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Surface charge properties of selected soils Hendershot, William Hamilton 1978

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SURFACE  CHARGE PROPERTIES  OF SELECTED SOILS  by WILLIAM HAMILTON  HENDERSHOT  B . S c , University of Toronto, 1972 M . S c , McGill University, 1975  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY  in  THE FACULTY OF GRADUATE STUDIES (Department of Soil Science)  We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA June 1978 William Hamilton Hendershot,  1978  In  presenting  this  an a d v a n c e d  degree  the  shall  I  Library  f u r t h e r agree  for  scholarly  by h i s of  this  written  at make  that  it  for  freely  permission  purposes  thesis  in p a r t i a l  the U n i v e r s i t y  may  representatives.  is  financial  University  2075 Wesbrook Vancouver, V6T 1W5  of  British  Place  Canada  June 8,  1978  British  by  for  gain  shall  Columbia  the  that  not  requirements  Columbia,  I  agree  r e f e r e n c e and copying  t h e Head o f  understood  Soil Science  of  of  for extensive  be g r a n t e d  It  fulfilment of  available  permission.  Department The  thesis  of my  copying  t  study.  this  thesi  Department or  publicati  be a l l o w e d w i t h o u t  my  - i -  ABSTRACT The aim of this thesis was to examine the use of surface charge c h a r a c t e r i s t i c s as a measure of pedogenic development in selected s o i l s of the humid, temperate environment of southwestern B r i t i s h Columbia. A secondary objective, using a wider range of s o i l  types, was to gain  further knowledge of the factors which influence the values of ZPC (the zero point of charge) and  (its  displacement from the zero point of  t i t r a t i o n , ZPT), so that these measurements might be better understood. Measurement techniques, using potentiometric t i t r a t i o n , have a s i g n i f i c a n t effect on the values of ZPC and  obtained i n the laboratory.  The fast-adsorption procedure measures the fast reaction taking place at the p a r t i c l e surface, while the slow-adsorption procedure measures the additional slow reaction resulting from the incorporation of H and +  OH" ions into the structure of oxide coatings.  Therefore the values  obtained using the slow-adsorption procedure r e s u l t i n higher ZPC values and lower  values than the fast-adsorption procedure.  NaCl-saturation  of the exchange complex p r i o r to t i t r a t i o n results i n the exchange of strongly bonded ions such as A l ties of the surface.  3 +  and P0 ~ 3  h  and thus alters the proper-  In the case of untreated samples with ZPC values  below pH 5.0 and Oj values less than -0.2 meq/lOOg there was a s h i f t lower ZPC and  to  values; i f the values for the untreated samples were  above t h i s , then the s h i f t was i n the opposite d i r e c t i o n .  The f a s t -  adsorption method using untreated samples i s therefore considered to be the most accurate means of measuring the surface charge properties as they e x i s t in the f i e l d .  - ii -  Indirect evidence suggested that the presence of organic matter caused a decrease i n the ZPC and of simple c o r r e l a t i o n coefficients  values.  This evidence is i n the form  between organic C and a...  The results  of p a r t i a l correlation analysis removing the effect of organic matter indicate strong relationships between ZPC and s o i l age and also between cr.j and s o i l age.  Evidence of this relationship is also supported by  d i r e c t measurement.  The removal of a portion of the organic matter using  a pretreatment of NaOCl resulted i n a s i g n i f i c a n t increase i n both the ZPC and  values.  Potentiometric t i t r a t i o n is a useful measure of surface charge char a c t e r i s t i c s and of s o i l genesis.  In s o i l s with large amounts of clay  minerals, as the sesquioxide content increased the ZPC became better defined and moved to a higher pH and a- approached zero. the values of ZPC and  In sandy s o i l s ,  are only s i g n i f i c a n t l y related to s o i l age when  the effect of s o i l organic matter content has been eliminated.  On the  other hand, the ApH value, defined as the difference between ZPC and pH(KCl), compensates  for differences  good i n d i c a t o r of the extent of s o i l  i n organic matter and provides a development.  iii  -  TABLE OF CONTENTS  1.  INTRODUCTION  1  Li terature Ci ted  2.  3.  4.  THE USE OF ZPC TO ASSESS PEDOGENIC DEVELOPMENT  5  6  Abstract  6  Introduction  7  Materials and Methods  10  Results  11  and Discussion  Conclusions  21  Literature Cited  22  MEASUREMENT TECHNIQUE EFFECTS ON THE VALUE OF ZERO POINT OF CHARGE AND ITS DISPLACEMENT FROM ZERO POINT OF TITRATION  24  Abstract  24  Introduction  25  Materials and Methods  26  Results  26  and Discussion  Conclusions  31  Literature Cited  32  VARIATION IN SURFACE CHARGE CHARACTERISTICS IN A SOIL CHRONOSEQUENCE  33  Abstract  33  Introduction  34  Materials and Methods  35  Results  36  and Discussion  Conclusions  46  Literature Cited  47  - iv -  5.  6.  THE EFFECT OF NaCl-SATURATION AND ORGANIC MATTER REMOVAL ON THE VALUE OF ZERO POINT OF CHARGE Abstract  49  Introduction  50  Materials and Methods  51  Results and Discussion  54  Conclusions  58  Literature Cited  59  SUMMARY AND CONCLUSIONS  APPENDIX  49  61 65  -  V -  LIST OF TABLES  2.1  Morphological properties of three s o i l p r o f i l e s ranging from Dystric Eutrochrept to Spodic Ferrudalf.  12  Organic carbon, p a r t i c l e size a n a l y s i s , and chemical extraction data for the three s o i l s .  14  2.3  Mineralogy of the <2um f r a c t i o n .  16  2.4  pH and ZPC values for the three s o i l s .  19  3.1  Surface charge characteristics of the three s o i l s measured by three different techniques.  27  2.2  4.1  Some chemical and surface charge characteristics of the seven s o i l s studied.  38  4.2  Extractable sesquioxide data f o r  4.3  Selected columns of the correlation matrix.  5.1  Soil c l a s s i f i c a t i o n and sampling location for the ten s o i l s . Soil texture and extractable sesquioxide for the ten s o i l s .  55  pH, surface charge c h a r a c t e r i s t i c s , and total carbon for the ten s o i l s .  56  5.2 5.3  the seven s o i l s .  39 40  52  - vi -  LIST OF FIGURES  2.1  Potentiometric t i t r a t i o n curves showing the r e l a t i o n ship between ZPC, ZPT, IEP(s) and a . 1  2.2  3.1  4.1  4.2 4.3  9  Potentiometric t i t r a t i o n curves of three horizons indicating the three classes of t i t r a t i o n curves.  18  Graph showing the relationship of ZPC and a three s o i l s .  28  i  for the  Showing the r e l a t i o n s h i p between the ZPC and age for the seven s o i l s .  42  Showing the relationship between seven soiIs .  43  and age for the  Showing the relationship between ApH and age for the seven soiIs .  45  ACKNOWLEDGEMENTS  Numerous people in the Department of Soil Science greatly aided my research during the course of my program. thank:  Bev Herman  S p e c i f i c a l l y , I would l i k e to  for drafting and help with the laboratory  analysis;  J u l i e Armanini, Terry Walters and Margaret Holm for laboratory analysis; Bernie von Spindler for photographic reproduction of the figures; Mark Sondheim for help with the s t a t i s t i c a l  analysis; and Donna Farley and  Valerie Marshall f o r typing e a r l i e r drafts of some of the chapters. I would also l i k e to thank Les Lavkulich for his supervision and friendship during the past three years. a great deal by his useful  Glen Singleton has assisted me  c r i t i c i s m of my manuscripts and by allowing  me to include i n my research samples from his study of Cox Bay. Very special  thanks are due to S . E . Stewart, who spent a great deal  of e f f o r t editing my material and typing the f i n a l draft of my t h e s i s . This research would not have been possible without the financial assistance of a Leonard S. Klinck Fellowship from the Faculty of Graduate Studies and the National Research Council  (Grant Number A4463).  - 1-  Chapter One INTRODUCTION  The processes of s o i l genesis operate at the boundary between the s o i l particles and the s o i l s o l u t i o n . from infancy of a spodosol  If we v i s u a l i z e the development  (podzol), for example, then we can trace the  a l t e r a t i o n of the p a r t i c l e surfaces of the parent m a t e r i a l .  Initially  the s o i l solution may be i n d i r e c t contact with the c r y s t a l l i n e surface of the s o i l mineral grains; with time, the most e a s i l y soluble minerals weather through processes such as s o l u t i o n , oxidation, and hydrolysis. Eventually, weathering rinds composed of the least soluble  constituents  of the underlying minerals develop on the surfaces of the s o i l c l e s , subsequently reducing the rate of mineral weathering.  parti-  On minerals  such as quartz, coatings of amorphous material accumulate as a result of p r e c i p i t a t i o n ; iron and aluminum hydrous oxides have been shown to be common agents i n the formation of such amorphous coatings.  The  r e s u l t is that the surface in contact with the s o i l solution changes with time from one composed of c r y s t a l l i n e minerals to one composed of the a l t e r a t i o n products of s o i l weathering. Pedologists  studying s o i l genesis have used different approaches  to study the chemistry of non-crystalline material making up the surfaces of the s o i l  particles.  Since 1922, s e l e c t i v e chemical dissolution  techniques have been employed with considerable success (Mitchell et al.,  1964).  Despite the length of time that these various techniques  - 2 -  have been in use, the exact form of the material extracted i s s t i l l entirely i d e n t i f i e d .  not  Although i n the past this approach has provided a  considerable amount of information on s o i l genesis and is used today as an aid to the c l a s s i f i c a t i o n of s o i l s in Canada and the United States (Canada Soil Survey Committee, 1978; Soil Survey Staff,  1975), the author  believes that r e l a t i v e l y small gains i n knowledge are to be made by f u r ther research along these l i n e s . One of the possible alternative approaches to the study of amorphous coatings on s o i l particles is to study the exchange reactions which take place at the interface between the s o i l particles and the s o i l  solution.  This can be done using the potentiometric t i t r a t i o n technique, which utilizes  the adsorption and desorption of H and OH" ions to measure the +  surface charge c h a r a c t e r i s t i c s .  S p e c i f i c a l l y , the t i t r a t i o n curves at  different ionic strengths cross at a common point, thus defining the zero point of charge (ZPC, the pH at which the net e l e c t r i c charge i s  zero),  and providing a measure of the permanent or pH-independent exchange capacity (a-,-, the displacement of the crossover from the zero point of titration). This technique has been applied to a limited extent to s o i l s of tropical regions (Gallez e_t al_., 1976; Morais et^ al_., 1976; van Raij and Peech, 1972), and to areas of s o i l s developed on volcanic ash (Espinoza et al_., 1975), but only very recently has attention been given to s o i l s of temperate regions (Laverdiere and Weaver, 1977; Laverdiere et al_., 1977).  These researchers have focussed t h e i r attention on the  type of exchange reactions taking place i n these s o i l s .  The present  research attempts to expand the scope of investigation to concepts of soil  genesis.  - 3-  The theory that measurement of ZPC and a- could be used as measures n  of s o i l genesis was suggested by the work of Parks and de Bruyn (1962), who state that the ZPC is the pH of minimum s o l u b i l i t y of pure oxide minerals.  This statement was largely based on empirical evidence,  although theoretical considerations dictate that the amount of hydrolysis  taking place at the surfaces  the ZPC.  of particles w i l l be at a minimum at  In a system containing many different compounds, the ZPC w i l l  be a function of a l l of the surfaces, and the ZPC w i l l indicate the point of minimum s o l u b i l i t y for the whole system.  Using this concept  with s o i l s leads to the hypothesis that as the ZPC of the s o l i d phase approaches the pH of the s o i l s o l u t i o n , the s o l u b i l i t y of the s o i l w i l l approach a minimum and the s o i l the s o i l  particles w i l l approach equilibrium with  solution.  Two experiments were performed to test the hypothesis  that with  increasing pedogenic development the ZPC approaches the pH of the s o i l . In the f i r s t experiment (Chapter Two), morphological and chemical e v i dence of sesquioxide development.  accumulation was used as the measure of pedogenic  In the second experiment (Chapter Four), the additional  evidence of the ages of s o i l s in a dated chronosequence was included. Two additional experiments were performed to evaluate some of the f a c tors which control the values of ZPC and o-j obtained i n the laboratory. In Chapter Three the effects of fast-adsorption and slow-adsorption potentiometric t i t r a t i o n techniques were discussed,  and the effect of  NaCl-saturation of the exchange complex prior to t i t r a t i o n was evaluated. Chapter Five also evaluated the effect of NaCl-saturation; i n addition, d i r e c t evidence is presented regarding the effect of organic matter.  - 4 -  Throughout the t h e s i s , s o i l c l a s s i f i c a t i o n Taxonomy manual (Soil Survey Staff, was two-fold:  according to the Soil  1975) has been used.  The purpose  f i r s t , the chapters presented i n this thesis were written  in a s t y l e suitable for publication in the S o i l Science Society of America Journal (American Society of Agronomy, 1976), and second, the terminology of this system provides more descriptive information than i s provided by the terminology of the Canadian System of Soil cation (Canada S o i l Survey Committee, 1978). the reader, the c l a s s i f i c a t i o n  Classifi-  For the convenience of  according to the Canadian system is  ded in the f i r s t table of each chapter.  inclu-  - 5 -  LITERATURE CITED  1.  American Society of Agronomy. 1976. Handbook and Style Manual. Am. Soc. Agron., Madison, Wisconsin.  2.  Canada S o i l Survey Committee. 1978. The Canadian System of S o i l Classification. Agriculture Canada, Ottawa, Ont. (In press)  3.  Espinoza, W., R.G. Gast, and R.S. Adams, J r . Charge characterist i c s and n i t r a t e retention by two Andepts from south-central C h i l e . Soil S c i . Soc. Am. Proc. 39: 842-846.  4.  G a l l e z , A . , A.S.R. Juo, and A . J . H e r b i l l o n . 1976. Surface and charge c h a r a c t e r i s t i c s of selected s o i l s i n the t r o p i c s . Soil S c i . Soc. Am. J . 40: 601-608.  5.  Laverdiere, M.R., and R.M. Weaver. 1977. Charge characteristics of spodic horizons. Soil S c i . Soc. Am. J . 41: 505-510.  6.  Laverdiere, M . R . , R.M. Weaver, and A. D'Avignon. 1977. Character i s t i c s of the mineral constituents of some a l b i c and spodic horizons as related to their charge properties. Can. J . Soil Sci . 57: 349-359.  7.  M i t c h e l l , B . D . , V . C . Farmer, and W.J. McHardy. 1964. Amorphous inorganic materials in s o i l s . Adv. in Agron. 16: 327-384.  8.  Morais, F . I . , A . C . Page, and C.S. Lund. 1976. The effect of pH, s a l t concentration and nature of electrolytes on the charge c h a r a c t e r i s t i c s of B r a z i l i a n tropical s o i l s . Soil S c i . Soc. Am-; J . ; . 40: 521-527.  9.  Parks, G . A . , and P . L . de Bruyn. 1962. The zero point of charge of oxides. J . Phys. Chem. 66: 967-973.  10.  S o i l Survey S t a f f . 1975. S o i l Taxonomy. No. 436, Washington, D.C. 754 p.  Agriculture Handbook  11.  Van R a i j , B . , and M. Peech. 1972. Electrochemical properties of some Oxisols and A l f i s o l s i n the tropics. S o i l S c i . Soc. Am. Proc. 36: 587-593.  - 6 -  Chapter Two THE USE OF ZPC TO ASSESS PEDOGENIC DEVELOPMENT  ABSTRACT  The pH at the zero point of charge (ZPC) has been used to characterize the electrochemical properties of s o i l s .  To date, most studies  have focussed on s o i l s high in oxides with low p h y l l o s i l i c a t e  content.  The study reported here attempts to use ZPC determinations to charact e r i z e the surface charge characteristics of s o i l s from a temperate region.  Three s o i l s were examined; these ranged in pedogenic develop-  ment, as expressed by s o i l morphology, from a small accumulation of sesquioxides  to a r e l a t i v e l y high one.  The s o i l s were a Dystric Eutro-  chrept, a Typic Ferrudalf, and a Spodic Ferrudalf.  With increased  pedogenic development the ZPC became more c l e a r l y defined and approached the natural pH of the s o i l , and there was a decrease i n the r e l a t i v e significance of the pH-independent charge. measure of pedogenic development.  The ZPC may be used as a  -7  -  INTRODUCTION Previous researchers  (Es pi noza et a]_., 1975; Gallez et al_., 1976;  Laverdiere and Weaver, 1977; Morais e_t al_., 1976; van Raij and Peech, 1972) have examined the surface charge characteristics of a number of s o i l s of varying pedogenic age from d i f f e r e n t parts of the world.  The  evidence presented by these authors suggests that with increased s o i l development, the surface charge c h a r a c t e r i s t i c s of s o i l s in o x i d i z i n g , free leaching conditions become dominantly amphoteric.  In other words,  with increased pedogenic age the pH-dependent charge generated by oxide surfaces tends to become dominant over the pH-independent charge generated by isomorphous substitution in clay minerals. r e s u l t from a combination of factors: s i t e s by amorphous oxides; ( i i )  (i)  This is thought to  blocking of pH-independent  dissolution of clay minerals; and ( i i i )  the increasing predominance of pH-dependent charge surfaces  of amorphous  or c r y s t a l l i n e oxides and hydrous oxides, primarily of iron and aluminum. In discussing surface charge c h a r a c t e r i s t i c s i t is important to c l a r i f y the definitions  of the terms used.  In the recent l i t e r a t u r e  these terms have been used d i f f e r e n t l y by d i f f e r e n t authors.  The ZPC  is the pH at which the net total charge on the s o l i d phase is  zero,  whether the charge arises from pH-independent charge associated with isomorphous substitution or from pH-dependent charge associated with hydroxy*!ated oxide or organic matter surfaces. point of the solid) lated surfaces  The IEP(s)  (isoelectric  is the pH at which the net charge on the hydroxy-  (pH-dependent charge) is zero.  The ZPT (zero point of  - 8 titration)  is the pH or range of pH values resulting from the reaction  of the s o l i d species with the i n d i f f e r e n t e l e c t r o l y t e of varying concentrations 1967).  i n the absence of added acid or base (Figure 2.1)  (Parks,  In a pure oxide system the ZPC, IEP(s), and ZPT are coincident.  In a system containing a source of pH-independent charge, such as clay minerals, the measured ZPC w i l l be different from the IEP(s) of the Hydroxylated surface and the cross-over point w i l l be displaced above or below the ZPT by an amount (a^) equal to the net charge of the permanent (pH-independent) exchange s i t e s . Parks (1967) states that materials with a large pH-independent negative charge w i l l not have a unique ZPC; potentiometric t i t r a t i o n will  not y i e l d a unique cross-over point u n t i l a l l of the net negative  charge has been s a t i s f i e d by added H* ions.  This depresses the ZPC  below the ZPT, and often makes the ZPC unattainable within a range of pH ( i . e . ,  pH above 3) that does not r e s u l t i n an excessive amount of  the oxides being s o l u b i l i z e d .  An accumulation of iron and aluminum  oxides and hydroxides causes the ZPC to approach the ZPT; ultimately, if  the s o i l behaves as a pure oxide system, the ZPC w i l l occur at the  ZPT. The ZPC is the pH at which hydrolysis of the particulate  surfaces  by H or OH" ions is at a minimum; as a r e s u l t , the s o l u b i l i t y of the +  material (in a pure oxide system at least) is also at a minimum (Parks and de Bruyn, 1962).  Using this concept with s o i l s leads to the hypo-  thesis that as the ZPC of the s o l i d phase approaches the pH of the s o i l s o l u t i o n , the s o l u b i l i t y of the s o i l w i l l also approach a minimum and the s o i l particles w i l l approach equilibrium with the s o i l  solution.  FIGURE 2 . 1 :  Potentiometric t i t r a t i o n curves showing the relationship between ZPC, ZPT, IEP(s) and a-j of:  a) a pure oxide system,  and b) a s o i l system with a f i n i t e amount of net charge.  negative  -  10 -  The objective of this study was to test the hypothesis  that with  increased pedological development (increasing amounts of sesquioxides) the ZPC approaches the pH of the s o i l .  In contrast to the s o i l s used  in the studies referred to above, which had a low p h y l l o s i l i c a t e - c l a y content,  the s o i l s i n this case contain high amountsoof clay minerals  (phyllosilicates)  and varying amounts of sesquioxides.  They are deve-  loped from glacio-marine deposits and support a 20- to 30-year-old, second-growth Douglas f i r  forest.  MATERIALS AND METHODS F i e l d Study The three s o i l s were from Vancouver Island, B r i t i s h Columbia, Canada.  The s o i l s examined were:  chrept); the Alberni Series dic  the Saanichton Series  (Dystric Eutro-  (Typic Ferrudalf); the Memekay Series  Ferrudalf) (Day et al_., 1959; Soil Survey S t a f f ,  T975).  (Spo-  S o i l s were  described and sampled i n the f i e l d and the samples were returned to the laboratory for study. Laboratory Procedures Following a i r - d r y i n g , the samples were passed through a 2 mm sieve and this material was used for a l l subsequent determinations.  Soil pH  was measured i n water (1:1,  (1:2,  Peech, p. 922, 1965), 0.01M C a C l  2  Peech, p. 923, 1965), and 1N_ KCl (1:2.5, Hesse, p. 30, 1971). different extractions  of amorphous material were made using:  Three ( i ) sodium  pyrophosphate (p), one overnight extraction at pH 10 (McKeague, 1976); (ii)  acid ammonium oxalate (o), one four-hour extraction at pH 3.0  (McKeague and Day, 1966); and ( i i i )  sodium-citrate, -bicarbonate,  ^dithionite ( c ) ,  extractions  two fifteen-minute  (Mehra and Jackson, 1960).  1(  - 11 -  The extracted Fe and Al were determined by atomic absorption spectroscopy, and pyrophosphate-extractable carbon was determined by the Walkely-Black wet oxidization technique ( A l l i s o n , pp. 1374-1376, 1965). Total s o i l organic carbon was determined by Leco Analyser.  The samples  used for p a r t i c l e s i z e analysis and X-ray d i f f r a c t i o n analysis were pre-treated with sodium hypochlorite to remove organic matter (Lavkulich and Wiens, 1970)  and acid ammonium oxalate (McKeague and Day, 1966)  remove amorphous m a t e r i a l . sieving and pipette analysis  to  P a r t i c l e s i z e analysis was accomplished by (McKeague, 1976).  X-ray d i f f r a c t i o n was  performed on the <2 ym f r a c t i o n of selected horizons (B and C) i n unsaturated random powder mounts and also as oriented aggregate mounts in the Mg-saturated, a i r - d r i e d , and ethylene-glycol-solvated  states,  and K-saturated, a i r - d r i e d , heated to 300°C and 550°C states (Whittig, 1965).  Potentiometric t i t r a t i o n s f o r determination of the ZPC were  done on NaCl-saturated samples using the method of van Raij and Peech (1972).  RESULTS AND DISCUSSION The description of the s o i l s is presented i n Table 2.1.  The  three s o i l s represent a t r a n s i t i o n i n morphological expression varying from a Dystric Eutrochrept to a Spodic Ferrudalf.  In the former, the  colours i n the B22 are r e l a t i v e l y yellow (10YR) and the accumulation of extractable sesquioxides (Table 2.2) was the least of the three  soils.  The Typic Ferrudalf indicates further pedogenic development by the presence of abundant hard concretions, in the B21cn, redder hues and an increased amount of extractable sesquioxides.  The Spodic Ferrudalf  TABLE 2.1: Morphological properties of three s o i l profiles ranging from Dystric Eutrochrept to Spodic Ferrudalf.  HORIZON  DEPTH  COLOUR MOIST  DRY , (crushed)  STRUCTURE  TEXTURE  DYSTRIC EUTROCHREPT (ORTHIC DYSTRIC BRUNISOL) - SAANICHTON SERIES 2-0 0-2 2-33 33-62 62-95 9 5-, 105+  0 Al B21 B22 CI C2g  10YR 2/2 7.5YR.-3/2 7.5YR 4/4 10YR 5/4 10YR 4/3 2.5Y 4/2  10YR 10YR 1QYR 1QYR 10YR 2.5Y  3/3 4/3 6/4 7/3 5/3 6/2  SiL SiL SiL SiCL SiCL  wk. med. granular wk. med. subangular blocky S t . med-coarse subangular blocky S t . coarse platy S t . coarse platy  TYPIC.FERRUDALF (ORTHIC DYSTRIC BRUNISOL) - ALBERNI SERIES 0 B21 n B22 n B23 B3 C C  C  t  2-0 0-5 5-25 25-55 55-73 73-105+  10YR 2/2 5YR 3/2 5YR 4/4 7.5YR 5/4 7.,5YR 5/6 - 2.5Y 5/2 7.,5YR 3/2 - 2.5Y 5/2  10YR 5YR 7.5YR 10YR 2.5Y 2.5Y  4/3 4/3 5.5/4 6/4 7/4 6/3  -  SiC C: HC C. C  mod . med. granular mod . fine subangular blocky mod . med. subangular blocky S t . med. angular blocky S t . coarse platy  SPODIC FERRUDALF (PODZOLIC GRAY LUVISOL) - MEMEKAY SERIES 0 A2 B 21 i r B22ir B23 B3 C t  9-0 0-1 1-12 12-40 '40-50 50-70 70-100  5YR 2,5/2 5YR 3/3 2.5YR 3/4 5YR 4/4 5YR 3/4 2.5YR 4/3 - 5YR 4.5/2 5Y 4/2  5YR 5YR 5YR 7.5YR 7.5YR 2.5Y 5Y  3/3 5/6 5/6 5/6 5/6 6/3 6/2  -  SiL SiL SiL SiL SiL SiL  wk. mod mod mod mod St.  . . . .  fine granular med. granular coarse subangular blocky coarse subangular blocky s t . coarse subangular blocky coarse platy  TABLE 2.1  HORIZON  (cont'd):  CONSISTENCE MOIST  CONCRETION  CUTANS  DRY  DYSTRIC EUTROCHREPT (ORTHIC DYSTRIC BRUNISOL) - SAANICHTON SERIES 0 Al B21 B22 CI C2g  v. f r i a b l e v. f r i a b l e firm v. firm v. firm  soft soft hard hard to v. hard hard to v. hard  few small weak -  few thin clayey dark brown Mn  TYPIC FERRUDALF (ORTHIC DYSTRIC BRUNISOL) - ALBERNI SERIES 0 B21cn B22cn B23t B3 C  friable friable friable v. firm v. firm  s i . hard s i . hard s i . hard hard hard to v. hard  ab. fine to med. hard few med. hard few med. hard  * com. thin clayey * f thin clayey dark brown Mn e w  -  SPODIC FERRUDALF (PODZOLIC GRAY LUVISOL) - MEMEKAY SERIES 0 A2 B21ir B22ir B23t B3 C  -  v. f r i a b l e friable friable friable f r i a b l e to firm v. firm  -  soft s i . hard s i . hard si . hard si . hard to hard hard to v. hard  p l . fine hard few med. hard few med. hard  -  * Personal communications, A . C . Research S t a t i o n , Vancouver, B.C.  thin  * com. clayey * few thin clayey  -  TABLE 2.2:  HORIZON  Organic carbon, p a r t i c l e size analysis, and chemical extraction  ORGANIC C  Sand 2-.5mm  PARTICLE SIZE ANALYSIS SiltClay F. Clay .5-.002mm <.002mm <.0002mm  Fe  PYROPHOSPHATE Al„ C„ n  data for the three s o i l s . OXALATE Fe, AL  CITRATE Fe, Al,  DYSTRIC EUTROCHREPT 0 Al B21 B22  CI  C2g  18.6 9.4 1.7 1.7 • .3 ' .3  7.6 7.4 5.5 1 .9 .8  62.9 67.6 76.6 62.1 60.2  TYPIC FERRUDALF 0 B21cn B22cn B23t B3 C  22. 7. 2, 1.  39.9  16.8 11.9 11.2 18.1 8.2  34,0 28.7 27.8 32.2  - • 11.9 11 .7 22.7 ' 21 .3 7.8 .5  72 0 66.1 55.1 56.8 77.1 78.5  -  -  23.5 25.0 17.9 36.0 39.0  6.4 6.5 4.0 7.7 9.8  -  -  43.3 54.1 60.1 54.1 59.6  8.8 11.3 12.9 5.5 9.0  16.1 22.2 22.2 21.9 21.1 21.0  2.0 3.2 .7 1 .3 2.9 2,8  .21 .37 .40 .25 .07 < •.06  .25 .44 .44 .20 .12 .08  .002 .017 .006 .003 .001 .002  .-5.3 .95 .99 .82 .79 .60  :36 .58 .78 .24 .25 .21  .86 1.28 1.38 .93 1 .26 1.34  .39 .45 .45 .14 .10 .12  .35 .51 .53 .32 .06 .06  .51 .82 .85 .64 .27 .10  .035 .015 .007 .005 .001 .001  .66 1 .21 .78 .98 .66 .74  .64 1 .07 1.06 .80 .63 .51  .95 2.41 2.54 2.01 1.50 1.32  .76 1 .03 1.04 .58 .26 .16  .21 .59 .83 .28 .16 .15 ' .07  .34 .39 .88 >.86 .69 .51 .28  .045 .013 .010 .008 .006 .004 .001  .29 1 .43 1.64 1 .40 1 .12 .79 .57  .34 .48 1.16 2.34 2.02 1 .41 .72  .62 .51 .60 .62 .25 .16 .90  .48 .52 .94 1 .33 1.33 .66 .26  SPODIC FERRUDALF 0 A2 B21ir B22ir B23t B3 C  35.7 4.1 2.6 2.0 1 .5 • .9 .2  (  -  - 15 represents  a degraded A l f i s o l with accumulation of amorphous iron and  aluminum, the presence of hard concretions, the red hues, and the large amounts pf extractable sesquioxides in the B21ir and B22ir horizons, all  of which tend to mask the a l f i c nature of the p r o f i l e . Pyrophosphate, oxalate,  and c i t r a t e extraction data indicate that  the amount of sesquioxide iron and aluminum increased  substantially  from the Dystrtc Eutrochrept to the Typic Ferrudalf and then again to the Spodic Ferrudalf (Table 2.2).  The pyrophosphate-extractable  iron  and aluminum (Fep and Alp) have somewhat different distributions in the three s o i l s .  This is interpreted as indicating a difference i n the  d i s t r i b u t i o n of active organic-complexing agents.  In the Dystric Eutro-  chrept and Spodic Ferrudalf, the maximum accumulations are reeordedfin the B21 horizons, while the Typic Ferrudalf has a r e l a t i v e l y even distribution i n the B21 and B22 horizons.  Oxalate extraction data i n d i -  cate that the maximum amount of amorphous iron compounds is found i n the B21 horizons of a l l three s o i l s ; however, with increased pedogenic development, as inferred from total extractable sesquioxides,  the amor-  phous aluminum content maxima are displaced downwards i n the p r o f i l e . In the present case the Alo maximum is i n the B21 horizon of the Dystric Eutrochrept, evenly d i s t r i b u t e d between B21 and B22 of the Typic Ferrud a l f , and i n the B22 of the Spodic Ferrudalf.  These results  suggest  ahatncreased degree of spodic character with increased p r o f i l e development.  Similar results were obtained from the citrate-extractable  iron  and aluminum data. The mineralogy of representative horizons of the three s o i l s presented i n Table 2.3.  is  X-ray d i f f r a c t i o n has not indicated major -  - 16 -  TABLE 2.3:  HORIZON  Chlorite  Mineralogy of the <2ym f r a c t i o n .  Vermiculite  mite  Quartz  Feldspar  Zircon  DYSTRIC EUTROCHREPT B21  2  3  3  1  2  2  C2g  3  2  2  1  2  2  -  -  2  3  2  2  3  2  2  2  2  2  2  2  2  2  TYPIC FERRUDALF B22cn C  . 2 3  SPODIC FERRUDALF B21ir  2  -  C  2  -  1: Dominant  2: Common  3: Trace  3  ^: None  -indifferences cifically,  i n the mineralogy, although some variations do occur.  Spe-  the amounts of c h l o r i t e in the Dystric Eutrochrept and Typic  Ferrudalf decrease with increasing depth from the B2 to the C horizons, with a corresponding increase i n the i l l i t e and vermiculite content. This trend is not evident i n the Spodic Ferrudalf.  The r e l a t i v e amount  of quartz i n the Dystric Eutrochrept is s l i g h t l y greater than i n the other two s o i l s .  The B22 horizon of the Typic Ferrudalf contains only  a trace of feldspar, whereas this mineral is found in greater quantities i n the other s o i l s .  There is a trend i n each of the p r o f i l e s to have a  lower amount of feldspar i n the B horizon as compared to the C horizon. Potentiometric t i t r a t i o n s Three types of potentiometric t i t r a t i o n curves were encountered in this study.  Type I , represented by Figure 2.2a, shows no cross-over  point of the four t i t r a t i o n curves at different concentrations of the indifferent e l e c t r o l y t e ; therefore the ZPC is undefined.  Type II  (Figure 2.2b) has a d i s t i n c t cross-over point for the three t i t r a t i o n curves at concentrations of 0.1N, 0.01J\[, and O.OOlN^NaCl.  The f a i l u r e  of the l.ON^ NaCl t i t r a t i o n curve to achieve cross-over at the same pH value is an indication that the surface has a lower than expected  net  negative charge at this concentration; the mechanism for this is not known, but i s probably related to the ordering of Na and H ions i n +  the double l a y e r .  +  In this case the ZPC was defined as being the cross-  over point of the three lower concentration t i t r a t i o n curves.  Type III  possessed a c l e a r l y defined ZPC; a l l four of the t i t r a t i o n curves crossed over at very nearly the same point (Figure 2.2c). The ZPC data for the three samples are presented in Table 2.4 and i d e n t i f i e d according to type.  The Dystric Eutrochrept B21 horizon and  FIGURE 2.2:  Potentiometric t i t r a t i o n curves of three horizons indicating the three classes of t i t r a t i o n curves:  a) Type I - no cross-over point; b) Type II - three curves only cross over; and  c) Type III - a l l four t i t r a t i o n curves cross over.  -  TABLE 2.4:  19 -  pH and ZPC values for the three  soils.  i meq/lOOg a  HORIZON  H0 2  .01M CaCl  2  N. KCL  ZPC  pH(KCL)-ZPC  DYSTRIC EUTROCHREPT 0  5.57  5.24  5.01  -  Al  6.11  5.58  5.26  u  B21  5.97  5.19  4.68  4.0 *  B22  5.54  4.56  4.00  u  CI  5.55  4.87  3.83  C2g  6,23  5.48  -10.0  0.68  -  u  -  4.04  u  -  -  -  -  TYPIC FERRUDALF  -  0  5,57  5,11  4.85  -  B21cn  5.62  5.07  4.61  3.9 *  -20.0  0.46  B22cn  5,74  5.00  4.49  4.2 *  -  0.29  B23t  5.10  4.43  3.93  3.65*  -20.0  B3  5.01  4.49  3.70  u  -  -  C  5.54  5.20  3.84  u  -  -  -  9.5  0.28  SPODIC 1FERRUDALF  -  0  4.32  3.55  3.27  A2  4.62  3,83  3.63  B21ir  5.40  4.52  4.34  4.25  -  5.0  0.09  B22ir  5.99  5.26  5.11  5.0  -  2.0  0.11  B23t  6.05  5.32  5.11  4.85  -  2.0  0.26  B3  6.05  5.09  4.74  4.5  -  2.5  0.24  C  6.09  5.02  4.39  4.2 *  -  5.0  0.19  u: Undefined  - : Not determined  -  -  *: Defined by three curves only  - 20 the Typic Ferrudalf B21, B22 and B23 horizons have ZPC values as Type I I .  The a-j values indicate the presence of 9.5 to 20 meq/lOOg  of pH-independent charge in these horizons. demonstrates  defined  The Spodic Ferrudalf  the dominant effect of the pH-dependent charge generated  by the sesquioxide surfaces; the ZPC of the B21ir, B22ir, B23t, and B3 horizons are a l l Type III with r e l a t i v e l y small a-,- values (-2.0  to  -5.0). The +pH(KCl) - ZPC values indicate that the ZPC is approaching the s o i l pH with increased s o i l development.  The B21 horizon of the  Dystric Eutrochrept has a ZPC within 0.68 pH units of the pH(KCl), while the horizons above and below do not have a defined ZPC. A l l of the B2 horizons of the Typic Ferrudalf have a ZPC defined by only three t i t r a t i o n curves, and the difference between the ZPC and the pH(KCl) is between 0.46 and 0.28 pH u n i t s ; the ZPC of the B3 and C horizons are undefined.  The Spodic Ferrudalf, the s o i l with the largest accu-  mulation of extractable iron and aluminum, has a defined ZPC for a l l of the subsurface horizons, and except for the C horizon they are defined by a l l four t i t r a t i o n curves.  In this s o i l the  differences  between the ZPC and the pH(KCl) decrease to within 0.09 and 0.26 pH units. Comparison of the ZPC, a-j, and  pH(KCl) - ZPC values with the  total organic C, pyrophosphate-rextractable C, and p a r t i c l e size anal y s i s data do not reveal any obvious c o r r e l a t i o n s . cate, however, that with increasing sesquioxide  The data do i n d i -  content the ZPC  approaches the ZPT (decreasing a-j) and the ZPC also approaches the pH ( K C l ) .  - 21 Although the pH values obtained i n KCl are not necessarily  the  pH of the s o i l s o l u t i o n , they are an indication of the pH of the solution i n close proximity to the p a r t i c l e surfaces, since most of the exchangeable a c i d i t y w i l l be brought into s o l u t i o n .  For this reason  they were chosen for the comparison with the ZPC. Similar r e s u l t s , with larger difference values, are obtained by comparing the ZPC with the pH(H 0) and pH(CaCl ). 2  2  CONCLUSIONS The experiment reveals that the three s o i l s studied range i n the degree of their pedological development from a s o i l with morphological and chemical c h a r a c t e r i s t i c s indicative of only a small accumurliation of sesquioxides sive.  to a s o i l i n which sesquioxide accumulation i s  exten-  The surface charge properties indicate that the increase in  morphological development hassbeen accompanied by a decrease in the r e l a t i v e significance of pH-independent charge, as compared to the pH-dependent charge.  As a r e s u l t , the ZPC becomes more c l e a r l y defined  and approaches the natural pH of the s o i l .  -  22  -  LITERATURE CITED  1.  Allison, L . E . 1 9 6 5 . Organic carbon. J J I C.A. Black ( e d . ) . Methods of Soil A n a l y s i s . Part 2 . Agronomy 9 : 1 3 6 7 - 1 3 7 8 . Amer. Soc. Agron., Madison, Wisconsin.  2.  Day, J . H . , L . Farstad, and D.G. L a i r d . 1 9 5 9 . Soil Survey of Southeast Vancouver Island and Gulf Islands, B r i t i s h Columbia. Report No. 6 , B . C . S o i l Survey.  3.  Espinoza, W., R.G. Gast, and R.S. Adams, J r . 1 9 7 5 . Charge charact e r i s t i c s and n i t r a t e retention by two Andepts from south-central C h i l e . Soil S c i . Soc. Am. Proc. 3 9 : 8 4 2 - 8 4 6 .  4.  G a l l e z , A . , A.S.R. Juo, and A . J . H e r b i l l o n . 1 9 7 6 . Surface and charge characteristics of selected s o i l s i n the t r o p i c s . S o i l S c i . Soc. Am. J . 4 0 : 6 0 1 - 6 0 8 .  5.  Hesse, P.R. i l > 9 7 1 . A Textbook of Soil Chemical A n a l y s i s . Murray Publishers, London. 5 2 0 p.  6.  Laverdiere, M . R . , and R.M. Weaver. 1 9 7 7 . Charge c h a r a c t e r i s t i c s of spodic horizons. S o i l S c i . Soc. Am. J . 4 1 : 5 0 5 - 5 1 0 .  7.  Lavkulich, L . M . , and J . H . Wiens'. 1 9 7 0 . Comparison of organic matter destruction by hydrogen peroxide and sodium hypochlor i t e and i t s effect on selected mineral constituents. Soil S c i . Soc. Am. Proc. 3 4 : 7 5 5 - 7 5 8 .  8.  McKeague, J . A . ( e d . ) . 1 9 7 6 . Manual on Soil Sampling and Methods of A n a l y s i s . S . R . I . , Agriculture Canada, Ottawa.  9.  McKeague, J . A . , and J . H . Day. 1 9 6 6 . Dithionite and oxalate extractable Fe and Al 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 . 4 6 : 1 3 - 2 2 .  John  10.  Mehra, O . P . , and M.L. Jackson. 1 9 6 0 . Iron oxide removal from s o i l s and clays by a d i t h i o n i t e - c i t r a t e system buffered with sodium bicarbonate. Clays and Clay Minerals 7 : 3 1 7 - 3 2 7 .  11.  Morais, F ; I . , A?6.APage,?aand QnS. Lund. 1 9 7 6 . The effect of pH, s a l t concentration and nature of e l e c t r o l y t e s on the charge characteristics of B r a z i l i a n tropical s o i l s . Soil S c i . Soc. Am.  J.  40:  521-527.  12.  Parks, G.A. 1 9 6 7 . Aqueous surface chemistry of oxides and complex oxide minerals. Adv. Chem. 6 7 : 1 2 1 - 1 6 0 .  13.  Parks, G . A . , and P . L . de Bruyn. of oxides. J . Phys. Chem.  1 9 6 2 . The zero point of charge 66:  967-973.  - 23 14.  Peech, M. 1965. Hydrogen-ion a c t i v i t y . Jji C A . Black ( e d . ) . Methods of Soil Analysis. Part 2. Agronomy 9: 914-926. Am. Soc. Agron., Madison, Wisconsin.  15.  Soil Survey S t a f f . 1975. Soil Taxonomy. No. 436, Washington, D.C.  16.  Van R a i j , B . , and M. Peech. 1972. Electrochemical properties of some oxisols and a l f i s o l s i n the t r o p i c s . Soil S c i . Soc. Am. Proc. 36: 587-593.  17.  W h i t t i g , L . D . 1965. X-ray techniques for mineral i d e n t i f i c a t i o n and mineralogical composition. IJX C A . Black ( e d . ) . Methods of Soil A n a l y s i s . Part 1. Agronomy 9: 671-698. Am. Soc. Agron., Madison, Wisconsin.  Agricultural Handbook  - 24 -  Chapter Three MEASUREMENT TECHNIQUE EFFECTS ON THE VALUE OF ZERO POINT OF CHARGE AND ITS DISPLACEMENT FROM ZERO POINT OF TITRATION  ABSTRACT  Three procedures for measuring ZPC (the zero point of charge) and a-j (its  displacement from the zero point of t i t r a t i o n ) were investigated.  The slow-adsorption potentiometric t i t r a t i o n technique was found to produce higher ZPC values and lower nique.  values than the fast-adsorption tech-  NaCl-saturation of the exchange complex p r i o r to t i t r a t i o n  resulted in a s h i f t of ZPC and a^ values compared to untreated samples. For ZPC and a - values below pH 5.0 and -0.25 meq/lOOg respectively, n  as  measured on untreated samples, the NaCl-saturation resulted in lower values; for values above t h i s , the change was to higher values. fast-adsorption procedure performed on untreated samples i s  The  considered  to be the most suitable for s o i l s because the values obtained w i l l most closely characterize the surface charge properties i n the f i e l d .  c.  - 25 -  INTRODUCTION In recent years there has been an increasing interest in the use of potentiometric t i t r a t i o n to study the surface charge characteristics of s o i l s .  This interest stems from the recognition of the importance  of the pH-dependent exchange capacity of many s o i l s high in oxides and hydroxides of iron and aluminum.  It has been recognized that these  s o i l s respond d i f f e r e n t l y to management practices than s o i l s in which the pH-independent exchange capacity dominates.  In order that the  results of d i f f e r e n t authors in different parts of the world be comparable, i t is important to know whether the methods used by the different authors produce the same or s i m i l a r results for the surface charge characteristics. Several d i f f e r e n t techniques have been used i n the past for the determination of the zero point of charge of s o i l s (ZPC, the pH at which the net charge i s zero).  Van Raij and Peech (1972) and Espinoza et a l .  (1975) employed a technique using an e q u i l i b r a t i o n period of thRee days during the potentiometric t i t r a t i o n .  Laverdiere and Weaver (1977)  state that i d e n t i c a l information could be obtained using a much faster technique which employed an e q u i l i b r a t i o n period of only two minutes; and that NaCl-saturation of the samples prior to t i t r a t i o n did not affect  the value obtained for the ZPC, although i t did cause an increase  in the displacement of the cross-over point (defined here as a^) below the zero point of t i t r a t i o n (ZPT).  - 26 MATERIALS AND METHODS The samples used in this study are from three s o i l s on Vancouver Island, B r i t i s h Columbia, developed on s i m i l a r glacio-marine parent material.  In contrast to the s o i l s used by previous researchers, the  s o i l s used in this case contained high amounts of clay minerals (phyllosilicates)  and therefore have the potential of developing high permanent  cation exchange c a p a c i t i e s . •Two.  These s o i l s are discussed f u l l y i n Chapter  The NaCl-saturated samples were prepared with four washings of  lf[ NaCl and then washed free of excess s a l t with methanol /water and acetone/water s o l u t i o n s . 4 0 ° C. (i)  The samples were subsequently oven-dried at  The three t i t r a t i o n methods investigated i n this study were:  the slow-adsorption method using NaCl-saturated samples and an  e q u i l i b r a t i o n period of three days (van Raij and Peech, 1972); ( i i )  the  fast-adsorption method using NaCl-saturated samples and e q u i l i b r a t i o n period of two minutes (Laverdiere and Weaver, 1977); and ( i i i )  the f a s t -  adsorption method using untreated samples (Laverdiere and Weaver, 1977). In a l l cases the s o i l to e l e c t r o l y t e r a t i o was 1:20 (gm:ml) and the i n d i f f e r e n t e l e c t r o l y t e was NaCl in concentrations of 0.001NU O.OIJi, 0.1N, and IN.  RESULTS AND DISCUSSION Comparing the results for the NaCl-saturated samples by the slowadsorption and fast-adsorption methods, Table 3.1 and Figure 3.1 show that with the exception of the Spodic Ferrudalf B22, B23t and B3 h o r i zons, the slow procedure resulted i n higher ZPC values for the three s o i l s studied.  In a l l cases, the slow technique resulted i n a greater  displacement of the cross-over point below the ZPT, as indicated by  TABLE 3.1:  Surface charge characteristics of the three s o i l s measured by three different  l i n n T 7 m i  HORIZON  Z P C  meq/lOOg  DYSTRIC EUTROCHREPT (ORTHIC DYSTRIC RRUNISOL) B21  4.00*  B22  u  CI  F  Slow NaCl-Saturated  -10.0  -  u  a s t  F a s t  NaCl-Saturated Z  P  C  techniques.  meq/lOOg  Untreated Z  P  meq/lOOg  C  - SAANICHTQN SERIES 3.17*  -  u  9.0  -  u  3.72*  -  4.3  -  u u  TYPIC FERRUDALF (ORTHIC DYSTRIC BRUNISOL) - ALBERNI SERIES B21cn  3.90*  -20.Q  3.10*  -19.5  3.89*  -  7.0  B22cn  4.20*  -  3.76*  -  -  4.6  B23t  3.65*  -20.0  u  -  3.89 3.56  -  5.3  u  -  u  -.  C  9.5  6.9  -  u  SPODIC FERRUDALF (PODZOLIC GRAY LUVISOL) - MEMEKAY SERIES B21 i r  4.25  -  5.0  4.19  - 1 .9  4.51  -  0.4  B22ir •'  5.00  -  2.0  5.31  -  0.1  5.27  -  0.3  B23t  4.85  -  2.0  5.36  + 0.2  5.18  -OU  B3  4.50  -  2.5  4.61  -  0.8  4.71  -  0.6  C  4.20*  -  5.0  3.42*  -  4.8  3.91*  -  2.1  *: Defined by three of the four curves only u: Undefined  - 28 -  ZPC  FIGURE.3.1:  Graph showing the relationship of ZPC and a-j for the three soils.  The three regression lines are:  A-A, log  (-1.9 - a-,-) = 8.76-1.97 ZPC, R = 0.94;  B-B, log  (0.58 - a,-) = 3.05-0.63 ZPC, R = 0.95;  C-C, log  (-0.25- a ^ = 4.95-1.15 ZPC, R = 0.93.  2  2  2  - 29 larger negative values of a j .  Otherwise, the samples, which did.not  have a defined ZPC when measured by the slow-adsorption method, were also undefined by the fast-adsorption method.  Of the samples studied  in this experiment, the Spodic Ferrudalf had the highest amounts of extractable iron and aluminum i n the B21 and B22 horizons, and the pHdependent charge dominated over the pH-independent charge (Chapter Two). In these samples the ZPC was defined more c l e a r l y and at a higher pH for both methods.  As a r e s u l t , the difference between the ZPC values  of these samples measured by the fast-adsorption and slow-adsorption methods was much less pronounced.  This can be seen graphically on  Figure 3 . 1 , where the regression lines representing the NaCl-saturated, fast-,  and slow-adsorption ZPC values come closest together at high  values of ZPCandda-j values close to zero. The differences  i n the results obtained with the fast-adsorption  as compared to the slow-adsorption procedure are due to the i n the adsorption reactions with the two methods.  differences  Atkinson et a l .  (1967) and Blok and de Bruyn (1970) found that the i n i t i a l  rapid adsorp-  t i o n is a reaction between the p a r t i c l e surfaces and the potential determining ions ( H and OH"), whereas the slow-adsorption which follows +  is a reaction involving the incorporation of H and OH" ions into the +  s o l i d phase.  For this reason, the fast procedure, which measures  the  i n i t i a l fast-adsorption, is a better indicator of the charge character i s t i c s of the s o i l samples at the surface proper. Comparing the results for the fast-adsorption methods with NaClsaturated and untreated samples, Table 3.1 shows that, with the exception of the Typic Ferrudalf B23t horizon, the ZPC was undefined for the same samples.  As with the comparison between the f a s t - and slow-  - 30 -  adsorption methods, the differences  in the values measured by the two  methods were at a minimum with the samples which had the highest ZPC values and a-j values closest to zero.  In the samples i n which the pH-  independent charge is comparatively more important than the pH-dependent charge (as indicated by l a r g e r , negative t i v e l y large differences  values), there were r e l a -  i n the measured values of ZPC and a-j between  the NaCl-saturated and untreated samples.  Figure S.^showshcthat'for ZPC  values below 5.0 (and a-j values lower than -0.25), there was a decrease i n the measured values of both ZPC and compared to the untreated samples.  for the NaCl-saturated samples  At ZPC vailues above 5.0 (and  values above - 0 . 2 5 ) , the reverse r e s u l t was obtained and there was an increase i n the values of both ZPC and a-j. 3.1,  As can be seen from Figure  the regression lines for the NaCl-saturated and untreated samples  measured by the fast-adsorption method are s i m i l a r , and the results measured by the different techniques are merely shifted i n one d i r e c tion or the other along the curve (assindicated by the arrows connecting pairs of samples). The differences  between the values of ZPC and a-,- for the NaCl-  saturated and untreated samples, for the fast-adsorption method are attributed to the replacement of strongly-bonded cations and anions adsorbed on the exchange s i t e s by Na and CI~. +  In the case of the sam-  ples which responded to the NaCl-saturation by y i e l d i n g lower ZPC and values, the treatment caused more pH-independent cation exchange s i t e s to be made accessible during the potentiometric t i t r a t i o n . 3  would r e s u l t from the replacement of Al  This  +  ions, which block permanent  cation exchange s i t e s , by the readily exchangeable Na ions. +  In the  case of the samples which responded to NaCl-saturation by y i e l d i n g  - 31 higher ZPC and  values, the treatment caused more anion exchange sites  to be made accessible.  This would result from the replacement of 3 • -  strongly-bonded anions such as PCH  by readily exchangeable CI". A l -  though both of these processes w i l l occur i n a l l of the samples,  the  dominance of one or the other w i l l determine the net change which results.  \  Due to the change in the measured values following NaCl-satu-  r a t i o n , i t is concluded that untreated samples w i l l give a more accurate estimate of the surface charge characteristics as they occur i n the field. CONCLUSIONS Laverdiere and Weaver (1977) stated that the ZPC values obtained for NaCl-saturated and untreated samples would be the same, and that NaCl-saturation would lower the value of a-j. that:  (a)  The present study found  the ZPC values for the two techniques would be very close  only when the cross-over occurs close to the ZPT, and (b) the change in the value of a-j w i l l depend on the nature of the p a r t i c l e surfaces under study. This study has shown that i n some cases these methods of measuring ZPC and a-j do not y i e l d the same r e s u l t s . close to zero, the differences niques w i l l be at a minimum. w i l l be quite d i f f e r e n t .  When the value of a-j is -en-  obtained with various measurement techWhen a-j is not close to zero, the values  Therefore, care must be taken when comparing  the work of different researchers, i f identical laboratory procedures have not been employed.  LITERATURE CITED  Atkinson, R . J . , A.M. Posner, and J . P . Quirk. 1967. Adsorption of potential-determining ions at the f e r r i c oxide-aqueous electrolyte interface. J . Phys. Chem. 71: 550-558. Blok, L . , and P . L . de Brjayn. 1970. The ionic double layer at the ZnO/solution i n t e r f a c e : I . The experimental point of zero charge. J . C o l l o i d . Interface S c i . 32: 518-525. Espinoza, W., R.G. Gast, and R.S. Adams, J r . 1975. Charge charact e r i s t i c s and n i t r a t e retention by two Aridepts from southcentral C h i l e . S o i l S c i . Soc. Am. Proc. 39: 842-846. Laverdiere, M . R . , and R.M. Weaver. 1977. Charge characteristics of spodic horizons. Soil S c i . Soc. Am. J . 41: 505-510. van R a i j , B . , and M. Peech. 1972. Electrochemical properties of some Oxisols and A l f i s o l s in the t r o p i c s . Soil S c i . Soc. Am. Proc. 36: 587-593.  - 33 -  Chapter Four VARIATION IN SURFACE CHARGE CHARACTERISTICS IN A SOIL CHRONOSEQUENCE  ABSTRACT  The surface charge characteristics of the B horizons of seven soils  in a chronosequence developed on sandy beach material were studied.  The s o i l s range i n age from 127 to 550 years and exhibit morphological and chemical characteristics ranging from Typic Udipsamment to Aquic Haplorthod.  The difference between the zero point of charge (ZPC) and  the pH of the s o i l decreased as the age of the s o i l s  increased, from  a maximum value at the youngest s i t e of 0.27 to a minimum value at the oldest s i t e of 0.11.  The decrease i n this ApH value is interpreted as  indicating that the s o i l s  are approaching a steady-state  with time.  The ApH value is presented as a measure of pedogenic development.  - 34 -  INTRODUCTION With time and increasing pedogenic development, the surface charge c h a r a c t e r i s t i c s of s o i l p a r t i c l e s change.  In the B horizon of  s o i l s developing under the climate and vegetation that r e s u l t i n the development of a spodosol, this change is a function of the increase in sesquioxide content.  As a result of this increase, the p a r t i c l e sur-  faces approach a condition in which these oxides and hydroxides generate the majority of.exchange sites (Clark, McKeague, and Nichol, 1966), When this has occurred, the exchange capacity w i l l be largely pH-dependent and the surfaces can be said to be amphoteric (Chapter Two). Potentiometric t i t r a t i o n can be used to measure certain parameters which reveal the surface charge c h a r a c t e r i s t i c s of amphoteric particles (Parks, 1965).  The zero point of charge (ZPC) is the pH at  which the net total charge on the p a r t i c l e surfaces is zero, i . e . , number of positive and negative charge s i t e s is equal.  the  At pH values  above the ZPC a net negative charge w i l l be generated at the oxide surface; and at pH values below the ZPC, a net positive charge w i l l be generated, as represented schematically for a f e r r i c oxide surface below.  For F e 0 2  3  and A 1 0 2  the ZPC has been measured at 8.5 and 6.9  3  respectively (Parks and de Bruyn, 1962). pH< ZPC  \  pH > Z P C  pH • ZPC  \  OH.  ro 3 H 0 + 2  0  OH  \/ Fe  ?  ' ^OH,  3H-.0  +  0  Fc  OH  \ l /  3 OK  -  >  .  0 + 3 H 0  0  2  X  Fe  Fe  |\  OH  /  /  - 35 According to Parks (1967), the ZPC is a measure of the charge properties of the system as a whole, and the ZPC of a mixture w i l l be determined by the weighted average of the charge on the different  surfaces.  In a soil:: system containing mixtures of c r y s t a l l i n e and amorphous i n o r - , ganic compounds and various organic compounds, the ZPC w i l l be a function of the proportion of the surface that is made up of different components. Therefore, as a s o i l develops, measurable differences characteristics should be observed.  i n surface charge  The objective of this study was to  test the hypothesis that with increasing pedogenic development o f the B horizon, as indicated by increasing age and sesquioxide content: the ZPC increases; ( i i )  the absolute value of  decreases;  (i)  and ( i i i )  the ApH value decreases, where ApH is defined as the difference between the ZPC and the pH(KCl).  This hypothesis was tested on a chronosequence  developed on sandy beach material in the humid temperate environment o f west-coast Vancouver Island.  MATERIALS AND METHODS Characterization of the Soil Samples The s o i l s used i n this study were collected along a chronosequence on the West Coast o f Vancouver Island.  The detailed descriptions o f  these s i t e s are part o f the Ph.D. program o f G.A. Singleton (Department o f S o i l Science, University o f B r i t i s h Columbia, Vancouver, Canada). The s o i l s range in age from 127 to 550 years old and are c l a s s i f i e d as a sequence from a Typic Udipsamment to an Aquic Haplorthod.  For this  study, samples of the f i r s t B horizon and the next lower horizon were used.  The s o i l p r o f i l e s were described and sampled i n the f i e l d ; on  - 36 return to the laboratory the samples were a i r - d r i e d and passed through a 2 mm sieve.  This material was used for a l l subsequent  determinations.  Total organic carbon content was measured with a Leco Analyser.  Extrac-  table iron and aluminum was determined on samples ground to pass a 100 mesh sieve using three methods: 1968); ( i i )  ( i ) sodium pyrophosphate (Bascomb,  acid ammonium oxalate (McKeague and Day, 1966); and ( i i i )  sodium-citrate, -bicarbonate, - d i t h i o n i t e (Mehra and Jackson, 1960). pH measurements  in Iff KCl were made according to the method of Hesse  Cp. 30, 1971), and are interpreted as being a good indicator of the pH i n close proximity to the p a r t i c l e  surfaces.  Potentiometric T i t r a t i o n As was discussed more f u l l y in the previous chapter, the f a s t adsorption method using untreated samples produces results which are most applicable to the exchange reactions that take place i n the f i e l d . For this reason the fast-adsorption potentiometric t i t r a t i o n method of Blok and de Bruyn (1970) was applied to untreated s o i l (Laverdiere and Weaver, 1977). t r o l y t e i n concentrations  samples  NaCl was used as the i n d i f f e r e n t elec-  of 0.001^, 0.01N, 0.05N, and 0.2N.  Forty ml  of the indifferent electrolyte and 4 g of untreated, <2 mm s o i l were t i t r a t e d with 0.1 ml aliquots of O.lN^HCl or NaOH.  The samples were  s t i r r e d continuously and, after a two-minute e q u i l i b r a t i o n period, the resulting pH was measured with a calomel reference-glass  electrode pair  on a Radiometer PHM 62.  RESULTS AND DISCUSSION The data for the f i r s t two horizons below ei-ther an 0 or A horizon i n the seven s o i l s ranging from a Typic Udipsamment to an Aquic  - 37 -  Haplorthod (Soil Survey S t a f f , 4.2.  1976)  are presented i n Tables 4.1 and  At a l l s i t e s the two horizons examined were both B horizons,  except at s i t e 1, where there was only one B horizon i d e n t i f i e d .  The  seven s o i l s form a transect i n a continuous depositional beach chronosequence and the s i t e s range i n age, as dated by dendrochronology, from 127 years at s i t e 1 to 550 years at s i t e 7. As an aid to assessing the functional relationships between the variables  measured, a Pearson product-moment c o e f f i c i e n t  of c o r r e l a t i o n  analysis program was run on the data i n Tables 4.1 and 4.2.  Selected  columns of the resulting correlation matrix are presented as Table 4.3. With increasing age, there i s a s t a t i s t i c a l l y  s i g n i f i c a n t increase in  the amounts of extractable iron and aluminum and organic matter (Table 4.3).  The increase in these values with increasing age is not constant  from s i t e 1 to s i t e 7; the variations are explained by minor variations in s o i l s i t e factors such as microtopography and p a r t i c l e s i z e d i s t r i bution of the parent m a t e r i a l . subsurface horizon  With the exception of s i t e 1, the f i r s t  had the highest content of these materials.  The  best correlation between extractable sesquioxides and age was obtained with the pyrophosphate and citrate-bicarbonate-dithiom*te  extractable  aluminum; the correlations with extractable iron are not as strong. best c o r r e l a t i o n between i r o n plus aluminum and age was obtained with the pyrophosphate extraction values.  This supports the conclusion of  the Canadian S o i l Survey Committee (1978) and the S o i l Survey Staff (1976) that the pyrophosphate-extractabl e iron plus aluminum is best indicator of Spodosol (Podzol)  the  development.  Due to the increasing amounts of extractable iron and aluminum  The  - 38 -  TABLE 4.1: Some chemical and surface charge characteristics of the seven s o i l s studied. . SITE  HORIZON  ZPC  i (meq/lOOg.) a  ApH ^  y  r  S  ;  Organic Carbon %  pH(KCl)  TYPIC UDIPSAMMENT (ORTHIC DYSTRIC BRUNISOL) B2  3.45  -1.15  0.72  127  0.61  4.17  CI  3.70  -0.68  0.42  127  0.46  4.12  TYPIC UDIPSAMMENT (ORTHIC DYSTRIC BRUNISOL) B2  3.60  -0.40  0.30  170  0.30  3.90  B3  3.87  -0.25  0.25  170  0.23  4.12  TYPIC HAPLORTHOD (ORTHIC DYSTRIC BRUNISOL) B2  3.68  -0.60  0.48  265  0.76  4.16  B3  4.05  T0.23  0.43  265  0.08  4.48  TYPIC HAPLORTHOD (ORTHIC HUMO-FERRIC PODZOL) B21ir  3.55  -0.73  0.22  370  0.91  3.77  B22  3.82  -0.35  0.26  370  0.61  4.08  TYPIC HAPLORTHOD (ORTHIC HUMO-FERRIC PODZOL) B21ir  3.35  -1.35  0.26  446  1.67  3.61  B22ir  3.80  -0.28  0.23  446  1.03  4.03  TYPIC HAPLORTHOD (ORTHIC HUMO-FERRIC PODZOL) B21ir  3.80  -0.55  0.17  480  1.60  3.97  B22ir  3.98  -0.30  0.12  480  1.14  4.10  AQUIC HAPLORTHOD (ORTHIC HUMO-FERRIC PODZOL) B21ir  3.65  -0.45  0.19  550  1.67  3.84  B22ir  3.85  r0.25  0.11  550  1.14  3.96  TABLE 4.2:  SITE  1  2  3  4  5  6  7  Extractable sesquioxide data for the seven s o i l s (percent of total sample).  SOIL CLASSIFICATION  TYPIC UDIPSAMMENT  TYPIC UDIPSAMMENT  TYPIC HAPLORTHOD  TYPIC HAPLORTHOD;  TYPIC HAPLORTHOD  TYPIC HAPLORTHOD  AQUIC HAPLORTHOD  PYROPHOSPHATE  ACID AMMONIUM OXALATE  HORIZON  CITRATE-BICARBONATE -DITHIONITE  Fe  Al  Fe+Al  Fe  Al  Fe+Al  Fe  Al  Fe+Al  B2  0.13  0.09  0.22  0.27  0 .12  0.39  0.32  0.10  0.42  CI  0.11  0.12  0.23  0.28  Q .17  0.45  0.35  0.13  0.48  B2  0.13  0.15  0.28  0.26  0 .15  0.41  0.30  0.12  0.42  B3  0.07  0.10  0.17  0.19  0 .13  0.32  0.22  0.09  0.31  B2  0.16  0.14  0.30  0.27  0 .15  0.42  0.32  0.12  0.44  B3  0.06  0.10  0.16  0.20  0 .14  0.34  0.21  0.08  0.29  B21ir  .0.28  0.14  0.42  0.36  0 .17  0.53  0.44  0.17  0.61  B22  0.14  0.18  0.32  0.25  0 .22  0.47  0.29  0.19  0.48  B21ir  0.49  0.19  0.68  0.54  0 .20  0.74  0.63  0.23  0.86  B22ir  0.21  0.22  0.43  0.28  0 .26  0.54  0.36  0.27  0.63  B21ir  0.50  0.26  0.76  0.60  0 .30  0.90  0.64  0.32  0.96  B22ir  0.31  0.32  0.63  0.39  0 .32  0.71  0.45  0.30  0.75  B21ir  0.34  0.29  0.63  0.48  0 .29  0.77  0.48  0.28  0.76  B22ir  0.19  0.25  0.44  0.27  0 .25  0.52  0.33  0.23  0.56  CO  - 40 -  TABLE 4.3: -  •  -  ' '•  Selected columns of the correlation matrix (R-values). — -IT  —•  '""  ZPC ZPC a  i  a  ApH  i  Age  1.00  0.87**  -0.34  0.16  0.87**  1 .00  -0.45  0.17 -0.76**  ApH  -0.34  -0.45  1 .00  Age  0.16  0.17  -0.76**  1.00  -0.33  -0.32  -0.50  0.81**  0.46  0.47  -0.48  0.69**  Organic Carbon  0.67**  pH(KCl)  -0.45  PYROPHOSPHATE Fe  0.33  -0.41  Al  0.22  0.25  -0.74**  0.88**  -0.15  -0.20  -0.62**  0.82**  Fe  -0.35  -0.43  .0.39  0.61*  Al  0.29  0.28  -0.73**  0.86**  -0.14  -0.20  -0.56*  0.76**  -0.39  0.59*  .0.71**  0.88**  -0.55*  0.75**  Fe+Al ACID AMMONIUM OXALATE  Fe+Al  CITRATE-BICARBONATE-DITHIONITE Fe  -0.41  -0.50  Al  0.09  0.08  -0.23  -0.30  Fe+Al  '  \ •  *  ~—~~  <r  S i g n i f i c a n t at the .05 level  **  S i g n i f i c a n t at the .01 level  - 41 -  with increasing s o i l age,  the ZPC was expected to increase.  Although  the general trend in Figure 4.1 indicates an increase i n ZPC with i n creasing s o i l age, there is an extremely large amount of scatter, and Table 4.3 indicates ficant.  that this relationship is not s t a t i s t i c a l l y  On Figure 4.1,  signi-  the f i r s t and second B horizons appear to be  separated, with the f i r s t having a lower ZPC than the second; this is in s p i t e of the higher sesquioxide content of the f i r s t B horizon.  The  higher organic matter content of the upper horizons causes this decrease in the ZPC values; the large fluctuation in ZPC values between s i t e s  is  also strongly influenced by organic matter, as has been found by other researchers (van Raij and Peech, 1972; Gallez et al_., 1976; Morais et al.,  1976; Laverdiere and Weaver, 1977).  This explanation i s further  supported by the fact that the p a r t i a l correlation c o e f f i c i e n t ZPC and age, with effect of organic matter removed (0.77), i s t i c a l l y s i g n i f i c a n t at the 0.01 coefficient  between statis-  l e v e l , while the simple correlation  between ZPC and age (0.16) is not.  In a s i m i l a r manner,  the pH(KCl) tends to decrease with increasing age of the s o i l ; superimposed on this is the effect of organic matter.  High levels of  organic matter content cause a decrease i n the measured pH(KCl); therefore there is a co-variation of ZPC and pH(KCl) (R = 0.67, at the 0.01  significant  level).  The displacement of the crossover point below the ZPT, defined as o-j, was expected to approach zero with increasing s o i l age.  The results  presented i n Table 4.1 and on Figure 4.2 show that this was not proven by the data.  Although the general trend indicates the predicted r e l a -  t i o n s h i p , the great amount of scatter prevents any definite  conclusion.  4.40.  O ZPC OF O Z P C OF  FIRST B HORIZON SECOND B HORIZON  4.20. O  4.00._  O  pH  O  3.80.-  <•>  o.  3.60.  3.40J  <3>  <3> o  —5  o  o o  o o  3.20. 00  i  300  200 \A G E  SITE I SITE 2  FIGURE 4.1:  SITE 3  400  \ 500  6  0  0  (YEARS) SITE 4  Showing the relationship between the ZPC  SITE 5  SITE 6  SITE 7  and age for the seven s o i l s .  0  FIGURE 4.2:  Showing the relationship between a-j and age for the seven s o i l s .  - 44 -  The poor correlation between a-j and age also appears to be due to the variations i n organic matter content.  This is suggested by the compa-  rison of the simple c o r r e l a t i o n coefficient with the p a r t i a l correlation coefficient  between a^ and age (0.17)  between  and age with the  effect of organic matter removed (0.78, s i g n i f i c a n t at the 0.01 The differences values in Table 4.1  level).  between the ZPC and pH(KCl) are presented as ApH and on Figure 4.3.  In this figure, the scatter of  points around the regression l i n e is much reduced and s t a t i s t i c a l l y s i s reveals that the regression l i n e is s t a t i s t i c a l l y the 0.01  level.  significant  The trend of decreasing ApH values with time  that, as hypothesized,  anaat  indicates  the ZPC i s approaching the pH of the s o i l with  increased pedogenic development.  The ApH value is highly correlated  with the aluminum extracted by pyrophosphate, oxalate,  and c i t r a t e -  bicarbonate-dithionite, and with the amounts of iron plus aluminum removed by these extractants.  The ApH value also indicates  increasing age the "active" surfaces librium with the s o i l s o l u t i o n .  that with  i n the s o i l are approaching equi-  This l a s t statement is derived from  the empirical relationship between the ZPC and the pH of minimum solub i l i t y of pure oxides; since the hydrolysis of the surfaces  i s at a  minimum at the ZPC, the pH of minimum s o l u b i l i t y w i l l occur at the ZPC (Parks and de Bruyn, 1962). Although the s o i l is not a pure system, the decrease i n ApH with time is interpreted as indicating that the s o i l state.  is approaching steady-  Most of the components i n the system w i l l not actually be in  thermodynamic equilibrium with the s o i l  solution; nonetheless, the  results indicate that the "active" surfaces, which form the  interface  1.0  O  1  100  ! •  SITE I  FIGURE 4.3:  200 j i  SITE 2  !  1  -  O  ApH  OF FIRST  <•>  ApH  OF SECOND  :  300 !  AGE (YEARS)  i"  SITE 3  ;  400  ;  HORIZON  B  B  1  HORIZON  r  \ 500  600  j !:  SITE 4  I  SITE 5  i  SITE 6  :  SITE 7  Showing the relationship between ApH and age f o r the seven s o i l s (significant at the 0.01  level).  - 46 between the s o l i d phase and the s o l u t i o n , are approaching a  steady-state  when considered as a whole.  CONCLUSIONS The study reveals that as spodic s o i l s characteristics change.  develop, the surface charge  The ZPC value was expected to increase and the  a-j value to approach zero from the youngest to oldest s i t e .  Due to  differences i n organic matter content, these trends were not c l e a r l y defined.  The results show that both the ZPC and pH(KCl) values varied  together,  as a function of organic matter content, such that the d i f f e -  rence between the ZPC and the s o i l pH decreased with time from a maximum value of 0.72 at s i t e 1 to a minimum value of 0.11 at s i t e 7.  This  trend is related to the increase in sesquioxide content of the B h o r i zons.  The hypothesis presented is p a r t i a l l y supported by the experi-  mental r e s u l t s ; the increase i n the ZPC and the decrease i n the absolute value of aj were not proven to be s i g n i f i c a n t with the data a v a i l a b l e . However, the ZPC does approach the pH of the s o i l , indicating that the chemistry of the "active" surface is approaching a steady-state. ApH value is presented as a measure of pedogenic development.  The  - 47 -  LITERATURE CITED  1.  Bascomb, C L . 1968. Distribution of pyrophosphate extractable iron and organic carbon in s o i l s of various groups. J . S o i l S c i . 19: 251-267.  2.  Blok, L . , and P . L . de Bruyn. 1970. The i o n i c double layer at the ZnO/solution i n t e r f a c e . I. Composition model of the surface. J . C o l l o i d . Interface S c i . 32: 527-532.  3.  Canada S o i l Survey Committee. 1978. The Canadian System of Soil Classification. Agriculture Canada, Ottawa, Ont. (In Press)  4.  Clark, J . S . , J . A . McKeague, and W.E. Nichol. 1966. The use of pH-dependent C . E . C . for characterizing the B horizons of b r u n i s o l i c and podzolic s o i l s . Can. J . S o i l S c i . 46: 161-166.  5.  G a l l e z , A . , A.S.R. Juo, and A . J . H e r b i l l o n . 1976. Surface and charge characteristics of selected s o i l s in the t r o p i c s . Soil S c i . Soc. Am. J . 40: 601-608.  6.  Laverdiere, M . R . , and R.M. Weaver. 1977. Charge c h a r a c t e r i s t i c s of spodic horizons, S o i l S c i . Soc. Am. J . 41: 505-510.  7.  Hesse, P.R. 1971. A textbook of S o i l Chemical A n a l y s i s . Murray Publishers ( L t d . ) , London. 520 pp.  8.  McKeague, J . A . , and J . H . Day. 1966. Dithionite and oxalate extractable Fe and Al as aids in d i f f e r e n t i a t i n g various classes of soils. Can. J . S o i l S c i . 46: 13-22.  9.  Mehra, O . P . , and M.L. Jackson. 1960. Iron oxide removal from s o i l s and clays by a d i t h i o n i t e - c i t r a t e system buffered with sodium bicarbonate. Clays and Clay Minerals 5: 317-327.  10.  Morais, F . I . , A . C . Page, and C S . Lund. 1976. The effect of pH, s a l t concentration and nature of electrolytes on the charge characteristics of B r a z i l i a n t r o p i c a l s o i l s . S o i l S c i . Soc. Am. J . 40: 521-527.  11.  Parks, G.A. 1967. Aqueous surface chemistry of oxides and complex oxide minerals. Adv. Chem. 67: 121-160.  12.  Parks, G.A. 1965. The i s o e l e c t r i c points of s o l i d oxides, s o l i d hydroxides and aqueous hydroxo complex systems. Chem. Rev. 65: 177-198.  13.  Parks, G . A . , and P . L . de Bruyn. 1962. The zero point of charge of oxides. J . Phys. Chem. 66: 967-973.  John  - 48 -  14.  S o i l Survey S t a f f . 1975. Soil Taxonomy. No. 436, Washington, D.C. 754 pp.  Agriculture Handbook  15.  Van R a i j , B . , and M, Peech. 1972. Electrochemical properties of some Oxisols and A l f i s o l s in the t r o p i c s . S o i l S c i . Soc. Am. Proc. 36: 587-593,  - 49 -  Chapter Five THE EFFECT OF NaCl-SATURATION AND ORGANIC MATTER REMOVAL ON THE VALUE OF ZERO POINT OF CHARGE  ABSTRACT  Ten s o i l s with a wide range of surface charge properties and extractable sesquioxide contents were studied.  The zero point of charge (ZPC)  and i t s displacement from the zero point of t i t r a t i o n (o^-) were measured on untreated samples, on samples which were NaCl-saturated, and on samples from which a portion of the organic matter had been removed. saturation was shown to cause a s h i f t of the ZPC and  .  NaCl-  In addition,  removal of organic matter resulted in an increase i n both the ZPC and the a,.  - 50 -  INTRODUCTION The factors which affect the measured value of the zero point of charge (ZPC) are important to the interpretation of the surface charge characteristics of s o i l s .  Recent work by Laverdiere and Weaver (1977)  indicates that for s o i l s with low contents of p h y l l o s i l i c a t e clay miner a l s , NaCl-saturated samples and untreated samples give v i r t u a l l y the same measured value of ZPC.  In contrast, s o i l s with higher clay  content,  and hence with a potentially high permanent negative charge capacity, do not y i e l d the same ZPC values when measured in the NaCl-saturated as compared to untreated states (Chapter Three). Further, on the basis of i n d i r e c t evidence, several authors have concluded that organic matter has a depressing effect on the ZPC (van Raij and Peech, 1972; Gallez et al_., 1976; Morais et al_., 1976; Laverdiere and Weaver, 1977; and Chapter Four).  The evidence presented by  these authors is based on comparison of the surface charge characteristics of samples which contain different amounts of organic matter, but which are s i m i l a r in other  respects.  In the present experiment, ten s o i l s with a broad range of surface charge properties and extractable sesquioxide contents were used.  The  ZPC and a- values were measured on untreated samples, NaCl-saturated n  samples, and samples from which a portion of the organic matter had been extracted i n the laboratory.  The aim was to determine:  (i) whether  the results of Chapter Three regarding the effect of NaCl-saturation could be confirmed for a wider range of s o i l  types; and ( i i )  whether  d i r e c t evidence of the effect of organic matter on the ZPC and be obtained.  could  - 51 -  MATERIALS AND METHODS S o i l Samples The samples used i n t h i s study were collected from southwestern B r i t i s h Columbia, Canada, with the exception of the Typic Acrorthox and the Typic Hapludult, which were provided by members of the Soil Conservation S e r v i c e , United States Department of A g r i c u l t u r e . c l a s s i f i c a t i o n of the ten s o i l s (Soil Survey S t a f f ,  The s o i l  1975; Canada S o i l  Survey Committee, 1978) and the sampling location of each is given i n Table 5.1 . Sample Pretreatment Following a i r - d r y i n g , the samples were passed through a 2 mm sieve. Subsamples were taken and prepared as follows:  (i)  The untreated sam-  ples were analysed after grinding to pass a 0.50 mm sieve but without any further treatment,  (ii)  The NaCl-saturated samples were prepared  with 6 washings o f IN NaCl followed by repeated washings with methanol/ water and acetone/water  u n t i l free of CI" (AgN0 t e s t ) , then washed 3  twice with acetone and oven-dried at 4 0 ° C for 48 hours; f i n a l l y the samples were ground to pass a 0.50 mm sieve,  ( i i i ) The organic matter  extracted samples were treated three times with NaOCl according to the procedure of Lavkulich and Wiens (1970), followed by the same NaCl-saturation procedure as above, except that during the final  NaCl washing the  pH of the samples was adjusted to that of the NaCl-saturated samples and maintained u n t i l equilibrium was obtained (about one week).  This step  was necessary to prevent the high pH of the NaOCl extraction from i n t e r fering with the measurement of the ZPC (Ferreiro and Helmy, 1976)*.  TABLE 5.1:  SAMPLE NUMBER  S o i l c l a s s i f i c a t i o n and sampling location for the ten s o i l s . SOIL SERIES  CANADIAN CLASSIFICATION  U.S.D.A. CLASSIFICATION  1  TYPIC HAPLUMBREPT  B21  Orthic Ferro-Humic Podzol  Bhf  2  TYPIC HAPLUMBREPT  B21  Sombric Humo-Ferric Podzol  B f  3  TYPIC HAPLAQUEPT  B2g  Orthic Humic Gleysol  Bg  4  SPODIC FERRUDALF  B21ir  Orthic Humo-Ferric Podzol  B f  5  TYPIC UDIPSAMMENT  B21  Orthic Dystric Brum'sol  6  TYPIC HAPLORTHOD  B21ir  Orthic Humo-Ferric Podzol  7  TYPIC HAPLORTHOD  B21ir  8  AQUIC HAPLORTHOD  9 10  Marblehill Durieu  l  SAMPLING LOCATION 1  Agassiz, B . C . Durieu, B . C .  2  -  Durieu, B.C.  Memekay  Campbell River, B . C .  Bm  Cox Bay #2"  Tofino, B . C .  B f  l  Cox Bay #4"  Tofi no , B . C .  Orthic Humo-Ferric Podzol  B f  l  Cox Bay  #6  h  Tofino, B . C .  B21ir  Orthic Humo-Ferric Podzol  Bf  Cox Bay #7  k  Tofino, B . C .  TYPIC ACRORTHOX  B22  No Canadian Equivalent  Nipe  Oeste SCD, Puerto Rico  TYPIC HAPLUDULT  B22t  No Canadian Equivalent  Facevilie  3  l x  x  5  6  Johnston Co.., No. Carolina  1  Luttmerding, H . A . , and P.N. Sprout.  1967.  Soil Survey Preliminary Report No. 8, B . C .  2  Luttmerding, H . A . , and P.N. Sprout.  1967.  Soil Survey Preliminary Report No. 9, B . C .  3  Day, J . H . , L . Farstad, and D.G. L a i r d .  ^  Singleton, G.A.  5  Personal Communication.  1978.  Luis H. Rivera, U . S . D . A . , Puerto Rico.  6  Personal Communication.  1978.  Hubert J . Byrd, U . S . D . A . , North C a r o l i n a .  1959.  Soil Survey Report No. 6, B . C .  Ph.D. Thesis, Department of Soil Science, UBC.  (In  preparation)  - 53 -  Characterization of the Soil Samples The following determinations were performed on samples ground to pass a 0.50 mm sieve. 1965), 0.01M C a C l p. 30, 1971). using:  2  S o i l pH was measured in water (1:1,  (1:2,  922,  Peech, p. 923, 1965), and IN KCl (1:2.5, Hesse,  Three different extractions of sesquioxides were made  (i) sodium pyrophosphate, one overnight extraction at pH 10  (McKeague, 1976); ( i i )  acid ammonium oxalate, one four-hour extraction  at pH 3.0 (McKeague and Day, 1966); and ( i i i ) nate, - d i t h i o n i t e , 1960).  Peech, p.  two fifteen-minute  sodium-citrate, -bicarbo-  extractions  (Mehra and Jackson,  The extracted Fe and Al were determined by atomic absorption  spectroscopy.  Total s o i l organic carbon was determined by Leco Analyser.  Potentiometric T i t r a t i o n Potentiometric t i t r a t i o n for the determination of the ZPC was performed with a s o i l  to e l e c t r o l y t e  ratio of 1:20  (gm:ml).  The i n d i f f e r e n t  e l e c t r o l y t e was NaCl i n concentrations of 0.001 N, 0.01N, 0.05N_, and 0.2N. In a l l cases the fast-adsorption method of Blok and de Bruyn (1970) was used with a two-minute interval between additions of 0.1N_HC1 or NaOH. Statistical  Analysis  Correlations between variables for the ten s o i l s were analysed using the Pearson product-moment correlation coefficient  r.  of variance tests were performed using the ZPC or NaCl-saturated and organic matter extracted samples.  Two-way analysis values from the This was done to  determine whether these values came from the same or d i f f e r e n t populations .  - 54 -  RESULTS AND DISCUSSION Untreated Samples The s o i l s studied have a wide range of texture and sesquioxide content, i n keeping with the variety of s o i l types and sampling locations (Table 5.2).  The p a r t i c u l a r form of the sesquioxide materials depends  on the pedogenic processes and parent materials which contributed to the formation of each s o i l .  The s o i l s from B r i t i s h Columbia contain an  appreciable amount of t h e i r extractable sesquioxides  as organically com-  plexed iron and aluminum; this is evidenced by the r e l a t i v e l y large amount of these elements being extracted by pyrophosphate as compared to the other two extractants  (McKeague et al_., 1971).  In contrast, the sam-  ples from Puerto Rico and North Carolina contain much of t h e i r extractable iron i n the form of c r y s t a l l i n e iron oxide, as indicated by the large difference between the amounts of Fe extracted by CBD and by oxalate (McKeague and Day, 1966). The pH and surface charge data for the ten s o i l s are presented in Table 5.3.  In a l l the samples except sample 9, the pH value measured  in water was greater than that measured in KCl (pH(H 0)>pH(CaCl )> 2  2  pH(KCl)), indicating that the ZPC of the untreated samples was located below the ZPT (a-j negative).  Sample 9 has a higher pH in KCl than in  water (pH(H 0)<pH(CaCl )<pH(KCl)), and the ZPC is located above the ZPT 2  2  (a.j p o s i t i v e ) . ' The ZPC values generally increase with increasing amounts of pyrophosphate- and CBD-extractable sesquioxides; with increasing total C content, the a^ values become more negative, indicating a higher permanent cation exchange capacity.  These trends are not constant for a l l of  TABLE 5.2:  Soil texture and extractable sesquioxides  PYROPHOSPHATE SAMPLE NUMBER  SOIL CLASSIFICATION  T F Y T I IDF  F  E  A  1  F  E  +  A  1  for the ten s o i l s .  AMMONIUM OXALATE  F  E  A  1  F  E  +  A  1  CITRATE-BICARBONATE -PITHIONITE F  E  A  1  F  E  +  A  1  itAiUKt  1  TYPIC HAPLUMBREPT  B21  SiL  0.46  0.46  0.92  0.89  0.60  1.49  1.54  0.61  2.15  2  TYPIC HAPLUMBREPT  B21  SiL  0.41  1.26  1.67  1.52  3.38  4.90  2.38  2.31  4.69  3  TYPIC HAPLAQUEPT  B2  SiL  0.34  0.57  0.91  0.42  1.31  1.73  1.05  0.84  1.89  4  SPODIC FERRUDALF  B21  SiL  0.83  0.88  1.71  1.64  1.16  2.80  3.60  0.94  4.54  5  TYPIC UDIPSAMMENT  B21  S  0.13  0.15  0.28  0.26  0.15  0.41  0.30  0.12  0.42  6  TYPIC HAPLORTHOD  B21  S  0.28  0.14  0.42  0.36  0.17  0.53  0.44  0.17  0.61  7  TYPIC HAPLORTHOD  B21  S  0.50  0.26  0.76  0.60  0.30  0.90  0.64  0.32  0.96  8  AQUIC HAPLORTHOD  B21  S  0.34  0.29  0.63  0.48  0.29  0.77  0.48  0.28  0.76  9  TYPIC ACRORTHOX  B22  C  3.14  0.97  4:11  0.33  0.24  0.57  21.5  3.17  24.7  10  TYPIC HAPLUDULT  B22  SL  0.02  0.10  0.12  0.18  0.21  0.39  3.17  0.38  3.55  >  TABLE 5 . 3 :  SAMPLE NUMBER  SOIL CLASSIFICATION  p H , s u r f a c e c h a r g e c h a r a c t e r i s t i c s , and t o t a l  carbon f o r the ten  UNTREATED -n  " H 0  CaCl  2  NaCl-SATURATED  o-j  pn 2  KCl  soils.  ZPC  Jjjg.  \  0  a-j ZPC  ^  ^ ^ J tXIKAUhD R  A  T  E  R  o-j  \  ZPC  \  1  TYPIC HAPLUMBREPT  B21  5.91  5.46  5.27  4.83  -3.8  6.45  3.10  -17.5  3.75  3.20  -10.0  0.47  2  TYPIC HAPLUMBREPT  B21  5.32  4.80  4.73  5.02  -0.2  4.27  5.03  -OJ  3.86  6.40  +4.0  1.05  3  TYPIC HAPLAQUEPT  B2  5.38  4.54  4.33  4.52  -0.7  1.41  4.42  -1.8  1.44  4.60  -1.8  0.38  4  SPODIC FERRUDALF  B21  5.40  4.52^  4.34  4.51  -0.4  2.80  4.19  -1.9  2.51  6.10  +2.0  0.30  5  T Y P I C UDIPSAMMENT  B21  5.08  4.28  3.90  3.94  -0.5  0.47  u  -  0.34  u  _  0  6  TYPIC HAPLORTHOD  B21  5.02  4.24  3.77  3.34  -1.7  1.24  u  -  1 .07  u  _  0  7  TYPIC HAPLORTHOD  B21  5.27  4.28  3.97  3.86  -0.7  1 .82  3.84  -0.4  1 .69  7.23  +0.7  0.08  8  AQUIC HAPLORTHOD  B21  5.02  4.15  3.84  3.92  -0.5  1 .61  3.75  -2.1  1.44  6.70  +0.3  0.04  9  TYPIC ACRORTHOX  B22  4.70  5.33  6.13  6.57  +0.9  1.07  7.12  +1.9  1.07  8.28  +6.0  0.'66  10  TYPIC HAPLUDULT  B22  5.19  3.94  3.75  3.86  -0.4  0.53  u  0.54  3.20  -5.5  0.28  u:  Undefined  -  -  57 -  the samples, but correlation analysis reveals that the relationships are s i g n i f i c a n t at the 0.05  level.  NaCl-Saturated Samples As was discussed previously (Chapter Three) NaCl-saturation of the exchange complex of the samples p r i o r to potentiometric t i t r a t i o n results in  a s h i f t of both the ZPC and the a-j values (Table 5.3).  For samples  which had a a^ value of less than -0.2 meq/lOOg and ZPC values less than pH 5.0 when untreated, t h i s s h i f t was to lower ZPC and  values; at a-  values of -0.2 meq/lOOg or higher and ZPC values higher than pH 5.0 when untreated, the s h i f t was to higher ZPC and a - values, as in samples 2 n  and 9.  The t i t r a t i o n curves for samples 5 , 6 ,  and 10 did not achieve  crossover p r i o r to discontinuation of the t i t r a t i o n at pH 3.0. The changes in ZPC and a - are attributed to the substitution on the n  exchange complex of readily exchangeable Na and C l ~ ions for strongly +  bonded ions such as A l  3 +  and P O ^ . 3-  Although both of these reactions  will  occur in a l l of the samples, the balance between the amounts of  Al  and P O i *  3 +  3-  exchanged w i l l determine whether NaCl-saturation w i l l  r e s u l t in more positive or more negative exchange s i t e s being made access i b l e during the potentiometric t i t r a t i o n .  This in turn w i l l control  the d i r e c t i o n , and the amount, of the s h i f t in ZPC and a . . Organic Matter Extracted Samples The data on the effect of organic matter extraction on the ZPC, a-j,  and total organic carbon content of the ten s o i l s are presented i n  Table 5.3.  The amount of carbon extracted from the different samples  was v a r i a b l e , indicating that to different degrees the organic matter was incorporated within the amorphous material and therefore was not  - 58 -  attacked by the NaOCl s o l u t i o n .  The amount of carbon remaining after  treatment ranges from 0% to 60% of the o r i g i n a l . The extraction of organic matter has s i g n i f i c a n t l y altered the surface charge c h a r a c t e r i s t i c s of the s o i l samples.  The effect can best be  evaluated by comparing the organic matter extracted samples with the NaCl-saturated samples, since they both have NaCl-saturated exchange complexes.  In every case there is an increase in both the ZPC and De-  values following the organic matter extraction treatment, indicating that the organic matter has a depressing effect on the ZPC and  .  To  test these apparent r e l a t i o n s h i p s , analysis of variance tests were performed with the r e s u l t that the relationships were found to be s i g n i f i cant at the 0.05 level .  This confirms the assumptions of previous  researchers, who on the basis of i n d i r e c t evidence concluded that the presence of organic matter has the effect of lowering the value of the ZPC and a . i  CONCLUSIONS The present study confirms the results of Chapter Three in that, using a broader range of s o i l types, s i m i l a r s h i f t s  i n the value of ZPC  and a-j were measured as a r e s u l t of NaCl-saturation.  Although the NaOCl  treatment was unable to extract a l l of the organic carbon from a l l of the samples, there was a s i g n i f i c a n t increase in the measured values of ZPC and a- following the treatment. hypothesis  The results therefore support the  that organic matter depresses the ZPC and a-j values of s o i l s .  - 59 -  LITERATURE CITED  1.  Blok, L . , and P . L . de Bruyn. 1970. The i o n i c double layer at the ZnO/solution i n t e r f a c e . I. The experimental point of zero charge. J . C o l l o i d . Interface S c i . 32: 518-525.  2.  Canada S o i l Survey Committee. 1978. The Canadian System of S o i l Classification. A g r i c u l t u r e Canada, Ottawa, Ont. (In press)  3.  F e r r e i r o , E . A . , and A . K . Helmy. 1976. The point of zero charge of hydrous oxide. Z. Pflanzenernaehr. Bodenkd. 6: 767-775.  4.  G a l l e z , A . , A . S . R . Juo, and A . J . H e r b i l l o n . 1976. Surface and charge characteristics of selected s o i l s in the t r o p i c s . S o i l S c i . Soc. Am. J . 40: 601-608.  5.  Hesse, P.R. 1971. A Textbook of Soil Chemical Analysis. (Murray Publishers ( L t d . ) , London. 520 p.  6.  Laverdiere, M . R . , and R.M. Weaver. 1977. Charge characteristics of spodic horizons. S o i l S c i . Soc. Am. J . 41: 505-510.  7.  Lavkulich, L . M . , and J . H . Wiens. 1970. Comparison of organic matter destruction by hydrogen peroxide and sodium hypochlor i t e and i t s effect on selected mineral constituents. Soil S c i . Soc. Am. Proc. 34: 755-758.  8.  McKeague, J . A . ( E d . ) . 1976. Manual on Soil Sampling and Methods of Analysis. S . R . I . , Agriculture Canada, Ottawa, Ont.  9.  McKeague, J . A . , J . E . Brydon, and N.M. Miles. 1971. Differentiation of forms of extractable iron and aluminum in s o i l s . S o i l S c i . Soc. Am. Proc. 35: 33-38.  John  10.  McKeague, J . A . , and J . H . Day. 1966. Dithionite and oxalate extractable Fe and Al as aids i n d i f f e r e n t i a t i n g various classes of . soils. Can. J . Soil S c i . 46: 13-22.  11.  Mehra, O . P . , and M.L. Jackson. 1960. Iron oxide removal from s o i l s and clays by a d i t h i o n i t e - c i t r a t e system buffered with sodium bicarbonate. Clay and Clay Minerals 5: 317-327.  12.  Morais, F. I . , A . C . Page, and C S . Lund. 1976. The effect of pH, s a l t concentration and nature of electrolytes on the charge c h a r a c t e r i s t i c s of B r a z i l i a n t r o p i c a l s o i l s . Soil S c i . Soc. Am. J . 40: 521-527.  13.  Peech, M. 1965. Hydrogen-ion a c t i v i t y . In C.A. Black ( E d . ) . Methods of S o i l Analysis. Part 2. Agronomy 9: 914-926. Am. Soc. A g r o n . , Madison, Wisconsin.  - 60 -  14.  S o i l Survey S t a f f . 1975. Soil Taxonomy. No. 436, Washington, D.C. 754 p.  Agriculture Handbook  15.  Van R a i j , B . , and M. Peech. 1972. Electrochemical properties of some Oxisols and A l f i s o l s i n the t r o p i c s . S o i l S c i . Soc. Am. Proc. 36: 587-593.  - 61 -  Chapter Six SUMMARY AND CONCLUSIONS  The aim of this thesis was to examine the use of surface charge characteristics as a measure of pedogenic development i n selected s o i l s of the humid, temperate environment of southwestern B r i t i s h Columbia. A secondary objective was to gain further knowledge o f the factors which influence the values o f ZPC and o\j obtained i n the laboratory, so that interpretations o f the results might be more c l e a r l y understood. Chapter One presents a b r i e f discussion of the approach taken i n this series o f experiments.  The basic concept was introduced that s o i l  genesis proceeds at the interface between the s o i l p a r t i c l e s and the soil solution.  From this develops  the r e a l i z a t i o n o f the importance of  surface charge phenomena as a measure o f the a l t e r a t i o n o f the parent m a t e r i a l , or i n short, as a measure o f s o i l  genesis.  The f i r s t experiment, presented i n Chapter Two, demonstrated that for  three s o i l s containing large amounts of clay minerals, the surface  charge properties were strongly related to chemical and morphological measures of s o i l development.  The results indicated that as the pedo-  genic development proceeded and the sesquioxide content increased, pHdependent charge became dominant over pH-independent (permanent) charge. As a r e s u l t , the a - values approached zero; the ZPC became more c l e a r l y n  defined and approached the pH of the s o i l . Chapter Three examined the effect that different  potentiometric  t i t r a t i o n procedures had on the measured values of ZPC and a,-.  I t was  - 62 -  found that the slow-adsorption method produced lower values of  and  higher values of ZPC compared with the fast-adsorption method.  In the  fast-adsorption method the reaction being measured i s one between the surface proper and the potential determining ions H and OH"; i n con+  t r a s t , the slow adsorption includes in the measurement H and OH" ions +  incorporated into the hydrous oxide coatings; i t is therefore not considered to duplicate accurately a surface phenomenon. It was also found that NaCl-saturation p r i o r to t i t r a t i o n caused the ZPC and samples.  values to change compared to values obtained on untreated  For ZPC and  values below pH 5.0 and -0.25 meq/lOOg respec-  t i v e l y , as measured on untreated samples, the NaCl-saturation resulted in lower values; for values above pH 5.0 and -0.25 meq/lOOg the change was to higher values.  This change in surface charge characteristics  is  attributed to the displacement from the exchange complex of strongly bonded ions such as A l  3 +  and PO^ ". 3  The fast-adsorption technique using  untreated samples i s considered by the author to be the most accurate measure of the surface charge characteristics i n the f i e l d , since i t measures the properties at the surface and involves the least a l t e r a t i o n of the properties of that surface p r i o r to t i t r a t i o n . In Chapter Four the fast-adsorption potentiometric t i t r a t i o n method and untreated samples were used to study the changes i n surface charge characteristics along a s o i l chronosequence developed on sandy beach material.  The v a r i a t i o n of the organic matter contents at the seven  sites resulted i n poorly defined trends between ZPC and s o i l age and between a- and s o i l age.  Partial c o r r e l a t i o n analysis revealed that i f  the effect of organic matter was eliminated, both of these trends were  - 63 highly s i g n i f i c a n t .  The ApH value, defined as the difference between  the ZPC and the pH measured i n 1 N_ KCl, was found to correlate highly with s o i l age, since the effect of organic matter cancelled out. this chronosequence, ApH proved to be a good indicator of s o i l  In  genesis;  the values decreased from the youngest to the oldest s i t e , indicating that the s o i l p a r t i c l e surfaces are approaching a steady-state  condition  with respect to the s o i l s o l u t i o n . Chapter Five re-examined the effect of NaCl-saturation on the ZPC and a.j values using ten s o i l samples from southwestern B r i t i s h Columbia, Puerto Rico, and North Carolina.  These samples were chosen because they  presented a wide range of extractable sesquioxide contents and surface charge properties.  The results confirm the conclusions presented i n  Chapter Three, that NaCl-saturation prior to t i t r a t i o n changes the ZPC and a-j values. pH 5.0 and ZPC and  In the case of untreated samples with ZPC values below values less than -0.2 meq/lOOg, there was a s h i f t to lower  values following NaCl-saturation; when the ZPC and  were  above pH 5.0 and -0.2 meq/lOOg respectively, the s h i f t was in the opposite direction.  The effect of organic matter was also evaluated and  the removal of a portion of this material with NaOCl resulted in higher measured values of both ZPC and o\j..  This experiment has produced d i r e c t  confirmation that organic matter has a depressing effect on ZPC and  .  Measurement techniques have a s i g n i f i c a n t effect on the values of ZPC and a- obtained. n  The fast-adsorption procedure measures the fast  reaction at the p a r t i c l e surface, while the slow-adsorption procedure measures the additional slow reaction resulting from the incorporation of H and OH" ions into the structure of the oxide coatings. +  NaCl-satu-  ration p r i o r ' t o t i t r a t i o n results i n the exchange of strongly bonded  - 64 -  ions and thus alters  the properties of the surface.  The fast-adsorption  method using untreated samples is therefore considered to be the most accurate means of measuring the surface charge properties as they e x i s t in the f i e l d . Indirect evidence suggested that the presence of organic matter caused a decrease in the ZPC and a- values. of simple correlation coefficients  This evidence is i n the form  between organic C and a..  The results  of p a r t i a l c o r r e l a t i o n analysis removing the effect of organic matter indicate strong relationships between ZPC and s o i l age and also between a-j and s o i l age.  Evidence of this relationship is also supported by  d i r e c t measurement.  The removal of a portion of the organic matter using  a pretreatment of NaOCl resulted i n a s i g n i f i c a n t increase i n both the ZPC and  values.  Potentiometric t i t r a t i o n is a useful measure of surface charge char a c t e r i s t i c s and s o i l genesis. rals the ZPC and sandy s o i l s ,  In s o i l s with large amounts of clay mine-  change as the sesquioxide content increases.  In  the values of ZPC and a-j are only s i g n i f i c a n t l y related to  s o i l age when the effect of differences in the s o i l organic matter content has been eliminated. for differences extent of s o i l  The ApH value, on the other hand,  compensates  i n organic matter and provides a good indication of the development.  - 65 -  APPENDIX  The appendix consists  of p r o f i l e descriptions for those s o i l s  described elsewhere i n the thesis.  not  Samples from the Cox Bay transect  are used i n the experiments described i n Chapters Four and F i v e , and the morphological properties are presented here in tabular form.  Five  of the samples discussed i n Chapter Five are described here i n the form of f i e l d descriptions (Samples 1, 2, 3, 9, and 10); the others are i n cluded i n the descriptions i n Chapter Two, or in the descriptions of the s o i l s from Cox Bay.  MORPHOLOGICAL PROPERTIES OF COX BAY TRANSECT NOTE: SITE N 0  Texture of a l l mineral horizons is fine sand. HORIZON^ U.S CDN  Smi  :  ,  STRUCTURE  c o y o u R  =  "fJSS^ (  M  o  i  s  t  )  TYPIC UDIPSAMMENT (Orthic Dystric Brunisol)  -  -  02  FH  6-0  5YR 2/1  B2  Bftf  0-10  5Y  4/3  wk. subangular blocky  v.  friable  CI  CI  10-25  5Y  3/2  v. wk. subangular blocky  v.  friable  C2  C2  25-46  5Y  5/2  v. wk. subangular blocky  loose  C3  C3  46+  5Y  5/2  v. wk. subangular blocky  1 oo se  TYPIC UDIPSAMMENT (Orthic Dystric Brunisol)  -  -  02  FH  8-0  B2  Bm  0-15  2.5Y  5/4  v. wk. subangular blocky  v.  B3  BC  15-56  5Y  4/3  v. wk. subangular blocky  1 oose  C  C  56+  5Y  4/3  wk. subangular blocky  loose  5YR 2/2  friable  TYPIC HAPLORTHOD (Orthic Dystric Brunisol)  -  -  02  FH  10-0  5YR 2/1  A2  Aej  0-1  10YR 3/1  v. wk. subangular blocky  loose  B2ir  Bm  1-38  10R  2/2  mod.  subangular blocky  v.  friable  B3  BC  38-69  2.5Y  4/4  mod.  subangular blocky  v.  friable  C  C  69+  5Y  4/3  v. wk. subangular blocky  v.  friable  MORPHOLOGICAL PROPERTIES OF COX BAY TRANSECT (Cont'd) SITE NO.  4  HORIZON U.S.  . CDN  DEPTH cm  STRUCTURE  COLOUR  CONSISTENCE (Moist)  TYPIC HAPLORTHOD (Orthic Humo-Ferric Podzol)  -  02  FH  8-0  ~5YR 2/1  A2  Ae  0-3  5YR 5/1  mod. subangular blocky  v. f r i a b l e  B21ir  Bf  '3-18  10YR 3/4  mod. subangular blocky  v.  B22ir  Bm  18-46  10YR 6/6  mod. subangular blocky  firm  B3  BC  46-91  C  C  91 +  friable  2.5Y  4/4  v. wk. subangular blocky  friable  5Y  4/3  v. wk. subangular blocky  friable CT)  5  TYPIC HAPLORTHOD (Orthic Humo-Ferri c Podzol) 02  FH  10-0  5YR 2/1  A2  Ae  0-5  10YR 6/2  B21ir  Bfl  5-26  B22ir  B'f2"-  26-36  B23ir  Bm  36-58  2.5Y  B3  BC  58-99  C  C  99+  -  -  mod. subangular blocky  v.  friable  7.5YR 3/2  s t . subangular blocky  firm  10YR 3/3  wk. subangular blocky  f i rm  5/6  wk. subangular blocky  friable  2.5Y  4/4  wk. subangular blocky  friable  2.5Y  4/2  single grain  loose  MORPHOLOGICAL PROPERTIES OF COX BAY TRANSECT (Cont'd)  STRUCTURE  CONSISTENCE (Moist)  -  -  TYPIC HAPLORTHOD (Orthic Humo-Ferri c Podzol) 02  LFH  8-0  5YR 2/2  A2  Ae  0-5  10YR 5/2  wk. subangular blocky  v.  B21ir  Bfl  5-10  2.5YR 3/2  wk. subangular blocky  loose  B22ir  Bf2  10-20  2.5YR 3/2  mod . subangular blocky  firm  B23ir  Bm  20-43  7.5YR 4/4  mod . subangular blocky  firm  B3  BC  43-74  TOYR 5/4  v.  wk. subangular blocky  v. f r i a b l e  C  C  74+  10YR 5/4  v.  wk. subangular blocky  loose  friable  AQUIC HAPLORTHOD (Orthic Humo-Ferri c Podzol)  FROM:  02  LFH  A2  Ae  0-6  A&B  A&B  6-18  B21ir  Bfl  18-30  B22ir  Bf2  B3  BC  G.A. Singleton.  20-0  2.5Y  2/0  -  -  v. wk. subangular blocky  friable  mod . subangular blocky  friable  10YR 2/1  wk. subangular blocky  friable  30-56  10YR 2/2  mod . angular blocky - coarse platy  fi rm  56  10YR 3/3  wk. angular blocky  f i rm  1978.  +  10YR 4/2  -  Ph.D. Thesis, Dept. of S o i l Science, UBC.  (In preparation)  - 69 -  FIELD DESCRIPTION OF MARBLEHILL SERIES Soil  Classification:  Locati on:  HORIZON  TYPIC HAPLUMBREPT (Orthic Ferro-Humic Podzol) On top of a ridge 1 km SE of Agriculture Canada experimental farm, Agassiz, B . C .  DEPTH cm  DESCRIPTION  0  (LFH)  2--0  Deciduous l i t t e r i n various states of decomposition .  Al  (Ah)  0--5  Very dark brown (10YR 2/2, m.); fine sandy loam; weak, fine granular; very f r i a b l e ; abundant, fine and medium roots; abrupt, smooth boundary to:  B21  (Bhf)  5 -15  Brown (7.5YR 4/3, m.); s i l t loam; weak, fine granular; v. f r i a b l e ; abundant, fine and medium roots; abrupt, wavy boundary to:  B22  (Bf)  15 -44  Brown (7.5YR 4/4, m.); s i l t loam; weak, f i n e , subangular blocky; very f r i a b l e ; p l e n t i f u l , fine and medium roots; clear wavy boundary to:  B3  (BC)  44-80  Yellowish brown (10YR 5/5, m.); s i l t loam; moderate, f i n e , subangular blocky; very f r i a b l e ; few, fine and medium roots; common, f i n e , d i s t i n c t mottles (7.5YR 4/4, m.); diffuse boundary to:  C  (C)  80-150  +  Brown (10YR 4/3, m.); s i l t loam; moderate, medium, subangular blocky; very f r i a b l e ; few, medium roots; common, f i n e , d i s t i n c t mottles (7.5YR 4/4, m.) .  - 70 -  FIELD DESCRIPTION OF DURIEU SERIES  Soil Classification:  TYPIC HAPLUMBREPT (Sombric Humo-Ferric Podzol)  Location:  Durieu County, B r i t i s h Columbia.  HORIZON  DESCRIPTION  D E P T H  cm  0  (LFH)  3-0  Coniferous l i t t e r composition.  Al  (Ah)  0-13  Very dark brown (10YR 2/2, m.); s i l t loam; weak, fine granular; very f r i a b l e ; abundant f i n e , medium, and coarse roots; abrupt, wavy boundary to:  A2  (Ae)  13-14  Very dark grayish brown (10YR 3/2, m.); s i l t loam; f r i a b l e ; few f i n e , p l e n t i f u l medium and few coarse roots; abrupt, wavy boundary to:  B21ir  (Bfl)  14-30  Dark reddish brown (2.5YR 3/4, m.); s i l t loam; moderate, medium, subangular blocky; f r i a b l e ; few f i n e , p l e n t i f u l medium and few coarse roots; gradual, wavy boundary to:  B22ir  (Bf2)  30-50  Brown (7.5YR 4/4, m.); s i l t loam; moderate, medium, subangular blocky; f r i a b l e ; few f i n e , p l e n t i f u l medium and few coarse roots; d i f fuse, wavy boundary to:  B3  (BC)  50-90  Dark yellowish brown (10YR 3/6, m.); s i l t loam; moderate, medium, subangular blocky; f r i a b l e ; few f i n e , p l e n t i f u l medium, few coarse roots; clear smooth boundary to:  C  (C)  90-110  +  in various states of de-  Grayish brown (2.5Y 3/2, m.); sandy loam; strong, medium to coarse, subangular blocky; firm; weakly cemented; few medium and coarse roots; common, fine to medium, d i s t i n c t mottles (7.5YR 5/6, m.).  - 71 -  FIELD DESCRIPTION OF UNNAMED ASSOCIATE OF DURIEU  Soil  Classification:  TYPIC HAPLAQUEPT (Orthic Humic Gleysol)  Location:  HORIZON  Durieu County, B r i t i s h Columbia.  DEPTH cm  DESCRIPTION  (LFH)  1-0  Deciduous l i t t e r , raw to  Al  (Ah)  0-12  Black (10YR 2/1, m.); loam; weak, fine to medium granular; very f r i a b l e ; abundant, fine and medium roots; abrupt, wavy boundary to:  B2g  (Bg)  12-22  Brown (10YR 4/3, m.); s i l t loam; moderate, medium to coarse, subangular blocky; firm; few, fine and medium roots; common, medium, prominent mottles (5YR 5/8, m.); c l e a r , wavy boundary to:  Clg  (Cgl)  22-50  Grayish brown (2.5Y 5/2, m.); loam; moder a t e , coarse, subangular blocky; firm; few, medium roots; common, medium, prominent mottles (5YR 5/8, m.); c l e a r , wavy boundary to:  C.2g  (Cg 2)  50  1  well-decomposed.  Grayish brown (2.5Y 5/2, m.); s i l t y clay loam; moderate, coarse, subangular blocky; firm; few, medium roots; many, medium, prominent mottles (5YR 3/3, m.); below water table.  - 72 -  FIELD DESCRIPTION OF NIPE SERIES  Soil C l a s s i f i c a t i o n :  TYPIC ACRORTHOX (No Canadian Equivalent)  Location:  Oeste SCD, Puerto Rico; 1 mile E of Mayaguez; 0.5 mile W of km marker 5.5 of highway 349. On top of a h i l l .  HORIZON  DEPTH in.  Ap  0-11  Bl  11-18  Dark reddish brown (2.5YR 3/4, m.); clay; weak fine angular blocky structure; very f r i a b l e , nonsticky, s l i g h t l y p l a s t i c ; many fine pores; common fine roots; very strongly a c i d ; clear smooth boundary.  B21  18-28  Dark red (7.5R 3/8, m.); c l a y ; weak fine angular blocky structure; very f r i a b l e , nonsticky, s l i g h t l y p l a s t i c ; many fine pores; few fine roots; very strongly acid; diffuse smooth boundary.  B22  28-38  Dark red (7.5R 3/6, m.); c l a y ; massive; firm, nonsticky, s l i g h t l y p l a s t i c ; many fine pores; few fine iron concretions; strongly a c i d ; diffuse smooth boundary.  B23  38-48  Dusky red (7.5R 3/4, m.); c l a y ; massive; f r i a b l e , nonsticky, s l i g h t l y p l a s t i c ; many fine pores; few fine iron concretions; strongly acid; gradual smooth boundary.  B24  48-62  Dark red (7.5R 3/6, m.); c l a y ; massive; f r i a b l e , nonsticky, s l i g h t l y p l a s t i c ; many fine pores; medium a c i d ; diffuse smooth boundary.  B25  62-80  Dusky red (7.5R 3/4, m.); c l a y ; massive; f r i a b l e , nonsticky and nonplastic; many fine pores; medium a c i d .  FROM:  DESCRIPTION  Dark reddish brown (2.5YR 2/4, m.); clay; strong fine granular structure; f r i a b l e , nonsticky, s l i g h t l y p l a s t i c ; many fine roots; strongly acid; clear smooth boundary .  H  Luis H . Rivera, Soil Conservation Service, U . S . D . A . , San Juan, Puerto Rico.  - 73 -  FIELD DESCRIPTION OF FACEVILLE SERIES  Soil C l a s s i f i c a t i o n :  TYPIC HAPLUDULT (No Canadian Equivalent)  Location:  About 6600 feet W ( 2 8 0 ° ) from the intersection of Johnston County Roads 1700 and 1715, 900 feet from the Neuse River, at the end of a logging road.  HORIZON  D  ^  T  H  DESCRIPTION  Ap  0-7  Dark brown (7.5YR 4/2); sandy loam; common medium f a i n t brown (7.5YR 5/4) mottles; weak medium granular structure; very f r i a b l e ; common fine roots; common fine pores; strongly a c i d ; clear wavy boundary,  A2  7-10  Brown (7.5YR 5/4); sandy loam; common medium prominent dark red (2.5YR 3/6) mott l e s ; massive; f r r a b l e ; few fine roots; few fine pores; strongly a c i d ; clear wavy boundary .  B21t  10-50  Dark red (2.5YR 3/6); sandy c l a y ; moderate medium subangular blocky structure; f r i a b l e ; few fine and medium roots; common thin d i s t i n c t continuous clay films on faces of peds; strongly a c i d ; diffuse smooth boundary.  B22t  50-93  Dark red (2.5YR 3/6); sandy c l a y ; few medium d i s t i n e t yellowish red (5YR 5/6) and few medium prominent yellowish brown (10YR 6/4) mottles; moderate medium subangular blocky structure; f r i a b l e ; common thin d i s t i n c t continuous clay f i l m s ; very strongly a c i d ; diffuse smooth boundary.  C  93-144  Red(2.5YR 4/6); clay loam; common medium prominent l i g h t gray (10YR 7/1) and pale brown (10YR 6/3) mottles; massive; f r i a b l e ; few thin f a i n t clay films along root channels; very strongly a c i d .  FROM:  Hubert J . Byrd, S o i l Conservation S e r v i c e , U . S . D . A . , Raleigh, North Carolina.  

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