t much of i t s phosphate sorption capacity. Farmer and Mi t c h e l l (196 3) found consider-able amounts of oxalato-aluminum and o x a l a t o - f e r r i c complexes i n peroxide extracts of s o i l clays, e s p e c i a l l y i n clays with a high content of X-amorphous components. Anderson (196 3) has suggested the use of NaOCl solutions, adjusted to pH 9.5, for the destruction of organic matter. He indicated that NaOCl was more e f f e c t i v e i n destroying organic matter than was peroxide and that the NaOCl method was less destructive than peroxide to sesqui-oxides, s i l i c a coatings or c r y s t a l l i n e clay components. It was the purpose of t h i s study to compare the effectiveness of organic matter destruction by ^2^2 a n <^ NaOCl and the r e l a t i v e amounts of S i , A l , Fe and Mn removed from several s o i l s . 68 MATERIALS AND METHODS The s o i l samples used i n thi s study were selected A, B and C horizons from f i v e s o i l s of varying pedogenic development. The samples were chosen to represent v a r i a t i o n with respect to percent carbon, percent amorphous aluminum and i r o n , texture and parent material. Selected c h a r a c t e r i s t i c s and c l a s s i f i c a t i o n of the s o i l s are presented i n Table 1. Hydrogen peroxide treatment of the s o i l s was carried out i n two ways, namely: (1) Five g s o i l were placed into a 100 ml centrifuge tube, and 10 ml of water and 1 ml of 30% H2O2 were added. The suspension was placed i n a water bath f o r 15 minutes at 60-70°C. The sample was subjected to centrifugation and the supernatant solution decanted. This treatment was repeated f i v e times and i s referred to as H2O2 I. (2) Ten g s o i l were placed i n a 250 ml centrifuge b o t t l e , 20 ml of water and 5 ml of 30% H2O2 were added. The reaction was allowed to proceed at room temperature and then at 6 0-70°C i n a water bath. When the reaction had subsided, the treatment was repeated u n t i l no further v i s i b l e reaction could be detected by addition of more U^O^' An additional 5 ml of ^ 0 2 was added and the s o i l was allowed to digest for 3 hours. Fifteen ml of sat-urated NaCl were added, the suspension s t i r r e d , subjected to centrifugation and washed several times with water. This Table 1 - - C l a s s i f i c a t i o n and selected c h a r a c t e r i s t i c s of s o i l s Textural S o i l s Class pH Oxalate extractable Al Fe Citrate d i t h i o n i t e extractable Fe C l a s s i f i c a t i o n Canadian* Approx. U.S.D.A. Abbotsford Ap Bir Alouette Ap Cloverdale Ap C Langley Ap Whatcom Ap Bir s i l 5.35 2.42 1.00 0.76 1.00 s i c l 5.05 0.84 0.78 0.35 0.68 s i c l s i c l 5.9 8.6 si c 5. 3 4.88 0.22 0.46 0.26 0. 86 0.42 8.88 1.20 1.50 0.73 0.72 1.44 1 5.25 6.90 0.67 0.99 0.70 s i l 5.80 2.60 1.68 1.20 0.85 Mini Humo-Ferric Typic Haplorthod Podzol or Haplic Cryorthod s i l 4.12 28.84 1.02 0.78 0.30 Orthic Gleysol Humic Eluviated Gleysol Typic Haplaquept or Typic Cryaquept Mollic Albaqualf or Argic Cryaquoll Humic Eluviated Mollic Albaqualf Gleysol or Argic Cryaquoll Bisequa Mini Humo-Ferric Podzol A l f i c Haplorthod or B o r a l f i c Cryorthod •'Canadian C l a s s i f i c a t i o n , 196 8 •U.S.D.A. Comprehensive System, 1960 and 1967 CD ID 70 treatment i s r e f f e r r e d to i n t h i s paper as H^ O^  I I . This i s a modification of Jackson's (1956) method where the s o i l s are not buffered at pH 5 with NaOAc. This was considered unnec-essary since most of the s o i l s used had pH values near 5 (Table 1). Sodium hypochlorite treatment was performed as outlined by Anderson (1963). This procedure involved treating 5 g s o i l samples i n 100 ml centrifuge tubes with 10 ml NaOCl solution (minimum 6% available chlorine) which had been adjusted to pH 9.5 immediately p r i o r to use. This treatment was repeated up to f i v e times, heating the suspension i n a b o i l i n g water bath f o r 15 minutes during each treatment and decanting the supernatant solution a f t e r centrifugation. During a l l procedures the supernatant solutions were saved for selected elemental analyses. The o r i g i n a l s o i l s and residues following each of the three treatments were extracted f o r amorphous Fe, A l , Mn and S i by the acid ammonium oxalate procedure (McKeague and Day, 1966). S i m i l a r l y , extraction of the s o i l s and the residues was carried out using 0.5 N b o i l i n g NaOH (Jackson, 1965) to give a measure of amorphous aluminosilicates. The extracts (supernatant solutions) from ^2^2 a n <^ NaOCl treatments and acid ammonium oxalate extractions were analyzed for Fe, A l , Mn and S i . The extracts from the NaOH treatment were analyzed for A l and S i . 71 Elemental analysis was carried out by atomic absorption spectrophotometry, using a Perkin-Elmer 303 spectrophotometer, with an air-acetylene gas mixture for Mn and Fe and ^O-acetylene for Si and A l . Carbon analyses, as a measure of organic matter content, were carried out by dry combustion using a high temperature induction furnace ( A l l i s o n et a l . , 1965). The t - t e s t of significance as applied to paired values was used to compare differences between treatments. This method i s used when the number of samples i s limited and the variations between pairs i s greater than v a r i a t i o n between units within p a i r s . The assumptions are that the sample pairs are random and the population variances are equal. Computations involved c a l c u l a t i n g differences between control and treatment members of paired observations and the mean of these differences as well as the variance. The p r o b a b i l i t y of finding a larger difference was then determined by t e s t i n g the significance of the t-value calculated from the formula: where x i s the mean of the differences, n i s the number of observations, and s i s the variance of the differences. Analyses were carried out using an IBM 360-67 computer at the University of B r i t i s h Columbia Computing Centre and 72 the t - t e s t subroutine of the Triangular Regression Program (TRIP) i n the Computer Program Library. RESULTS AND DISCUSSION With the exception of the Langley Ap sample, NaOCl treatment removed more organic carbon than did the ^ 2 ^ 2 treatments (Table 2). This greater e f f i c i e n c y of NaOCl was a consistent trend and was i n agreement with results of Anderson (1963) although not found to be s t a t i s t i c a l l y s i g n i f i c a n t (Table 6). The reason for the greater e f f i c i e n c y was not cl e a r . The electrode pot e n t i a l of NaOCl at pH 9.5 i s , however, greater than the electrode potential for ^ 2 ^ 2 (Anderson, 1963). This should indicate that NaOCl at pH 9.5 i s a more powerful oxidizing agent than i s H 2 O 2 . The lack of s t a t i s t i c a l s i g nificance may be a r e s u l t of limited sampling of s o i l s with large variations i n the amounts of native % organic C (Table 2). The Langley, Cloverdale and Alouette are poorly drained, c u l t i v a t e d s o i l s with high amounts of well decomposed organic matter i n intimate association with the mineral s o i l . Consequently, i t i s probably d i f f i c u l t to oxidize the organic matter. The amounts of acid ammonium oxalate extractable S i 0 2 ) Mn, Fe and A l i n residues a f t e r treatment are shown i n Table 3. Higher values were obtained for oxalate extractable S i 0 2 , Mn, Fe and A l i n the residues a f t e r NaOCl treatment than i n residues a f t e r H o 0 o treatments. 73 Table 2—Organic carbon i n s o i l and remaining i n residue a f t e r treatment Organic carbon „ ., . S o i l 5xNaOCl 5xH_0.I H o0 oII S o i l series 2 2 2 2 Abbotsford Ap 2.42 0.38 1.34 0.48 Bi r 0.84 0.19 0.67 0.36 Alouette Ap 28.84 19.40 25.80 20.67 Cloverdale Ap 4.88 0.93 1.13 0.94 C 0.22 0.17 0.17 0,15 Langley Ap 8.88 3.02 2.52 1.72 Whatcom Ap 6.90 1.23 1.79 1.47 Bir 2.60 0.26 1.74 1.20 Mean 6.94 3.19 4.39 3.37 Table 3—Oxalate extractable S i 0 2 , Mn, Fe, and A l in residues af t e r treatments S i 0 2 Mn Fe Al S o i l series 5x NaOCl 5x H 20 2I H 20 2II 5x NaOCl 5x H 20 2I H 20 2II 5x NaOCl 5x H 20 2I H 20 2II 5x NaOCl 5x H 20 2I H 20 2II Abbotsford ppm Ap Bi r 0. 64 6.57 0.60 0.51 0.47 0.55 266 46 202 30 131 27 0.73 0.33 0.68 0.31 0.38 0.23 0.97 0.60 0.86 0.70 0.83 0.77 Alouette Ap 0.11 0.02 0.02 3 6 7 0.49 0.77 0.16 0.57 0.36 0.11 Cloverdale Ap C 0.12 0.37 0.08 0.32 0.08 0.27 73 356 134 352 80 354 0.87 0.47 1.18 0.39 0.53 0.19 0.44 0.30 0.30 0.26 0.27 0.23 Langley Ap 0.20 0.12 0.15 680 148 138 1.11 1.79 0.89 0.70 0.66 0.62 Whatcom Ap B i r 0.24 0.92 0.13 0.92 0.10 0.69 640 680 236 536 182 400 1.13 1.22 1.16 1.12 0.58 0.60 0.72 1.60 0.45 1.80 0.34 1.45 Mean 0.40 0.34 0. 29 343 206 165 0.79 0.93 0.45 0.74 0.67 0.58 - J 75 S t a t i s t i c a l l y the differences between NaOCl and H 20 2 treatments were s i g n i f i c a n t at the 1% l e v e l i n the case of S i 0 2 and Fe, and at the 5% l e v e l i n the case of Mn and A l . The difference between NaOCl and H 20 2 I treatments was s i g n i f i c a n t at the 1% l e v e l i n the case of S i 0 2 (Table 6). These re s u l t s indicated that the inorganic components extractable by oxalate were less affected by NaOCl than by H 20 2. It i s possible that the Fe and A l were s o l u b i l i z e d to a greater degree by NaOCl at the r e l a t i v e l y high pH, reprecipitated as hydroxides and subsequently extracted by acid ammonium oxalate, thereby leading to higher values of oxalate extractable A l and Fe i n NaOCl than i n H 20 2 residues. However, evidence presented i n Table 7 does not appear to substantiate t h i s i nterpretation. It can be seen from Table H that with few exceptions the amounts of S i 0 2 , Mn, Fe and A l dissolved by the NaOCl were lower than the amounts dissolved by the H 20 2 solutions. S t a t i s t i c a l analysis showed that S i 0 2 , Mn and A l removed by the H 20 2 II treatment was s i g n i f i c a n t l y greater (5% level) than that removed by the NaOCl treatment (Table 6). Also, S i 0 2 removed by the H 20 2I treatment was s i g n i f i c a n t l y greater (1% level) and Fe and A l s i g n i f i c a n t l y greater (5% le v e l ) than that removed by the NaOCl treatment. Extractable amounts of S i 0 2 and Al^O^ using 0.5 N NaOH are presented i n Table 5. Amounts of S i 0 9 extracted Table 4--SiO,,, Mn, Fe and Al i n extracts a f t e r treatments SxNaOCl 5 x H 2 ° 2 I H 2 ° 2 1 1 S o i l series SiC>2 Mn Fe A l S i 0 2 Mn Fe A l S i 0 2 Mn Fe Al Abbotsford Ap Bir 126 0.4 0.7 29 0 81 134 590 406 0.8 5.6 61 3 1885 197 503 250 163 32 140 18 1800 600 Alouette Ap 429 0.6 708 1660 825 1.4 1216 3125 3275 10 7175 11500 Cloverdale Ap C 134 281 5.0 0.1 87 0 165 0 1219 1786 22.6 2.6 852 126 3505 271 1200 187 118 30 1650 38 4000 60 Langley Ap 182 4.6 147 520 1886 31.1 737 3625 2325 150 1850 8000 Whatcom Ap Bir 365 199 15.6 0.5 193 10 630 19 1326 465 106.5 22.8 460 13 2810 325 1625 200 625 318 2025 20 5750 1200 Mean 245 3.4 147 401 1063 24.2 433 1968 1196 180 .6 1614 4114 - J CO 77 were greater f o r the residues following H^ O^  treatments than for residues a f t e r NaOCl treatments. This was also found for A l when comparing the NaOCl and ^2®2 * treatment residues. However, the reverse was observed i n comparison of A l extracted following NaOCl and H 20 2 II treatments. The p o s s i b i l i t y of using NaOCl adjusted to lower pH values, more si m i l a r to the natural s o i l pH, was considered. It was thought that the higher electrode potentials at lower pH values might r e s u l t i n oxidation of more organic matter and d i s s o l u t i o n of smaller amounts of inorganic amorphous constituents. Sodium hypochlorite solutions with pH adjusted to successively lower values were prepared and the electrode potentials were measured. These solutions were reacted with various s o i l samples. An example of some of the c h a r a c t e r i s t i c s of the solutions, extracts and residues following treatment of the Whatcom-Ap are presented i n Table 7. It can be seen (TAble 7) that the % C remaining i n the residue as well as the amount of extracted Fe i n the solution was lowest at pH 9.5. These res u l t s confirm Anderson's (1963) convictions that pH 9.5 was optimum for organic matter destruction with minimum destruction of oxides and x-ray i d e n t i f i a b l e minerals. From the foregoing NaOCl was accepted as a more suitable reagent than H_09 f o r 78 Table 5—0.5 N NaOH e x t r a c t a b l e S i 0 2 and A 1 2 0 3 i n s o i l and i n r e s i d u e s a f t e r treatments S o i l 5xNa0Cl 5 x H 2 ° 2 I H 2 ° 2 1 1 S o i l s e r i e s S i 0 2 A 1 2 0 3 S i 0 2 A 1 2 0 3 S i 0 2 AlJOg S i 0 2 A 1 2 0 3 A b b o t s f o r d Ap 2.55 6.95 1.62 5.59 2.17 5.70 2.40 3.42 B i r 2.18 6.04 1.30 4.00 1.62 4.79 1.30 2.28 A l o u e t t e Ap 8.25 6.27 3.00 4.00 15.30 3.49 16.70 1.40 C l o v e r d a l e Ap 6.62 7.97 3.97 5.02 7.76 7.29 6.25 3.98 C 3.60 3.00 2.64 2.46 3.98 3.36 3.60 1.88 Langley Ap 4.90 7.18 2.24 6.72 7.28 8.61 6.10 4.27 Whatcom Ap 2.80 9.07 1.23 3.48 3.33 5.13 3.10 2.66 B i r 3.34 7.06 1.78 8.83 3.50 11.52 3.25 5.70 Mean 4.28 6.69 2.22 5.01 5.61 6.24 5.29 3.20 Table 6 — S t a t i s t i c a l l y s i g n i f i c a n t differences between residues, residues and s o i l s , and extracts of treatments oxalate 0.5 N NaOH Extract content extractable extractable differences differences differences Carbon Treatment pairs difference S i 0 2 Mn Fe A l S i 0 2 Mn Fe A l S i 0 2 A l S o i l 1 " - 5xH 0 I * N.A. N.A. N.A. N.A. - - - - - -So i l 1 " - 5xNaOCl * N.A. N.A. N.A. N.A. - - - - ft S o i l 1 " - H 20 2 II * N.A. N.A. N.A. N.A. & ft ft ft ft - ftft 5xNaOCl-5xH20 2 I ftft - ft ft ft ft - - - - ftft 5xNa0Cl-H 20 2 II ft ft - ft ft ft ft ft* ft - ftft S o i l indicates untreated '^Significant at the 5% l e v e l ^ ^ Significant at the 1% l e v e l N.A. Not applicable -Not s i g n i f i c a n t 80 Table 7--Reagent, extract and Whatcom Ap residue c h a r a c t e r i s t i c s at various pH values NaOCl C i n residue solution Electrode af t e r Fe i n pH potentials treatment extracts V % ppm 9.5 + 0. 95 1.92 126 8.5 1.10 2 .40 160 7.5 1.18 3.52 323 6.5 1.27 3.66 389 5.5 1.33 4.20 343 4.5 1.38 3.68 292 81 lO.Or WHATCOM Ap CLOVERDALE Ap WHATCOM Bir ABBOTSFORD Ap I 2 3 4 NO. OF TREATMENTS Figure 1. % carbon remaining In s o i l following successive treatment with NaOCl 82 rapid routine destruction of s o i l organic matter p r i o r to oxide determinations or chemical and mineralogical analyses. To investigate carbon removal as a function of repeated NaOCl treatments, selected s o i l s were treated with NaOCl as stated previously. Following each treatment (up to 5) the amount of carbon remaining i n the residue was determined. The r e s u l t s are presented i n Figure 1. On the basis of the r e s u l t s presented i n Figure 1 for H s o i l samples i t can be seen that most of the s o i l carbon i s removed afte r three treatments. A study with 16 s o i l samples showed that up to 9 8% of the oxidizable s o i l carbon was removed by three successive NaOCl treatments. Three treatments were proposed by Anderson (1963). Since the additional amount of organic matter removed a f t e r three treatments i s minimal and that with each additional treatment more inorganic components are s o l u b i l i z e d , three treatments with NaOCl appear to be j u s t i f i e d for organic matter destruction from a wide variety of s o i l s with minimum destruction of oxide constituents. Highly organic s o i l s may require add i t i o n a l treatments. For mineralogical or p a r t i c l e size investigations the s o i l sample i s , thus, la r g e l y free of organic cementing agents and i s also Na-saturated and i n the dispersed state. The eff e c t of NaOCl at pH 9.5 on other chemical and mineralogical composition requires further study. 83 LITERATURE CITED 1. A l l i s o n , L.E., W.B. Bollen, and Moodie, CD. 1965. Total carbon. In CA. Black (ed.). Methods of s o i l analysis. Agronomy 9: 1316-1366. 2. Anderson, J.U. 1963. An improved pretreatment f o r mineralogical analysis of samples containing organic matter. Clays and Clay Minerals 10: 3 80-3 88. 3. Bourget, S.J., and C B . Tanner. 1953. Removal of organic matter with sodium hypobromite for p a r t i c l e -size analysis of s o i l s . Can. J. AGr. S c i . 33: 579-585. 4. Drosdoff, M. and Miles, E.F. 1938. Action of hydrogen peroxide on weathered mica. S o i l S c i . 46: 391-395. 5. Farmer, V.C, and B.D. M i t c h e l l . 1963 . Occurrence of oxalates i n s o i l clays following hydrogen peroxide treatment. S o i l S c i . 96: 221-229. 6. H e l l i n g , CS., G. Chesters, and R.B. Corey. 1964. Contribution of organic matter and clay to s o i l cation-exchange capacity as affected by the pH of the saturating solution. S o i l S c i . Soc. Amer. Proc. 28: 517-520. 7. Jackson, M.L. 1956. S o i l chemical analysis—Advanced course: Published by the author, University of Wisconsin, Madison, Wisconsin. 8. Jackson, M.L. 1965. Free oxides, hydroxides, and amorphous aluminosilicates. Iii CA. Black (ed.). Methods of s o i l .analysis. Agronomy 9 : 578-603 . 9. Martin, R.T. 1954. Calcium oxalate formation i n s o i l from hydrogen peroxide treatment. S o i l S c i . 77: 143-145. 10. McKeague, J.A., and J.H. Day. 1966. D i t h i o n i t e -and oxalate-extractable Fe and A l as aids i n d i f f e r e n t i a t i n g various classes of s o i l s . Can. J. S o i l S c i . 46: 13-22. 11. McLean, E.O., D.C Reicosky, and C. Lakshmanan. 1965. Aluminum i n s o i l s : VII. Interrelationships of organic matter, liming, and extractable aluminum with "permanent charge" (KCl) and pH-dependent cation exchange capacity of surface s o i l s . S o i l S c i . Soc. Amer. Proc. 29: 374-378. 84 12. McLean, E.O., and E.J. Owen. 1969. Effects of pH on the contributions of organic matter and clay to s o i l cation exchange capacities. S o i l S c i . Soc. Amer. Proc. 33: 855-858. 13. M i t c h e l l , B.D., V.C. Farmer, and W.J. McHardy. ^1964. Amorphous inorganic materials i n s o i l s . Adv. Agron. 16: 327-383. 14. National S o i l Survey Committee (Canada). 1968. Report of the 7th Nat 11. Meet. Edmonton. Can. Dept. Agr. Ottawa. 15. S o i l Survey St a f f . 1960. S o i l c l a s s i f i c a t i o n , A comprehensive system. 7th Approximation and 1967 Supplement, U.S.D.A., Washington, D.C. 16. Williams, E.G., N.M. Scott, and M.J. McDonald. 1958. S o i l properties and phosphate sorption. J . S c i . Food AGr. 9: 551-559. 85 SUMMARY Incubation of s o i l s with CaC0 3 and t i t r a t i o n with Ca(0H>2 showed that CaCOH)^ t i t r a t i o n underestimated lime requirements f o r most s o i l s used. This was due at least i n part to the suspension e f f e c t as pH measurements were made i n a r a t i o of 1:2 ( s o i l to water) i n the case of CaCO^ incubations and i n a r a t i o of 1:20 ( s o i l to water) i n the case of the Ca(0H)2 t i t r a t i o n s . Evaluation of the Shoemaker, McLean and Pratt buffer method and the Woodruff buffer method for use with the s o i l s of the present study, showed these methods to be rather unsuitable. The buffer pH depression was small per unit lime requirement and the scatter of i n d i v i d u a l points about the c a l i b r a t i o n l i n e was large, leading to p o s s i b i l i t i e s of large errors i n predicting lime requirements. Investigations into the nature of the a c i d i t y of these s o i l s showed a s i g n i f i c a n t c o r r e l a t i o n between pH, lime pot e n t i a l and corrected lime p o t e n t i a l and measures of exchangeable a c i d i t y . Correlations between pH, lime p o t e n t i a l , and corrected lime p o t e n t i a l and measures of pH-dependent a c i d i t y were non-significant. Aluminum exchangeable with 1 N KCl did not account for a l l a c i d i t y t i t r a b l e to pH 5 as determined by CaCOg incubation. Measures of pH-dependent a c i d i t y were largest for horizons highest i n % C and for some podzolic B horizons high i n A l and Fe extractable with acid ammonium oxalate. I 86 Oxalate extractable amounts of A l and Fe were greater than the amounts of these elements extractable with 0.1 M Na-pyrophosphate. Amounts of these elements extractable with both of these extractants appeared to be related at least to a certain extent to pH-dependent a c i d i t y . Stepwise multiple regression analysis equations derived to predict buffer capacities, explained v a r i a t i o n of buffer capacity below pH 5 and above pH 6 reasonably well. Between pH 5 and 6, however, components related to buffer capacity apparently were not measured, or the ranges used were poorly defined with respect to the range of buffering of the components measured. The model combining the series of regression equations to predict lime requirement i n d i f f e r e n t buffer equations, appeared to be a good o v e r a l l approximation, considering the limited number of samples used to derive the equations and to test the model. Such a model might be used to construct buffer curves for a number of widely varying s o i l s . The NaOCl method compared to the peroxide method for s e l e c t i v e removal of organic matter appeared promising. It was found that i n general more organic matter was removed by t h i s method and that the content of oxalate extractable A l , Fe, Si02 and Mn i n the residues was s i g n i f i c a n t l y greater a f t e r treatment with NaOCl than af t e r treatment with H„0 o. Studies 87 employing t h i s method f o r removal of organic matter p r i o r to t i t r a t i o n before and a f t e r extraction with acid ammonium oxalate were inconclusive. This was a r e s u l t of uncertainties with respect to the nature of the saturation of the exchange complex. More work of t h i s nature using t h i s method appears to be necessary. APPENDIX I Chemical properties of s o i l s incubated with reagent grade CaCOg for a period of f i f t e e n and one-half months 1 N KCl S o i l Series Lime increment Mean* pH CEC %B.S. L • P • c • L • P « A l Fe Mn E a s i l y + reducible Mn Abbotsford tons/acre 0 2 4 6 8 10 12 14 5, 6. 6, 6, 7, 7, 7, 7 , 59 31 62 95 16 22 41 41 meq/lOOg 6.11 7.91 9.11 10.39 10.39 10.99 11.17 12.37 99.17 99.12 100.0 100.0 100.0 100.0 100.0 100.0 3 4 4, 5 6 5, 6 5 89 51 96 63 02 83 07 96 3 , 4, 4, 5, 6, 5, 6 5, 89 92 96 63 02 83 07 96 30.4 12.4 2.1 12.4 11.6 ppm 46 , 8, 4, 1, 1, 1, 1, 1, 45.5 57.0 51.7 49.5 47.0 38.2 38.3 39.0 Alouette 0 2 4 6 8 10 12 14 16 18 3, 3, 3 , 3, 3, 4, 4, 4, 4, 4, 70 65 86 84 87 05 22 30 61 62 8.09 9.21 10.85 11.26 13.53 14.17 15.90 18.30 19.93 20.57 27.81 51.69 56.68 74.68 80.47 90.90 94.23 97.11 98.26 98. 85 2 , 2, 3 , 3, 3 , 3, 3, 3, 3, 4, 71 59 08 11 28 12 30 22 59 06 3 3, 4 4 4 4 4 4 4 4 71 75 10 15 24 27 44 51 58 75 1240.0 1090.0 740.0 710.0 580.0 395.0 260.0 104.0 87.0 47.0 24.8 22.7 17.0 17.9 18.0 15.2 15 14 13.0 13 . 0 Cloverdale 0 2 4 6 8 10 12 14 4 4 4 5, 5, 5, 6 6 21 35 84 35 55 99 25 51 6.13 8.53 10.17 15.75 15.69 18.31 20.73 20.84 79.57 96.74 98. 81 99.79 99.79 99.92 99.87 99.89 3 3 3, 3, 3, 4 4 4 11 38 47 95 95 13 78 75 4, 4, 4. 3, 3, 4, 4, 4, 00 15 46 95 95 13 78 75 63.9 14.0 32.8 12.5 9 11.4 9 -0 -3 -37.0 23.6 7 , 3 , 1, 2, 12 6 10 3 3 2 16.0 23.0 27.5 28 .8 21.0 22.0 18.0 18.8 o o CO Lime S o i l Series increment Mean* pH CEC %B.S. L • P • C.L.P. 1 N KC1 Easily" 1" reducible A l Fe Mn Mn tons/acre Langley 0 4.94 2 5.13 4 5.38 6 5.57 8 5.79 10 5.96 12 6.25 14 6.43 16 6.50 Monroe 0 4.57 2 5.29 4 6.00 6 6.59 8 7.07 10 7.19 12 7.34 14 7.36 Ryder 0 5.10 .2 5.77 4 6.17 6 6.68 8 7.00 10 7.27 12 7.43 14 7.55 meq/lOOg 13. 61 99. 45 3. 59 4. 54 15. 41 99. 51 3. 57 4. 76 18. 40 99. 66 3. 64 4. 66 21. 19 100. 0 3. 82 4. 96 23. 01 99. 89 3. 83 3 . 83 21. 45 100. 0 3. 93 3. 93 25. 69 100. 0 4. 01 4. 01 32. 89 100. 0 4. 42 4. 42 25. 69 100. 0 4. 99 4. 99 7. 77 98. 48 3. 50 4. 45 10. 09 100. 0 3. 88 5. 01 11. 59 100. 0 4. 20 4. 95 13. 43 99. 97 4. 89 5. 18 14. 26 99. 95 5. 94 5. 94 15. 13 99. 91 5. 99 5. 99 15. 67 100. 0 6. 10 6. 10 14. 96 100. 0 6. 04 6. 04 4. 34 93. 27 3. 84 4. 81 8. 12 99. 29 3. 71 4. 77 9. 65 99. 83 5. 32 5. 21 11. 52 97. 95 4. 42 5. 07 13. 61 100. 0 4. 39 4. 39 14. 04 99. 90 5. 65 5. 65 13. 25 99. 88 6. 00 6. 00 13. 77 99. 91 6. 06 6. 06 ppm 27.3 12. 2 5.1 29.0 10.0 12. 2 4.5 23.0 6.1 11. 9 3.8 23.0 4.6 11. 9 3.1 20.8 2.4 11. 9 2.2 19.5 4.2 11. 9 1.8 18.0 3.1 9. 8 1.6 17.5 - 12. 8 1.5 11.2 - 11. 4 1.3 -35.2 12. 10 47.0 44.0 2.5 - 8.6 53 .8 1.0 - 5.3 50.3 - - 2.3 48.9 - - 2.2 48 .2 - -• 2.1 36.8 - - 1.8 55.7 - - 1.8 40.6 12.8 12. 4 6.5 60.8 4.9 11. 9 3.0 43 .8 2.4 - 1.4 39.8 2.4 - 1.2 54. 5 2.4 - 1.2 26.0 0.5 - 1.2 27.4 - - 1.2 27 .7 — • — 0.9 28.5 1 N KCl S o i l Series Lime increment Mean* PH CEC %B.S. L.P. C.L.P, A l Fe Mn Easily" 1" reducible Mn Spetifore tons/acre 0 2 4 6 8 10 12 14 16 18 4.00 4.34 4.75 5.04 5 5 6 6 6 6 30 67 44 48 62 70 meq/lOOg 6.77 15.91 9.01 11.13 13.18 13.04 8.28 17.11 17.44 19.10 47.59 100.0 94.60 98.44 99.92 100.0 76.99 99.92 100.0 100.0 82 71 31 57 76 22 30 95 73 09 3 5 4 4 4 4 4, 4, 5, 6, 91 02 40 51 57 76 18 95 69 09 680.0 400.0 101.5 40.0 8.9 1.9 IS, 15 13, 11, 12, 12, 12, 13, 13.0 12.1 ppm 5, 5, 4, 3, 3 , 2, 1, 1, 1, ,5 ,6 ,2 .5. ,8 ,9 ,4 ,1 ,0 ,3 Whatcom 0 2 4 6 8 10 12 14 ,50 ,70 01 35 67 83 22 52 9.77 10.49 13.26 16.27 16.87 17.90 19.09 96.38 99.24 99.99 99.73 99. 86 99. 97 99.91 99.92 ,35 ,64 , 89 ,71 ,91 ,22 ,39 ,74 4 4 4, 4, 5, 5, 5, 5, 60 76 94 87 16 24 07 31 21.8 29 7 3 3 4 4 4 ,7 ,6 ,8 ,8 ,8 ,7 ,7 14.0 12.4 12.0 11.9 11, 11, 72 50 2 4 2 2 14.0 6.2 102.0 159.0 125.0 128 .0 43.5 85.0 66.8 74.0 *Means of two determinations +Mn extracted with IN NH^OAc (pH 7) + 0.2% hydroquinone by shaking lOg with 100 ml f o r one hour following leaching with IN KCl CO 92 APPENDIX II Discontinuous CaCOH^ t i t r a t i o n curves of s o i l s used i n the present study PH — i — 1 1 1 1 i i i ' • 20 10 0 10 20 30 40 50 60 70 <— HCl j Ca(0H)2 — > (meq/100 g.) I (meq/IOOg.) 00 9 8 PH 20 10 HCl 0 (meq./lOO g.) 10 .20 30 40 Ca(0H)2 > (meq./lOO g.) RYDER 50 60 70 vo 9 r <r- HCl I Ca(OH)2 —> (meq/100 g.) I , (meq/100 g.). t-1 o 

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