I 70-20,509 PAILOOR, Govind, 1940VARIATIONS IN CATION EXCHANGE CAPACITIES OF SOME REPRESENTATIVE MICHIGAN SOILS WITH ANALYTICAL PROCEDURES AND THEIR RELATIONSHIPS TO ACIDITY, CLAY MINERALOGY AND ORGANIC MATTER. Michigan State University, Ph.D., 1970 Agriculture, soil science U n ive rsity M icrofilm s, A XEROX C o m p a n y , A n n A rb o r, M ich ig an V A R I A T I O N S IN C A T I O N EXCH A N G E CAPACI T I E S OF SOME R E P R E S E N T A T I V E M I C H I G A N SOILS W I T H A N A L Y T I C A L PR O C E D U R E S A N D T H E I R R E L A T I O N S H I P S TO ACIDITY, CLAY MINERALOGY AND ORGANIC MATTER By G o v i n d Pailoor A THESIS Submi t t e d to M i c h i g a n State Un i v e r s i t y in par t i a l f u l f i llment of the r e q u i rements for the degree of D O C T O R OF PHILOSOPHY D e p a r t m e n t of C r o p and Soil Sciences 1969 ABSTRACT V A R I A T I O N S IN C A T I O N E X C H A N G E C A P A C I T I E S OF SOME R E P R E S E N T A T I V E M I C H I G A N SOILS W I T H A N A L Y T I C A L P R O C E D U R E S A N D T H E I R R E L A T I O N S H I P S TO ACIDITY, CLAY M I N E R A L O G Y A N D ORGA N I C M A T T E R By Govind P a i l o o r T h e CECs were d e t e r m i n e d by the following common m e t h o d s on 38 r e p r e s e n t a t i v e acid to near neutral M i c h i g a n soil samples from 15 soil types: the KC1 method, (1) the C a C l 2 method, (3) the NH^OAc method, m a t i o n m e t h o d and (5) (2) (4) the c a t i o n s u m ­ the N a O A c method. T h e results o b t a i n e d w e r e g r o u p e d a c c o r d i n g to the f o l l o w i n g kinds of soil horizons and subjected to s t a t i s t i ­ cal analyses: spodic B^, (1) the surface A p and A^, and B ^ r , (3) (2) the illuvial the illuvial Bt a n d Bg, and (4) the A 2 , A '2 and C^ h o r i z o n s of u n c o a t e d materials. The pr e d i c t i v e equations for CEC among the five m e t h ­ ods w e r e all highly s i g n i f i c a n t on all but the spodic h o r i ­ zons. In spodic horizons, however, only NH^EC vs N a E C and KEC vs C a E C could be p r e d i c t e d hi g h l y significantly for the soils u s ed in this study. T h e mult i p l e r e g r e s s i o n analysis showed an 11 to 4 5 m e q of c harge c o n t r i b u t i o n p e r 1 0 0 g of clay as w o u l d be Govind Pailoor n o r m a l l y expe c t e d from soils of d o m i n a n t l y m i x e d clay m i n e r a logy. The charge c o n t r i b u t i o n f r o m o r g a n i c m a t t e r to NaEC w a s h i g h e s t of all horizons and u n r e a s o n a b l y h i g h though h i g h l y s i g n i ficant in surface horizons. The C a E C and KEC o n spodic horizons showed a low ch a r g e con t r i b u t i o n fro m o r g a n i c matter, 14 and 25 m e q p e r 100 g respectively. The o r ganic m a t t e r charge c o n t r i b u t i o n was w i t h i n the norma l l y e x p e c t e d range of 87 to 255 m e q per 100 g for all o t h e r C E C v a l u e s o n all horizons other than the illuvial B+. t and B_ g horizons. The high charge c o n t r i b u t i o n f r o m org a n i c m a t t e r found in B. and B horizons for all CEC values indicate d t g that a d i f f e r e n t kind of organic exchange c o m p l e x is p r e ­ sent t h e r e . The m a r k e d increase in both CaEC a n d KEC va l u e s on the same soil samples after 1 N N a O A c treatment were sh o w n as e v i d e n ce that 1 N NaOAc commonly e m p l o y e d in CEC d e t e r ­ m i n a t i o n alters the native soil exchange properties to a s i g n i f i c a n t extent. This is due to one or more of the m e c h a n i s m s of anion retention, d i s s o l u t i o n of a m o r phous c o a tings of F e 20 3 and A ^ O ^ , d i s s o l u t i o n of organic Fe and A1 complexes and partial removal of the A l - i n t e r l a y e r s w h e n present. Some or all of these c h a r acteristics are p r e s e n t in surface horizons of most M i c h i g a n soils par t i c u l a r l y Spodosols, and the spodic horizons. Due to the reasonable charge c o n t r i b u t i o n s from b o t h clay (23 to 45 meq/100 g) and organic ma t t e r (156 to 392 Govind Pailoor me q / 1 0 0 g) contents of soils revealed in NH^EC on all h o r i ­ zons, and the v a l u e of N H ^ E C being i n t e rmediate b e t w e e n C a E C and NaEC, it was t h o u g h t to b e the b e s t estimate of the net n egative charge of the M i c h i g a n soil m a t e r i a l s . T h e soil exch a n g e acid i t y va l u e s w e r e o b t a i n e d by: (1) B a C l 2+ T E A method, and (2) KC1 method, (3) the NH ^ O A c method, (4) the Shoemaker, M c L e a n and P r a t t It was c o n c l u d e d that the E A ( B a C l 2 +TEA) (SMP) bu f f e r method. and the SMP buffer m e t h o d c o u l d be p r e d i c t e d s i g n i f i c a n t l y o n all h o r i z o n groupings of the acid to near neutral r e p r e s e n t a t i v e M i c h i ­ g a n soil m a t e r i a l s % Higher va l u e s w e r e o b t a i n e d by the SMP m e t h o d p a r t i c u l a r l y on spodic horizons. This indic a t e d t h a t the lime r e q u i r e m e n t r e c o m m e n d a t i o n s for S p o d o s o l s may be o v e r e s t i m a t e d due to the m i x i n g of spodic horizons, norm­ a l l y o c c u rring a t a depth of six to twelve i n c h e s , w i t h the surface h ori z o n s by plowing. It w a s c o n c l u d e d therefor e t h a t the d e t e r m i n a t i o n of e x c h a n g e acidity by B a C l 2+ T E A or an a d j u s t m e n t of the EA(SMP) s h i p to E A ( B a C l 2 +TEA) values b a s e d on its r e l a t i o n ­ m a y g i v e a m o r e r e l i a b l e e s t i m a t e of the lime req u i r e m e n t of c o m m o n M i c h i g a n soil m a t e r i a l s , p a r t i c u l a r l y the S p o d o s o l s . TO MY FATHER, MO T H E R UNCLE, AUNT SISTERS, BROTHERS SWEET SHARADE PEOPLE A T HOME AND IN M I C H I G A N ACKNOWLEDGMENTS T he a u t h o r e x p r e s s e s his solemn g r a t i t u d e to his m a j o r professor. Dr. E. P. Whiteside, ance, for his kind a s s i s t ­ c r i t i c i s m s and e n c o u r a g e m e n t throughout this study. He sincerely appreciates the g u i d a n c e of Dr. B. G. Ellis as c o - d i r e ctor of this thesis. He has a high es t e e m for the other m embers of his guidance committee. M. M. M ortland, Drs. R. L. Cook, A. E. E r i c k s o n and H. E i c k for their c o ­ o p e r a t i o n in this study. The a u t h o r thanks in e a r n e s t Dr. G. L. J o h n s o n for the concepts in A g r i c u l t u r a l Economics d e v e l o p e d through his association. He is mind f u l of the p l e a s a n t a t m o s p h e r e of rea s s u r a n c e amo n g s t his colleagues and m e m b e r s of the Department. T h e au t h o r admires culture, Soils and M e n . the title of an Yearbook of A g r i ­ He is grateful to his A l m a Mater, M i c h i g a n State University, for gi v i n g h i m an o p p o r tun i t y to p e e p into the nature of b o t h t h e s e . TABLE OF CONTENTS Pa g e ACKNOWLEDGMENTS ........................................... iii L I S T O F T A B L E S ............................................. V L I S T O F F I G U R E S ............................................ vii INTRODUCTION ................................................ LITERATURE REVIEW ........................................ E a r l y Hist o r y of C a t i o n E x c h a n g e Capa c i t y . . . . C a t i o n E x c h a n g e Theo r i e s ............................. Sources of Ca t i o n E x c h a n g e in Soils .............. E x c h a n g e a b l e A l u m i n u m and Soil A c i d i t y as Factors I n f l u encing C a t i o n Exchange ............ M e t h o d s of C a t i o n E x c h a n g e Capa c i t y D e t e r m i n a t i o n ...................................... 1 3 3 4 11 18 22 M A T E R I A L S A N D M E T H O D S .......................................25 Soils U s e d in the S t u d y ............................... 25 M e t h o d s U s e d in this S t u d y ............................. 35 C a C l 2 m e t h o d for CEC d e t e r m i n a t i o n ............... 36 KC1 m e t h o d for C E C d e t e r m i n a t i o n ................. 37 N H 4 O AC m e t h o d for d e t e r m i n a t i o n of CEC and e x c h a n g e a b l e bases ............................ 37 NaOAc m e t h o d for CEC d e t e r m i n a t i o n ............... 39 B a r i u m chloride plus t r i e t h a n o l a m i n e m e t h o d for the d e t e r m i n a t i o n of exchange a c i d i t y . 40 KC1 e x t r a c t i o n and fluoride titration p r o ­ cedure for d e t e r m i n a t i o n of e x t r a c t a b l e a c i d i t y and e x c h a n g e a b l e a l u m i n u m ............ 41 RESULTS AND DISCUSSION SUMMARY AND CONCLUSIONS .................................... ................................. 43 82 N E E D F O R F U R T H E R R E S E A R C H .................................. 87 LITERATURE CITED APPENDIX ........................................... 88 99 LIST OF TABLES T able Page 1. Soil type names and legal descriptions of l o c a ­ tions of the profiles s t u d i e d .................. 26 2. Information on soils s t u d i e d ....................... 30 3. E ffect of washing procedures in CaCl~ method of CEC d e t e r m i n a t i o n ................................ 45 4. R e lationship between effective replacement of K + by NH^+ with increasing number of washings . . 48 5. C a t i o n exchange capacity values for 15 soil samples determined by the NaOAc me t h o d at pHs 7.0 and 8 . 2 . ................................ 49 6. T h e m e a n CEC values determined by five methods grouped according to the kinds of soil h o r i ­ zons ..................................................53 7. Regression equations and correlation coefficients a mong CEC values determined by five methods grouped according to the kinds of soil h o r i z o n s ......................................... 56 8. Relationships between CEC values and clay and carbon contents, their partial and multiple correlation coefficients and levels of s i g n i f i ­ cance, on soils grouped according to horizons . 9. Relative charge contributions from clay to CEC values grouped according to the kinds of soil h o r i z o n s .................................... 58 10. Relative charge contributions from organic m a tter to CEC values grouped according to the kinds of soil h o r i z o n s .................... 60 11. The effect of IN NaOAc on CEC of soil materials 12. T h e m e a n values of acidity components grouped according to the kinds of soil horizons . . . . v . 57 70 74 LIST OF TABLES - Continued. Table 13. 14. 15. Page R e l a t ionships bet w e e n soil acidity m e a s u r e m e n t s a n d clay a n d o r g a n i c carbon contents gro u p e d ac cor d i n g to the kinds of soil horizons . . . 76 R e l a t ive aci d i t y contributions f r o m clay to e x cahnge acidities grouped a c c o r d i n g to the k i nds of soil h o r i z o n s ........................ 77 R e l a t ive acidity contributions from organic m a t t e r to exch a n g e acidities grouped a c c o r d ­ ing to the kinds of soil h o r i z o n s ............ 78 16. Data on chemical analyses of soils studied . . . 100 17. E s t i m a t i o n of clay m i n e r a l s in the clay f r a c ­ t i on of the horizons of similar soil types ........................ 1 0 2 as used in this study LIST OF FIGURES Figure 1. The charges on the edges o f clay particles under acid and alkaline conditions as affec t e d by mineralogical composition ....................... Page 13 2. Map of Michigan showing location of r e p r e s e n t a ­ tive soils used in this s t u d y ...................... 27 3. Depth functions of p H of soils s t u d i e d ............... 32 4. Depth functions of percent clay in soils s t u d i e d ............................................... 33 5. Depth functions of per c e n t carbon in soils s t u d i e d ............................................... 34 6. Depth functions of CaEC and NaEC in soils s t u d i e d ............................................... 52 7. Depth functions of soil acidity components in soils s t u d i e d ........................................ 73 INTRODUCTION E v e r since Way p u b l i s h e d a p a p e r "On the p o w e r of soils to re t a i n manure" o v e r a hundred years ago, the i n ­ t e r e s t in studying ion exchange has conti n u e d in o r d e r to b e t t e r u n d e r s t a n d the p h y s i c o - c h e m i c a l proce s s e s t h a t a f ­ fect soil fertility. The chemical and phys i c a l proce s s e s m o r e or less intimately c o n n e c t e d w i t h ion exch a n g e i n ­ clude: w e a t h e r i n g of minerals, plants, swel l i n g and shrin k i n g of clay and leaching of electrolytes. nutrient a b s o r p t i o n by The w e a t h e r i n g processes in time alter the c o m p o s i t i o n of the soil m a t e r i a l r e s u lting in changes ion exchange and o t h e r phy s i c o - c h e m i c a l properties. in turn change the soil p r o f i l e properties, a b i l i t i e s and m a n a g e m e n t requirements. in T hese land use c a p ­ N u t r i e n t cations a n d h y d r o g e n exch a n g e r e v e r s i b l y w i t h soil collo i d a l s u r ­ faces, a n d those surfaces act as a storehouse of food for plants. Cat i o n exchange capacity, therefore, is a m e a s u r e of the p o t e n t i a l n u t r i e n t cation r e t e n t i o n status of a soil. K elly (1948) defines ca t i o n exchange as "the total c a t ions that can be repl a c e d from a given substance under a set of gi v e n conditions." A l t h o u g h ca t i o n exchange c a p a c ­ ity is one of the m o s t commonly meas u r e d soil properties, it is s eldom highly precise. It is a kn o w n fact that no two a n a l y t i c a l methods agree w i t h each other in their 1 2 values. These variations m a y be attributed to the pH of the e q u i librium system, the nature and concentrations the reacting and replacing ions, wash solvents used, of time of interaction and o t h e r v a r i a b l e s . As a valuable soil measurement, the cation exchange capacity ideally needs to be a defined characteristic under a given set of conditions so that the soil data can be accurately interpreted or diagnosed. In the light of the inherent variations mentioned above, an attempt has been m a d e in this study to compare the results of commonly used methods of cation exchange capacity, their relationship to each other, and the mai n soil p roperties that affect them. A suitable me t h o d for routine use wh i c h is reproducible but economical and that gives a reliable estimation of the net negative charge of the kinds of soil materials common in M i c h i g a n w o u l d be very helpful in facilitating efficient soil management. F a i l i n g such a generally applicable method, the limitations of the methods most suitable for particular kinds of soils need to be evaluated. LITERATURE REVIEW E arly H i s t o r y of Ca t i o n Excha n g e C a p a c i t y A c c o r d i n g to Kelly (1948), r e c o g n i t i o n of the p h e n ­ o m e n o n of ca t i o n exch a n g e is at t r i b u t e d to two Englishmen, Thompson (1850) and Way (1850). Way (1850) in his first p u b l i c a t i o n listed several conclusions of his work. They were: 1. In r e a c t i o n b e t w e e n soil and salt solutions, c a l c i u m in the soil exchanges pl a c e s w i t h ca t ions in solution, anions r e m a i n i n g in s o l u t i o n u n l e s s an insoluble c a l c i u m salt is formed. 2. Salts of lime are not adsorbed w h e n f i l t e r e d through the soil, but Ca(OH) 2 are adso r b e d whole and C a t H C O ^ ^ (in m o l e c u l a r form) like a l k a ­ line compounds of o t h e r c a t i o n s . 3. The clay p o r t i o n of soil has the p o w e r to ad s o r b cations. Sand, r a w organic matter, calcium car­ bonate and free alumina do not poss e s s this power. 4. P r e h e a t i n g of soil d i m i n i s h e s its a d s o r p t i v e power. 5. A d s o r p t i o n is a rapid reaction, as b e t w e e n m i n e r a l acid and alkalies. 6. A m m o n i u m carbonate and a m m o n i u m h y d r o x i d e are adso r b e d as m o l e c u l e s . 3 4 7. A d s o r p t i v e power of clay increases with i n c r e a s ­ ing c o n c e ntration of solution and as the ratio of solution to soil increases. 8. Cation exchange is exhibited with the soil by K + , N a + and M g ^ + in addition to NH^+ . 9. Cation exchange is irreversible. Interestingly, except for conclusions 2, 6 and 9, others for the m o s t part have proved to be correct. m a t t e r particularly as humus, the exchange property. only, Organic is of course known to exhibit Of course calcium ions are not the though they are commonly the chief, exchangeable cations present in the soil. Ca t i o n Exchange Theories There have b e e n several explanations proposed for the ion exchange behavior. charged colloids, When dealing with negatively if we consider the cation distributio n be t w e e n the solid and liquid phases, we observe the p h e n ­ o m e n o n of cation e x c h a n g e . A n y equation that gives the d i s t r i b u tion of cations bet w e e n a suspension and its dialyzate may be called a cation exchange equation. Generally, simple s toichiometric equivalence between ions taken up and ions released is assumed to be present in the r e a c t i o n s . But the exceptions are usually explained in terms of a d ­ s orption or by the formation of complex i o n s . point of view, F r o m another the phenom e n o n of adsorption is a precursor 5 of the ion exchange. A d s o r p t i o n is a n e t r e s u l t of the i n t e r a c tion b e t w e e n a t t r a c t i v e and r e p u l s i v e forces that are a cting b e t w e e n the n e g a t i v e l y c h a r g e d sur f a c e and the n e a r b y e x c h a n g e a b l e cations. A c c o r d i n g to N o r r i s h (1954), w h e n the r e l a t i o n s h i p of the c a t i o n to the surface is s i m i ­ lar to that of a p o i n t charge to a thick p l a n e conductor, the a t t ractive e n e r g y is e x p r e s s e d in the follo w i n g form: ea Where - (1 > is the surface ch a r g e density, a v is the ionic v a l ­ ence, e is the e l e c t r o n i c charge, d is the d i s t a n c e b e t w e e n the ions and the surface and e However, is the d i e l e c t r i c constant. if the i n t e r p a r t i c l e cations a n d c h a r g e d surfaces a re r e g a r d e d as the plates of a p a r a l l e l pl a t e condenser, the a t t ractive e n e r g y b e c o m e s : EA Actually, - 2_jr_afa the at t r a c t i v e en e r g y will b e t w e e n the above two e q u a t i o n s . apart, gether, (2) equation equation likely b e a co m p r o m i s e W h e n the cati o n s are far (1 ) wil l apply; w h e n they are close t o ­ (2) w i l l apply. Primarily, the at t r a c t i o n b e t w e e n the clay surface and the e x c h a n g e a b l e ca t i o n is e l e c t r o s t a t i c in nature o b e y i n g C o u l o m b ' s law. In short r a n g e s , o t h e r forces like h y d r o g e n b o n d i n g b e t w e e n o x y g e n atoms a nd h y d r o x y l groups in a d j a c e n t surfaces occur. Also v an d e r Waal *s-London forces contribute to attraction in the short range. Many of these forces depend on the nature and properties of the atoms under consideration and t h e r e ­ fore o n the mineralogical composition of the surfaces. Re­ p u l s i o n occurs when the atoms in adjacent surfaces are in such close p r o x imity that their outer shell electrons o v e r ­ lap. This repulsion is the so-called Born repulsion. The r e s u lting repulsive energy E R is given by the following equation from Pauling (1945): Where B is a constant, e is the electronic charge, R is the distance b et w e e n atoms in adjacent surfaces and n has a value in the neighborhood of 9 but which depends on the kinds of atoms involved. Dipole-dipole interaction also causes r e p ulsion according to Olphen m i neral surfaces undergo hydration, (Low and Deming, (1954). Also, when they are forced apart 1953; Hemwall and Low, 1956; MacEwan, 1954) The adsorption phenom e n o n has been considered in great d etail by several workers beginning from F r e u n d l i c h 1s classical adsorption isotherm equation W i e g n e r and Jenny, Barken, 1940; (Langmuir, 1918; 1927; Vageler and Waltersdorf, Dunken, 1940). Hogfeldt (1955, p. 19 30; 151) re­ v i e w e d empirical equations of Krocker, Vageler, Weisz, Boedeker, Freundlich, W i e g n e r and Jenny, V a n Dranen, Rothmud-Kornfield, and Yamabe and Sato. Mokrushin (1945) 7 s howed h o w such basic equations of col l o i d chemistry, or Gibb's a d sorp t i o n equation, and Langm u i r and F r e u n d l i c h a d s o r p t i o n equations, and others can be d e d u c e d by use of the M a x w e l l - B o l t z m a n equations. A c c o r d i n g to G r i m the a p p l i cations of these empir i c a l equations is limite d by such v ariables as nature of the clay mineral, the ion, other ionic concentration, (1968) nature of clay c o n c e n t r a t i o n and factors. T h e or i e s of ion exchange e q u i l i b r i a in soils are u s ually b a s e d on the d i s t r i b u t i o n of ions in w a t e r abou t a n e g a t i v e l y c h a r g e d plate. m o d e l systems, Of the two m a j o r c a t e g o r i e s of the double layer theory employs the Gouy d i s t r i b u t i o n equation. for this theory. Helmholtz In this theory, (1879) p r o v i d e d the basis charge d e n s i t y o n the surface of the particles is assumed to be uniform, the ions are taken as p o i n t c h a r g e s , and any specific i n t e r actio n s b e t w e e n the p a r t i c l e and the ion are neglected. This d i s ­ t r i b u t i o n is such that the bulk of the cations are near the < surface of the negatively charged particle and the r e m a i n ­ ing cations are d i s t r i b u t e d so that the c o n c e n t r a t i o n d e ­ c r e ases w ith distance from the particle. Anion concentra­ tion increases as the ca t i o n c o n c e n t r a t i o n d e c r e a s e s , a n d these changes continue as a function of d i s t a n c e f r o m the p a r t i c l e until the c o n c e ntration of both ions is equal. Stern (1924) proposed two c o r r e ctions to the Gouy d i s t r i b u t i o n theory: (1) The size of the ions d e t e r m i n e s 8 the distance of closest approach of the center of their p o s itive charge to the particle, and (2 ) specific ad s o r p ­ tion potentials exist w h i c h may be different for each ion species. Bolt Shainberg and Kemper (1955) (1966) cited the work of to indicate that no appreciable short-range i nteraction is possible unless dehydration of the ions occurs close to the surface and stated "in case of cations as counter ions, de h y d r a t i o n does not seem probable, in general, unless the dielectric constant of the colloid e x ­ ceeds that of water." A c cor d i n g to Rich (1968), such ion distributions in soils should be viewed with reference to the cations studied, their concentration and particularly the spacial relationships of particles, example, surfaces, and solution. For if the individual layers of montmorilIonite p a r t i ­ cles saturated w i t h diva l e n t ions or ions of higher valence, O do not separate more than 10 A a Gouy distribution cannot d e v e l o p in this interlayer space (Norrish and Rausell- Colom, 1962). 1963; Aylemore and Quirk, Many soil mont- m o r i l I o n ites and vermiculites are less subject to e x p a n ­ sion. Thus, the cations on internal surfaces of expansible layer silicates of m o s t soils should be viewed as different from those in a model based on the Gouy distribution. Oe Haan's work (1965) indicated that the inter-layer region of soil m inerals is not included in the diffuse layer. The surface area of 1 2 soils determined by anion exclusion was 9 a n a v e rage of only 26 per cent: of that d e t e r m i n e d by an e t h y l e n e glycol method. E l - S w a i f y et a l . (1967), the b a s i s of anion e x c l u s i o n measurements, also on stated that v e r m i c u l i t e has two d i s t i n c t and s e p a r a t e d ionic r e g i o n s . S h ain b e r g and Kemper (1966) h a v e sugge s t e d an i m ­ p r o v e m e n t o n the dif f u s e d o u b l e layer theory w h i c h takes into c o n s i d e r a t i o n the h y d r a t i o n e n e r g y of the i o n s . Ad­ s o r b e d cations are cl a s s i f i e d as b e i n g in the d i f f u s e or S t e r n layer a c c o rding to them, d e p e n d i n g on w h e t h e r the e nergy of h y d r a t i o n (resulting from ion di p o l e interaction) is s u f f i c i e n t to m a i n t a i n a m o l e c u l e of w a t e r b e t w e e n the a d s o r b e d ca t i o n and the m i n e r a l surface and thus the p r e ­ d i c t i o n of d i f f e r e n c e in the a d s o r p t i o n c h a r a c t e r i s t i c s of ions w i t h the same valences can be made. In the second model e x p l a i n i n g the ion exchange equilibria, the suspen s i o n is a s s u m e d to be c o m p o s e d of two d i s c r e t e phases. O n e phase contains o n l y the e x c h a n g e a b l e ions and an infinitesimal a m o u n t of el e c t r o l y t e and the o t h e r is a h o m o g eneous solut i o n of electrolyte: This m o d e l is the basis for the m a s s - a c t i o n a p p r o a c h and the s t a t i s t i ­ cal t h e r modynamic approach. In the m a s s - a c t i o n theory, d i s c r e t e unambiguous phases in the s u s p e n s i o n are the c h a n g e phase" and the "solution phase." two "ex­ The process of c a t i o n e xchange m a y then be r e p r e s e n t e d as an intercha n g e of ions b e t w e e n these two phases. B u t this idea confl i c t s w i t h the diff use double layer con c e p t in w h i c h adso r b e d ions a n d solution ions are not d e f i n a b l e as separate 10 en t i t i e s (Kelly, layer theory, 1948, p. 42). O n the basis of the d o u b l e c a t i o n e x c h a n g e is m e r e l y the r e a r r a n g e m e n t of c a t i o ns and c a n n o t be c o n s i d e r e d a chemical r e a c t i o n in the o p i n i o n of Davis (1945). Davis has cr i t i c a l l y a n a l y z e d the sign i f i c a n c e of the cation e x c h a n g e e q u i l i b ­ r i u m c o n c e p t a n d has sugge s t e d that the en t i r e c o n c e p t as a true t h e r m o d y n a m i c e q u i l i b r i u m is not valid. Wiklander However, (1964) m a i n t a i n s that the law of mass ac t i o n c a n be a p p l i e d to the study of ion exch a n g e b e c a u s e of the p r e ­ sent k n o w l e d g e about the struc t u r e of the d i f f u s e double layer and its r e l a t i o n s h i p to the s u r r o undings b e i n g d e ­ p e n d e n t o n the a c t i v i t y of the d i f f u s i b l e ions and also c o n n e c t e d w i t h changes in free energy. The sta t i s t i c a l t h e r modynamic m o d e l assumes d i s c r e t e a d s o r p t i o n sites and l o c a l i z a t i o n of the adso r b e d ions. Babcock (1963) favors this approach as it should be a p p l i c ­ able w h e n the dista n c e b e t w e e n the a d s o r p t i o n sites is large r e l a t i v e to the size of the ions. d e v e l o p e d by K r i s h n a m o o r t h y and others This m o d e l was (1949) o n s t a t i s t i c a l t h e r m o d y n a m i c s of G u g g e n h e i m and is b a s e d (1945). D o n n a n e q u i l i b r i u m theory is c o n c e r n e d w i t h the state of e q u i l i b r i u m in a sy s t e m composed of o r d i n a r y e l e c t r o ­ lytes and c o l l o i d a l e l e c t r o l y t e s separated by a m e m b r a n e w h i c h is i m p e r meable to c o l l o i d a l particles. In soils, clay p a r t i c l e w i t h its s u r r o u n d i n g d i f f u s e do u b l e layer m a y be looked upon as a m i c r o - D o n n a n s y s t e m w h e r e the a t t r a c t i v e elec t r i c forces b e t w e e n p a r t i c l e surface and a 11 c o u n t e r Ions act as a restraint, cau s i n g a n o n - u n i f o r m d i s ­ t r i b u t i o n of the c o u n t e r ions in the (Babcock, 1963). micellar soluti o n T h e r m o d y n a m i c a l l y , the e q u i l i b r i u m c o n ­ d i t i o n of a D o n n a n s y s t e m is c h a r a c t e r i z e d by the fact that the c h e m ical p o t e n t i a l (v) of e v e r y d i f f u s i b l e e l e c t r o l y t e and the e l e c t r o c h e m i c a l p o t e n t i a l of every d i f f u s i b l e ion species are c o n s t a n t th roug h o u t the system. concept, Wiklander (1964) E m p l o y i n g this has s h o w n that the p r o d u c t of ion a c t i v i t y is a c o n s t a n t and t h a t its m a g n i t u d e is d e ­ p e n d e n t on the t e m p e r a t u r e and o n the e l e c t r o c h e m i c a l p o ­ tentials of the two ions, d i f f u s e dou b l e layer, and thus on the structure of the ion concentration, ion interaction, and i n t e r a c t i o n w i t h the e x c h a n g e r both in e l e c t r o s t a t i c and n o n - e l e c t r o s t a t i c ways. S ources of C a t i o n E x c h a n g e in Soils T he sources of ca tion e x c h a n g e in soils c a n be c o n ­ s i dered in two b r o a d categories: the inorganic or the clay f r a c t i o n and the o r g a n i c matter. In the inorganic fraction, d e p e n d i n g on the kind of clay mineral, of c a t i o n excha n g e m a y be due to: the d o m i n a n t source br o k e n bonds at m i n e r a l termi n a t ions w h i c h c o u l d be b a l a n c e d by adso r b e d c a t i o n s , i s omorphous s u b s t i t u t i o n in the lattice, or the h y d r o g e n of 3+ 4+ the e x p o s e d h y d r o x y l s . S u b s t i t u t i o n s of A1 for Si in the t e t r a hedral layer framework of silicates and in a l l o p h a n e and/or s u b s t i t u t i o n of cations of lower val e n c e for h i g h e r v a l e n c e ions in the o c t a h e d r a l layer accou n t for 12 the "permanent charge" (Schofield, 1949) w h i c h does not change in m a g n i t u d e or s t r e n g t h b y changes in p H of the system. In the three layer and smectites, silicates, illite, vermiculite p e r m a n e n t charge accounts for three fourths of the ca t i o n excha n g e capacity. This n e g a t i v e charge n e u t r a l i z e d by a counter charge M + m a y be r e p r e s e n t e d in the ideal b e i d e l l i t e formula as: M y + (Si 8 _yA l y )Al 4 O 2 0 n H 2 ° In the two layer silicates, p e r m a n e n t charge m a y a c c o u n t for only a small p o r t i o n of the exch a n g e c a p a c i t y son, et a l ., 1954; C o l e m a n and Craig, 1961). (Robert­ Follet (1965) o b s e r v e d the r e t e n t i o n of p o s i t i v e l y c h a r g e d iron oxides on k a o l i n i t e plane faces, but not o n edges. This is a d d i ­ tional e vid e n c e that su pports the p r e s e n c e of a p e r m a n e n t n e g a t i v e ch a r g e in kaolinite. Bailey (1966) Studies of B r o w n (1965), and have indi cated that the m i n e r a l o g i c a l c o m ­ p o s i t i o n affects the p r o x i m i t y of m u l t i v a l e n t cations and thus its suscep t i b i l i t y for r e p l a c e m e n t or exchange, d e g r e e of localized charge imbalance, the the i n t e r i o n i c d i s ­ tances and the interionic bond a n g l e s . In the smectites and v e r m i c u l i t e s , the site of n e g a t i v e charge m a y be in the t e t r a h e d ral sheets, the octahe d r a l sheets, or b o t h (Foster, 1960) . Since the interlayer cations w o u l d be at d i f f e r e n t d i s t a n c e s w i t h r e s p e c t to the site of charge, one w o u l d e x ­ p e c t c a t i o n s to be held m o r e tightly w h e r e t e t r a hedra l 13 r a t h e r t h a n o c t a h e d r a l charge field and Sam p s o n is dominant. W o r k of S c h o ­ (1953) has shown that the edges of the clay p a rti c l e s m a y be e i t h e r p o s i t i v e l y or n e g a t i v e l y c h arged d e p e n d i n g on the p H of the system. Low d i s c u s s e d the w o r k of S c h o f i e l d and Sam p s o n (1953) w i t h the aid of a m o d i f i e d d i a g r a m M o d e r a t e l y acid Edge charges, w i t h M g in octahedral OH , Mg /| AO H / OH \Si/ +1/3 /OIH \l / \Si/ +1/3 OH +1/3 Edge charges, / | \O H A \O H +1/2 O H +1/2 H +1 -2/3 -1 1/3 w i t h A l 3+ in oc t a h e d r a l positions OH y \lA 1/ Fi g u r e 1. -2/3 OH v -2/3 \l / -1/3 OH AO H A0 , Mg +2/3 /W positions Mg \ Alkaline OH \Si/ has (Figure 1). V e r y sligh t l y alkal i n e 2+ (1968) v AOH +1/2 WAI/ /(\ O H -1/2 0 AO \l A] /I -1/2 O H -1/2 -1 The charges on the edges of clay p a r t icles under acid and a l k a l i n e condit i o n s as affected by m i n e r a l o g i c a l composition. 14 A t o m i c g roupings at the edges of the clay m i n e r a l s containing M g 1:1 2+ (as in 2:1 layer silicates) layer silicates) and A1 3+ (as in in o c t a h e d r a l p o s i tions are shown in u p p e r a n d lower p a r t s of F i g u r e 1, respectively. In b o t h 4+ cases Si occu p i e s tetrahedral posit i o n s and the coor i n a ted anions are d e t e r m i n e d by the pH. Because of m a s s a c ­ tion, H + tends to associate w i t h O- atoms at the edge at low p H values, it tends to d i s s o c i a t e from these atoms at high pH values. The bonds joining the cations to the c o ­ o r d i n a t e d anions have s trengths equal to the v a l e n c e of the c a t i o n div i d e d by the c o o r d i n a t i o n number. t r o - n e u t r a l i t y to be maintained, For e l e c ­ the sum of the bond strengths to each a n i o n m u s t h a v e a va l u e equal to its valence. Otherwise, there is a local i z e d ch a r g e imbalance that is equal in m a g n i t u d e to the d i f f e r e n c e b e t w e e n the two quantities. Thus, d i f f e r e n t edge charges c a n o c c u r d e ­ p e nding on the pH of the system. fore, It is possible, there­ for a t t r a c t i o n to e x i s t b e t w e e n posi t i v e edges and n e g a t i v e planar surfaces under acid c o n d i t i o n s . Probably the a t t r ac t i v e en e r g y is d e s c r i b e d by either e q u a t i o n or e q u a t i o n a (1 ) (2). F r o m Figure 1 it can well be seen that 2+ 3+ (surface charge density) depends o n w h e t h e r M g or A1 o c c u p i e s the octahedral positions or by the m i n e r a l o g i c a l c o m p o s i t ion of the clay. It can also be noted from Figure 1 t h a t the io n i z a t i o n of Si-OH groups (Si-OH SiO“ + H+ ) once thought to be con t r i b u t o r y to pH d e p e n d e n t CEC is an overs i m p lification. The silicic acid is too w e a k for S i O H 15 to ionize ap p r e c i a b l y in the p H range of c o n c e r n in soils (Goates and Anderson, is a b o u t 9.7 1956). The pK for Si-OH = S i O “ + H + (Kargin and R a b i n o w i t s c h , 1935). A n d thus, this g r o u p w o u l d be active o n l y at v e r y h i g h pH. (-A1 O ^ ) + 1/2 is simila r to that p r o b a b l y p r e s e n t at the edge of gibbsite, ions (Jackson, The g r o u p hydroxy-Al polymers, 1960, 1963a). Fripiat and h y d r a t e d A1 (1964) 3+ has s u m m a r i z e d the c a t ion exch a n g e beh a v i o r of a l l o p h a n e s w h i c h ap p e a r to be p o o r l y c r y s t a l l i z e d halloysites, in terms of their Al content, w h e t h e r the Al was in 4 or 6 coordination, the c o o r d i n a t i o n number depe n d e d u p o n pH. A n o t h e r pH d e ­ p e n d e n t c o m p o n e n t of CEC, c h a r a c t e r i s t i c of clays acid soils and of clay mine r a l s and h o w from m a n y like k a o l i n i t e or m o n t m o r - i lIonite are those that have b e e n i n t e r l a y e r e d w i t h Al or Fe h y d r o u s oxides (Thomas and Swoboda, 1964; de V i l l i e r s and Jackson, 1967). 1963; C o l e m a n et a l . Apparently, h y drous oxide coatings are p o s i t i v e l y c h a r g e d Rich, 1960; Jackson, 1963a, b . , Hsu and Bates, the (Hsu and 1964) with the m a g n i t u d e of the posi t i v e charge v a r y i n g inver s e l y w i t h pH. C o l e m a n and Thomas (1967) in their r e v i e w o n basi c c h e m i s t r y of soil acidity h a v e d i s c u s s e d the c a t i o n e x c h a n g e b e h a v i o r of layer s i l i c a t e - s e s q u i o x i d e compl e x e s as r e s u l t ­ ing from the ne ga t i v e charge of the layer silicate w h i c h does not vary w i t h pH but the chan g i n g o p p o s i t e charge on the c l a y - s e s q u i o x i d e com p l e x does. The net charge, there­ fore, v aries from positive at low pH to n e g a t i v e at hi g h pH (Coleman and Thomas, 1964; S c h w e r t m a n n and Jackson, 1964; 16 Vo l k and Jackson, charge of the 1964). It is sesquioxide zero w h e n the positive just equals the lattice charge of the layer silicate and reaches a net negative charge wh i c h essentially equals lattice charge of the layer s i l i ­ cate at p H near 8 . Schematically they can be represent e d as follows: silicate]X~\x + ^H^ ([Layer [Al(OH) _ x ]2X+ OH” 3 2 pH /[Layer s i l i c a t e ] X “ \[A1(OH) 3 _x ]X+ I 2 pH ^ 4 [Layer silica t e ] X “ \x [A1(0H)3 ]0 pH J 8 This leads to the large v a r i ation in effective CEC with pH and prevents the identification of CEC at pH 6 with lattice charge. The number of O H ” groups on the sesquioxide group increases as pH rises and thus, p olyca t i o n is reduced. the positive charge of the This liberates negative sites on w h i c h other cations can be retained. Other tightly held anions besides O H have the same effect of increasing CEC. Thus, F" or H 2 P 0 4~ ions, which are bound more tightly by Fe and Al 3+ than is the clay, result in apparent increases in c a tion exchange capacity. Sulphate and even chloride or nitrate salts also interact with clay mineral sesq u i o x ­ ide complexes, with the sorption of the anion on the 17 hy d r o u s oxide c o m p o n e n t and the c a t i o n o n the layer s i l i ­ cate (Thomas and Swoboda, 1963; C h a n g and Thomas, 1963). T he acid functional gr o u p s of o r g a n i c m a t t e r as the source of ca t i o n exchange c a p a c i t y are c a r b o x y l s , p h e n o l s , enols, and per h a p s the a l c o h o l i c h y d r o x y l s B r o a d b e n t and Bradford, (Gillam, 1952; Lewis and Broadbent, 1940; 1961; M o r t e n s e n and Himes, 1964; S c h n i t z e r and Desjardins, S c h n i t z e r and Gupta, 1964, 1965; 196 3; and Schni t z e r and Wright, 1962; S c h n i t z e r and Skinner, 1960). Thus the c o n t r i b u ­ tion to CEC from org a n i c m a t t e r d e p e n d on the source of h u m i c c ompounds and the stage of decom p o s i t i o n . B u l k of the e x c h a n g e sites are a s s o c i a t e d w i t h the lignin fraction. C o l e m a n and Thomas (1967) in their r e v i e w state that o n l y the c a r boxyl groups are strongly e n o u g h ac i d i c to ionize ap p r e c i a b l y w h e n the pH is b e l o w 7.0. However, some p o l y p h e n o l s and s u b s t ituted phenols m a y c o n t r i b u t e as w e l l (Lewis and Broadbent, 1961). C a r b o x y l s a c c o u n t e d for a p ­ p r o x i m a t e l y 55 per cent of C E C of o r g a n i c m a t t e r a c c o r d i n g to B r o a d b e n t and Bradford (1952) in their study. Phenolic and e n o l i c groups c o n t r i b u t e d anot h e r 35 per c e n t and imide nitrogen, 10 per cent. Schni t z e r and S k i n n e r (1963) also a t t r i b u t e d 55 per cent of the CEC of o r g a n i c m a t t e r from the Bh h o r i z o n of a podzol to c a r b o x y l g r o u p s . de r w a s due to phen o l i c and en o l i c g r o u p s . The r e m a i n ­ The w e a k acid c h a r a c t e r of o r g a n i c m a t t e r results f r o m the fact that 3+ 34. m e t a l o r g a n i c ion complexes, p r i m a r i l y Al and Fe , ra t h e r than the C O O H groups pres e n t (Martin, 1960; 18 M a r t i n and R e e v e , 1960; Mortensen, Gupta, 1964; Bhuxnbla and McLean, 1963; 1965). S c h n i t z e r and Pr a t t and Ba i r (1962) m e a s u r e d CECs of 15 acid C a l i f o r n i a surface soils a t p H ' s b e t w e e n 3 and 8 and c o n c l u d e d that the pH d e p e n d e n t C E C w a s due b o t h to clay and o r g a n i c matter. Helling et a l . (1964) m e a s u r e d CEC of 60 W i s c o n s i n soils at p H value s b e ­ t w e e n 2.5 and 8 and by m u l t i p l e c o r r e l a t i o n a n a l y s i s d e t e r ­ m i n e d the c o n t r i b u t i o n s of org a n i c m a t t e r and clay at e a c h p H a n d the v a r i a t i o n in C E C of e a c h as p H was changed. T h e y found that for the soils they studied, o r g a n i c m a t t e r was the m a j o r c o n t r i b u t e r to the p H d e p e n d e n t CEC. These r e s u l t s s h o w e d C E C of clay was n e a r l y c o n s t a n t in the p H r a n g e of 5 to 7. This near c o n s t a n c y of CEC of c l a y w a s a l s o found in the studies of Ross e t a l . (1964) for some M i c h i g a n soils. E x c h a n g e a b l e A l u m i n m n and Soil A c i d i t y as F a c t o r s In f l u encing C a t i o n E x c h a n g e Robinson (1961) has m a d e a g o o d b r i e f r e v i e w of the f o l l o w i n g factors in f l u e n c i n g c a t i o n exchange; forces, cations, a c c e s s i b i l i t y of cations, the b i n d i n g i o n i z a t i o n of a d s o r b e d r e l a t i v e size of the ions h y d r a t e d a n d n o n - h y d r a - ted, p a r t i c l e size, surface area, d i l u t i o n effects, pH, temperature, valence, c l o g g i n g a t c a t i o n exch a n g e p o s i ­ tions, hydrolysis, h e a t of wetting, ions and zeta potential. anions, complementary The s o u r c e s of pH d e p e n d e n t c o m ­ p o n e n t of C E C are m e n t i o n e d e a r l i e r in the r e v i e w as d u e to the m i n e r a l o g i c a l c o m p o s i t i o n and o r g a n i c matter. 19 Aluminum, b e c a u s e of its a b u n d a n c e and atomic p r o ­ pe r t i e s , plays as i m p o r t a n t role in soil m i n e r a l structure o and behavior. Its t r i v a l e n t radius, 0.51 A (Sienko and Plane, 1963), is favor a b l e for a c c o m m o d a t i o n to b o t h tetra hedral a n d oc t a h e d r a l c o o r d i n a t i o n w i t h oxygen. ly a c i d solutions, a l u m i n u m exists as a t r i v a l e n t catio n c o m p l e x w i t h each Al in 6 coordination. In strong 3+ ion s u r r o u n d e d b y 6 w a t e r molec u l e s S c h o f i e l d and Ta y l o r (1954) s u g g est e d the first stage of Al h y d r o l y s i s as: [A1(6H 2 0 ] 3+ + H 2 O v * [Al(OH) (5H 2 0 )]2+ + H 30 + As p H is further increased, m o n o v a l e n t h y d r o x y Al cations form (Rich, 1960): [Al (OH) (5H 2 0) ) 2 + + H 2 0 ^ = ^ [Al (OH) 2 (4H 2 0) ]+ + H 3 Q + [Al(OH) 2 (4HzO ) ] + + H 2 0 v The A l ( O H ) 3 * [Al(OH) 3 (3H 2 0 ) ] + H 3 0 + . 3H20 is ins oluble and p r e c i pitates. The e x ­ te n t of p r e c i p i t a t i o n depends on the ionic stre n g t h of the solution, d e n s i t y of ch a r g e on the clay m i n e r a l 1960) and ionic species p r e s e n t (Jackson, (Rich, 1963a). With f u r t h e r increase in pH above 7, the fourth w a t e r m o l e c u l e loses a n H + ion forming the a l u m i n a t e ion Al(OH)^. and the s olubility of Al increases. 2 H 2 0~ Data on solubi l i t y of Al in solutions at d i f f e r e n t p H values were gi v e n by M a g i stad (1925). 20 It can be seen, therefore, that m i l d l y acid w e a t h e r ­ ing causes o c t a h e d r a l a l u m i n u m to r e a c t w i t h p r o t o n s at c r y s t a l edges and thereby p r o d u c i n g e x c h a n g e a b l e A l shall, (Mar3+ 1964), p o s t u l a t e d to exist p r i m a r i l y as A l d J j O ) ^ (Jackson, 1963a). These a l u m i n u m ions tend to be a d s o r b e d by the r e m a i n i n g clay mine r a l s (Jackson, 1963a). Sinc e m o s t of the exchange sites of the 2 : 1 e x p a n d i n g layer s i l i c a t e m i n e r a l s are on the faces of the crystals due to is o m o r p h ic s u b s t i t u t i o n s , m a n y of the a l u m i n u m ions r e ­ leased by w e a t h e r i n g w i l l be adsor b e d in the i n t e r l a y e r areas. As the exchange sites be c o m e saturated w i t h h y d r a ­ ted a l u m i n u m ions the h y d r a t e d ion structures to steric p i n c h i n g (Jackson, 1960) are s u b j e c t e d bec a u s e the a r e a o c c u ­ p i e d by individual exch a n g e sites is less than the size of an a l u m i n u m h e x a h y d r o x y polymer. for v e r m i c u l i t e density. (Jackson, This is e s p e c i a l l y true 1963a) w h i c h has a h i g h char g e The adjacent a l u m i n u m polymers tend to p o l y m e r ­ ize by s haring hydroxyls, b u t the polymers r e t a i n a ne t p o s i tive c h a r g e . The r e s u l t i n g c h a r g e d hydroxy a l u m i n u m p o l y m e r m a y be v e r y large and thus becomes e s s e n t i a l l y u n e x c h a n g e a b l e . St udies by Thomas (1960) and Rich (1960) also indic a t e d t h a t these Al h y d r o x y ions are stro n g l y adso r b e d b y soils as they are not e x t r a c t a b l e by neutral salt solutions of 1 N concentration. Ca:Al exch a n g e studies by C o u l t e r (1969) h a v e also shown strong a l u m i n u m a d s o r p t i o n by soil m i n e r a l s , the s t r ength of w h i c h d e p e n d e d on the type of clay and the 21 m l n e r a l o g i c a l composition. This results in a net r e d u c t i o n of the c a t i o n e x c h a n g e capa c i t y of the clay. T h e e x c h a n g e a b l e Al is p o s t u l a t e d to ex i s t p r i m a r i l y as A 1 ( H 2 0 ) 6 3+ (Jackson, 1963a); whereas, Al polymers pr e - c i p i t a t e d on clay surfaces Coleman, 1960; (Jackson, 1963a; and S c h w e r t m a n and Jackson, c o m p l e x e d by o r g a n i c m a t t e r 1963) (McLean et a l ., 1965; S c h n i t z e r and Skinner, 1964) c a h n g e a b l e forms. aL The Ragland and and Al and have been propo s e d as non-ex- n e u t r a l i z e d u p o n liming includes b o t h e x c h a n g e a b l e and n o n - e x c h a n g e a b l e forms and is o f t e n r e f e r r e d to as acidic Al. Poinke and Corey (1967), in their studies o n the relations b e t w e e n acidic a l u m i n u m and soil pH, clay and o r g a n i c matter, c o n s i d e r e d the Al e x t r a c t e d by 1 N N H ^ O A c at p H 4.8 as exch a n g e a b l e plus n o n - e x c h a n g e a b l e acidic Al, and p r o p o s e d the following reactions of acid i c Al in soil: Al(OH)3 Al OH 2+ The symbols used are d e f i n e d as follows: Al 3+ represen t s the a c t i v i t y of h y d r a t e d triva l e n t Al ions in the soil solution; A l - X refers to KC1 exc h a n g e a b l e Al; Al-OM refers to that c o m p o n e n t of n o n - e x c h a n g e a b l e acidic Al 22 c o m p l e x e d by org a n i c matter; and A ^y (°H );3y _ z refers to that c o m p o n e n t of n o n - e x c h a n g e a b l e acidic Al that is p o l y ­ m e r i z e d and prob a b l y r e s i d i n g on p a r t i c l e surfaces. P o inke and Corey (1967) e x p l a i n e d that this d i a g r a m p r e d i c t s an increase in the n o n - e x c h a n g e a b l e acidic Al for an increase in org a n i c m a t t e r for soils at a c o n s t a n t pH 3+ and a g i ven c o n c e n t r a t i o n of Al in solution; w h e r e a s an increase in clay w o u l d increase the e x c h a n g e a b l e Al at the e x p ense of Al-OM. The addi t i o n of salt w o u l d displace e x ­ c h a n g e a b l e Al to the soil solution, a l t e r i n g the e q u i l i b ­ r i u m in favor of the f o r m a t i o n of A l - O M c o m p l e x e s and i n ­ o r g a n i c polymers. The hydrol y s i s r e s u l t i n g f r o m polym e r f o r m a t i o n w o u l d depress soil p H b y r e l e a s i n g h y d r o g e n ions to the soil solution. In a c c o rdance w i t h this, Poinke and C o r e y have found better c o r r e l a t i o n of pH w i t h e x c h a n g e ­ able Al w h e n KC1 is u s e d and also w i t h the o b s e r v e d r e ­ lationships of exc h a n g e a b l e Al and n o n - e x c h a n g e a b l e acidic Al w i t h percent clay and p e r c e n t o r g a n i c matter. M e t h o d s of C a t i o n E x c h a n g e C a p a c i t y D e t e r m i n a t i o n T h e CEC d e t e r m i n a t i o n involves m e a s u r i n g the net n e g a t i v e charges per unit w e i g h t of soil. The C E C values o b t a i n e d vary d e p e n d i n g on the m e t h o d employed, particu­ larly: the time the e x c h a n g i n g salt, of interaction, and pH. s a l t concentration, Several m e t h o d s of CEC d e t e r m i n a ­ tion are n o w in vogue and m a n y h a v e b e e n proposed. son (1961) has b r i e f l y r e v i e w e d the following: Robin­ ammonium 23 method, b a r i u m method, method, ra d i o a c t i v e tracer c h r o m a t o g r a m c o l o r i m e t r i c method, m e t h y l e n e b l u e dye, c o n d u c t o m e t r i c method, and by e m u l s i f i c a t i o n . Chapman using (1965) has g r o u p e d the m e t h o d s for d e t e r m i n i n g C E C into the f o l ­ lowing categories: (1 ) those in w h i c h the soil is e l e c t r o - d i a l y z e d or leached w i t h a dil u t e acid, e.g. HC1, h y d r o g e n and a l u m i n u m s atur a t e d exchange mater i a l and the is titrated to pH 7.0 w i t h B a ( O H ) 2 or to about p H 8.5 w i t h NaOH: (2) those in w h i c h exchange capacity is c o n s i d e r e d to be the sum of r e p l a c e a b l e h y d r o g e n and r e p l a c e a b l e bases; (3) those in w h i c h the exchangeable cations are r e ­ p l a c e d b y the acetate of ammonium, barium, c a l c i u m or s o d i u m and the amounts of the ca t i o n adsorbed are d e t e r ­ m i n e d by a p p r o p r i a t e means; l i b r a t i n g soils so l u t i o n (4) those w h i c h involve e q u i ­ (preleached w i t h C a ( O A c ) 2 ) w i t h a dilu t e (100 p p m Ca) (Blume and Smith, of C a ( N O ^ ) 2 contai n i n g Ca 45 and Ca 40 1954). T h e CEC values are generally d e t e r m i n e d at pH 7 or 8.2 (Jackson, 1958). The p r e f e r e n c e for p H 7.0 arises from the fact that it is the neutral point of wa t e r and m a y m o r e nearly r e p r e s e n t the pH of the s o i l - b i c a r b o n a t e c a r bonic acid buffer sy s t e m at par t i a l pressure of C 0 2 likely to pre v a i l in the atmosphere of a fertile soil d u r ­ ing the s e a s o n of ac t i v e growth. The pH 8.2 is p r e f e r r e d be c a u s e it is closer to the e q u i l i b r i u m pH bet w e e n soil and CaCO^ at the p a r t i a l p r e s s u r e of C 0 2 in the a t m o s p h e r e and also b e c a u s e the exchange m a t e r i a l s of soils are w e a k 24 acidoids. Studies of Coleman and Thomas (1964) have in- 3+ dicated that the complete neutralization of sorbed Fe or 3+ Al ions occurs at or near pH 8 . The CEC determinatio n may also be made at the p H of the soil, or at least at the pH of the soil-salt solution mixture using an unbuffer e d salt solution like KC1 or C a C l 2 Pr a t t and Bair, C h apman (Coleman, et a l ., 1959; 1962; Bhumbla and McLean, 1965). (1965) has described two commonly used NH^OAc and NaOAc methods of CEC determination. He ment i o n s the advantages of the NH^OAc method as its high buffering capacity, ease of determination, and the ease of d e t e r m i n ­ ation of d i s p laced cations because of its volatility. According to Cha p m a n (1965) the disadvantages of this me t h o d are that in soils containing high amounts of 1 : 1 layer silicates or organic matter it will give lower CEC values as compared to Ba(OAc)2 method incomplete replacement of adsorbed H + (Mehlich, and Al 3+ . 1945) due to Also, w h e n soils contain vermiculite clay, interlayer cations 2+ 2+ + + f UCT |cMUOr«JM\ iniHiK , r i' J I 1 irfomL_ .J Soil No. 1 _________________ ANTRIM Soil Series (f/L ____ 1___ ± ! « « J 'M “ EAND. TRAV.J 1 Miami 4 Plainfield alpen a i f ____ i____ lc R A M f0 R 0 , o , e o ° * | I I Rl c o n a | - L — / M A N I t T I ^ W C X T O R O ^ g ^ ^ ^ ROICON. I OSKNAV i IORCO 6 8 V o linia 11 Saugatuck 14 O naway 15 Brookston 17 On t o nagon 19 /_ Kalamazoo ^ - lPODIZOL^REQION L. ia r o n T l a r i i OC IAN A r o » f O L A f C L A ) ll * • ■ i* 4 i i i i * 1 i i 24 Spinks 34 Kalkaska 37 38 Blount Hillsdale 39 Pewamo IK Uj 1 ft AAftY rt . I ' I — SANILAC J I i _ _j 1 ,->l a r c c r 1 I CLINTON .R H IAW A. | 3 9 ,x ©__ i_ Ig _ \24~ T ■ | l a ir ' istTiTl . - I _ l _ I r--4- __.___ . OASLI OAKLAND |W C O i , l luv,",*T0". •CMICN MAIiCH T“ILl5MtxflcNAVCC J*■«' PODZOLlC REGIQN I Figure 2. HURON ’ V ; IO NIA Mu n ising a r in a c I '■*>/ 1MECOSTA |I*A R E L L A I m io LANO . / / ( Iron River 23 Hil a o m Tn 7 l , i L, i I- Map of M i c h i g a n showing locations of r e p r ese n t a ­ tive soils used in this study. 28 24 to 42 inches thick, o v e r stratified, non-calcareous gravel a nd sand. K a l a m a z o o sandy lo am is a w e l l - drained, dalf (Gray Br o w n P o d z o l i c soil) Ty p i c Haplu- d e v e l o p e d in silty or loamy ou t w a s h m a t e r i a l u n d e r l a i n by s t r a t i f i e d n o n - c a l c a r e o u s gravel a n d sands at depths from 24-42 inches. S a u gatuck sand is a some w h a t p o o r l y drained, Aeri e Haplaguod (sandy G r o u n d - W a t e r P o d z o l ) . O n a w a y loam consists of w e l l - d r a i n e d and m o d e r a t e l y well-drained Alfic Haplorthod (soils w i t h a Podzol upper sequence and a lower G r a y - W o o d e d sequence) which developed in r e d d i s h or pinkish ca l c a r e o u s l o a m till. O n t o n a g o n silty clay is a m o d e r a t e l y w e l l -drained , Typic Eutroboralf (Gray-Wooded soil) d e v e l o p e d f r o m clay to silty clay lacustrine sediments d e r i v e d from a v a r i e t y of rocks, but with colors strongly influe n c e d by the hi g h l y ferruginous formations of the Lake Superior region. Iron River silt l o a m is a w e l l - d r a i n e d to m o d e r a t e l y well-drained Alfic Fragiorthod (Podzol soil) on glacial up l a n d d e v e l o p e d from gla c i a l d r i f t in the L a k e Superio r region. M u n i s i n g loamy sand is a w e l l to m o d e r a t e l y w e l l drained, Alfic Fragiorthod a fragipan) (minimal to m e d i a l Podzol, with d e v e l o p e d in s t r o n g l y acid, r e d d i s h sandy loam gl acial till der i v e d from red s a n d s t o n e of the L a k e S u p e r ­ ior r e g i o n of the N o r t h e r n Lake s t a t e s . 29 Spinks loamy fine sand is a well-drained, Psanunentic H apludalf (Gray Brown Podzolic soil) developed in c a l c a r ­ eous or neutral loamy s a n d s , sands or fine s a n d s . Kalkaska sand is a well - d r a i n e d Typic Haplorthod (Podzol) developed in deep sands that m a y contain a little calcareous material. B lount clay loam is an A e r i e Ochraqualf poorly drained, Gray Brown Podzolic soil) (somewhat developed in calcareous clay loam to silty clay loam till. Hillsdale sandy loam is a w e l l - drained Typic H a p l u ­ dalf (Gray Brown Podzolic soil) sandy loam till with thickness developed in calcareous of the solum ranging from 40 to 66 inches or more. Pewamo clay loam is a poorly to very poorly drained Typic Argiaquoll (Humic Gley soil) developed in calcareous silty clay loam or clay loam till. O t h er relevant information o n these soil types, shown in Table 2, i n c l u d e : natural drainages, their family placements in the new Soil Classi f i c ation System, to July, 1969) their parent m a t e r i a l s , their 7th A p p r o x i m a t i o n 1965 (as revised in addition to their Great Soil Groups in the 1947 C lassification System in the U.S. Table 2, also shows the horizons in these profiles chosen for this study as the ones more commonly developed in Michigan. The soil materials, from the horizons studied, varied w i d e l y in their physical and chemical properties. The range of some of their characteristics relevant to the TABLE 2.— Information on soils studied. Soil Type Great Soil Group, U.S. 1947 System 7th Approximation Natural nomenclature (as Drainage revised to July 1969) Horizons* Studied Parent Material Miami loam Gray Brown Podzolic Typic Hapludalf, fine-loamy, mixed, mesic WD Loamy till Ap, A 2 , B*,. 1 2 3 Plainfield loamy sand Regosol Typic Udipsamment mixed, mesic WD Sand Ap 4 Volinia loam Brunizem Typic Argiudoll, WD fine-loamy over sandy or sandy skeletal, mixed, mesic Stratified, loams/sand and gravel Stratified, loams/sand and gravel Kalamazoo loam Gray Brown Podzolic Typic Hapludalf, fine-loamy over sandy or sandy skele­ tal, mixed, mesic WD Saugatuck sand Ground Water Podzol Aerie Haplaquod, sandy, mixed, frigid, orstein SWP Alfic Haplorthod, fine-loamy, mixed, frigid Typic Argiaquoll fine-loamy, mixed, non-calc., mesic WD-MWD Loamy till PD Loamy till Typic Eutroboralf, very fine, illitic, frigid MWD Onaway loam Podzol Bisegua Brookston loam Humic Gley Ontonagon silty clay Gray Wooded Sand 6 Ap, 8 ^1 101 9 Al' B21h' B3ir 11 12 13 Ap/ ® 22 ir' B21 t 14 32^ir 33 Blg* B22 g 15 Lacustrine clay 7 16 Ap, Blt 17 18 TABLE 2.— Information on soils studied, (continued). Soil Type Iron River silt loam Munising loamy sand Great Soil Group, U.S. 1947 System Podzol, Bisegua Podzol, Bisegua 7th Approximation NatUral nomenclature (as revised to July 1969) Dralnage Alfic Fragiorthod, coarse-loamy, mixed, frigid WD-MWD Alfic Fragiorthod, coarse-loamy, mixed, frigid WD-MWD Parent Horizons* Materlal Silt over loamy till Studied Ap, 19 Bhir' A 2 ' 20 2x , 29 Gray Brown Podzolic Kalkaska sand Podzol Blount clay loam Psammentic Hapludalf, WD-MWD sandy, mixed, mesic Sandy drift Ap, 24 Typic Haplorthod, sandy, mixed, frigid WD Gray Brown Podzolic Aerie Ochragualf, fine, illitic, mesic SWP Hillsdale sandy loam Gray Brown Podzolic Typic Hapludalf, coarse-loamy, mixed, mesic Pewamo clay loam Humic Gley Typic Argiaguoll, fine, mixed, noncalcareous, mesic 22 Acid, sandy Ap, A 2 ' B 22 ir' loam drift 23 27 28 A1 Spinks loamy fine sand 21 Sand A 22 Clay loam till 34 Ap 37 WD-MWD Sandy loam till Ap 38 PD Clay loam till Ap 39 B 22 t # C1 30 31 A22' A2B3t 25 26 ' B2 2 ir' C 1 35 36 Numbers below the designated horizons were used for laboratory identification of the soil samples and their identifications elsewhere follows on page 1 0 1 . PH 4 5 6 7 4 5 6 7 4 5 6 7 4 5 6 7 //////// A 4 5 6 7 4 5 6 7 P ////////////////z 10 20 7/////////////, 50 B 22 21 t B Kalamazoo Loam Spinks Loamy Fine Sand Ontonagon Silty Clay Volinia Loam 22 g Brookston Loam (in inches) 50 Miami Loam ig m 40 60 B Blt Depth w IO 4 5 6 7 4 5 6 7 W //M A, 4 5 6 7 '////////// % 7////////// B 2 2 ir //////////////// R1 W////,~ 2 2 ir 21 h ///////////, //////// 3ir 21 t Kalkaska Sand Figure 3. Onaway Loam Iron River Silt Loam Munising Loamy sand Saugatuck Sand Depth functions of pH of soils studied. » Per cent clay 20 40 20 40 20 40 20 40 20 40 ///////////////////// fa 10 20 A" 1 „ >////////, B B 21t 30 id B 22 t SO 60 Miami Loam Kalamazoo Loam 2 3t Spinks Loamy Fine Sand Ontonagon Silty Clay Volinia Loam Depth (in inches) 40 20 40 20 40 20 40 ////// 10 20 22 B2 2 ir 30 m //////, 20 A2 B 2 2 ir 20 40 2 2 ir I B B 21 t 40 21 h 3ir 40 90 60 Kalkaska Sand Figure 4. Onaway Loam Iron River Silt Loam Munising Loamy Sand Depth functions of per cent clay in soils studied. Saugatuck Sand Per cent carbon I I 2 2 I 2 I I 2 2 io^ a A“ F ? 20 22 B21t ■ B 22 t 30 40 •0 Miami Loam Kalamazoo Loam | A2B3t Spinks Loamy Fine Sand Ontonagon Silty Clay Volinia Loam Brookston Loam Depth (in inches) 50 B hir 2 2 ir 21t 1 21 h Bi 1 A 2x B 22 t Kalkaska Sand Onaway Loam Saugatuck Sand Iron River Silt Loam Munising Loamy sand Figure 5. Depth functions of per cent carbon in soils studied. 35 study are shown as depth functions in Figures 3, 4 and 5 and grouped according to horizons in Table 16 of the A p p e n ­ dix. The pH of the horizons studied from 4.3 in Kalkaska A 2 2 horizon Ap horizon of Miami loam (Figure 3), ranged (sample 34) to 7.1 in the (sample 1). The percent clay, Figure 4, ranged from 0.6 per cent in the A 22 horizon of Kalkaska sand (sample 34) to 54.4 per cent in B lt horizon of Ontonagon silty clay (sample 18). The carbon content, Figure 5, ranged from 0.02 per cent in the Mu n ising horizon of (sample 31, Table 16) to 2.46 per cent in the Ap horizon of Pewamo clay loam (sample 39) not shown. Methods Used in this Study The five methods of CEC determination are describe d below. The C a C l 2 method and the KC1 m e t h o d are m o d i f i c a ­ tions of the Alexiades and Jac k s o n NH^OAc method, (1965) procedure. The the NaOAc me t h o d and the summation method are modifications of those desdribed by Chapman (1965) . The b a r i u m chloride plus triethanolamine method for the determination of exchange acidity and KC1 extraction and fluoride titration procedure for determination of extractable acidity and exchangeable aluminum are also m o d i f i c a ­ tions from Chapman (1965) . 36 C a C l 2 M e t h o d for C E C D e t e r m i n a t i o n F i v e grains of soil w e r e p l a c e d in a 100 m l P y r e x c e n ­ tr i f u g e tube w i t h 10 m l of 1 N C a C l 2 and m i x e d well w i t h a V o r t e x Jr. m i x e r for 1 minute. The side w a l l of the c e n t r i ­ fuge tube was ri n s e d w i t h 5 ml of 1 N C a C l 2 and c e n t r i f u g e d at 3500 r.p.m. for 10 minutes. The s u p e r n a t a n t liquid w h e n c l e a r was decanted. This t r e a tment was r e p e a t e d 5 times to 2+ 2+ a s s u r e c o mplete Ca satura t i o n of the s a m p l e . The Ca s a t u r a t e d soil sample was then washed simil a r l y o n c e w i t h 15 m l w a t e r and then five times w i t h 99% methanol. the C a 2+ w a s e x c h anged with Mg 2+ Finally, by w a s h i n g and c e n t r i f u g ­ ing five times in the same man n e r as above w i t h 1 N M g C l 2 . This time, m i x i n g was done 2 min u t e s each to assure complete r e p l a c e m e n t and 5 ml of water was added to rinse the w a l l of the c e ntri f u g e tube before centrifugation. The s u p e r n a ­ t a n t s o l u t i o n was c o l l e c t e d in a 1 0 0 m l v o l u m e t r i c flask a n d m a d e to volume w i t h w a t e r to o b t a i n a p p r o x i m a t e l y 0.5 N 2+ M g C l 2 . The Ca was d e t e r m i n e d on a 303 A t o m i c A b s o r p t i o n 2+ S p e c t r o p h o t o m e t e r a g a i n s t standard Ca solutions u s i n g 1% l a n t h a n u m oxide to p r e v e n t interference by o t h e r i o n s . O t h e r wor k e r s (Rich, 1962; and Frink, 1964) have i n ­ d i c a t e d that the p r o c e d u r e for w a s h i n g the excess salts from Ca 2+ saturated soil samples can be done m o r e e f f i c i e n t ­ ly by using a low c o n c e n t r a t i o n of the same salt u s e d for s aturation, instead of 99% methanol. w e i g h t of the r e t a i n e d solution, T h e n by k n o w i n g the the c o r r e c t i o n for excess 37 salt retained can be made. Therefore, a comparison was made using 0.0001 N C a C l 2 as the wash i n g solution and 99% m e t hanol to obtain CEC values. The fourth and fifth c e n ­ trifugations usually needed 30 minutes to obtain clear suspensions; some finer textured soil samples also needed 5 ml or 10 ml of 99% acetone to prevent dispersion during the fourth and fifth washings. T h o rough mi x i n g of the soil with the solution p r e ­ sented a p r o b l e m particularly with fine textured samples. To a ccomplish this the clay globules present w e r e carefully dispersed by triturating with a rubber tipped glass rod. KC1 m e t h o d for CEC determination A 5 g r a m soil sample was saturated with potas s i u m using 1 N KC1, but otherwise the same procedure as for the C a C l 2 m e t h o d was followed. 0.001 N KCl was used. For washing out the excess salts The K + saturated sample was then dried in an oven at 100° C over-night. The unfixed K + was then exchanged by w a s h i n g with 1 N NH^Cl. Care was taken every time to see that there was a thorough m i x i n g of the sample with the solution as stated for the C a C l 2 p r o c e d u r e . The s u pernatant solution was collected in a 100 ml v o l u m e t ­ ric flask. P o t a s s i u m was determined with a Cole m a n flame photometer. NH^OAc m e t h o d for d e t e r mination of CEC and exchangeable bases Five grams of soil were placed in a 100 ml centrifuge 38 tube, m i x e d w e l l twice w i t h 10 m l of 1 N NH^OAc, the w a l l w a s h e d w i t h 5 ml of 1 N N H ^ O A c and a l l o w e d to stand o v e r ­ night. The s u s p e n s i o n was t h e n c e n t r i f u g e d and the cl e a r s u p e r n a t a n t s o l u t i o n was c o l l e c t e d in a 1 0 0 m l v o l u m e t r i c flask. C e n t r i f u g a t i o n was r e p e a t e d five times using 10 ml of 1 N N H ^ O A c to m i x a n d 5 ml o f 1 N N H ^ O A c for w a s h i n g the w a l l of the tube. F r o m the th i r d time of N H ^ O A c t r e a t m e n t o n w a r d s the clear s u p e r n a t a n t s o l u t i o n was tested, licate samples, for p r e s e n c e of calcium. on d u p ­ The c a l c i u m test c o n s i s t e d of adding five drops e a c h of 1 N NH^ Cl and 10% a m m o n i u m o x a l a t e and 2 m l of 0.1 N N H ^ O H to 2 ml of the c l e a r s u p e r natant solu t i o n and h e a t i n g the solu t i o n to n e a r b o i l i n g point. The p r e s e n c e of c a l c i u m w a s i n d i c a t e d b y a w h i t e p r e c i p i t a t e or turbidity. In this e x p e r i m e n t all the fo u r t h w a s h i n g s sh o w e d n e g a t i v e results for C a ++ and t h e r e ­ fore five w a s h i n g s w e r e q u i t e s u f f i c i e n t to as s u r e comp l e t e N H ^ + saturation. O n the c o l l e c t e d s u p e r n a t a n t solu t i o n d i l u t e d to a vo l u m e of 1 0 0 ml the e x c h a n g e a b l e bases w e r e determined. The N H ^ + s a t u r a t e d soil sample in the c e n t r i f u g e tube w a s then tre a t e d four times w i t h 1 N N H ^ C l u s i n g 10 m l e a c h t i m e to m i x and 5 ml to rinse off the w a l l of the c e n t r i ­ fuge tube. T h e excess N H 4+ was w a s h e d o u t w i t h 99% i s o p r o ­ pyl alcohol. N AgNO^. The p r e s e n c e of c h l o r i d e w a s tested u s i n g 0.1 A l l samples gave n e g a t i v e chlo r i d e tests in the 39 third or fourth washings and therefore five washings were consid e r e d sufficient for removing the excess N H ^ + . The adsorbed NH.+ was determined as follows: 4 NH^ The saturated soil sample in the centrifuge tube was treated w i t h acidified 10% NaCl and m i x e d well, centrifuged and the clear supernatant solution was collected in a 1 0 0 ml volum e t r ic flask. This w a s h procedure was repeated 5 times and made to volume w i t h acidified NaCl. A 2 ml, 5 ml or 1 0 ml a liquot of this solution was placed in the micro Kjeldahl falsk depending on the amount of N H 4+ adsorbed. Ten ml of 1 N NaOH was added and about 40 ml was distilled into 5 ml of 2% BO^. Five drops of Fleisher (Fisher) m ethyl p urple indicator was added and the boric acid s o l u ­ tion was titrated against standard sulfuric acid to a purple end point. Blanks were run on the reagents. The titration figure w a s corrected for the blanks and m i l l iequivalents of a m m o n i u m in 1 0 0 grams of soil were calculated. NaOAc M e t h o d for CEC Determination F i v e grams of soil were placed in a 100 ml pyrex centrifuge tube. Ten ml of 1 N NaOAc (pH 8.2) was added, m i x e d well for 5 minutes and centrifuged. liquid was decanted. repeated 5 times. This N a + saturation procedure was Then the sample was washed with 99% isopropyl alcohol 4 t i m e s . washing, The supernatant Usually for the second or third ferric chloride yielded a negative test for acetate. 40 The a d s o r b e d s o d i u m was r e p l a c e d by w a s h i n g five times w i t h 10 ml plus 5 ml p o r t i o n s of 1 N N H ^ O A c d e c a n t i n g e a c h w a s h i n g into a 100 m l v o l u m e t r i c flask. The s o l u t i o n w a s m a d e to v o l u m e w i t h N H ^ O A c and the N a + was d e t e r m i n e d w i t h a C o l e m a n flame photometer. B a r i u m c h l o r i d e plus Tri.e t h a n o l amine m e t h o d for the d e t e r ­ m i n a t i o n of e x c h a n g e a c i d i t y . Five grams of soil were p l a c e d in a 100 m l Pyrex c e n t r i f u g e tube. T e n ml of 0 . 5 N B a C l 2 + 0.055N T r i e t h a n - o l a m i n e at p H 8.0 was ad d e d two times m i x i n g w e l l each time. T h e w a l l of the c e n t r i f u g e tube was r i n s e d w i t h an a d d i t i o n a l 5 ml of e x t r a c t i n g s o l u t i o n and a l l o w e d to s t a n d overnight. The s u s p e n s i o n was c e n t r i f u g e d and the clear s o l u t i o n w a s c o l l e c t e d in a 100 ml v o l u m e t r i c flask. The p r o c e d u r e w a s r e p e a t e d five times u s i n g 1 0 ml of the e x ­ t r a c t i n g s o l u t i o n to m i x and 5 ml to w a s h off the w a l l of the c e n t r i f u g e tube and the clear solu t i o n was c o l l e c t e d in a 100 m l v o l u m e t r i c flask. A k n o w n a l i q u o t of the s o l u t i o n w as t i t r a t e d aga i n s t standard HC1 to a p i n k end po i n t (pH 5.1) w i t h the usual b r o m c r e s o l g r e e n - m e t h y l red i n d i c a ­ tor. The m i x e d i n d i c a t o r s o l u t i o n was 0.22 g r a m of b r o m ­ c r e s o l g r e e n and 0.075 g r a m of me t h y l r e d d i s s o l v e d in 96 ml of 95% e t h a n o l c o n t a i n i n g 3.5 m l of 0.1 N NaOH. E x c h a n g e acidity calculated EA - (EA) as f o l l o w s : (B-S) N (20 D) in m e q per 100 grams of soil was 41 where B - ml of acid required to titrate an equal aliquot of original extracting solution. S - ml of acid required to titrate a known aliquot of the soil extract. N » normality of the acid. D * dilution factor. KC1 extraction and fluoride titration procedure for d e t e r ­ m i n ation of extractable acidity and exchangeable a l u m i n u m . Five grams of soil were pl a c & d centrifuge tube. well. in a Ten ml of 1 N KC1 was 100 ml Pyrex added and mixed The wall of the centrifuge tube was rinsed w i t h 5 m l of 1 N K C 1 , centrifuged and the clear solution was decan t e d into a 100 ml volumetric flask. This opera t i o n was repeated five times and the solution was made to volume with 1 N KC1. A k n o w n aliquot of this extracted solution containing ex3+ i. changeable A1 and H was transferred to a 200 ml Erlenm e y e r flask and titrated against standard NaOH to a p e r m a n ­ ent pink end point w i t h alternate stirring and standing, using 5 drops of phenolphthalein indicator. A few more drops of the indicator was added to replace that adsorbed by the precipitate of Al(OH)^, if needed. The amount of the base used was equivalent to the total amount of acidity in the aliquot taken. One drop of standard 0.1 N HC1 was then added to bring the solution back to the colorless c o n ­ d i t i o n and 10 ml of NaF solution was added. the solution constantly, While stirring the solution was titrated against standard 0.1 N HC1 until the color just disappeared. or two drops of the indicator was added. If the color One 42 appeared, additions of acid w e r e c o n t i n u e d until the color just d i s a p p e a r e d and d i d n o t re t u r n w i t h i n two minutes. The m i l l i e q u i v a l e n t s of acid used was a m e a s u r e of the ex3+ c h a n g e a b l e A1 . This value was s u b t racted from the m i l l i ­ e q u i v a l e nts of total acidity (initial base titration) o b t a i n the m i l l i e q u i v a l e n t s of e x c h a n g e a b l e H + . to RESULTS A N D D I S C U S S I O N The five m e t h o d s used in this study for the CEC d e t e r m i n a t i o n invo l v e d ess e n t i a l l y the s a t u r a t i o n of the e x ­ c h a n g e sites of the soil m a t e r i a l w i t h the r e f e r e n c e ca t i o n w h i c h is then r e p l a c e d and determined. The four m a i n steps i n v o l v e d in such d e t e r m i n a t i o n are: (a) t r e a t m e n t of the soil sample w i t h a salt s o l u ­ tion to replace the native exc h a n g e a b l e cations w i t h the r e f e rence cation, (b) rem o v a l of the o c c l u d e d salt s o l u t i o n by e x t r a c ­ tion w i t h a solvent, (c) r e p l a c e m e n t of the a d s o r b e d reference c a t i o n and (d) d e t e r m i n a t i o n of the r e p l a c e d reference cation. Each of the first three steps m a y e n c o u n t e r some a n a l y t i c a l error. Thus, in the first step, m e n t o f native cations m a y be incomplete; step, the d i s p l a c e ­ in the second error m a y res u l t unless the loss of the a d s o r b e d r e f ­ e r e n c e c a t i o n b y hydrolysis is b a l a n c e d by r e t e n t i o n of some e x c e ss of the s a t u r a t i n g salt; and in the third step, the r e p l a c e m e n t of the a d s o r b e d r e f e r e n c e ca t i o n should be c o m p l e t e but e x c e s s i v e use of the r e p l a c i n g salt c o u l d r e ­ sult in m i n e r a l solution. In o r d e r to avoid or keep these errors to a minimum, some p r e l i m i n a r y o b s e r v a t i o n s were m a d e in this study. The salt s o l u t i o n of the r e f e r e n c e c a t i o n of 1 N c o n c e n t r a t i o n was c o n s i d e r e d more than a d e ­ q u a t e to replace the native e x c h a n g e a b l e cations and to fill in the e x c h a n g e sites of the soil m a t e r i a l in step 43 (a) 44 A m i n i m u m of two hours of total c o n t a c t time of the s a t u r ­ at i n g or replacing solut i o n was c o n s i d e r e d s u f f i c i e n t to r e a c h the exchange equilibrium. M a l c o l m and K e n n e d y (1969), u s i n g specific ion e l e c t r o d e t e c h n i q u e s , m e a s u r e d the rate of c a t i o n exchange on kaolinite, montmorilIonite between K + and Na illite, v e r m i c u l i t e and + and Ba 2+ , Ca 2+ and M g 2+ T h e y c o n c l u d e d that m o r e than 85 per cent of the e x c h a n g e takes p l a c e w i t h i n the first two m i n u t e s of m i x i n g and e q u i l i b r i u m is e s s e n t i a l l y complete w i t h i n 17 m i n u t e s of mixing time. T o accomp l i s h removal of the o c c l u d e d salt solu t i o n in step (b), A l e x i a d e s and J a c k s o n (1965) e m p l o y e d one w a s h i n g w i t h H 20 and 5 w a s h i n g s w i t h 99.0% methanol, adding a c e t o n e as required to p r e v e n t dispersion. et a l . (1962) Okazaki, s uggested no w a s h i n g af t e r s a t u r a t i o n of the sample w i t h the reference c a t i o n b u t c a l c u l a t i n g the a m o u n t of the o c c l u d e d salt s o l u t i o n by w e i g h t d i f f e r e n c e and us i n g this c o r r e c t i o n in the final CEC value. Frink (1964) sug­ g e s t e d the use of 0 . 0 0 1 N salt solution of the r e f e r e n c e c a t i o n for occlu d e d salt d e t e r m i n a t i o n and c o r r e c t i o n for soil samples in the C a C l 2 m e t h o d of CEC d e t e r m i n a t i o n . agrees w i t h Peech, He et a l . (1962) on isopropyl alc o h o l as a w a s h s o l vent for use in the c o n v e n t i o n a l N H ^ O A c procedure. L ower a l cohols were found to solubilize some a m m o n i a t e d organic matter complexes. TABLE 3.— Effect of washing procedures in CaC]^ method of CEC determination CaEC meg/100 g soil Soil Sample No. Once water + 5 MeOH washings Once water + 7 MeOH washings Differences in CEC Once water + 4 washings with 0.0001 N CaCl2 CaEC (I-H) CaEC (I—III) I II III 1 9.0 9.0 7.5 0 1.5 2 5.2 5.2 4.4 0 0.9 3 8.4 8.1 7.4 0.2 1.0 6 10.9 11.1 10.5 -0.2 .4 8 5.6 5.2 5.0 0.4 .6 13 0.8 0.7 0.6 0.1 .1 15 24.2 22.0 21.8 2.2 2.5 18 14.2 14.4 14.2 -0.2 -0.1 21 2.5 2.3 2.0 0.1 .5 23 3.7 3.3 2.9 0.4 .8 26 1.3 1.1 0.9 0.2 .4 32 4.6 4.7 3.4 -0.1 1.2 35 1.7 1.4 1.2 .4 .5 39 30.0 29.0 28.5 1.0 1.5 46 In the present study a comparison of the CEC values was m a d e to know the effectiveness of meth a n o l and Jackson, (Alexiades 1965) and 0.0001 N C a C l 2 as w a s h solvents. The data in Table 3 indicate that w a s h i n g the samples once with water plus five times w i t h methanol after calcium saturation gave consistently higher values as compared to procedures II and III where the samples were wa s h e d once w i t h w a t er plus 7 times w i t h m e t h a n o l or once with water plus 4 times w i t h 0.0001 N C a C l 2 , respectively. In procedure III where 0.0001 N C a C l 2 was used as the w a s h i n g solution, the we i g h t difference bet w e e n the wet sample after washing, centrifuging and decan t i n g the s u p e r ­ natant liquid and the dry sample could be used to calculate the e x a c t amount of occluded Ca 2+ For samples studies, weight of the 0.0001 N C a C l 2 2+ usually did not exceed 2.5 g r a m s . The Ca present in this 2 *f w e i g h t of solution is 0.00025 meq. This amount of Ca was considered negligible to deduct from the meq C a ++/100 g soil obtained. A t this low c o n c e ntration of 0.0001 N C a C l 2 the possibility that wa t e r as a polar solvent may h y d r olyze Ca 2+ is negligible beca u s e of the saturation of 2+ clay and the presence of a low amount of Ca ions in the solution. The CEC values obtained by procedure III were used for the purposes of comparison in this study as they w e r e m o r e precise. To determine the number of washings that are n e c e s ­ sary to insure complete rep l a c e m e n t of the reference cation 47 in s t e p (c) of the KC1 m e t h o d of CEC, K + was d e t e r m i n e d in e a c h s u c c e s s i v e w a s h i n g as shown in Table 4. T h e s e da t a i n d icate t h a t 5 times w a s h i n g w i t h a salt s o l u t i o n of the d i s p l a c i n g cation displaces the refer e n c e c a t i o n e f f i c ­ iently. A m o n g the five m e t h o d s of C E C d e t e r m i n a t i o n e m p l o y e d in this study, the N a O A c p r o c e d u r e was d o n e at p H 8.2, H+ u s e d in S u m EC was d e t e r m i n e d at pH 8.0, three p r oced u r e s w e r e e m p l o y e d at p H 7.0. tions w e r e m a d e w i t h the N a O A c p r o c e d u r e the and the other CEC determina­ (Table 5) at pH 7.0 and 8.2 to see if the p H difference w o u l d s i g n i f i c a n t l y a f f e c t the CEC values. The CEC values d e t e r m i n e d by the N a O A c m e t h o d at p H 7.0 and p H 8.2, as shown in T a b l e 5, a g r e e w e l l w i t h each other for the soils studied. It t h e r e f o r e seems that ess e n t i a l l y the same e x t e r n a l and i n ­ ternal c harges of the soil e x c h a n g e sites are s a t i s f i e d at pHs 7.0 and 8.2. Apparently, the C E C values d e t e r m i n e d by N a O A c m e t h o d at p H 8.2 can w e l l be compared w i t h C E C v a l u e s d e t e r m i n e d by other methods at pH 7.0 w i t h o u t a r e a s o n a b l e d o u b t t h a t there m a y be an appreciable c o n t r i b u t i o n to the C E C v a l u e s b e t w e e n these two pH values. The c o m p a r a b l e v alues b e t w e e n the SumEC and the N H ^ E C also b e a r o u t this r elationship, Table 6 . The five m e t h o d s of C E C d e t e r m i n a t i o n u s e d in this study were: (1) c a l c i u m s a t u r a t i o n or C a C l 2 method, p o t a s s i u m s a t u r a t i o n or KC1 method, or N H ^ O A c method, (2) (3) a m m o n i u m s a t u r a t i o n (4) s o d i u m saturation or N a O A c method, TABLE 4.— Relationship between effective replacement of K+ by NH^+ with increasing number of washings. Soil Mo. Total K+ PPi 1st 2nd 3rd 4th 5th 6th 7th 1 62.5 14.0 3.0 0.4 0.1 0 0 80.1 2 25.0 7.5 1.3 0.2 0 0 0 34.0 4 59,0 9.0 2.1 0.3 0 0 0 70.4 6 132.5 19.0 7.4 2.2 0.5 0.2 0 161.6 9 112.0 16.0 6.3 1.7 0.5 .1 0.1 137.1 13 11.0 1.4 .5 0.1 0.1 0 0 15 222.5 63.0 19.1 6.0 2.3 0.8 0.3 313.1 16 162.5 44.0 12.0 3.3 1.2 .3 0.1 223.0 13.0 00 TABLE 5,-^Cation exchange capacity values for 15 soil samples determined by the NaOAc method at pHs 7.0 and 8.2. Soil Sampie MO • So^ Series Horizon NaEC meg/100 g Increase with pH pH 7.0 pH 8.2 meq/100 g 11.1 11.4 + .3 15.1 15.7 + .4 24.3 23.9 - .4 13.6 13.6 0. 15.2 16.0 +0.8 22.3 23.1 + .9 20.0 20.9 + .9 Big 32.5 33.4 + .8 Ontonagon Ap 29.4 31.0 +1.6 19 Iron River Ap 26.4 26.5 + .1 20 Iron River 14.1 14.5 + .4 27 munising 9.4 9.2 - .2 33 Onaway 21.5 21.3 - .3 35 Kalkaska 15.5 16.3 + .8 39 Pewamo 46.5 45.6 -1.0 1 Miami Ap 3 Miami 6 Volinia 7 Volinia 9 Kalamazoo 12 Saugatuck 14 Onaway B21h Ap 15 Brookston 17 B21t Ap B22t B2t Bhir A2 B21t B22ir Ap 50 and (5) s u m m a t i o n of cations method. The CEC v a l u e s o b ­ tained by these m e t h o d s w i l l h e r e i n a f t e r be r e f e r r e d to as C a E C , KEC, N H ^ E C , NaEC, and SumEC respectively, expressed in m e q / 1 0 0 g of soil. T h e s e five m e t h o d s w e r e c o m p a r e d w i t h r e g a r d to their s u i t a b i l i ty in terms of accuracy, r e a s o n a b l e quickness, reliability, simplicity, and their proper s i g n i f i c a n c e in the fo l l o w i n g kinds of soil h o r i z o n s : (a) the surface h o r i z o n s A p and (13 s a m p l e s ) , (b) the illuvial spodic horizons B^, and B ^ r (6 s a m p l e s ) , (c) the illuvial B. and B_ h o r i z o n s t g (10 s a m p l e s ) , (d) the leached A 2 h o r i z o n of Spodosols (2 s a m p l e s ) , the leached A 2 and A£ horiz o n s of A l f i s o l s or Al f i c intergrades (4 s a m p l e s ) , and the p a r e n t m a t e r i a l or C^ h o r i z o n T h e d a t a o b t a i n e d for A 2 , g r o u p e d together, (d) above, (3 s a m p l e s ) . a £ and C^ horiz o n s w e r e as they all c o n t a i n e s s e n t i a l l y u n c o a t e d m i n e r a l s p o s s i b l y b e h a v i n g similarly. In Table 16 in the A p p e n d i x the C E C va l u e s o b t a i n e d by five methods, the soil acid i t y c o m p o n e n t s determined, and the e s t i m a t i o n of v e r m i c u l i t e contents in these samples as d e t e r m i n e d by A l e x i a d e s and J a c k s o n ' s (1965) procedure are s h o w n . T h e v e r m i c u l i t e con t e n t in soils w e r e calcul a t e d (Alexiades and Jackson, 1965) assu m i n g 154 meq/100 g as 51 the i n t e r layer c h a r g e of v e r m i c u l i t e as follows: , .^ ^ p e r c e n t v e r m i c u l i t e in Soil (CaEC - KEC) X 100 (B) « --------- ------------ p e r c e n t v e r m i c u l i t e in clay B x 100 (C) - % cl-ay ln fche soil The p e r c e n t v e r m i c u l i t e in soil clay c a l c u l a t e d f r o m this p r o c e d u r e m a y be only a q u a l i t a t i v e g u i d e p a r t i c u l a r l y for samples w i t h low soil clay c o n t e n t s . Th e d e p t h functions of N a E C and C a E C of the soil horiz o n s studied are s h o w n in F i g u r e 6 . The m a g n i t u d e of the N a E C and CaEC va l u e s for speci f i c p r o f i l e s {Figure 6 ) showed c o n s i s t e n t l y h i g h e r N a E C v a l u e s on all h o r i z o n s . The d i f f e r e n c e b e t w e e n these two CEC v a l u e s was p r o m i n e n t in S p o d o s o l s , p a r t i c u l a r l y in spodic h o r i z o n s as c o m p a r e d to A l f i s o l s or Mollisols. Spodosol, However, in M u n i s i n g C^ horizon, a there was less d i f f e r e n c e b e t w e e n N a E C and C a E C values. The m e a n CEC values o b t a i n e d by the five m e t h o d s g r o u p e d a c c o rding to soil horizons are shown in T a b l e 6 . Th e va l u e s in Table 6 indic a t e the general trend of CEC values b e i n g equal or h i g h e r in the illuvial B fc and B g h o r izons as c o m p a r e d to the sur f a c e A p or A^ h o r i z o n s a n d lower C E C va l u e s in spodic horizons. However, the hor i z o n s in each v ert i c a l c o l u m n are n o t all f r o m the same p r o f i l e . Thus, the d e p t h functions in F i g u r e 6 are m o r e truly i n d i c a ­ tive of the situations in p a r t i c u l a r soil profiles. CEC meq/100 g of soil 10 20 10 20 10 10 20 20 10 10 20 20 *Tt> B 21t B ig 22g A2B3t a) Miami Loam Kalamazoo Loam Spinks Loamy Fine Sand Ontonagon Silty Clay Volinia Loam Brookston Loam c Ul to •H 10 glO B 20 20 10 20 10 20 a 22 21h VAW V , B0 40 90g Cx •0 Kalkaska Sand Onaway Loam Iron River Silt Loam Saugatuck Sand i Munising Loamy Sand Figure 6. Depth functions of CaEC and NaEC in soils studied. CaEC NaEC TABLE 6.— The mean CEC values determined by five methods grouped according to the kinds of soil horizons. Mean CEC meq/100 g of soil Horizon KEC CaEC SumEC Ap and 6.4 8.4 11.8 Ratio n h 4ec NaEC NaEC/CaEC 12.4 18.2 2.2 Ui u> 2'1 1.8 6.8 6.5 13.5 11.4 B. and B„ t g 7.3 9.4 11.7 12.9 17.2 1.8 Aj, A*2 and C^ 1.6 1.9 3.3 3.4 5.1 4.3 V Bhir and Bir 54 The decreasing order of the mean CEC values d e t e r ­ mined by five methods on the surface, and the illuvial B. and t g the A 2 + A£ + C^, horizons are; Na EC > N H 4 EC >_ SumEC > C a E C > KEC However, a slightly different pattern was observed for spodic horizons: N a E C > SumEC _> NH^EC > KEC >_ CaEC U n der a given set of conditions, it may be possible to p r e d i c t the CEC values among the five methods used in this study according to the predic t i o n equations given in Table 7 for the respective soil horizons of representative Michi g a n s o i l s . The prediction equations were highly s i g ­ n ificant o n all the soil horizon groupings except the s p o ­ dic horizons and correlation of the NaEC with the CaEC and KEC o n the A 2 , A£ and C^ horizons. For spodic horizons, however, only N H ^ E C vs NaEC and KEC vs CaEC could be highly significantly predicted while the SumEC vs NaEC and SumEC vs N H ^ E C were only significantly correlated and the others were correlated at the significance levels shown in the Table 7, part B. These prediction equations can be i n t e r ­ preted as denoting the relative magnit u d e s of CEC values to each other w i t h a positive or a negative constant. For 55 example, 2.43. in the surface horizons, C a E C was .6 N a E C minus T h ere seems to be a 1:1 r e l a t i o n s h i p b e t w e e n KEC a nd C a E C in spodic horizons. Variations in rela t i v e m a g n i t u d e s a m o n g CEC va l u e s b y a g i v e n m e t h o d are due u s u a l l y to the influ e n c e of clay c o n t e n t and o r g a n i c m a t t e r p r e s e n t in soils. Regression a n a l y s e s w e r e p e r f o r m e d to know the ext e n t of influence of clay a n d organic m a t t e r and the results are shown in Table 8. To facilitate better i n t e r pretation of the r e g r e s s i o n e q u a t i o n s p r e s e n t e d in Table 8 , the rela t i v e m a g n i t u d e of the c h a r g e contr i b u t i o n s to each CEC value from clay and o r g a n i c m a t t e r were listed in Table 9 and 10 respectively. Th e c h a r g e c o n t r i b u t i o n s from o r g a n i c m a t t e r (Table 10) w e r e c a l c u l a t e d on the basis of the con v e n t i o n a l m u l t i p l i ­ c a t i o n factor 1.72 to c o n v e r t p e r c e n t c a r b o n to p e r c e n t o r g a n i c m a t t e r p r e s e n t in the soil. As seen from the results in Table 9, the charge c o n ­ t r i b u t i o n f r o m clay con t e n t of the soil a m o u n t e d f r o m as l o w as 11 meq/100 g for KEC in illuvial B^ and Bg horiz o n s (Significant at .11 level) to as high as 45 meq/100 g for N H ^ E C in group D horizons of unco a t e d m a t e r i a l s at .01 level). (significant The decre a s e in charge c o n t r i b u t i o n by clay w a s c o n s i s t e n t from surface to spodic to illuvial B^ and B^ h o r i z o n s though in spodic hori z o n s its c o n t r i b u t i o n was 56 TABLE 7.— Regression equations and correlation coefficients among CEC values determined by five methods grouped according to the kinds of soil horizons. A. horizons Ap and A1 Surface 1 CaEC KEC n h 4ec SumEC KEC n h 4ec SumEC NH4EC SumEC SumEC C. = => - .59 .41 .63 .69 .66 .98 1.13 1.51 1.70 1.06 NaEC NaEC NaEC NaEC CaEC CaEC CaEC KEC KEC n h 4ec Illuvial B _ + + + + + + - 2.43 1.11 .95 .74 .82 4 .18 2.28 2.78 .92 1.40 and : B r .924** .955** .934** .918** .991** .937** .973** .965** .978** .956** horizons 9 CaEC KEC n h 4ec SumEC KEC n h 4ec SumEC n h 4ec SumEC SumEC m m .70 .50 .74 .80 .70 1.03 1.15 1.49 1.62 1.02 * ** ( ) NaEC NaEC NaEC NaEC CaEC CaEC CaEC XEC KEC nh 4ec - + + + + - 2.54 1.26 .21 2.12 .73 3.21 .89 2.08 .11 1.49 B. Illuvial spodic horizons Bh' Bhir and Bir CaEC KEC NH4EC SumEC KEC n h 4ec SumEC n h 4ec SumEC SumEC S = = ** = = = - .08 .09 .46 .34 1.00 1.92 1.06 2.07 1.33 .67 NaEC NaEC NaEC NaEC CaEC CaEC CaEC KEC KEC nh 4ec + .83 + .86 + .25 +2.21 + .25 +2.96 +4. 89 +2.18 +4 .07 +2. 51 r .420(.41) .505(.31) .919** .837* .988** .677 (.14) .458 (.36) .736 (.10) .581(.23) .821* D * A2 ' A 2 and C^ horizons .962** .977** .949** .962** .989** .958** .933** .972** .987** .952** Significant at .05 level Significant at .01 level Significant at level shown. CaEC KEC n h 4ec SumEC KEC n h 4ec SumEC NH4EC SumEC SumEC = - .41 .32 .77 .64 .73 1.42 1.19 1.89 1.64 .81 NaEC NaEC NaEC NaEC CaEC CaEC CaEC KEC KEC nh 4ec .18 - .02 - .51 - .05 + .22 + .74 +1.04 + .39 + .68 .54 - .711* .743* .882** .839** .973** .929** .896** .930** .926** .927** TABLE 8.--Relationships between CEC values and clay and carbon contents, their partial and multiple correlation coefficients and levels of significance on soils grouped according to horizons. A. The surface horizons A^ and A1 ICarbon tClay .37 .66 .02 .33 •57 .05 .24 .65 .02 .44 .79 .01 .41 .60 .04 NaEC a b CaEC a b KEC a b NH.EC a b SumEC a b + ♦ + + ♦ 12.14 .82 .01 4.07 .39 .21 3.01 .48 .11 3.92 .50 .10 4.38 .37 .23 C. The:illuvial Bt and NaEC a b CaEC a b KEC a b nh4ec b SumEC a b - .24 .60 .09 .14 .48 .19 .11 .57 .11 .23 .67 .05 .16 .56 .12 ♦ + ♦ + 9 B. The Spodic horizons B^, ®h;IX And Bir -4.57 .811** -2.35 .637** -1.41 .737** ♦0.28 .832** -0.58 .656** horizons 10.17 .77 .02 7.93 .77 .02 5.60 .82 .01 6.75 .71 .03 9.45 .83 .01 IClay r2 NaEC m a b CaEC ■ a b KEC — a b nh4ec m 4 1 b SumEC m a b «Carbon .31 + .33 .59 .22 + .93 .02 .22 + .92 .03 .38 + .73 .16 .20 + .66 .22 6.11 + 5+58 .74 .15 .24 + 0+38 .41 .49 .43 + 0+45 .60 .28 3.03 + 1.32 .81 .10 3.01 + 2.69 .91 .03 r2 .557{.3) .866* .853(.06) .724(.15) .832(.07> 0. The A2, A’ and C^ horizons +7.34 .832** +2.76 .805** +2.38 .855** ♦4.77 .827** +3.73 .861** NaEC ■ a b CaEC ■ a b KEC ■ a b NH4EC a b SumEC m a b a - partial correlation coefficients. b « significance levels of the partial correlation coefficients ( ) ■ significance levels of multiple correlation coefficients .31 + 5.03 ♦ 2.28 .846** .78 .88 .01 .02 .34 + .90 ♦ .02 .972** .99 .81 .01 .01 .74 + .22 .929** .25 + .96 .69 .06 .01 .45 + 2.68 +53 .934** .95 .87 .01 .01 + .40 1.49 + 1.00 .798** .88 .54 .17 .01 * Significant at 0.05 level *' Significant at 0.01 level TABLE 9.— Relative charge contributions from clay to CEC values grouped according to the kinds of soil horizons. Horizon (Significance levels shown in parenthesis) CEC Values Surface and A. P 1 Illuvial spodic V Bhir and Bir Illuvial B. and B„ A2, A£ and C^ meg per 100 g clay NaEC 37 (.02) 31 (.59) 24 (.09) 31 (.02) CaEC 33 (.05) 22 (.02) 14 (.19) 34 (.01) KEC 24 (.02) 22 (.03) 11 (.11) 25 (.01) n h 4ec 44 (.01) 38 (.16) 23 (.05) 45 (.01) SumEC 41 (.04) 20 (.22) 16 (.12) 40 (.01) 59 si g n i f i c a n t only for CaEC and KEC. These charge c o n t r i b u ­ tions w e r e in a fairly normal r a n g e for soil clays of m i x e d m ineralogy, c h a r a c t e r i s t i c of m a n y of the r e p r e s e n t a t i v e M i c h i g a n soils used in this study. S e veral w o r k e r s W u r m a n et a l . , 1959; M ortland, 1969) (Cummings, Ross, 1965; 1959; Franzmeier, R i e k e , 1963; 1962; Reiman and have studied the m i n e r a l o g i c a l c o m p o s i t i o n of the soil m a t e r i a l s of horiz o n s of soil types similar to those used in this study. The q u a n t i t a t i v e e s t i m a t i o n of the clay m i n e r a l s they repor t e d are p r e s e n t e d in Table 17 of the Appendix. Since the h o r i z o n samples they studied w e r e n o t the same, but similar to the ones u s e d in this study, these d a t a can o n l y be a q u a l i t a t i v e guide. O n the basis of these data, or the Ap, A^ and illuvial h o r i z o n s of the soils studied have d o m i n a n t l y a m i x e d m i n e r a l o g y w i t h kaolinite, illite, c h l o r i t e and v e r m i c u l i t e d i s t r i b u t e d a p p r o x i m a t e l y equally, w i t h low amo u n t s of smectites and A l - i n t e r g r a d e minerals. In the illuvial sp o d i c horizons B h , B h ^r and B^r , there is a p r e d o m i n a n c e of A l - i n t e r g r a d e minerals. The C^ h o r i z o n of K a l a m a z o o loam has also a h i g h a m o u n t of v e r m i c u l i t e (53.8%) in its clay fraction. The results in Table 10 show that the charge c o n t r i ­ b u t i o n s f r o m organic m a t t e r to N a E C was h i g h e s t on all h o r i z o n s and unr e a s o n a b l y h i g h though h i g h l y s i g n i f i c a n t in TABLE 10.— Relative charge contributions from organic matter to CEC values grouped according to the kinds of soil horizons. Horizon (Significance levels shown in parenthesis) CEC values Surface Ap & Ax Illuvial spodic Bh , Bhir and Bir Illuvial Bfc and Bg A,, A' 6 C1 meq per 100 g of organic matter NaEC 706 (.01) 355 (.15) 599 (.02) 292 (.01) CaEC 237 (.21) 14 (.49) 461 (.02) 52 (.01) KEC 175 (.11) 25 (.28) 326 (.01) 43 (.06) NH.EC 4 228 (.10) 176 (.10) 392 (.03) 156 (.01) SumEC 255 (.23) 175 (.03) 549 (.01) 87 (.17) su rface horizons. F o r C a E C and KEC, they w e r e u n r e a s o n a b l y low in b o th the illuvial spodic h o r i z o n s and hori z o n s of u n c o a t e d m a t e r i a l s and w e r e least s i g n i f i c a n t in spodic horizons. The org a n i c m a t t e r charge c o n t r i b u t i o n was w i t h i n the n o r m a l l y expected range of a low of 87 to a h i g h of 255 m e q/100 g for all other C E C values o n all h o r i z o n s excl u d i n g the illuvial B. and B horizons. t g The low charge c o n t r i b u t i o n f r o m o r g a n i c m a t t e r to KEC and C aEC in spodic hori z o n s m a y be due to the fact that these u n b u f f e r e d chloride salts do not disp a l c e A l 3+ com- p l e x e d b y organic m a t t e r from the p H d e p e n d e n t sites at pHs above that of the soil. Rich a n d Thomas (1960) Works of Thomas (1961) and have i n d i cated that the a d s o r b e d h y d r o x y Al ions are n o t e x t r a c t e d by neutral salt solutions of 1 N concentration. However, in this study, N H ^ O A c m e t h o d gave h i g h e r values than the C a C l 2 or KC1 method. T h e r e was a high c h a r g e c o n t r i b u t i o n from o r g a n i c m a t t e r to all CEC v a l u e s in the illuvial B. and B horizons t g (Table 10) w h e r e the o r g a n i c ma t t e r c o n t e n t is n o r m a l l y e x p e c t e d to be the lowest in the profile. This m a y be p a r t i a l l y e x p l a i n e d by the fact that the c o n v e n t i o n a l factor used for subsoil h o r i ­ zons w i t h low amount of o r g a n i c m a t t e r should be m o r e than two as B r o a d b e n t (1953) and Ra n n e y (1969) h a v e discussed. This increase charge c o n t r i b u t i o n from org a n i c m a t t e r to CEC values in the illuvial B. and B„ h o r i z o n s as c o m p a r e d to t g surface or spodic horiz o n s has a g e n e t i c s i g n i f i c a n c e in 62 that the o r g a n i c exchange complex h a v i n g m o r e charge is e v i d e n t l y car r i e d farther d o w n in the natural leaching column, the soil profile in the course of its development. Thus, the interpretations f r o m r e g r e s s i o n equati o n s p r e s e n t e d in T a b l e 8 show that the charge contributions from both clay and o r g a n i c ma t t e r contents w e r e fairly c o n ­ s i s t e n t for NH^EC. The m e a n NH^EC values (Table 6 ), w e r e i n t e r m e d i a t e b e t w e e n the CaEC and NaEC values. Also, they c l o s e l y a p p r o x i m a t e d the SumEC w h i c h includes the e x c h a n g e ­ able bases plus the exchange acidity m e a s u r e d by E A ( B a C l 2+ TEA) . These facts lead one to conclude that for the M i c h i ­ g a n soil m a t e r i a l s studied, the NH^OAc m e t h o d is the b e s t for C E C determination. However, the clay cha r g e estima t i o n s w e r e r e l a t i v e l y m o r e si g n i f i c a n t in spodic horizons for CaEC a n d K E C values. Also, CaEC and KEC r e a s o n a b l y e s t i ­ m a t e d the relative charge c o n t r ibutions f r o m b o t h clay and o r g a n i c m a t t e r on surface horizons. In order to bet t e r u n d e r s t a n d the o b s e r v e d h i g h NaEC va l u e s as comp a r e d to the other four m e t h o d s u s e d in this s tudy on all horizons, p a r t i c u l a r l y in the spodic horizons, the p r o b a b l e causes of their variat i o n s are d i s c ussed below. The four factors that m a y influence these v a r i a ­ tions a r e : 1. The posi t i o n of the saturating c a t i o n N a + in r ela t i o n to its r e p l a c i n g c a t i o n N H ^ + w i t h i n the lyotropic s e r i e s . 63 2. A n i o n r e t e n t i o n by the amorp h o u s p o s i t i v e edge g r o u p s , of h y d r o x y a l u m i n u m layers or iron oxides n e u t r a i y z i n g their charge and thus r e l i e v ­ ing the net nega t i v e ch a r g e on the exch a n g e sites of the layer silicates for ca t i o n exchange. 3. Poss i b l e d i s s o l u t i o n of the amorphous F e 2 0^ p r e ­ sent in the spodic h o r i z o n by s o d i u m acetate to an u n m e a s u r e d b u t s i g n i f i c a n t e x t e n t and thus expo s i n g the b l o c k e d charges of the layer s i l i ­ cate e d g e s . 4. Poss i b l e m i l d d i s s o l u t i o n of A l - i n t e r l a y e r s a b u n d a n t in spodic horiz o n s by the s o d i u m a c e ­ tate solu t i o n and thus e x p o s i n g b l o c k e d nega t i v e charges of the clay minerals. In the first cause m e n t i o n e d a b o v e « due to the mass a c t i o n s i tua t i o n forcing the r e p l a c e m e n t to completion, the re l a t i v e positions of cations in the lyotropic series are n o t relevant. C o n c e r n i n g the second reason, possibility, i.e., anion r e t e n t i o n a l u m i n u m interlajering is a natural pedoge n i c p r o c e s s a ccording to J a c k s o n (1960). As the de g r e e of i n t e r ­ l a y e r i n g i n c r e a s e ^ the degree of collapse f r o m 1 4 °A spacing to 10°A decreases upon K + s a t u r a t i o n and air dr y i n g t r e a t ­ m e n t in the X - r a y analysis. The r e s u l t i n g cha r g e d a l u m i n u m p o l y m e r is large and e s s e n t i a l l y u n e x c h a n g e a b l e r e s u l t i n g in r e d u c t i o n of CEC. The r e d u c t i o n in CEC in excess of 64 that accounted for by oxidation of ferrous to ferric iron (Raman and Jackson, 1966), results from protonation of hydroxyls at defects developed in the structure through removal of Al, Mg or Fe Jackson, 1966) (Jackson, 1960, 1963a; Huang and according to the equation: Layer - OH A 1 Q 33 + H+— >layer-OH 2 + 0 .33 A l 3+ The Al 3+ in the above equation can polymeryze as a p ositive hydroxy-Al coating on negative surfaces of clays (Jackson, can form 1960, 1963a, 1965). (Davidtz and Sumner, Positive iron oxide coatings 1965). The resulting Al h y ­ droxyl polymer, w h i c h is chlorite-like, has Al O H 2+ edge groups that are pH dependent and are hydrolyzable as are silicate layer edges as follows: (Jackson, 1968) -Al - OH - A l ----- > Al - O H _ 1 / 2 -Al - O H " 1 //2 + H +--- > A 1 - O H 2 + 1 / 2 T hese polymers or colloidal particles containing positively charged edge groups can directly react with anions. When these occur on external s u r f a c e s , and in an acid environment, anions as well as cations may be retai n e d by a r e a ction in wh i c h the positive charge is neutralized by the anion of a salt and the cation is then held by the released charges of the clay. As the pH is increased, 65 n e g a t i v e charge is released, b u t the edge groups of the p o l y m e r or c o l l o i d n o w take on OH*" i o n s . It m a y be thou g h t that w h e n O H ~ a d s o r p t i o n incr e a s e s in p r e f e r e n c e to the solut i o n anion, OAc", the O A c " r e m a i n s in s o l u t i o n and the n e u t r a l i z a t i o n of the b l o c k e d charges by 0 H ~ m a y lift the b l o c k a g e from e x c h a n g e sites of the c l a y m i n e r a l similar to that h y p o t h e s i z e d by B a r t l e t t and McIntosh (1969) in Sfc>odosols. In their studies of io n e x ­ c h a n g e in soils c o n t a i n i n g high amounts of a m o r p h o u s c o n ­ stituents, B i r r e l l a n d G r a d w e l l (1956), w o r k i n g w i t h the c l a y f r action of a v o l c a n i c ash subsoil, found that after N a O H d i s p e r s i o n b u t w i t h o u t the d e s t r u c t i o n of iron o x i d e coatings, the sample reta i n e d a b o u t 8 . 6 m e q of OAc*" p e r 100 g of soil at p H 7.0 f r o m B a t O A c ^ tion. of 1.072 N c o n c e n t r a ­ The studies of B i r r e l l a n d G r a d w e l l (1956) also i n ­ d i c a t e d that C l - ion r e t e n t i o n was a b o u t 1/20 as g r e a t as O A c ” ion r e t e n t i o n at pH 7.0 and that it was a b o u t 0.4 m e q / 1 0 0 g soil. Quirk (1960) found 3 m e q of C l ” r e t a i n e d at pH 1 b u t less than 0.8 meq/100 g chlor i d e was r e t a i n e d a t pH 6 and above. B erg and Th o m a s (1959) studied the anion e l u t i o n p a t t e r n s f r o m soils and soil clays and c o n c l u d e d that c h l o r i d e ions though a d s o r b e d g e t d e s o r b e d e a s i l y in the r a n g e of p H of soils under field conditions. and Jackson (1967) deVilliers also n o t e d little or no r e t e n t i o n of 66 Cl" ions by l i g a n d e x c h a n g e a b o v e pH 6.0. The increase in c h l o r i d e r e t e n t i o n b e t w e e n pH 4 and 5 is a t t r i b u t e d to the d e v e l o p m e n t at p H 5 of an increased n u m b e r of O H b r i d g e sites b e t w e e n A1 atoms of the p o l y m e r i c units by c o n t i n u e d p o l y m e r i z a t i o n or o l a t i o n (Bailar, 1956). Since C l ” r e t e n t i o n i n c r e a s e d w i t h increasing pH v a l u e b e t w e e n p H 4 a n d 5, w h e r e a s p o s i t i v e e l e c t r o s t a t i c ch a r g e of the s e s q u i o x i d e n o r m a l l y d e c r e a s e s w i t h incre a s e d pH, o w i n g to d e p r o t o nation, the "anion exchange" m e a s u r e d h e r e is c o n ­ s i s t e n t w i t h li g a n d exchange, -Al A l - + Cl * -Al Al- + O H ” OH r a t h e r than e l e c t r o s t a t i c e x c h a n g e of "swarm" anion. (de V i l l i e r s and Jackson, 1967) They a t t r i b u t e d the d e c r e a s e in the r e t e n t i o n of Cl" a b o v e pH 5 to the i n c r e a s i n g O H ”/ C l ” r a t i o in solution, w h i c h favors h y d r o x y l r e t e n t i o n in the p o l y m e r i c c o m p l e x e s in p r e f e r e n c e to the c h l o r i d e . Thus, it m a y s e e m that there m a y be a p o s s i b i l i t y of m o r e a c e t a t e r e t e n t i o n by the p o s i t i v e l y c h a r g e d grou p s c o m p a r e d to c h l o r i d e r e l e a s i n g soil exch a n g e sites for cation e x c h a n g e . P o s s i b l e d i s s o l u t i o n of a m o r p h o u s F e 2 0^ or o r g a n i c iron c o m p l e x e s by s o d i u m acetate s o l u t i o n thus m a k i n g a v a i l a b l e the n e g a t i v e e x c h a n g e sites of c l a y m i n e r a l s 67 for c a t i o n a d s o r p t i o n and r e l e a s e , o r , in o t h e r w o r d s , for e x c h a n g e m a y be d i s c u s s e d as f o l l o w s . Th e rela t i v e a b u n d a n c e of a m o r p h o u s material, A 1 2 0 3 and F e 2 0 3 in the spodic h o r i z o n s of M i c h i g a n Spodosols have b e e n p r o v e d by studies of p r e v i o u s w o r k e r s et a l . 1959; Franzmeier, R a m a n a n d Mortland, 1962; Rieke, (Wurman 1963; Lietzke, 1968; 1969). F o r c h a r a c t e r i z i n g the m i n e r a l na t u r e of the soil, the a m o r p h o u s coatings and crystals of iron oxides such as h e m a t i t e and goeth i t e w h i c h m a s k the true n a t u r e of the clay c o m p onents n e e d to be removed. M e h r a and J a c k s o n (1960) m e n t i o n e d the imp ort a n c e of this rem o v a l for e f f e c ­ tive s e g r e g a t i o n into d i f f e r e n t p a r t i c l e size f r a c tions and d i s p e r s i o n of silicate portions. For X-ray diffraction studies the removal of free iron oxi d e s g r e a t l y enha n c e s the p a r a l l e l o r i e n t a t i o n of layer sili c a t e clays and b r i n g s out some X-ray d i f f r a c t i o n peaks t h a t are o t h e r w i s e d i f ­ ficult o r impossible to detect. thermal analysis, D i f f e r e n t i a l and integral e l e c t r o n m i c r o g r a p h s and CEC are g r e a t l y i m p r o v e d after remo v a l of free iron oxides. Jackson (1953) A g u i l e r a and c o m p a r e d the m e t h o d e m p l o y e d by D e b who h a d p r o p o s e d the use of s o d i u m (1950) 'h y d r o s u l f i t e ' (Na 2 S 2 0 ^, s o d i u m d i t h i o n i t e or s o d i u m hyposulfite) and a 0 . 2 N so d i u m ta r t r a t e , 1 N s o d i u m acetate s o l u t i o n plus 2.0 grams of the r e d u c i n g agent in pH ra n g e s from 2.9 to 6.0 at 40°C. But this p r o c e d u r e c o n f r o n t e d a d i f f i c u l t y of F e S tation. T h e i r c o m p a r a t i v e studies pre c i p i ­ (Aguilera a n d Jackson, 68 1953) w i t h the use of 7.4% v e r s e n e and acetic acid r e m o v e d 88.9 p e r c e n t of the F e 2<)3 p r e s e n t in the sample b u t F e S precipitated. Later Aguilera and Jackson (1953) p r o p o s e d the d i t h i o n i t e m e t h o d and m o d i f i e d the same later to i n ­ c l u d e N a H C O ^ b u f f e r to m a i n t a i n the high o x i d a t i o n p o t e n ­ tial of N a 2 & 2 0 ^ (Mehra and Jackson, 1960), w h e r e i n b u f f e r and c h e l a t i n g actions of s o d i u m citrate and the r e d u c i n g a b ility o f N a 2 & 2 0 ^ w e r e u t i l i z e d a d v a n t a g e o u s l y at pH 7.3 not to d e s t r o y the iron layer silicate. Also, this i n ­ c u r r e d n o FeS precipitation. T h u s , it is r e a s o n a b l e to conclude that under the c o n g e n i a l m e d i u m p H 8.2, N a acetate m a y remove some of the a m o r phous or co a t e d F e 2 0 ^, p a r t i c u l a r l y their r e d u c e d forms w h e n present, though not to the extent of citrat e in the p r e s e n c e of ^ 2 8 2 0 ^, a r e d u c i n g agent. This mechanism can e x p o s e the excha n g e sites for exch a n g e w i t h Na* and its r e p l a c e m e n t by N H ^ + giving h i g h e r NaEC v a l u e s . In r e l a t i o n to the fourth cause, d i s s o l u t i o n of Al interlayers, F r i n k citrate, an analo g u e of Na acetate, i.e., p o s s i b l e m i l d (1965) used s o d i u m to e x t r a c t Al i n t e r ­ layers in his studies for c h a r a c t e r i z a t i o n of a l u m i n u m interl a y ers in soil clays k n o w n to be abundant in c h l o r i t i z e d vermiculite. Tamura (1958) u s e d so d i u m citrate, being a m i l d r e ­ a g e n t c o m p a r e d to fluoride or h y d r o x y l groups in F e 20 ^ removal, to r e m o v e the interlayers to cha r a c t e r i z e the 69 clay m i n e r a l o b s e r v e d bo behave like a d i o c t a h e d r a l v e r miculite. Therefore, it m a y be thought that N a ace t a t e m a y e x t r a c t some of the inter l a y e r - A l p r e s e n t e s p e c i a l l y in s podic h o rizons to an u n d e t e r m i n e d b u t s i g n i f i c a n t extent and thus e f f e c t an increase in CEC d u e to release of blocked exchange s i t e s . T h ese reasons lead one to ex p e c t an a d d i t i v e eff e c t of the three factors p a r t i c u l a r l y the latter two in o b t a i n ­ ing high N a E C values compa r e d to other m e t h o d s . To a s c e r t a i n w h e t h e r the above m e n t i o n e d m e c h a n i s m s o p e r a t e e f f e c t i n g the dissolution of amorphous and free F e 2°3 and a 1 2 ° 3 ' or9 a n ic iron complexes and A l - i n t e r l a y e r s and their influence o n CEC in 1 N NaOAc, the CaEC and KEC v a l u e s w e r e obta i n e d on the same 13 soil samples af t e r NaEC d e t e r m i n a t i o n as d e s c r i b e d earlier. The results o b ­ tained are shown in Table 11. The results shown in Table 11 i n d i c a t e d an increa s e in C a E C v a lues after 1 N N a O A c treat m e n t on seven of the 13 samples. This increase was p a r t i c u l a r l y s i g n i f i c a n t in spodic h o r izons or A p horizons of well d e v e l o p e d Spodosols. The s i x samples w h e r e the CEC values be f o r e and after 1 N N a O A c t r e a tment rema i n e d a p p r o x i m a t e l y the same w e r e the A p h o r izons of Miami and Onaway, B 22t illuvial of Brookston, M u n i s i n g and K a l a m a z o o and C^ hor i z o n of Kalamazoo. TABLE 11.— The effect of IN NaOAc on CEC of soil materials. Soil Sample no. Horizon Soil series 1 Ap Miami 14 Ap 19 11 27 28 12 13 35 15 30 9 10 n h 4ec SumEC CaEC NaEC Determination relative to before before before re-run KEC IN NaOAc treatment before after before after 9.0 9.7 12.3 10.9 7.5 7.6 5.4 6.4 Onaway 13.5 13.1 20.4 19.4 11.8 10.9 7.7 11.5 Ap Iron River 13.5 12.2 26.5 24.6 6.6 12.0 6.2 14.8 Ap Saugatuck 4.2 4.8 7.4 6.7 1.2 3.3 1.3 3.8 A2 Munising 5.3 4.4 9.4 9.0 2.5 4.8 2.2 4.8 Munising 4.4 .7.8 19.6 18.5 1.3 8.1 1.7 14.3 Saugatuck 10.6 9.8 22.4 20.3 1.8 9.1 2.2 10.0 Saugatuck 2.4 2.5 4.8 3.3 0.6 1.1 0.6 N.D. Kalkaska 5.5 6.3 15.4 13.9 1.2 6.0 1.5 6.7 Brookston 23.9 26.0 33.0 32.6 21.8 21.2 15.6 21.5 7.4 5.6 8.9 8.5 4.5 5.0 3.6 7.9 Kalamazoo 15.9 10.5 16.7 17.4 8.8 10.7 7.1 13.6 Kalamazoo 2.2 1.7 3.3 3.1 1.0 0.9 0.9 1.4 Bir Bhir Bir Bhir ig Bt Bt C1 Munising N.D. ■ Not Determined. *4 O 71 The KEC values were all higher after 1 N NaOAc t r e a t ­ ment. They were even higher than the CaEC values and were comparable to the NH^EC values in all cases except for s a m ­ ple 28, the B ^ r horizon of Muni s i n g where it approached more nearly the NaEC v a l u e s . These results clearly indicate that reactions such as the p ostulated d i s s o lution and/or anion retention m e c h a n ­ isms do operate during the 1 N NaOAc treatment and effect a significant alteration of the CEC of soil materials. Also, it is p l a usible that there may be a significant change in the organic exchange complex of the soil m a t e r i a l s . The soil acidity components w e r e also determine d to kn o w their influence on CEC values obtained by the five methods. These data included the exchange acidity d e t e r ­ m i n e d by B a C l 2 +TEA, NH^OAc and KC1 methods. Hereinafter these will be referred to as E A ( B a C l 2 + T E A ) , NH^EA, K E A r e ­ spectively. For the purposes of comparison and practical considerations, exchange acidity values were also obtai n e d through the courtesy of the University Soil Testing L a b o r a ­ tory w h i c h employs the SMP buffer m e t h o d and Pratt, 1961) (Shoemaker, Mc Lean for lime recommendations of M i c h i g a n farms. Those values will be referred to as EA(SMP) The exchangeable Al 3+ and H + hereinafter. determined by KC1 m e t h o d will h e n c e f o r t h be referred to as A l ^ + (KC1) and H+ (KC1). The d a t a o b t ained are shown in Table 16 of the Appendix. Several workers (Coleman e t a l ., 1959; Pratt and Bair, 1961) 72 h a v e r e f e r r e d to the d i f f e r e n c e b e t w e e n E A ( B a C l 2 +TEA) K E A as the p H d e p e n d e n t CEC. it has b e e n called and To identify that difference, "potential acidity" in this s t u d y and r e f e r r e d to as P A hereinafter. T he E A d e p t h functions are shown in F i g u r e 7 for s p e c i f i c profiles. F r o m F i g u r e 7 it can be seen that only the O n t o n a g o n and Sauga t u c k surface samples c o n t a i n e d Al 3+ ( K C 1 ) . B ut all spodic hori z o n s c o n t a i n e d Al (KC1) and 3+ o n l y h a l f of the B t horizons h a d Al (KC1). P o t e n t i a l 3+ a c i d i t y c o m p o n e n t was p r e s e n t in all soil h o r i z o n s ex c e p t the A 2 2 of K a l k a s k a sand and A 2x and B 22t of M u n i sing. Po­ tential a ci d i t y was c o m p a r a t i v e l y h i g h in spodic horiz o n s and it w a s the only soil a c i d i t y c o m p o n e n t in all horiz o n s of Spinks and B r o o k s t o n studied. T h e m e a n values of the a c i d i t y compon e n t s d e t e r m i n e d by m o d i f i e d C h a p m a n p r o c e d u r e and P r a t t bu f f e r m e t h o d general, the A 1 3 + (KC1) subsoil h orizons (1961) (1965) are shown in Ta b l e 12. In con t e n t incre a s e d from surface to (spodic or a r g i l l i c ) , the h i g h e s t b e i n g in the illuvial spodic horizons, o t h e r i n v estigators 1960) . and Shoemaker, M c L e a n as g e n e r a l l y o b s e r v e d by (Coleman et a l ., 1959; It is to be noted, however, Rich and Thomas, that these inferenc e s are d r a w n from the group i n g s of similar horiz o n s of d i f f e r ­ ent soil types. T h e d e c r e a s i n g or d e r of the m e a n e x c h a n g e aci d i t y v a l u e s in Table 12 are, by met h o d s of measurement: Soil acidity components - meg/100 g of soil 4___ 8 BT ,0 ■ N 20 3 B21t 30 40 30 60 8 8 Ap E B IB ig It - H B B 22t 22g A 2B3t Miami Loam Kalamazoo Loam Spinks Loamy Fine Sand Ontonagon Silty Clay Volinia Loam Brookston Loam Depth (in inches) 2 4 6 8 10 (*22 20 ■“ ■ = P ®22ir 21h B22i« □ B'lt 30 40 50 60 Kalkaska Sand Onaway Loam Iron River Silt Loam Saugatuck Sand Munising Loamy Sand Figure 7: Depth functions of soil acidity components in soils studied. I H+ (KC1) | A13+(KC1) ■ +l I KEA +0 + 1 | EA(BaCl2+TEA) □ Potential acidity lD» \ t TABLE 12.— The mean values of acidity components grouped according to the kinds of soil horizons Exchange Acidity Components meq/100 g soil Horizons Ap and A^ Bh» Bhir andBir EA(SMF) 4.2 9.3 NH.EA EA(BaCl~ + TEA) KEA Al3* (KC1) pA m H*(KCL) EA(BaCl?+ TEA)-KEA 2.8 2.7 0.4 0.2 0.2 2.3 4.8 5.0 1.6 1.1 0.4 3.4 Bt and Bg 3.0 3.5 2.1 0.9 0.5 0.3 1.2 A2, A£ and Cx 1.7 1.2 1.0 0.5 0.3 0.3 0.5 * Ew,. 75 EA(SMP) > N H 4E A >_ E A ( B a C l 2 +TEA) > KEA for the surface A p and A^ and A 2 # A£ and The EA(SMP) and the ill uvial B^, Bhir an<* B ir h 0*^-20*18* in the A p and A ^ or B^, Bh i r an<^ B ir ^o r i zons w e r e nearly do u b l e the NH^EA. The p a t t e r n of d e c r e a s e for the B. and B horizons were: t 9 EA(SMP) >_ E A ( B a C l 2 +TEA) > N H ^ E A > KEA T he r e g r e s s i o n equations p r e s e n t e d in Table 13 could be i n t e r p reted b e t t e r by a r r a n g i n g the acidity contribu t i o n s f r o m clay and org a n i c m a t t e r a c c o r d i n g to kinds of horizons as s h o w n in Tables 14 and 15. Acidity contribution from p e r c e n t car b o n has b e e n c o n v e r t e d to that from p e r c e n t organic matter (Table 25) e m p l o y i n g the c o n v e ntional c o n v e r ­ sion factor 1.72. The acidity c o n t r i b u t i o n from clay, Table 14, i n d i ­ c a t e d an u n u s u a l l y h i g h negative con t r i b u t i o n for EA(SMP) spodic h o r i z o n s (-238 m e q / 1 0 0 g ) . b e t w e e n a -10 m e q an d +14 m eq (EA(SMP), in All other values ran g e d in h o r i z o n of uncoated materials) (for N H ^ E A in spodic h o r i z o n s ) . However, the p a r t i a l c o r r e l a t i o n c o e f f icients o b t a i n e d for clay w e r e n o n - s i g n i f i c a n t on all horizons o t h e r than the P A in illuvial B. for all acidity components and B_ h o r i z o n s . TABLE 13.— Relationships between soil acidity measurements and clay and organic matter grouped according to dominant soil horizons. A. The surface horizons Ap and A^ %clay % carbon FA a b EA(BaCl.+TEA) = a 2 b KEA a b NH4EA a b EA(SMP) a b - .03 - .40 .20 - .02 - .16 .63 + .01 .22 .49 + .07 .31 .32 - .05 - .15 .65 + + + + 1.50 .75 .01 1.45 .62 .03 .05 .04 .90 .80 .19 .56 2.87 .43 .16 r2 + .58 + .82 + .24 + .57 + .77 PA a b .451* EA(BaCl,+TEA) * a 2 b .065 (.72) KEA a b * .277 (.20) NH.EA a b .212 (.30) EA(SMP) a b .586** C. The illuvial Bf c and Bg horizons PA a b EA(BaCl.+TEA) = a b KEA a b NH.EA a4 b EA(SMP) a b + .03 .75 .02 + .03 .38 .32 + .02 .21 .59 + .08 .36 .34 - .05 - .13 .79 + + + - .72 .68 .04 .38 .21 .59 .54 .41 .27 2.31 .41 .27 1.10 .18 .70 B. The spodic horizons B^, B^ir and B^r % clay % carbon - .03 - .11 .86 - .06 - .25 .68 0.0 - .02 .97 + .14 .40 .50 -2.38 - .66 .55 + + + + + 2.09 .82 .09 3.25 .91 .03 .74 .67 .22 3.16 .85 .07 5.53 .84 .37 r2 + 1.06 .685 (.18) + 2.05 .848 (.06) + .75 .453 (.41) .86 .724 (.15) + 9.66 .699 (.55) D. The & 2’ a2 and ci horizons + .35 .842** + 1.27 .337 (.24) + .72 .068 (.78) + 2.93 .185 (.49) - 4.39 .097 (.77) PA a b EA(BaCl.+TEA) * a b KEA a b NH. 4EA a b EA(SMP) a b a = partial correlation coefficients b = significance levels of the partial correlation coefficients ( } = significance levels of multiple correlation coefficients + .12 .12 .77 + .03 .17 .69 0.0 .01 .98 + .09 .46 .25 - .10 - .44 .28 + + + + + .39 .37 .37 1.23 .60 .12 .76 .47 .24 2.37 .81 .02 8.25 .97 .01 + .36 .156 (.60) + .53 .380 (.24) + .32 .224 (.47) + .09 .695* - .04 .933** Significant at 0.05 level ** Significant at 0.01 level * TABLE 14.— Relative acidity contributions from clay to the exchange acidities grouped according to the kind of soil horizons. fa vain«o eji vaiues Surface Ap and A^ Illuvial spodic ^ and B^ Illuvial and Bg A~, Al and CJ Difference (high-low) PA -3 (.2) -3 (.86) +3 (.02) 12 (.77) 15 EA(BaCl2+TEA) -2 (.69) -6 (.68) +3 (.32) 3 (.69) 9 KEA +1 (.49) 0 (.97) +2 (.59) 0 (.98) 2 NH4EA +7 (.32) +14 (.50) +8 (.34) 9 (.25) 22 EA(SMP) -5 (.65) -238 (.55) -5 (.79) -10 (.28) 228 TABLE 15.— Relative acidity contributions from organic matter to exchange acidities grouped according to the kinds of soil horizons. EA Values Surface Ap and Ax Illuvial spodic V and B.r Illuvial Bt and Bg A2, A£ an2.38 E A ( B a C l 2 +TEA) -2.13 .869 (.01) EA(SMP) - 0.77 N H 4E A +2.07 .557 (.05) Illuvial spodio horizons EA(SMP) = 1.41 E A ( B a C l 2 +TEA) +1.33 .926 (.07) EA(SMP) « 1.05 N H 4EA +4.25 .747 (.25) Illuvial B.t a n d B g horiz o n s EA(SMP) - 2.57 E A ( B a C l 2 +TEA) -1.95 .676 (.07) EA(SMP) - 2.30 N H 4EA +6.11 .176 (.30) 0.93 .651 (.06) .70 (.04) H o r i zons of u n c o a t e d mater i a l s EA(SMP) = 2.66 E A ( B a C l 2 +TEA) EA(SMP) = 1.91 N H 4E A 48 80 The above p r e d i c t i o n equations show a h i g h l y s i g n i f i ­ cant r e l a t i o n s h i p b e t w e e n E A ( B a C ^ + T E A ) face h o r i z o n s a t at horizons. levels) .07 and The EA(SMP) and EA(SMP) on sur­ .06 s i g n i f i c a n c e levels in other was significantly (at .05 and .04 c o r r e l a t e d w i t h N H ^ E A in surface h o r i z o n s a n d h o r i ­ zons of u n c o a t e d materia ls. values, However, the la r g e r EA(SMP) Table 12, o n all h o r i z o n s i n d i c a t e d that there may b e a p r o p o r t i o n a l o v e r e s t i m a t i o n of the soil a c i d i t y b y this m e t h o d p a r t i c u l a r l y in spodic h o r i z o n s . The results of the r e g r e s s i o n analysis o f b o t h the C E C v a l u e s and e x c h a n g e acidities w i t h clay and o r g a n i c m a t t e r c ontents of these acid to near neutral r e p r e s e n t a t i v e M i c h i g a n soils s h o w e d that b o t h of t h e m w e r e r e l a t i v e l y m o r e i n f l u e n c e d by o r g a n i c m a t t e r as c o m p a r e d to clay. In a d d i t i o n to the d i s s o l u t i o n e f f e c t of N a O A c on amorp h o u s a n d c l a y materi a l s , n e u t r a l i z a t i o n is another factor y i e l d ­ ing h i g h N a E C v a l u e s p a r t i c u l a r l y in spodic horizons. Similarly, the n e u t r a l i z a t i o n of soil acidity by B a C ^ + T E A at p H 8.0 was also r e s p o n s i b l e for c o m p a r a t i v e l y high SumEC values. T h e s e r e u s l t s raise a q u e s t i o n as to the p u r p o s e of the C E C d e t e r mination. If the p u r p o s e is to d e t e r m i n e the ne t n e g a t i v e ch a r g e of o n l y the c l a y m i n e r a l component s , it is n e c e s s a r y to rem o v e all the coat i n g s of iron ox i d e s and i am o r phous m a t e r i a l s inclu d i n g the organic m a t t e r w i t h c e r ­ ta i n t y b e f o r e the C E C determination. 81 O n the other hand, to be a realistic estimate of the net negative charge of the complex system such as the soil materials studied, the method should give results that should m o re resemble that system in its usual state as plants are grown on it. In the soil exchange complex, es­ sential and plant available cations are mo s t l y present in d i v alent form, except for K+ and C u + . C a l c i u m is a small O d i v alent cation of radius 0.99 A and is more representative of the common exchangeable ion population in the s o i l . the C a C l 2 met h o d of CEC determination, In the possibilities of chloride ion retention are negligible in the pH range of field conditions. However, in spodic horizons CaEC did not r e flect the potential charge contributions from organic matter. The NH^EC values were intermediate bet w e e n those of CaEC and NaEC. treatment, cases. The CaEC values, determined after 1 N NaOAc (Table 11), approached the NH^EC values in m o s t SUMMARY A N D CONCLUSIONS This s t u d y w a s initiated to g a i n a b e t t e r u n d e r ­ s t a n d i n g of a n d a m o r e r e a l i s t i c mea s u r e of the c a t i o n e x ­ change capacity of some r e p r e s e n t a t i v e acid to near n e u ­ tral m i n e r a l soils of Michigan. C a t i o n exch a n g e capa c i t y v a l u e s o b t a i n e d by the following m o r e co m m o n methods o n 38 h o r i z o n samples from 15 soil types were: 1. The C a C l 2 m e t h o d or c a l c i u m saturation. 2. The KCl m e t h o d or p o t a s s i u m saturation. 3. The NH^OAc m e t h o d or a m m o n i u m saturation. 4. The summa t i o n of cations m e t h o d . 5. The N a O A c m e t h o d or sod i u m saturation. The leaching pr o c e d u r e s followed c o n v e n t i o n a l l y for saturation, w a s h i n g and r e p l a c e m e n t of cations were r e ­ p l a c e d b y c e n t r i f u g a t i o n after thorough m i x i n g each time. T h e e f f i c i e n t removal of the o c c l u d e d salts in KEC and C a E C p r o c e d u r e s w e r e achie v e d by the use of their r e s p e c ­ tive solutions of 0.001 N and 0.0001 N concentration. T h e e x c h a n g e acid ities of these soil materials w e r e d e t e r m i n e d by: (1) the B a C l 2 + trietha n o l a m i n e method, the KCl m e t h o d , (3) the NH ^ O A c method, co n s i d e r ations, and (2) (4) for p r a c t i c a l the exch a n g e acidity values w e r e also o b ­ t a i n e d t hr o u g h the cour t e s y of the U n i v e r s i t y Soil T e s t i n g L a b o r a t o r y w h i c h r o u t i n e l y uses the Shoemaker, M c L e a n and P r a t t b u f f e r m e t h o d for lime recomm e n d a t i o n s to M i c h i g a n farms. 82 83 To facilitate m e a n i n g f u l i n t e r p r e t a t i o n s of the r e ­ sults p l a cing needed emphasis o n the process of d e v e l o p m e n t of soil p rofiles in g e n e r a l , the d a t a o b t a i n e d were gro u p e d a c c o r d i n g to the following kinds of hori z o n s and s u b j ec t e d to s tatistical analyses: A^? (a) the surface horizons: (b) the illuvial spodic horizons: (c) the illuvial B.c and B g horizons; h o r i z o n s of Spodosols, A p and B^, Bh i r and B i r * (d) the leached A-r the leached A 2 and A£ h o r i z o n of A l f i s o l s and A l f i c intergrades and the p a r e n t m a t e r i a l or the horizons. This last h o r i z o n g r o u p i n g e s s e n t i a l l y wa s one of unco a t e d m i n e r a l s a n d thus p o s s i b l y beha v i n g similarly. F r o m the discussions of the results obtained, these c o n c l u s i o ns were drawn: 1. The predic t i v e equat i o n s c a l c u l a t e d , a m o n g CEC v alues g r o u p e d according to the kinds of soil horizons, showed h i ghly significant r e l a t i o n s h i p s o n all horizons o t h e r than spodic. In spodic horizons, however, only N H ^ E C vs NaEC and KEC vs CaEC c o u l d b e p r e d i c t e d highly significantly. The SumEC vs N H ^ E C a n d N a E C w e r e b u t s i g n i f ­ icantly r e l a t e d in spodic hori z o n s and the o t h e r m e t h o d s at s i g n i f icance levels rang i n g from 0.1 to 0.41. 84 2• The r e g r e s s i o n analyses p e r f o r m e d -to know the r e l a t i v e m a g n i t u d e of the charge c o n t r i b u t i o n from clay and o r g a n i c m a t t e r contents of soils to CEC values obtaine d by several m e t h o d s g r o u p e d a c c o r d i n g to soil horizons showed the c h a r ge c o n t r i b u t i o n f r o m clay to be 11 to 45 m e q p e r 100 g w h i c h w a s c o n s i d e r e d a normal range for soil m a t e r - ials of d o m i n a n t l y a m i x e d clay m i n e r a l o g y . 3. The charge c o n t r i b u t i o n f r o m o r g a n i c matter was v e r y h i g h for N a E C p a r t i c u l a r l y in surface 100 g) a nd illuvial and B g (706 m e q per (599 m e q per 100 g) hori z o n s w h e r e a s its c o n t r i b u t i o n was too low for CaEC and KEC in spodic h orizons (14 and 25 m e q per 100 g r e s p e c t i v e l y ) . T h e s e m a y be d u e to n o n - e x c h a n g e a b i l i t y of hyd r o x y Al and Al 3+ c o m p l e x e d by orga n i c matter. The organic matter c o n ­ tributed to all CEC values relati v e l y highly in B^ and B g as c o m p a r e d to other hori z o n s w h i c h may be a s s o c i a t e d w i t h d i f f e r e n t kinds of orga n i c m a t t e r ac c u m u l a t e d in d i f f e r e n t horizons. For o t h e r CEC values o n all h o r i z o n s the charge c o n t r i b u t i o n from o r g a n i c m a t t e r amounted f r o m 87 to 255 m e q / 1 0 0 g, a normal range observed. 4. To ve r i f y the h y p o t h e s i s that the re l a t i v e l y h i g h N a E C c o m p a r e d to o t h e r CEC values have b e e n caused by: an a n i o n r e t e n t i o n possibility, (1) (2 ) d i s s o l u t i o n of a m o r ­ p h o u s a n d cry s t a l l i n e F e 20 3 and A 1 20 3 or organic excha n g e co m p lexes and (3) partial rem o v a l of A l - i n t e r l a y e r s , the CaEC and KEC w e r e d e t e r m i n e d on the same soil samples after IN N a O A c t r e a t m e n t in the NaEC determination. The results 85 showed an agreeable d u p l i c a t i o n of N a E C values b u t m a r k e d l y i n c r eased both the CaEC and KEC va l u e s on m o s t samples. This i n d i c a t e d that one or m o r e of the above m e n t i o n e d m e c h a n i s m s do o p e r a t e to an u n d e t e r m i n e d b u t s i g n i f i c a n t extent. 5. Thus, the ef f e c t of IN N a O A c in alte r i n g the soil m a t e r i a l cha r g e p r o p e r t i e s is of g r e a t s i g n i f i c a n c e and involves the very q u e s t i o n of the pur p o s e of the CEC determination. If the pur p o s e is to d e t e r m i n e the CEC of the clay m i n e r a l compon e n t s of soil m a t e r i a l s , then the e x t r a n e o u s m a t e r i a l s such as o r g a n i c m a t t e r and free sesq u i o x i d e s should be removed w i t h o u t d a m a g i n g the c r y s t a l ­ line materials. If the p u r p o s e is to d e t e r m i n e the net n e g a t i v e charge of soil m a t e r i a l s under field conditions, their n ature should be d e t e r m i n e d by a m e t h o d a p p r o x i m a t i n g the c onditions in nature. T h o u g h Ca 2+ is a small cat i o n r e p r e s e n t i n g m o s t of the d i v a l e n t ca t i o n p o p u l a t i o n p r e ­ sent in the soil e x c h a n g e c o m p l e x and though the CaEC e s ­ t i m a t e d b o t h the clay a n d o r g a n i c m a t t e r ch a r g e c o n t r i b u ­ tions in surface horizons, it c o u l d assess o n l y a v e r y low c h a r g e c o n t r i b u t i o n from o r g a n i c m a t t e r in spodic h o r ­ izons . T h e N H ^ E C reve a l e d a r e a s o n a b l e charge c o n t r i b u t i o n from both clay and org a n i c m a t t e r on all soil h o r i z o n s and w a s i n t e r mediate in v a l u e b e t w e e n C a E C and NaEC. fore, one m a y conclude that NH^OAc is the There­ best m e t h o d for CEC d e t e r m i n a t i o n for M i c h i g a n soil m a t e r i a l s . 86 6. T h e p r e d i c t i v e equat i o n s for the r o u t i n e l y m e a ­ sured e x ch a n g e acidity, E A (SMP) , and E A ( B a C l 2 + TEA) cor­ r e l a t e d h i g h l y s i g n i f i c a n t l y on surface h o r i z o n s and at 0.05 to .07 level in o t h e r h o r i z o n groupings. the larger EA(SMP) However, values indic a t e d that there m a y be a p r o p o r t i o n a l o v e r e s t i m a t i o n of the soil a c i d i t y by this m e t h o d p a r t i c u l a r l y in spodic horizons and thus r e s u l t i n g in h i g h e r lime r e c o m m e n d a t i o n s than r e q u i r e d b y o t h e r s t a n d a r d methods. A separate d e t e r m i n a t i o n of exchang e a c i d i t y by the B a C l 2 + T E A or an a d j u s t m e n t of the EA(SMP) va l u e s b a s e d on their relationships, there f o r e m a y give a m o r e r e a l i a b l e esti m a t e of the lime r e q u i r e m e n t s of co m m o n M i c h i g a n soil m a t e r i a l s . NEED F O R F U R T H E R RESEARCH 1. It should be noted that the conclusions arri v e d at from this study, data. Therefore, though significant, are b a s e d on limited an extensive study of these CEC d e t e r ­ mi n a t i o n s grouped according to soil horizons p r e v a l e n t under M i c h i g a n conditions will be of great value. Also, such studies should be done on alkaline and calcareous m i n e r a l soils and organic s o i l s . 2. materials, The p o s t ulated effect of 1 N NaOAc on amorphous coatings of A ^ O ^ and F e 2 0 ^ and A l - i n terlayer s parti a l l y d e m o n strated in this study needs to be i n v e s t i ­ g a t e d in detail before the actual mechanisms are known. 3. Under s t a n d i n g of the reasons for the differen c e s in CEC by various met h o d s in relation to their significa n c e to g r o w i n g plants are essential before the CEC of M i c h i g a n soil materials can be m o s t m e a n i n g f u l l y evaluated. 4. The observed low CaEC and KEC values in illuvial spodic horizons and the r elatively high charge cont r i b u t i o n from o r ganic ma t t e r in the illuvial B.t and B_ g horizons seem to have genetic significance and deserve further e x ­ ploration. During the course of profile d e v e l o p m e n t Al and Fe ions in soils may be held from mo v i n g d o w n through that natural leaching column by complexing w i t h relati v e l y low c h arged org a n i c complexes causing them to a c c u m u l a t e in 87 87a the s p o d ic h o r i z o n s , w h e r e a s the higher c h a r g e d p o r t i o n of the o r g a n i c m a t t e r is m o v e d further d o w n in the profile. 5. W i t h the study of CEC c h a r a c t e r i s t i c s of s podic horizons by C a C l 2 and N H ^ O A c methods, it m a y be p o s s i b l e to d e f i n e a c e r t a i n r a n g e in their ratios w h e r e the spodic horiz o n s can be identified. LITERATURE CITED LITERATURE CITED Aguilera, N. H. and Jackson, M. L. 1953. Iron oxide r e ­ m o v a l from w o i l s and clays. Soil Sci. Soc. A m e r . Proc. 17:359-364. Alexiades, C. A. a n d Jackson, M. L. 1965. A quantitative d e t e r m i n a t i o n of v e r m i c u l i t e in soils. Soil Sci. Soc. Amer. Proc. 29:522-527. Ay l e more, L. A. G. and Quirk, J. P. 1962. The Struc t u r a l Status of Clay S y s t e m s . Clays a n d Clay M i n e r a l s 9:104-149. Babcock, K. L. 1963. T h e o r y of the chemi c a l p r o p e r t i e s of soil c o l l o i d a l systems at equilibrium. Hilgardia 34:417-542. Bailar, J. C. 1956. C h e m i s t r y of the c o o r d i n a t i o n c o m ­ pounds. R e i n h o l d P u b l i s h i n g Corp., M e w York. Bailey, S. W. 1966. The status of clay m i n e r a l s t r u c ­ tures. Clays and Clay Minerals. 14:1-23 (Pergamon Press, N e w Y o r k ) . Barken, Y. G. 1940. The use of the e q u a t i o n of the e x ­ change a d s o r p t i o n i s o t h e r m for the d e t e r m i n a t i o n of the e x c h a n g e aci d i t y of the soil. Chem. Zentral bl. Vol. 2, p. 2363. Bartlett, R. J. and McIntosh, J. L. 1969. pH d e p e n d e n t b o n d i n g of p o t a s s i u m by a S p o d o s o l . Soil Sci. Soc. Amer. Proc. 33:535-539. Berg, W. A. and Thomas, G. W. 1959. Anion elution pat­ terns f r o m soils and soil clays. Soil Sci. Soc. Amer. Proc. 23:348-350. Bhumbla, D. R. and McLean, E. O. 1965. A l u m i n u m in soils: VI. Changes in pH d e p e n d e n t acidity, ca t i o n ex c h a n g e capacity, and ex t r a c t a b l e a l u m i n u m w i t h additio n s of lime to acid surface soils. Soil Sci. Soc. Amer. Proc. 29:370-374. Birrell, K. S. and Gradwell, M. 19 56. Ion e x c h a n g e p h e n ­ o mena on some soils c o n t a i n i n g amorp h o u s m i n e r a l c onstituents. J. Soil Sci. 7:130-147. 88 89 Blume, J. M. and Smith, D. 1954. D e t e r m i n a t i o n of e x ­ c h a n g e a b l e c a l c i u m and ca t i o n e x c h a n g e capa c i t y by e g u i l i b r i a t i o n w i t h Ca^S. Soil Sci. 79:9-17. Bolt, G. H. 1955. A n a l y s i s of the v a l i d i t y of the G o u y C h a p m a n theory of the electric double layer. J. C o l l o i d Sci. 10:206-218. Broadbent, F. E. 1953. The soil orga n i c traction. in Agric. 5:153-183. Adv. Broadbent, F. E. and Bradford, G. R. 1952. Cation exchange g r o u p i n g in soil org a n i c fraction. Soil Sci. 74:447-457. Brown, G. 1965. S i g n i ficance of r e c e n t structure d e t e r ­ m i n a t i o n of layer silicates for clay studies. Clay M i n e r a l s . 6:73-82. Chang, M. L. and Thomas, G. W. 1963. A s u g g ested m e c h a n ­ ism for sulfate a d s o r p t i o n by soils. Soil Sci. Soc. Amer. Proc. 27:281-283. Chapman, H. D. 1965. C a t i o n exchange capacity. In M e t h o d s of Soil A n a l y s i s , Part 2. C h e m i c a l and M i c r o b i o logical properties. ed. A. Black et a l . Amer. A g r o n o m y Soc. Madison, Wis. Coleman, N. T., Weed, S. W . , and McCracken, R. J. 1959. C a t i o n exch a n g e capa c i t y and e x c h a n g e a b l e cation s in P i e d m o n t soils of North Carolina. Soil Sci. Soc. Amer. Proc. 23:146-149. Coleman, N. T. and Craig, D. a t i o n of h y d r o g e n clay. 1961. The spontaneous a l t e r ­ Soil Sci. 91:14-18. Coleman, N. T., Thomas, G. W . , le Roux, F. H. and Bredell, G. 1964. Salt e xc h a n g e a b l e and ti t r a t a b l e acidity in b e n t o n i t e sesquioxide mixtures. Soil Sci. Soc. Amer. Proc. 28:35-37. Coleman, N. T. and Thomas, G. W. 1964. Bu f f e r curves of a c i d clays as affected by the pres e n c e of ferric iron and aluminum. Soil Sci. Soc. Amer. Proc. 28:187-190. Coleman, N. T. and Thomas, G. W. 1967. The b a s i c ch e m i s t r y o f soil acidity. In R. W. P e a r s o n and F. A d a m s (eds.) Soil A c i d i t y and L i m i n g . Amer. A g r o n o m y Soc., Madison, Wisconsin. 90 Coulter, B. S. 1969. The c h e m i s t r y of hyd r o u s and a l u m i ­ n u m ions in soils, clay m i n e r a l s and resins. Soils land Fert. 32:215-223. Cummings, S. L. 1959. R e l a t i o n s h i p s of p o t a s s i u m fixation and r e l e a s e to the clay m i n e r a l comp o s i t i o n s of some M i c h i g a n soils. M.S. Thesis, M i c h i g a n State U n i v e r s ­ ity, East Lansing, Michigan. Davis, L. E. 1945. Soil Sci. Vol. Theories of b a s e - e x c h a n g e equilibriums: 59:379-395. Davidtz, J. C. and Sumner, N. E. 1965. Blocked charge on clay m i n e r a l s in sub - t r o p i c a l soils. J. Soil Sci. 16:270-274. Deb, B. C. 1950. The e s t i m a t i o n of free iron oxides in soils and clays and their r e m o v a l . J . Soil S c i . 1 :212- 220. DeHaan, F. A. M. 1965. D e t e r m i n a t i o n of the specific s u r ­ face area of soils on the basis of an i o n e x c l u s i o n m e a surements. Soil Sci. 99:379-386. de Villiers, J. M. and Jackson, M. L. 1967. Cation ex ­ c h a n g e c a p a c i t y v a r i a t i o n w i t h pH in soil c l a y s . Soil Sci. Soc. Amer. Proc. 31:473-476. de V i l l i e rs, J. M. and Jackson, M. L. 1967. Aluminum c h l o r i t e o r i g i n of pH d e p e n d e n t cation exch a n g e c a p a c i t y variations. Soil Sci. Soc. Amer. Proc. 31:614-619. Dunken, H. 1940. A simple d e r i v a t i o n of the L a n g m u i r a d s o r p t i o n isotherm: Zeitschr. Phys. Chem. Abt. A. Vol. 187:105-106. El-Sawify, S., Coleman, N. J . , Bredell, G. a n d Acra, M. 1967. Negative adsorption by vermiculite salt e x ­ c l u s i o n f r o m interlayer volumes. Soil Sci. Soc. Amer. Proc. 31:464-466. Follett, E. A. C. 1965. The r e t e n t i o n of a m o r p h o u s colc oidal ferric hydr o x i d e by kaolinites. J. Soil Sci. 16:334-341. Foster, M. D. 1960. Layer charge relations in d i o c t a h e d ral and trioc t a h e d r a l micas. Amer. M i n e r a l 45:385-398. 91 Franzmeier, D. P. 1962. A chronosequence of podzols in N orthern Michigan. Ph.D. Thesis. Mich i g a n State University, E a s t Lansing, Michigan. Frink, C. R. 1964. The effects of wash solvents on cation exchange capacity measurements. Soil Sci. Soc. Amer. Proc. 28:506-511. Frink, C. R. 1'965. Characterization of aluminum i n t e r ­ layers in soil clays. Soil Sci. Soc. Amer. Proc. 29:379-382. Fripiat, J. J. 1964. Surface properties of aluminosilicates, p. 327-358. In W. F. Bradley (ed.) Clays and Clay M i n e r a l s , Proc. 12th Conf. Pergammon Press, L t d ., N e w Y o r k . Gillam, W. S. 1940. A study on the chemical nature of humic acid. Soil Sci. 49:433-453. Goates, J. R. and Anderson, of quartz. Soil Sci. Grim. K. 1956. Acidic properties 81:277-282. R. E. 1968. Clay M i n e r a l o g y . Book C o ., N e w Y o r k . 2nd Ed. McGraw- H i l l Guggenheim, E. A. 1945. Statistical Thermodynamics of mixtures with zero energies of mixing. Royal Soc. London Proc., Ser. A., Vol. 183:203-213. Helling, C. S., Chesters, G. and Corey, R. B. 1964. Con­ tributions of organic matter and clay to soil cation exchange capacity as affected by the pH of the saturating solution. Soil Sci. Soc. 28:517-520. Helmholtz, H. von. 1879. Studien uber elektische Grenzschichten: Ann. Phys. Chemistry, Vol. 7:337-383. Hemwall, J. B. and Low, P. F. 1956. The hydrostatic r e ­ pulsive force in clay swelling. Soil Sci. 82:135145. Hfigfeldt, Erik. 1955. Ion exchange equilibria; Pt. 3. Some empirical e q u a t i o n s : Acta Cemic Scandinavica, Vol. 9, pp. 151-165 (In English). Hsu, P. H. and Rich, C. I. 1960. synthetic cation exchanger. Proc. 24:21-25. A l u m i n u m fixation in a Soil Sci. Soc. Amer. Hsu, P. H. and Bates, J. P. 1964. Fixa t i o n of hydrox y alum i n u m polymers by vermiculite. Soil Sci. Soc. Amer. Proc. 28:763-768. 92 Huang, P. M. and Jackson, M. L . 1966. Fluoride inter­ a ct i o n w i t h clays in r e l a t i o n to third b u f f e r range. N a t u r e Lond. 211:779-780. Jackson, M. L. 1958. Soil C h e m i c a l A n a l y s i s . Hall Inc., E n g l e w o o d Cliffs, N e w Jersey. Prentice ________ . 1960. S t r u c t u r a l r o l e of h y d r o n i u m in layer s i l i ­ cates du r i n g soil genesis. Int. Congr. Soil Sci. 7th (Madison, Wisconsin) II 445-455. ________ . 1963a. A l u m i n u m b o n d i n g in soils: A unifying p r i n c i p l e in soil science. Soil Sci. Soc. Proc. Amer. 27:1-10. ________ . 1963b. I n t e r l a y e r i n g of e x p a n s i b l e layer s i l i ­ cates in soils by chem i c a l weathering, pp. 29-46. In W. F. Bradley (ed.) Clays and Clay M i n e r a l s , Proc. 11th Conf. M a c m i l l a n Co. ________ . 1965. Clay t r a n s f o r m a t i o n in soil genesis d u r i n g the Q u a r t e r n a r y . Soil Sci. 99:15-22. ________ . 1968. W e a t h e r i n g of p r i m a r y and s e c o n d a r y m i n ­ erals in soils. Trans, of 9th I n t e r n a t l . Congr. of Soil Sci. Adelaide, Australia. Vol. 4:281-291. Kargin, V. A. and R a b i n o w i s t s c h , A. J. 1935. chem i c a l p r o p e r t i e s of c o l l o i d a l silica. F a r a d a y Soc. 31:284-297. Kelly, W. P. 1948. C a t i o n E x c h a n g e in S o i l s . R e i n h o l d C o r p . , p . 144. Some e l e c t r o ­ Trans. N e w York: K r i s h n a m o o r t h y , C. and Overstreet, R. 1949. An experi­ m e n t a l e v a l u a t i o n of ion e x c h a n g e relationships . Soil Sci. 69:41-53. Langmuir, Irving. 1918. A d s o r p t i o n of gases on glass, mica, and platinum. Amer. Chem. Soc. Jour. Vol. 40:1361-1403. Lewis, T. E. and Broadbent, F. E. 1961. Soil orga n i c m e t a l c o m p l e x e s : 4. Nature and p r o p e r t i e s of e x ­ c hange sites. Soil Sci. 91:393-399. Lietzke, D. A. 1968. E v a l u a t i o n of spodic h o r i z o n c r i ­ teria, and c l a s s i f i c a t i o n of some M i c h i g a n soils. M.S. Thesis. M i c h i g a n State University, E. Lansing. Low, P. F. and Deming, J. M. 1953. M o v e m e n t and e q u i l i b ­ r i u m of w a t e r in h e t e r o g e n e o u s systems w i t h special r e f e r e n c e to soils. Soil Sci. 75:187-202. 93 Low, R. F. 1968. Mineralogical data requirements in soil physical investigations. In Mineralogy in Soil Science and E n g i n e e r i n g . Soil Sex. Soc. Amer. Pub. No. 3. MacEwan, D. M. C. 1954. Short range electrical forces b etween charged colloid particles. Nature. 174: 39-40. Magistad, O. C. 1925. The aluminum content of the soil solution and its relation to soil reaction and plant growth. Soil Sci. 20:181-226. Malcolm, R. L. and Kennedy, V. C. 1969. Rate of cation exchange on clay minerals as determined by specific ion electrode techniques. Soil Sci. Amer. Proc. 33:247-253. Marshall, E. E. 1964. The Physical Chemistry and M i n e r ­ alogy of S o i l s . Vol. 1. Soil M a t e r i a l s . John W iley & Sons, Inc., N e w Y o r k . Martin, A. E. 1960. Chemical studies of podzolic illuvial horizons: V. Flocculation of humus ferric and ferric iron and nickel. J. Soil Sci. 11:382-400. Martin, A. E. and Reeve, R. 1960. Chemical studies of podzolic illuvial horizons: IV. The flocculation of human by aluminum. J. Soil Sci. 11:369-381. McLean, E. V., Hourigan, W. R . , Shoemaker, H. E. and Bhumbla, D. R. 1965. A l u m i n u m in Soils: 5. Form of aluminum as a cause of soil acidity and a c o m p l i ­ c ation in its measurement. Soil Sci. 97:119-126. McLean, E. V., Reicosky, D. C. and Lakshman, C. 1965. A l u m i n u m in Soils: 7. Interrelationships of or ganic matter, lining and extractable aluminum w i t h p e r m a n ­ ent charge (KC1) and pH dependent cation exchange capacity of surface soils. Soil Sci. Soc. Amer. Proc. 29:374-378. Mehlich, A. 1954. Effect of type of soil colloid on c a ­ tion adsorption capacity and on exchangeable hyd rogen and calcium as measured by different methods. Soil Sci. 60:289-304. Mehra, O. P. and Jackson, M. L. 1960. Iron oxide from soils and clays by a dithionite citrate buffered with sodium bicarbonate. Clays and Minerals. Proc. 7th Natl. Conf. Clays and Minerals, 1958:317-327. removal system Clay Clay 94 Mokrushin, S. G. 1945. A p p l i c a t i o n o f the M a x w e l l - B o l t z m a n n D i s t r i b u t i o n law to C o l l o i d Chemistry: Zhur. Obshch. K h u m (U.S.S.R.) Vol. 15, pp. 259-268 (English summary). M ortensen, J. L. 1963. C o m p l e x i n g of me t a l s of soil o rg a n i c matter. Soil Sci. Soc. Amer. Proc. ,27: 179-186. M ortensen, J. L. and Himes, F. L. 1964. Soil o r g a n i c matter, pp. 206-241. In F . E. B e a r (ed.) C h e m i s t r y of the S o i l . 2nd Ed. Rein h o l d P u b l i s h i n g Corp., N e w York, p. 515. Norrish, K. 1954. T h e Swelling of M o n t m o r i l l o n i t e . cussions F a r a d a y Soc^ 18:120-134. Dis­ Norrish, K. and Raussel-Colom, J. A. 196 3. L o w angle X-ray d i f f r a c t i o n studies of the s w e l l i n g o f m o n t m o r i l l o n i t e and vermiculite. Clays and C l a y M i n e r a l s . 10:123149 (Pergamon Press, N e w Y o r k ) . Okazaki, R . , Smith, H. W. a n d Moodie, C. D. 1962. Develop­ m e n t of a c a t i o n exchange c a p a c i t y p r o c e d u r e w i t h few inherent errors. Soil Sci. 93:343-347. Pauling, L. 1945. T h e N a t u r e of the Chemi c a l Bond. 2nd Ed. Co rnell U n i v e r s i t y Press, Ithaca, N e w York. Peech, M . , Cowan, R. L. and Baker, J. H. 1962. A cr i t i c a l s tudy of the B a C l 2- T r i e t h a n o l a m i n e and the a m m o n i u m a c etate met h o d s for d e t e r m i n i n g the e x c h a n g e a b l e h y d r o g e n c o n t e n t of soils. Soil Sci. Soc. Amer. Proc. 26:37-40. Poinkey, H. B. a n d Corey, R. B. 1967. R e a c t i o n s bet w e e n a c i d i c a l u m i n u m and soil pH, c l a y and organic matter. Soil Sci. Soc. Amer. Proc. 31:749-752. Pratt, P. F. and Bair, F. L. 1962. C a t i o n exchange p r o ­ p e rties of some acid soils of California. Hilgardia. 33:689-706. Quirk, J. P. 1960. N e g a t i v e and p o s i t i v e a d s o r p t i o n of chloride b y kaolinite. Nature. 188:253-254. Ragland, J. L. and Coleman, N. T. 1960. T h e h y d r o l y s i s of a l umi n u m salts in clay and soil s y s t e m s . Soil S c i . Soc. Amer. Proc. 24:457-460. Raman, K. V. and Jackson, M. L. 1966. Layer charge r e l a ­ tions in clay minerals of micaleous soils and s e d i ­ ments. Clays and Clay Minerals. 14:53-68. Reiman, K. V. and Mortland, M. M. 1969. Amorphous m a t e r ­ ials in a Spodosol: Some Mineralogical and Chemical Properties. Geoderma 3:37-43. Ranney, R. W. 1969. A n organic carbon-organic ma t t e r c o n ­ v ersion equation for Pennsylvania surface soils. Soil Sci. Soc. Amer. Proc. 33:809-811. Rhoades, J. D. 1967. Cation exchange reactions of woil and specimen v e r m i c u l i t i e s . Soil Sci. Soc. Amer. Proc. 31:361-365. Rich, C. I. 1960. A l u m i n u m in interlayers of vermiculite. Soil Sci. Soc. Amer. Proc. 24:26-32. Rich, C. I. 1962. Removal of excess salts in cation e x ­ change determination. Soil Sci. 93:87-94. Rich, C. I. and Black, W. C. 1964. Potassium exchange as affected by cation size, pH and mineral structure. Soil Sci. 97:304-390. Rich, C. I. and Thomas, G. W. 1960. soils. Advan. Agron. 12:1-39. The clay fraction in Rich, C. I. 1968. Applications of Soil M i n e r a l o g y in Soil Chemistry and Fer tility I n v e s t i g a t i o n s . In M i n e r ­ alogy in Soil Science and Engineering. Soil Sci. Soc. Amer. Proc. Sp. P u b l . No. 3. Rieke, P. E. 1963. Relationship between alumi n u m and soil acidity in several M i c h i g a n soils and r e l a t e d m i n e r ­ alogy studies. Ph.D. Thesis, Michigan State U n i v e r s ­ ity* East Lansing, Michigan. Robertson, R. H. S., Brindley, G. W. and Mackenzie, R. C. 1954. Mineralogy of kaolin clays from Pugu, T a n g a n ­ yika. Amer. Mineral. 39:118-138. Robinson, B. P. 1961. Ion exchange minerals and disposal of radio-active w a s t e s — A Survey of literature. Geological Survey Water Supply, Paper 1616: U.S. Govt. Printing Office, Washington, D.C. 19 62. Ross, C. J., Lawton, K. and Ellis, B. G. 1964. Lime r e ­ q uirement related to physical and chemical properties of nine M i c h i g a n soils. Soil Sci. Soc. Amer. Proc. 28:209-212. 96 Ross, C. J. 1965. C h a r a c t e r i z a t i o n of a m o n t m o r i l l o n i t e in a N o r t h e r n M i c h i g a n Podzol. Ph.D. Thesis, M i c h i ­ gan State University, E a s t Lansing, Michigan. Schnitzer, M. and J. G. Des jardin. 1962. M o l e c u l a r and e quiva l e n t weights of the org a n i c m a t t e r of a P o d z o l . Soil Sci. Soc. Amer. Proc. 26:362-365. Schnitzer, M. and Gupta. 1964. Chemical c h a r a c t e r i s t i c s of the o r g a n i c m a t t e r e x t r a c t e d f r o m the O and B 2 horizons of a G r a y W o o d e d soil. Soil Sci. Soc. Amer. Proc. 28:374-377. Schnitzer, M. and Gupta, U. C. 1965. a c i d i t y in soil orga n i c matter. Amer. Proc. 29:274-277 D e t e r m i n a t i o n of Soil Sci. Soc. Schnitzer, M. and Skinner, S.I.M. 1963. Organo-metallic interactions in s o i l s : T h e r e a c t i o n b e t w e e n a number of m e t a l ions arid the organic m a t t e r of a pod z o l B, horizon. Soil Sci. 96:86-93. Schnitzer, M. and Wright, J. R. 1960. N i t r i c acid o x i d a ­ tion of the organic m a t t e r of a Podzol. Soil Sci. Soc. Amer. Proc. 24:273-277. Schofield, R. K. 1949. E f f e c t of pH on elec t r i c ch a r g e s c ar r i e d by clay particles * J. Soil Sci. 1:1-8. Schofield, R. K. and Sampson, H. R. 1953. The d e f l o c c u l a ­ tion of kaolinite suspensions and the a c c o m p a n y i n g ch a n g e - o v e r f r o m p o s i t i v e to negative c h l o r i d e a d ­ sorption. Clay Minerals Bull. 2:45-51. Schofield, R. K. and Taylor, A. W. 1954. The h y d r o l y s i s of a l u m i n u m salt solutions. J. Chem. Soc. 18 : 44454448. Schwertmann, V.and Jackson, M. L. 1963. H y d r o g e n a l u m i n u m clays: A third bu f f e r range appea r i n g in p o t e n t i o m e t r i c titration. Science 139:1052-1054. Schwertmann, V.and Jackson, M. L. 1964. Influence of h y d r o x y - a l u m i n u m ions on pH t i t r a t i o n curves of h y d r o n i u m a l u m i n u m clays. Soil Sci. Soc. Amer. Proc. 28:179-182. Shainberg, I. and Kemper, W. D. 1966. H y d r a t i o n status of adsorbed cations. Soil Sci. Soc. Amer. Proc. 30: 707-713. 97 Shoemaker, H. E . , McLean, E. V. and Pratt, P. F. 1961. B u f f e r methods for d e t e r m i n i n g lime r e q u i r e m e n t s of soils w i t h a p p r e c i a b l e amounts of e x t r a c t a b l e a l u m i n ­ um. Soil Sci. Soc. Amer. Proc. 25:274-277. Sienko, M. J. and Plane, C h e m i s t r y . W. A. R. A. 1963. P h y s i c a l Inorganic B e n j a m i n Inc. New Y o r k . Stern, O. 1924. Sur Theorie der E l e k t r o l y t i s c h e n D o p p e l schicht: Zeitschr. Elektrochem. Vol. 30, pp. 508516. Tamura, T. 1958. acid soils. I d e n t i f i c a t i o n of clay m i n e r a l s J. Soil Sci. 9:141-147. from Thomas, G. W. 1961. Forms of a l u m i n u m c a t i o n exchangers. Trans. 7th I n t e r n a t l . Cong. Soil Sci. 11:364-369. Thomas, G. W. and Swoboda. 1963. C a t i o n exch a n g e in k a o l i n i t e i o n oxide systems, pp. 321-326 in W. F. B r a d l e y (ed.) C l a y and Clay M i n e r a l s Proc. 11th C o n f . M a c m i l l a n Co., N e w York. Thompson, H. S. Royal Agr. 1850. O n the a b s o r b e n t p o w e r of soil. Soc. Jour. Vol. 11:68-74. Va g eler, P. and W a l t e rsdorf, J. 1930. B e i t r a g e zur F r a g e des B a s e n a u s t a u s c h e s und der Aziditaten: Zeitschr. P f l a n z e n e r n a h r u n g u. Dungung, A. 15, pp. 329-342. v a n Olphen, H. 1954. Interl a y e r forces in b e n o t i n i t e clays and clay minerals. 2:418-438 (Natl. Acad. Sci. Natl. Res. Cou n c i l Publ. 327). Volk, V. V. and Jackson, M. L. 1964. Inorg a n i c p H d e p e n d ­ ent cation excha nge charge of soils, pp. 281-285. In W. F. B r a d l e y (ed.) Clays and C l a y M i n e r a l s . Proc. 12th Conf. P e r g a m o n P r e s s , L t d ., N e w Y o r k . Way, J. T. 1850, 1852. On the p o w e r of soils to ab s o r b manure. Royal A g r i . Soc. (England) Jour. Vol. II: 313-371; Vol. 13:123-143. Wiegner, G e o r g and Hans, Jenny. 1927. Ueber B a s e n a u s -*f tausch an Permutiten: K o l l o i d Zeitschr. Vol. 42: 268-272. 98 Wikla n d er, L. 1964. C a t i o n and anion e x c h a n g e phenom e n a . In C h e m i s t r y of the S o i l / ed i t e d by F. Bear, 2nd Ed. R e i n h o l d P u b l i s h i n g Corp., N e w York. Wurman, E., Whiteside, E. P. and Mortland, M. M. 1959. P r o p e r t i e s and genesis of finer text u r e d subsoil b ands in some sandy M i c h i g a n soils. Soil Sci. Soc. Amer. Proc. 23:135-143. APPENDIX Group A: a cc e 0 S-l U h b 41 e a e e -h in b b 4-1 U V b «• 4-1 Q.M u u 4 Z o u 4 (J U u X u u V X z + 4 U + N . Z 0< + X i u S H + CM H u 4 A 5 H u « X 3 X 4 nt H < X J +"* X 3 ■e 1 meg per 100 g of soil 6.1 6.2 31.0 28.0 2.5 1.3 6.0 1.9 19.4 6.7 46.4 22.9 28.5 14.5 19.2 10.6 28.8 23.4 33.8 21.8 23.5 6.0 15.0 4.4 . . 29.9 19.7 4.9 6.9 6.2 7.1 44.0 14.9 17.0 9.0 2.1 1.3 1.7 2.7 1.8 1.3 0.8 1.4 3.0 17.8 7.5 15.3 30.2 20.4 23.4 12.3 12.4 11.8 10.5 7.5 10.4 20.7 7.7 13.5 8.6 15.6 5.4 9.0 16.6 14.4 14.5 9.7 8.5 9.5 10.0 7.0 4.4 2.2 1.0 1.2 . . . . .6 13.3 3.8 9.0 1.5 12.0 1.1 0.3 0 0 0 11.2 3.3 5.0 0 0 8.3 1.4 0.5 0 5.4 6.2 11.5 7.9 2.4 0.9 0.3 2.2 .9 11.1 26.5 9.5 6.6 5.0 6.2 3.7 13.5 7.0 12.2 7.9 6.5 6.0 1.2 .4 . . 7.9 4.3 6.5 1.4 8.0 0 3.0 0 5.9 8.2 1.3 .2 2.2 10.3 4.0 3.7 8.0 6.9 4.0 .6 . 4.8 2.1 4.0 4.6 6.2 1.3 .3 4.5 11.3 2.9 2.5 6.5 9.0 3.0 1.4 . 4.5 4.5 10.0 1.7 1.0 5.2 8.0 1.0 .1 1.4 9.3 2.3 2.0 7.6 6.0 3.0 0.6 . 3.7 2.3 4.0 0 0 5.5 4.7 4.0 0.8 .1 2.3 1.0 0 0 7.2 7.4 2.2 1.2 1.8 1.3 3.9 4.2 5.3 4.8 2.5 2.0 .5 . .4 . 3.2 2.5 2.1 2.3 2.0 0 3.6 ND 5.4 1 u Per cent base saturation a. e c Exchangeable Bases EA(SMP) X b Em e-H > 0 • + p* H u 4 0 V •H 0 4 Exchang * 4 O Ap and A^ horizons. 39 Pevaiso clay loan 0-6 37 Blount clav loan 0-6 17 Ontonagon silty clay 0-5 14 Onavay loan 0-6 6 Volinia loan 0-11 0-6 1 Miani loan 19 Iron River silt loan 0-5 8 Kalanazoo loan 0-8 1/2 4 Plainfield loany sand 0-8 33 Munising loany sand 0-8 38 Hillsdale sandy laon 0-6 24 Spinks loany fine sand 0-8 11 Saugatuck sand 0-7 Group B: c 0 u b SultiEC i w H M 0 u e M 0 clay z • H • a j. *» 2 >* i ! 3 O * it vennicu *u • Horizoii thickness (jLn inches) TABLE 16.— Data on chemical analyses of the soil studied. 3.9 2.1 4.0 0.3 0.5 0 4.0 0 0 0 0 0 3.6 2.1 0.9 0 0 0 2.2 7.9 77.3 1.1 1.6 91.4 3.3 4.5 77.0 1.4 0.7 85.2 0 0 4.3 1.4 0.5 82.7 .5 1.6 3.2 69.4 .7 2.8 2.0 50.0 2.3 3.8 62.2 .3 .5 0 0 0 3.7 5.6 88.4 90.6 64.8 .3 .7 2.1 0.6 1.5 1.7 60.7 52.1 1.2 0.9 .4 2.4 5.1 50.5 0 .9 0 Bh, Bhir and B^c horizons. 32 Onavay loan 20 Iron River silt loan 12 Saugatuck sand 28 Munising loany sand 35 Kalkaska sand 13 Saugatuck sand 9-12 5.5 13.7 0.7 0 0 14.5 3.5 3.6 8.8 7.3 3.0 0.6 .1 3.7 6-12 5.9 11-16 5.1 7.5 .7 0 3.5 2.3 0 0 0 14.2 22.4 2.7 1.8 2.8 2.2 7.2 10.6 7.2 9.8 2.5 1.0 0.6 0.2 .1 .1 3.2 4.0 ND 1.3 8.6 12.0 1.5 2.1 1.5 1.4 .0 .8 2.5 6.5 4.9 44.4 9.4 13.0 9-17 5.3 15-19 4.7 19-25 5.6 4.0 1.4 0 1.3 .7 0 2.8 .3 0 0 0 0 19.6 15.4 4.8 1.3 1.2 .6 1.7 1.5 .6 4.4 5.S 2.4 7.8 6.3 2.5 0.5 0.1 0.5 0.1 1.0 0.3 .2 .0 .1 0.8 7.1 11.0 2.1 0.6 5.7 12.0 2.1 1.4 1.2 2.0 0 1.4 1.7 .7 .4 2.0 3.6 3.6 4.9 1.0 1.0 1.2 1.1 53.2 0 0 TABLE 16. — Data on chemical analyses of the soil studied (continued). m0 -K X a Croup D: Aj> A£ and Cj horizons 27 Munising loamy 4.5 3.8 1.2 sand 1-9 4-13 4.3 0.6 0.0 34 Kalkaska sand 7-11 6.5 12.0 0.4 2 Miami loam 21 Iron River silt .2 5.4 12-20 4.9 loam 25 Spinks loamy .2 fine sand 14-25 5.6 4.5 29 Munising loamy 4.7 .2 29-40 5.2 sand 31 Munising loamy .0 62-82 5.7 10.1 sand 10 Kalamazoo .1 1.8 loam 34-41 1/2 5.7 36 Kalkaska sand 37-63 5.4 .6 .1 u u X ♦ N e u + Cl z + X § w 3 5 • Ci>1 — meq per 100 g of soil 4.3 .3 23.6 2.5 1.0 4.3 .3 18 .1 1.4 0.4 1 < 2 0 0 2.5 1.4 .4 90.6 1.8 92.8 a 0 c 41-4 C 44 5 X ea U k 3 k 4> ea & 10 14.1 10.8 33.0 22.6 21.8 15.6 16.5 11.2 23.9 19.4 26.0 19.4 1.8 1.2 1.1 1.6 1.0 3.3 5.4 4.9 8.0 6.9 25.7 21.4 16.7 16.3 12.9 14.7 10.0 8.8 7.4 5.5 11.5 8.3 7.1 4.9 5.4 20.5 12.3 15.9 9.6 10.3 18.7 12.2 10.5 9.2 7.4 .4 3.6 12.1 4.7 4.2 8.3 6.6 3.0 .4 .2 3.6 3.1 7.0 1.9 1.3 .6 11.4 8.9 4.5 3.6 7.4 5.6 3.0 1.3 .1 4.4 1.2 0 1.0 .5 0 2.5 .9 .9 1.7 3.2 2.0 0.3 .1 2.4 .8 0.3 0 0 0.1 20.0 .7 5.6 9.4 2.6 8.1 2.5 0.5 4.4 2.2 0.3 3.1 5.3 0.6 7.3 4.4 .7 6.0 2.0 0.5 4.0 .3 .1 .8 .1 .0 .1 2.4 0.6 4.9 2.1 10.0 .1 0.2 1.1 1.0 0 0 7.1 2.0 2.1 4.6 5.1 2.0 .7 .1 2.8 2.3 3.6 4.6 1.6 1.3 2.6 3.2 1.5 .5 .2 2.2 1.1 0.4 0 3.1 1.4 1.4 2.7 1.7 0.5 .3 .1 0.9 .9 1.0 1.0 .3 3.1 5.1 3.8 3.1 4.6 5.2 3.5 1.2 .1 4.8 .4 0.2 0 0 0 .4 0 92.4 1.0 0 53.9 0 3.3 2.9 1.0 .2 .9 .3 2.2 1.0 1.7 1.9 1.0 1.0 .4 .1 .1 .0 1.5 1.1 .2 0 .8 0.4 0 0 0 0 0 0 .2 .7 .8 0 88.6 59.1 0 .2 0 ND - Not Determined. ‘Explanation follows on page 101. 9.0 5.5 2.4 6.5 1.7 6.0 1.7 3.5 1.0 e.o .4 14.9 10 .5 .2 8.4 .2 7.9 .2 4.7 .1 0 0 +x e a a 3.9 3.3 19.0 13.5 0 0 H U X +■ n .H +fN «H u • ^9 5 1 ■— <5 O.H 3.8 ND 1.6 0.8 .6 3.1 5.7 79.8 1.7 1.8 85.9 1.7 0.5 0 0 0 3.1 7.0 2.1 1.1 .8 1.1 7.5 79.8 1.3 1.7 86.3 0 1.3 3.0 0 0 .8 6.1 60.6 2.7 5.0 1.9 1.4 .5 2.0 .6 1.2 4.8 53.5 .2 4.1 73.2 .8 1.4 73.7 .7 1.2 .5 0.0 .5 0 .5 .9 3.0 0.0 .5 0 .5 .6 2.5 53.4 85.7 81.3 1.5 0.9 .7 .8 1.8 54.5 1.1 .4 66.4 1.9 47.1 0 0 .5 0 0 0 0 .7 .3 0 100 Group C: B. and B„ horizons. t g 8-12 6.S 27.3 1.8 IS Brookston loam .4 16 Brookston loam 18-36 6.9 31.0 IB Ontonagon silty 5-15 4.8 54.4 1.0 clay .3 18-24 6.5 22.4 33 Onaway loam .3 9 Kalaatazoo loam 12-21 4.8 21.7 .3 3 Miami loam 16 1/2-21 6.1 20.0 .3 7 Volinia loam 21--28 1/2 4.9 14.0 22 Iron River .1 20-30 4.8 10.1 silt loam 30 Munisinq loamy 48-62 4.9 13.1 0.0 sand 26 Spinks loamy 6.4 48 3.1 .1 fine sand u k k <1 u a • ®'1 a> u 2 u X X z H + n H O Exchan acidit EA (SMP CD c C -H 0“ H -H • ka 0• *c Exchangeable Bases SumEC ■H 0 • a & H •H B— •H • *> V «-* e3 vu — CaEC I z M ■ — a— * iH 9 41 0 JJeH *» c S* £ 3 ec e u kk k • IS a per c« varmic aoil ~i---0• •H C * u 101 Table 16 Explanation * Samples 1 to 26 are from Dr. A. E. E r i c k s o n ' s u n ­ p u b l i s h e d data, C r o p and Soil Sciences Department, M i c h i g a n S t a t e University, E a s t Lansing, Michigan, w h e r e they are n u m b e r e d as follows: 8*48, 9*50, 16*305, 10*52, 17*328, 1*18, 11-203, 18-329, 2*19, 3*21, 12*205, 19*337, 4*64, 13*207? 20*338, 6*68, 14*270, 21*339, 7*70, 15-303, 22-340, 23*356, 24*423, 25*425 and 26*427. The p H s , and clay and c a r b o n p e r c e n t a g e s are from Dr. E r i c k s o n ' s d a t a w h e r e available. *Samples 27 to 36 are from the samples studied by Mr. D. A. L i e t z k e in his M.S. Thesis h o r i z o n criteria, soils." " E v a l uation of spodic and c l a s s i f i c a t i o n of some M i c h i g a n M i c h i g a n State University, E a s t Lansing, M i c h i g a n and the pHs, a n d clay and c a r b o n p e r c e n t a g e s are f r o m S.C.S. Beltsville Laboratory r e s u l t s . ♦Samples 37 * B l o u n t Ap, 38 * H i l l s d a l e No. 1 Ap and 3 9 * P e w a mo N o 1, A p are f r o m the samples s t u d i e d b y Mr. J. B. C ol l i n s in his M.S. Thesis, "Seasonal v a r i a b i l i t y of p H and lime r e q u i r e m e n t s in several S o u t h e r n M i c h i g a n soils w h e n m e a s u r e d in d i f f e r e n t ways," M i c h i g a n State U n i v e r s i t y , E a s t Lansing, Michigan. The pH va l u e s u s e d for these s a m ples are from A u g u s t readings o n air dry samples in water. TABLE 17.--Estimation uf clay mineral* in the clay fraction of tha horltont of similar aoil type* aa used in chi* study. Similar to soil sanple number Soil typa Horixon Clay par cent Xaolinite 111ite Chlo­- V e m i ­ Smec­ C-v rite culite* tite Alintargrada Quarts Amor­ phous mater­ ials* • 1 Miami loan *P 9.0 XX XX XX XXX(15.3) Mona 8 Kalaaaioo loan Bp* 7.9 0000 0 00 000 (11.1)1 00 24 Spinks loany f:.ne sand Bp 4.7 XX xx xx XX (2.3) X X 15.7 17 Ontonagon silty clay Bp 44.0 XX xxx XX X (3.0) BP 17.0 XX XX X XX (7.5) Nona XX X X 14.4 Volinia loan Bp Munising loany sand Ap 11.5 XX XX XX XX (2.2) XX X 8,8 23 (.2 XX xxx XX XX (4.5) X X 14 Onavay sandy loan BP 3 Miani loan Bm 9 Kalanatoo loan B2l” Ontonagon silty clay B71t* « 19 15 Brookston loan 1( Brookston loan 22 Iron Rivar silt loan 30 Munising loany sand 35 Kalkaska sand 28 Munising loany sand 2 Miani loan 21 Iron Rivar silt loan 27 Munising loany sand 10 Kalanesoo loan X > 0-10 parctnt XXXX ■ 50 - 70 par cent Note; 000 13.5 Blg B22g "it* B22t 20.0 XX 21.7 0000 XXXX X XX (8.0) 00 00 000 (4.9) 00 None 0 X Nona 00 Hone 54.4 00 0000 0 000 (3.3) 00 27.3 XX XX X XX (14.1) XX 31.0 XX XX XXX X (10.8) 10.0 000 00 000 0000(3.8) Nona 13.1 XX XX xxx X (11.4) X X X Nona 000 X 1.3 X 4.0 000 oo 00 00 (0.0) 00 Nona 0000 V 12.0 000 00 00 000(5.4) Hone 00 oo V 5.4 000 0 000 0000(0.0) Nona Nona 000 *2 3.8 0000 00 0 0 1.8 XX X XXXXI54.0I B22ir B22ir C1 ■ 102 18 Iron River silt loan X None XX'0.0) XXX 0000 Nona None XX 0; XX • 10-30 par cant • 00 and 000; XXX * 30-50 per cant ■ 14.0 X 0000; Quantitative detemination* vara baaed on X-ray, apacific auriace and total X analyaea and by solving simultaneous aquations, Rosa, 1005; Transaaiar (1903); Human atal. (1959); darnings (1959). * Quantitative estimations vara nade from X-ray tracinga (Rieka, 19(3). * values expressed in paranthases represent vemiculite in soil clay determined by Alexiadas and Jackson procedure (19(5). •* Data from Raaan and Mortland (19(9). 19.3