A Survey of the Aluminum Status of Some Soils in Louisiana.

Louisiana State University LSU Digital Commons LSU Historical Dissertations and Theses Graduate School 1977 A Survey of the Aluminum Status of Some Soils in Louisiana. Gilbert W. Landry Jr Louisiana State University and Agricultural & Mechanical College Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_disstheses Recommended Citation Landry, Gilbert W. Jr, "A Survey of the Aluminum Status of Some Soils in Louisiana." (1977). LSU Historical Dissertations and Theses. 3161. https://digitalcommons.lsu.edu/gradschool_disstheses/3161 This Dissertation is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Historical Dissertations and Theses by an authorized administrator of LSU Digital Commons. For more information, please contact gradetd@lsu.edu.

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I ) 78-7552 LANDRY, Gilbert W., Jr., 1949- A SURVEY OF THE ALUMINUM STATUS OF SOME SOILS IN LOUISIANA. The Louisiana State University and Agricultural and Mechanical College, Ph.D., 1977 Agronomy University Microfilms international, Ann A rbor, M ichigan 48106

A SURVEY OF THE ALUMINUM STATUS OF SOME SOILS IN LOUISIANA A D i s s e r t a t i o n S u bm itted to th e G raduate F a c u lty o f th e L o u isia n a S t a te U n iv e r s ity and A g r ic u ltu r a l and M echanical C o lleg e in p a r t i a l f u l f i l l m e n t o f th e req u ire m e n ts f o r th e d e g re e o f D octor o f P h ilo so p h y in The D epartm ent o f Agronomy by G ilb e r t W. L andry, J r. B.S., L o u isia n a S ta te U n iv e r s ity, 1971 M.S., L o u isia n a S ta te U n iv e rs ity, 1974 December, 1977

ACKNOWLEDGMENTS The a u th o r w ish es to e x p re s s h is s in c e r e a p p r e c ia tio n and g r a t i t u d e to th o se who gave him encouragem ent and a s s i s ta n c e th ro u g h o u t th e c o u rse o f t h i s p r o j e c t. S p e c ia l th an k s to : D r. B. J. M ille r, A s s o c ia te P ro fe s s o r o f Agronomy, L o u isia n a S ta te U n iv e rs ity f o r h i s c o u n sel and g u id an ce th ro u g h o u t th e g ra d u a te program, and f o r h i s a s s i s ta n c e in th e p r e p a r a tio n o f t h is m a n u s c rip t. D r. W. H. W i l l i s, Head o f th e Agronomy D epartm ent, who was in s tr u m e n ta l in m aking t h is stu d y p o s s ib le th ro u g h a g ra d u a te a s s i s t a n t s h i p. D r. P. E. S c h i ll in g, P r o f e s s o r of E x p e rim en ta l S t a t i s t i c s, f o r h i s a s s i s ta n c e i n th e s t a t i s t i c a l a n a ly s is o f th e d a ta. Members o f th e Agronomy D epartm ent who a s s i s t e d in th e r e s e a rc h, e s p e c i a l l y Susan L enhard, th e s tu d e n t a s s i s t a n t s, and th e p e rs o n n e l in th e S o il T e s tin g L a b o ra to ry. The members o f h i s g ra d u a te com m ittee f o r t h e i r c o u n se l. The S o il S c i e n t i s t s o f th e S o il C o n se rv a tio n S e rv ic e who p ro v id e d a s s i s ta n c e i n s e le c ti n g s o i l sam ples f o r t h i s i n v e s t ig a t io n. F i n a l l y, and m ost o f a l l, my w o n d erfu l p a r e n ts, Mr. and Mr. G ilb e r t L andry, S r. f o r t h e i r encouragem ent and su p p o rt w hich made the achievem ent o f t h i s g o a l p o s s ib l e. ii

TABLE OF CONTENTS Page ACKNOWLEDGEMENTS... LIST OF TABLES... i v LIST OF FIGURES...v i i ABSTRACT... ix INTRODUCTION... 1 REVIEW OF LITERATURE... 4 The R ole o f Aluminum in S o il D evelopm ent and M ineralogy... 4 M in e ra l S t a b i l i t y R e la tio n s h ip s o f Aluminum Compounds in S o i l s... 3 The R ole o f Aluminum in S o il A c i d i t y... 14 The E f f e c ts o f Aluminum on P la n t G r o w th... 22 Aluminum t o x i c i t y... 22 N u tr ie n t u p ta k e and u t i l i z a t i o n... 29 MATERIALS AND METHODS... 34 S o il Sam pling and P r e p a r a t i o n... 34 P a r t i c l e S iz e A n a ly se s.... 38 C hem ical A n a l y s e s... 39 S o il s u s p e n sio n p H... 39 S o i l o rg a n ic c a r b o n... 40 E xchangeable b a se s... 40 E xchangeable a c i d i t y... 40 E x tr a c ta b le a c i d i t y... 40 C a tio n exchange c a p a c ity... 41 E x t r a c ta b le alum inum.... 41 S e q u e n tia lly e x tr a c te d aluminum... 41 S o lu tio n e q u i l i b r i a... 42 S o il t e s t a n a ly s e s... 42 S t a t i s t i c a l A n a ly s e s... 42 RESULTS AND DISCUSSION... 45 G eneral P h y s ic a l and Chem ical C h a r a c t e r i s ti c s o f th e S o i l s... 48 P h y s ic a l c h a r a c t e r i s t i c s... 48 Chem ical c h a r a c t e r i s t i c s... 51 E xchangeable and E x tr a c ta b le Aluminum and A c id ity R e la tio n s h ip s... 61 iii

TABLE OF CONTENTS (continued) Page E x t r a c ta b le alum inum... 77 E x tr a c ta b le a c i d i t y...... 83 CEC and ph -dependent c h a r g e s... 85 S e q u e n tia lly e x t r a c t a b l e alum inum... 93 E q u ilib r a te d S o il- U a te r S u sp e n sio n s... 99 M in e ra l s t a b i l i t y.... 104 SUMMARY AND CONCLUSIONS....123 LITERATURE C IT E D... 135 APPENDICES...146 A ppendix 1... 146 Appendix 2... 154 Appendix 3... 160 Appendix 4... 166 Appendix 5... 172 VITA....174 iv

s LIST OF TABLES Table Page 1 The s o i l num ber, s e r i e s, i d e n t i f i c a t i o n num ber, c l a s s i f i c a t i o n, and sa m p lin g l o c a tio n o f th e s o i l sam ples used i n th e i n v e s t i g a t i o n... 35 2 The mean and ra n g e v a lu e s f o r c la y and o rg a n ic carb o n c o n te n t, ph^,, phk, ph^a, t o t a l ex c h an g e a b le b a s e s, GEC, and Base s a t u r a t i o n f o r 20 s o i l s i n L o u is ia n a grouped a c c o rd in g to c la y m in e ra l g ro u p... 49 3 The means o f ex ch an g eab le alum inum, alum inum s a t u r a t i o n, e x t r a c t a b l e alum inum, and e x t r a c t a b l e a c i d i t y i n 20 s o i l s i n L o u is ia n a grouped a c c o rd in g to c la y m i n e r a l o g y... 6 4 4 Sim ple c o r r e l a t i o n c o e f f i c i e n t s ( r) betw een e x c h an g e a b le aluminum and ph^, c la y c o n te n t, and o r g a n ic carbon c o n te n t f o r 20 s o i l s i n L o u is ia n a grouped a c c o r d in g to c la y m in e ra lo g y.... 65 5 Sim ple c o r r e l a t i o n c o e f f i c i e n t s (r) betw een e x c h a n g e a b le aluminum and phw, c la y c o n te n t, and o r g a n ic carbon c o n te n t f o r 15 s o i l s i n L o u is ia n a grouped a c c o r d in g to c la y m i n e r a l o g y...66 6 The means o f phw, c la y c o n te n t, o rg a n ic carb o n c o n te n t, ex changeable alum inum,*and alum inum s a t u r a t i o n f o r 20 s o i l s i n L o u isia n a grouped a c c o rd in g to c la y m i n e r a l o g y... 67 7 The means o f phw, c la y c o n t e n t, o rg a n ic c arb o n c o n te n t, ex c h an g e a b le alum inum, and alum inum s a t u r a t i o n f o r 15 s o i l s i n L o u isia n a grouped a c c o rd in g to c la y m i n e r a l o g y... 67 8 Sim ple c o r r e l a t i o n c o e f f i c i e n t s (r) betw een ex c h an g e a b le aluminum and phw, ph^a, and ph^ f o r 20 s o i l s in L o u is ia n a grouped a c c o rd in g to c la y m i n e r a l o g y... 70 9 Sim ple c o r r e l a t i o n c o e f f i c i e n t s (r) b etw een no n ex ch an g eab le alum inum and phw, c la y c o n te n t, and o r g a n ic carbon c o n te n t f o r 20 s o i l s in L o u is ia n a grouped a c c o r d in g to c la y m in e ra lo g y.... 82 v

LIST OF TABLES (continued) Table Page 10 The mean c a ti o n exchange c a p a c ity f o r 18 s o i l s i n L o u is ia n a grouped a c c o rd in g to c la y m i n e r a l o g y.... 87 11 E x t r a c ta b l e alum inum and a c i d i t y r e l a t i o n s h i p s i n n in e s o i l s In L o u is ia n a... 95 12 The ra n g e and m eans o f ph and c a ti o n c o n c e n tr a tio n s in e q u i l i b r a t e d s o il - w a te r s u s p e n s io n s f o r 2 0 s o i l s in L o u is ia n a grouped a c c o rd in g to c la y m i n e r a l o g y... 1 0 1 13 S im ple c o r r e l a t i o n c o e f f i c i e n t s ( r ) betw een Ca, Mg, K, and Na m easured in e q u i l i b r a t e d s o il - w a te r s u s p e n s io n s and i n a n e u t r a l, norm al NH4 OAC le a c h a te f o r 20 s o i l s i n L o u i s i a n a... 102 14 S ta n d a rd f r e e e n e r g ie s o f fo rm a tio n v a lu e s u sed i n c a l c u l a t i n g p h a s e diagram s and m in e r a l s t a b i l i t y r e l a t i o n s h i p s... 106 15 The maximum c o n c e n tr a tio n o f s o lu b le com ponents in th e e q u i l i b r a t e d s o i l - w a t e r s u s p e n s io n s... 108 16 Some p h y s ic a l and ch em ical p r o p e r t ie s o f 20 s o i l s i n L o u i s i a n a... 147 17 E xch an g eab le and e x t r a c t a b l e alum inum and a c i d i t y r e l a t i o n s h i p s o f 20 s o i l s i n L o u is ia n a... 155 18 ph and c a ti o n c o n c e n tr a tio n in e q u i l i b r a t e d s o i l - w a te r s u s p e n s io n s o f 20 s o i l s i n L o u i s i a n a... 161 19 S o il t e s t d a ta o f 20 s o i l s in L o u i s i a n a... 167 20 S im ple c o r r e l a t i o n c o e f f i c i e n t s ( r ) betw een v a rio u s m easurem ents o f 20 s o i l s i n L o u is ia n a grouped a c c o rd in g to c la y m i n e r a l o g y... 173 vi

LIST OF FIGURES Figure Page 1 Sampling lo c a tio n f o r th e s o i l s Included in th e s t u d y... 37 2 The p r o f i l e d i s t r i b u t i o n o f c la y ( < 0.002 mm) in th e B osw ell, Commerce, Crowley, and L oring s o i l s........ 50 3 The profile distribution of phy values measured in the Commerce and M yatt s o i l s... 53 4 The p r o f i l e d i s t r i b u t i o n o f ph^, v a lu e s m easured in th e Moreland and Mowata soils.... 54 5 The profile distribution of ph values measured in w ater (ph ), N KCl (phk), and 0.01 M CaCl2 (phca) s o lu tio n s i n th e Dundee s o i l... 57 6 The p r o f i l e d i s t r i b u t i o n of ph v a lu e s m easured in w a te r ( p l^ ), N KCl (phk), and 0.01 M CaCl2 (phca) solutions in the Beauregard s o i l... 57 7 The p r o f i l e d i s t r i b u t i o n o f exchangeable H, A l, and a c i d i t y i n th e Dundee s o i l... 63 8 The p r o f i l e d i s t r i b u t i o n o f exchangeable H, Al, and a c i d i t y in th e B eauregard s o i l.... 63 9 The r e l a ti o n s h ip betw een exchangeable aluminum and phw f o r a l l s o i l s which c o n ta in e d m easurable q u a n titie s o f exchangeable aluminum... 6 8 10 The s t a t i s t i c a l p r e d ic tio n e q u a tio n and a c tu a l d a ta p o in ts f o r exchangeable aluminum as a fu n c tio n o f ph^, f o r s o i l s in th e m ontm orill o n i t i c c la y m in e ra l g ro u p... 73 11 The p r o f i l e d i s t r i b u t i o n o f exchangeable aluminum, exchangeable a c i d i t y, e x tr a c ta b le aluminum, and e x tr a c ta b le a c i d i t y i n th e O liv ie r s o i l... 78 12 The p r o f i l e d i s t r i b u t i o n o f e x tr a c ta b le aluminum in th e tfy a tt, O liv ie r, and Sharkey s o i l s... 79 vii

LIST OF FIGURES (continued) Figure Page 13 The p r o f i l e d i s t r i b u t i o n of c la y c o n te n t and CEC ( e f f e c t i v e, NH^OAc, and BaCl -TEA) in th e M yatt s o i l... 8 8 14 The p r o f i l e d i s t r i b u t i o n o f e x c h a n g e a b le and e x t r a c t a b l e a c i d i t y i n th e S harkey and A l l ig a to r s o i l s... 89 15 The s e q u e n t i a l l y e x tr a c te d alum inum from s e le c te d h o r iz o n s o f th e M yatt s o i l... 94 16 S t a b i l i t y o f g i b b s i t e e x p re s s e d in term s o f ph and a c t i v i t i e s o f Al'*'^, A1 ( 0 H)2» and Al(OH)^ show ing r e s u l t s from th e B e au reg ard s o i l.... 110 17 S t a b i l i t y f i e l d s o f q u a r tz and am orphous s i l i c a in term s o f ph and p S i showing th e r e s u l t s from th e Dundee s o i l... 113 18 S t a b i l i t y f i e l d s o f am orphous s i l i c a, q u a r tz, k a o l i n i t e, and g i b b s i t e i n term s o f ph and a c t i v i t i e s o f H^SiO^, Al+ ^, A 1(0H )^, and A1(0H)^ i o n s... 115 19 S t a b i l i t y r e l a t i o n s h i p s o f g i b b s i t e, k a o l i n i t e, q u a rtz, and amorphous s i l i c a in term s o f ph and p S i show ing d a ta p o in ts f o r th e M yatt s o i l... 117 20 S t a b i l i t y f i e l d s f o r g i b b s i t e, k a o l i n i t e, K -m ica, K - f e ld s p a r s, q u a r tz, and amorphous s i l i c a in term s o f ph-pk and p S i show ing d a ta p o in ts f o r mean v a lu e s from s o i l s i n t h r e e s o i l m in e ra lo g y g ro u p s... 119 viii

ABSTRACT An i n v e s t i g a t i o n was c o n d u c te d to d e te rm in e th e Al s t a t u s o f s e le c te d s o i l s in L o u is ia n a. The 20 s o i l s s tu d ie d ran g e d in c h a r a c t e r i s t i c s from r e l a t i v e l y u n w e a th e re d, a l k a l i n e E n t i s o l s, I n c e p t i s o l s, and M o llis o ls to w e a th e re d, a c id I n c e p t i s o l s, A l f i s o l s, and U l t i s o l s. I n d iv id u a l h o riz o n s (130) from th e s o i l s w ere a n a ly z e d by s e v e r a l m ethods i n o r d e r to e v a lu a te t h e i r p r o f i l e d i s t r i b u t i o n and tre n d s w ith r e s p e c t to s o i l a c i d i t y and A l. The a n a ly s e s f o r Al in c lu d e d ; (1) e x c h a n g e a b le Al (ExAl) e x tr a c t e d by N KCl s o l u t i o n, (2) Al e x tr a c te d (E xta l) by N NH^OAc s o lu t i o n (ph 4. 8 ), (3) Al e x tr a c t e d by s e q u e n tia l e x t r a c t i o n w ith a 0.2 N NH^Cl s o l u t i o n (ph 4. 0 ), and (4) Al in e q u i l i b r a te d s o il - w a te r s u s p e n s io n s. S o il a c i d i t y was d e te rm in e d a t th e ph o f th e s o i l (K C l), 3 t ph 7.0 (NH^OAc), and a t ph 8.0 (BaCl2 - TEA). S o il ph, c la y c o n te n t, and o r g a n ic m a tte r c o n te n t w ere r e l a t e d to th e q u a n t i t i e s o f e x c h an g e a b le and e x t r a c t a b l e Al and a c i d i t y. M easu rab le q u a n t i t i e s o f ExAl w ere n o t e x tr a c t e d from h o riz o n s h a v in g ph v a lu e s g r e a t e r th a n 6.0. A ll h o r iz o n s h a v in g ph v a lu e s l e s s th a n 5.5 d id h av e m e a su ra b le q u a n t i t i e s o f ExAl. The p e r c e n t s a t u r a t i o n w ith ExAl in c r e a s e d m arkedly w ith d e c r e a s in g ph in h o riz o n s w ith ph v a lu e s below 5.5, and m ost h o r iz o n s w ith ph v a lu e s o f l e s s th a n 5.1 w ere m ore th a n 40% A l - s a t u r a t e d. The d i f f e r e n t Al and a c i d i t y m easurem ents had s im i la r d i s t r i b u t i o n s w ith in a s o i l. The q u a n t i t i e s o f Al m easured in th e in d iv id u a l h o r iz o n s t y p i c a l l y in c r e a s e d in th e o r d e r : Al i n e q u i l i b r i a s o l u t i o n s, e x c h a n g e a b le A l, e x t r a c t a b l e A l, s e q u e n t i a l ly e x tr a c t e d A l. The

q u a n tity o f a c i d i t y m easured was g e n e ra lly l e a s t when d eterm in ed a t th e ph o f th e s o i l, in te rm e d ia te a t ph 7.0, and g r e a t e s t a t ph 8.0. W ith in a s o i l, th e q u a n ti ti e s o f Al and a c i d i t y were t y p ic a ll y sm a ll in th e s u rf a c e h o riz o n and in c re a s e d w ith d e p th to a maximum in th e B h o riz o n below w hich th e q u a n t i t i e s v a rie d o n ly s l i g h t l y or d e c re a se d w ith d e p th. Seven o f th e s o i l s ( U l t i s o l s, A lf is o ls ) w ere 50% o r more s a tu r a te d w ith ExAl, fo u r ( A l f i s o l s, U l t i s o l s ) had 10-30% ExAl s a tu r a t i o n, and fo u r ( A l f i s o ls, I n c e p tis o ls ) had 1-10% ExAl s a tu r a ti o n w ith in th e r o o tin g d ep th of m ost c ro p s. F ive o f th e s o i l s ( E n tis o ls, M o lli- s o ls, I n c e p t is o l s ) lack ed m easu rab le q u a n ti ti e s o f ExAl In a l l h o r iz o n s. The s o i l s w ith p red o m in an tly e x p a n d in g - la ttic e c la y m in e ra ls had s m a lle r q u a n ti ti e s o f ex changeable and e x tr a c t a b le Al and a c i d i t y, and were l e s s s a tu r a te d w ith exchangeable Al th a n s o i l s dom inated by o th e r c la y m in e r a ls. They a ls o had g r e a t e r p e rc e n t b a se s a tu r a ti o n s, CEC's, and ph v a lu e s th an k a o l i n i t i c o r mixed m in e ralo g y group s o i l s. The s o i l s w ith no one c la y m in e ra l p red o m in atin g (mixed c la y m in eralo g y ) had g r e a t e r q u a n ti ti e s o f exchangeable and e x tr a c t a b le Al and a c i d i t y th a n s o i l s in th e m o n tm o rillo n itic o r k a o l i n i t i c c la y m in e ral g ro u p s. The s o i l s in th e mixed c la y m in eralo g y group had p e rc e n t b a se s a tu r a t i o n s, CEC's, and ph v a lu e s in te rm e d ia te betw een s o i l s in th e m ontm o r i l l o n i t i c and k a o l i n i t i c c la y m in eral g ro u p s. The s o i l s i n th e k a o l i n i t i c c la y m in e ra l group had q u a n ti ti e s o f exchangeable and e x t r a c t a b l e Al and a c i d i t y in te rm e d ia te betw een th o se in th e mixed and m o n tm o rillo n itic c la y m in e ra l g ro u p s. They a ls o had a g r e a te r p e rc e n t x

s a t u r a t i o n w ith e x c h a n g e a b le Al and low er p e r c e n t b a s e s a t u r a t i o n s, C E C 's, and ph v a lu e s th a n s o i l s i n th e o th e r c la y m in e r a l g ro u p s. T here w as a s i g n i f i c a n t p o s i t i v e c o r r e l a t i o n b e tw e e n s o i l ph and s o l u t i o n e q u i l i b r i a ph and b etw een e x c h a n g e a b le and s o l u t i o n e q u i l i b r i a c o n c e n t r a t io n s o f Ca, Mg, K, and Na. The q u a n t i t i e s o f Al m easured i n e q u i l i b r a t e d s o i l - w a t e r s u s p e n s io n s w ere n o t s i g n i f i c a n t l y r e l a t e d to q u a n t i t i e s o f Al o r a c i d i t y m ea su red i n th e s o i l s. A n a ly se s o f th e s o l u t i o n e q u i l i b r i a d a ta in d ic a te d t h a t a f t e r m ore th a n a y e a r e q u i l i b r a t i o n tim e ( 1 ) a l l th e s o i l h o r iz o n s w ere u n d e r s a t u r a t e d w ith r e s p e c t to q u a r tz ; ( 2 ) a l l b u t f o u r h o r iz o n s w ere s a t u r a t e d w ith r e s p e c t to k a o l i n i t e ; and (3) f o u r o f th e s o i l h o r iz o n s w e re s a t u r a t e d w ith r e s p e c t to g i b b s i t e.

INTRODUCTION The s o i l s in L o u is ia n a a re q u ite v a r ie d and ra n g e in c h a r a c te r i s t i c s from r e l a t i v e l y u n w eath ered, a l k a l i n e E n t i s o l s, I n c e p t is o l s and M o llis o ls d eveloped i n r e c e n t a llu v iu m to h ig h ly w e a th e re d, a c id A l f is o l s and U l t i s o l s d eveloped i n o ld C o a s ta l P la in d e p o s its. An e s tim a te d o n e - th ir d o r more o f th e s t a t e i s com prised o f s o i l s t h a t t y p i c a l l y have ph v a lu e s below 5.5 w ith in th e r o o tin g d ep th o f m ost agronom ic c r o p s. T hese in c lu d e la r g e a c re a g e s i n th e F la tw o o d s, C o a sta l P la in, and L o e s s ia l H i l l s and M is s is s ip p i T e rra c e s o i l a r e a s. Less e x te n s iv e a c re a g e s o f s o i l s w ith s im i la r l y low ph l e v e ls a ls o occu r i n th e C o a s ta l P r a i r i e s, and Red, O u a c h ita, and M is s is s ip p i R iv e r a l l u v i a l s o i l a r e a s. Numerous s tu d i e s have in d ic a te d t h a t w ith many c ro p s, p ro d u c tio n i n c r e a s e s r e s u l t from a p p lic a tio n s o f a g r i c u l t u r a l lim e to s o i l s in th e s e a re a s h a v in g low ph v a lu e s. E x te n s iv e r e s e a rc h i n many a re a s h as shown Al to be a m ajor f a c t o r i n th e a c i d i t y o f m in e ra l s o i l s such a s th e s e. I t h a s a ls o been d em o n stra ted t h a t Al t o x i c i t y can be a g r o w th -lim itin g f a c t o r f o r some p l a n t s grown on s o i l s w ith ph v a lu e s i n t h i s r a n g e. S tu d ie s have a ls o shown t h a t the r o le s o f Al a re m a n ifo ld and may depend on a number o f f a c t o r s such as ph, th e k in d and am ounts o f o rg a n ic m a tte r, p h y l l o s i l i c a t e and n o n p h y llo s ilic a te m in e r a ls, and, i n th e c a se o f p l a n t s, th e s p e c ie s o r c u l t i v a r grown. I t h a s a ls o been d e m o n strated t h a t none o f th e s e f a c t o r s can be u sed a s c o m p le te ly r e l i a b l e in d ic a to r s o f Al o r a c i d i t y le v e ls i n s o i l s. T hus, a lth o u g h g e n e ra l g u id e lin e s may be a v a ila b le f o r e v a lu a tin g p ro b a b le le v e ls o f Al in s o i l s, s p e c i f i c r e s e a r c h 1

2 i s n e c e s s a ry to d e te rm in e th e Al s t a t u s o f th e s o i l s w i t h i n a g iv e n r e g io n. T here i s a minimum o f a v a i l a b l e in fo r m a tio n c o n c e rn in g th e n a tu r e, q u a n tity and form s o f Al compounds i n s o i l s i n L o u is ia n a ; and t h is in fo r m a tio n i s l a r g e ly c o m p rise d o f t o t a l Al v a lu e s p u b lis h e d in p a r i s h s o i l su rv e y r e p o r t s. To th e a u t h o r 's know ledge t h e r e e x i s t s no p u b lis h e d in fo rm a tio n c o n c e rn in g Al t o x i c i t y l e v e l s and l e v e l s o f e x c h a n g e a b le, e x t r a c t a b l e, an d s o lu t i o n p h a se Al and t h e i r r e l a t i o n s h ip s to o t h e r s o i l p r o p e r t i e s i n L o u is ia n a. R esearch d e s ig n e d to p ro v id e such in fo r m a tio n i s n eeded in o r d e r to e v a lu a te th e Al s t a t u s o f m ajor s o i l s used e x t e n s i v e l y f o r a g r i c u l t u r a l p r o d u c tio n. I t i s a ls o needed t o i n d i c a t e w h e th e r p o t e n t i a l problem s e x i s t i n m a rg in a l s o i l s w h ich, i n th e f u t u r e, may be b ro u g h t i n t o p r o d u c tio n a s demands f o r fo o d and f i b e r i n c r e a s e. T h is i n v e s t i g a t i o n was d e s ig n e d to p ro v id e a su rv e y o f th e Al s t a t u s o f t h e s o i l s i n L o u is ia n a. I t c o n s t i t u t e s a p r e lim in a r y i n v e s t i g a t i o n o f Al s o i l a c i d i t y s o i l m in e ralo g y r e l a t i o n s h i p s, and i s a l s o In te n d e d to p r o v id e in fo r m a tio n n e c e s s a ry to th e p la n n in g and im p le m e n ta tio n o f s p e c i f i c and more com prehensive r e s e a r c h in th e s e and r e l a t e d a r e a s. H o p e f u lly, i t w i l l a l s o f u r n i s h o t h e r i n v e s t i g a to r s w ith in fo r m a tio n c o n c e rn in g p o s s ib l e s o i l - p l a n t and s o i l - p l a n t n u t r i e n t i n t e r a c t i o n s. The s p e c i f i c r e s e a r c h o b j e c t i v e s w e re : (1) to d e te rm in e w hich, i f any, m a jo r m in e ra l s o i l a r e a s i n L o u is ia n a c o n ta in s o i l s in w hich th e p o t e n t i a l f o r Al t o x i c i t y e x i s t s, (2) t o d e te rm in e th e q u a n t i t i e s and dom inant n o n m in e ral form s o f Al t h a t m ig h t be e x p e c te d i n th e d i f f e r e n t s o i l a r e a s s t u d i e d, (3) to e v a lu a te th e r e l a t i o n s h i p s

betw een s o i l p r o p e r t ie s such as ph, k in d s and am ounts o f c la y m in e ra ls, o rg a n ic m a tte r c o n te n t, and ex ch an g eab le c a tio n s and th e q u a n t i t i e s o f Al m easured by d i f f e r e n t m ethods, and (4) to e v a lu a te r e l a t i o n s h i p s betw een m in e ralo g y o f th e s o i l s and th e l e v e l s o f Al i n e q u i l i b r a t e d s o il - w a te r s u s p e n s io n s. S e le c te d s o i l s from each o f th e s i x m ajor m in e ra l s o i l a re a s in th e s t a t e w ere in c lu d e d in th e s tu d y. W ith in each a r e a, th e s o i l s sam pled in c lu d e d th o s e t h a t ( 1 ) occupy e x te n s iv e a r e a s, ( 2 ) a r e, or a p p ear to have a p o t e n t i a l f o r b e in g used e x te n s iv e ly i n a g r i c u l t u r a l p r o d u c tio n, and (3) app ro x im ate th e e x p e c te d ra n g e in s o i l a c i d i t y and n o n m in eral forms o f Al compounds. The s o i l s s e le c te d r e p r e s e n t members o f th e A l f i s o l, E n t i s o l, I n c e p t i s o l, M o llis o l, and U l t i s o l s o i l o r d e r s. Some s o i l s w ere i n t e n t i o n a l l y in c lu d e d i n w hich v e ry low le v e ls o f some form s o f Al w ere e x p e c te d.

REVIEW OF LITERATURE Aluminum i s c o n s id e re d one of th e m ost im p o rta n t ele m en ts from th e s ta n d p o in ts of s o i l g e n e s is and c l a s s i f i c a t i o n, m in e ralo g y, a c i d i t y, and s o i l - n u t r i e n t and s o i l - p l a n t r e l a t i o n s h i p s. A lthough th e s e to p ic s a re i n t e r r e l a t e d and d i f f i c u l t to d is c u s s in d iv id u a lly, t h i s re v ie w has been d iv id e d i n to fo u r s e c t i o n s. These a re : (1) th e r o l e o f Al in s o i l developm ent and m in e ra lo g y, (2) m in e ra l s t a b i l i t y r e l a t i o n s h i p s o f Al compounds in s o i l s, (3) th e r o l e of Al in s o i l a c i d i t y, and (4) th e e f f e c t s o f Al on p la n t grow th. The Role o f Aluminum i n S o il Developm ent and M ineralogy Aluminum i s th e t h i r d m ost abundant elem en t in th e e a r t h 's c r u s t and in m ost s o i l s. I t i s an i n t e g r a l p a r t o f a lu m in o s ilic a te m in e r a ls, and h a s long b een c a te g o riz e d by g e o lo g is ts and s o i l s c i e n t i s t s as one o f th e l e a s t s o lu b le ele m en ts r e le a s e d from m in e ra ls d u rin g w e a th e rin g and s o i l g e n e s is (B arshad, 1964; and M a r i ll, 1897). However, Huang and K e lle r (1970, 1971, 1972) have in d ic a te d t h a t Al is r e l a t i v e l y m o b ile, and com plexing o rg a n ic a c id s can be r e s p o n s ib le f o r th e d i s s o l u t i o n o f a lu m in o s ilic a te m in e ra ls and th e movement o f Al and S i in a w e a th e rin g s o i l p r o f i l e. The s o l u b i l i t y of Al h a s long been re c o g n iz e d to be ph -dependent and b e c au se o f th e s u s c e p t i b i l i t y o f many o rg a n ic a c id s to o x id a tio n, i t can a ls o be i n d i r e c t l y Eh- d ep en d en t (Huang and K e l l e r, 1972). These r e s u l t s p ro v id e geoc h em ical m echanism s f o r th e d i s s o l u ti o n, t r a n s p o r t, and d e p o s itio n o f Al compounds in th e zone o f w e a th e rin g. Huang and K e lle r concluded 4

5 t h a t n o t only may th e r a t e s o f w e a th e rin g, r e s id u a l a c cu m u la tio n, and p r e f e r e n t i a l d i s s o l u t i o n o f c la y m in e ra ls be a c c e le r a te d by o rg a n ic a c id s b u t th e s o lu tio n t r a n s p o r t of s p a r in g ly s o lu b le e le m e n ts, such as A l, i s a ls o f a c i l i t a t e d. They a ls o n o te d t h a t th e s e f a c to r s and th e abundance o f A l-com plexing a n io n s, such a s OH, PO4, and SIO4, t y p i c a l l y r e s u l t in s h o rt d is ta n c e s o f Al t r a n s p o r t. The d i s s o l u t i o n o f A l, Fe and Mn o x id e s and h y d ro x id e s in th e s o i l h e lp s d e f in e th e ty p e, d i r e c t i o n and e x te n t o f ped o g en ic p ro c e s s e s. For exam ple, S podosols t y p i c a l l y form under f o r e s t v e g e ta tio n and a re c h a r a c te r iz e d by B h o riz o n s e n ric h e d in o rg a n ic m a tte r, c la y, and Al and Fe compounds t h a t have been tr a n s p o r te d downward from o v e r- ly in g h o riz o n s (B arshad, 1964; B lanchar and S c riv n e r, 1972; and R u s s e ll, 1973). T h is m o b iliz a tio n o f Al and Fe compounds i s p a r t i a l l y due to t h e i r com plexing w ith o rg a n ic compounds (Huang and K e lle r, 1971; and R u s s e ll, 1973). M alcolm and McCracken (1968) r e p o r te d t h a t canopy d r ip was a n im p o rta n t so u rc e o f o rg a n ic m a tte r f o r Al and Fe m o b iliz a tio n a s w e ll a s c e r t a i n o th e r p ed o g en ic p r o c e s s e s o c c u rrin g i n s o i l s. The k in d of o rg a n ic compounds may a ls o in f lu e n c e s o i l developm ent. F o r exam ple, Dekirape and M a rte ll (1976) found s i g n i f i c a n tly more Al and Fe compounds in th e B h o r iz o n o f 10 Spodosols un d er c o n if e r s th a n under d e cid u o u s t r e e s. M ille r (1965, 1972) d e s c r ib e d a p o s s ib l e mechanism f o r b o th m o b ility and c o n s e rv a tio n o f Al in c e r t a i n s o i l s. He p o s tu la te d t h a t " e x tr a c ta b le " a c i d i t y m easured i n some n e u t r a l and a l k a l i n e s o i l h o riz o n s may be due to th e a m p h o te ric n a tu r e o f Al compounds which have formed and se rv e to " c o n se rv e " Al i n th e sy stem. In h is m odel, Al from compounds t h a t a r e d is s o lv e d in a c id s o i l h o r iz o n s may be

6 r e p r e c i p i t a t e d i n low er h o riz o n s t h a t a re l e s s a c id. He su g g e ste d t h a t th e r e p r e c i p i t a t e d m a t e r i a ls were l a r g e l y hydroxy-a l i n t e r la y e r s in e x i s t i n g th r e e - l a y e r p h y l l o s i l i c a t e s a n d /o r k a o l i n i t e or compounds s i m i l a r in c o m p o sitio n. In 1950, MacEwan i d e n t i f i e d a 14A m in e ra l in s o i l c la y s w hich he d e s c rib e d a s c o n s is tin g of m ic a -la y e r s i n t e r s t r a t i f i e d w ith Al or Fe o x id e s. S in c e th e n, many i n v e s t i g a t o r s i n th e U nited S t a te s have i d e n t i f i e d p a r t i a l l y i n te r la y e r e d p h y l l o s i l i c a t e s in s o i l s (Coleman and Thomas, 1964; R ich, 1968; and Rich and O benshain, 1955). There i s g e n e ra l a g re e m e n t th a t in many ca se s th e i n t e r l a y e r m a t e r i a l i s of a p p ro x im ately th e co m p o sitio n su g g e ste d by K lages and W hite (1957) A1 ( 0H)XH2 0^ 3 ^X^. B lack (1968) d e s c rib e d th e s e hydroxy-a l i n t e r la y e r s as in c o m p le te ly n e u t r a l i z e d, h y d ra te d Al io n s t h a t a re s ta b i li z e d a g a i n s t f u r th e r n e u t r a l i z a t i o n and a g a in s t r e l e a s e through io n exchange by p o ly m e riz a tio n, p h y s ic a l l o c a t io n, and ch em ical com bination w i t h a d ja c e n t l a y e r s. The s o i l c o n d itio n s g e n e r a lly c o n sid e red m ost fa v o ra b le f o r th e fo rm a tio n o f hydroxy-a l i n t e r l a y e r s in s o il s a re a c t i v e w e a th e rin g, a c id ph (a b o u t 5.0 ), low o rg a n ic m a tte r c o n te n t, and fre q u e n t w e ttin g and d r y in g o f th e s o i l (R ich, 1968). M ille r (1965, 1972) i n d ic a te s t h a t e x te n s iv e hydroxy-a l i n te r la y e r i n g a l s o occurs i n n e u t r a l o r a l k a l i n e h o riz o n s in some s o i l s. Huang and K e l l e r 's (1972) s tu d ie s o f io n ic form s o f Al compounds a s a fu n c tio n o f ph i n d ic a te t h a t hydroxy-a l form s a re dom inant a t ph v a lu e s above a b o u t 4.5. The e f f e c t s o f th e hydroxy-a l i n t e r l a y e r s on s o i l p r o p e r t i e s a re n o t f u ll y known. N e v e rth e le s s, th e r e i s g e n e ra l agreem ent t h a t hydroxy-a l i n t e r l a y e r s : (1) a r e r e s p o n s ib le f o r pedogenic

7 c h l o r i t i z a t i o n a n d /o r v e r m i c u l i t i z a t i o n o f e x p a n d in g - la ttic e c la y m in e ra ls (R ich, 1968), (2) re d u c e CEC by b lo c k in g exchange s i t e s (C lark, 1964; and F rin k, 1 9 6 5 ), (3) re d u c e NH^ and K io n f ix a t io n by l im it in g c o l l a p s i b i l i t y o f th e s i l i c a t e la y e rs (R ich, 1960; Shen and R ic h, 1962; and W hite, 196 2 ), (4) re d u c e th e e x p a n sio n c a p a b i li t y of s m e c tite s (K idder and R eed, 1972; and Tamura, 1957), and (5) s e rv e as a so u rc e o f s o i l a c i d i t y (Coleman and Thomas, 1964, 1967; and Kam prath, 1972), Ja ck so n (1963) r e p o r te d t h a t Al r e l e a s e d d u rin g w e a th e rin g ten d s to accu m u late i n th e i n t e r l a y e r p o s i t i o n of t h r e e - l a y e r p h y l l o s i l i c a t e s in s te a d o f form ing g i b b s i t e. In a s tu d y o f hydroxy- Al i n t e r l a y e r i n g in m o n tm o rilio n ite and v e r m ic u lite, Brydon and Turner (1972) found t h a t a s Al(0H)x a p p ro ach ed th e s o l u b i l i t y p ro d u ct o f g ib b s ite th e Al(CH)x moved from th e i n t e r l a y e r p o s itio n to form g i b b s i t e. U nlike m o n tm o rillo n ite, v e r m ic u lite r e t a in e d an a p p re c ia b le amount o f i n t e r l a y e r m a te r ia l and did n o t r e g a in i t s o r ig i n a l CEC. T h e re fo re, an a p p re c ia b le amount of i n t e r l a y e r A1(0H)X was s t a b l e i n v e rm ic u lite r e l a t i v e to g i b b s i t e, w hereas i n montm o r i ll o n it e i t was n o t. B a r n h is e l and R ich (1963) a ls o r e p o r te d t h a t g i b b s i t e form ed from h y d ro x y -A l i n t e r l a y e r s o f m o n tm o rillo n ite. They e s ta b lis h e d t h a t g ib b s ite form ed in th e p re s e n c e o f m o n tm o rillo n ite a t a ph o f l e s s th an 4.3. T hus, i t a p p e a rs t h a t in some a c id s o i l s g i b b s i t e may have formed w ith an in te r m e d ia te ste p in v o lv in g hydroxy- Al i n t e r l a y e r s in c la y m in e r a ls. M ajor r o l e s of Al in s o i l developm ent and m in e ralo g y may be summarized i n th e fo llo w in g m anner. I t h a s r e c e n tly been e s ta b lis h e d

8 t h a t Al i s s o lu b le i n o rg a n ic a c id s and may be q u ite m o b ile i n s o i l s. I n a d d it io n to b e in g p H -d ep en d en t, Al s o l u b i l i t y is r e p o r te d to be i n d i r e c t l y E h -d e p en d e n t. The am photeric n a tu r e o f Al h a s b e e n shown to e f f e c t i t s m o b ility and c o n s e rv a tio n th ro u g h hydroxy-a l i n t e r l a y e r f o rm a tio n. The c o n d itio n s g e n e r a lly c o n s id e re d most f a v o r a b le fo r h ydroxy-a l i n t e r l a y e r fo rm a tio n in s o il c la y m in e ra ls a r e a c t i v e w e a th e rin g, a c id ph, low o r g a n ic m a tte r c o n te n t, and f re q u e n t w e ttin g and d ry in g o f th e s o i l. I t i s g e n e ra lly a g re e d th a t hy d ro x y -A l i n t e r la y e r s ( 1 ) a re r e s p o n s ib le f o r pedogenic c h l o r i t i z a t i o n a n d /o r v e r m ic u liz a tio n o f e x p a n d in g - la ttic e c la y m in e r a ls, (2) re d u c e CEC, (3) re d u c e NH^ and K io n f i x a t i o n, (4) re d u c e sm e c tite e x p a n s i b i l i t y, and (5) s e rv e as a s o u rc e o f s o i l a c i d i t y. M in e ra l S t a b i l i t y R e la tio n s h ip s o f Aluminum Compounds i n S o ils In r e c e n t y e a r s th e r e h av e been s e v e r a l r e p o r ts c o n c e rn in g th e s t a b i l i t y of a lu m in o s i li c a te m in e r a ls in aqueous s o lu tio n s. Most of th e w ork h as d e a l t w ith system s su b je c te d to r a t h e r s t r i c t c o n tr o l over th e number and k in d s of m in e r a ls p r e s e n t. G a rre ls and C h r is t (1965) have summ arized and a p p lie d much o f th e th eo ry and m ethodology o f therm odynam ics to s o i l s and g e o c h em istry. S o ils a re open system s a n d, as such, a r e s u b je c t to changes d i c t a t e d by t h e i r en v iro n m en t. A lthough s o i l s a re m ix tu re s o f s e v e r a l m in e r a ls, th e s o lu t i o n phase may be dom inated by one o r o n ly a few m in e r a ls. S o ils i n g e n e ra l, and in p a r t i c u l a r, h o riz o n s w ith in a s o i l a re in flu e n c e d by rem oval and a d d it io n of c o n s t i t u e n t s. B ecause r a t e s

9 o f rem oval a re slow w ith re s p e c t to th e tim e r e q u ir e d fo r e q u i l i b r a t i o n i t i s p o s s ib le to sample a p a r t i c u l a r s o i l h o riz o n, e q u i l i b r a t e the sample w ith w a te r, and, in essen ce, c lo s e th e system f o r a p e rio d com parable to an e q u i l i b r a t i o n tim e. S ince s o ils g e n e ra lly h av e been in c o n ta c t w ith w ater and th e atm osphere f o r very long p e r io d s, they may be n e a r a s t a t e o f e q u ilib riu m. Thus, i t seems re a s o n a b le to assum e t h a t s o ils w i l l rea c h some c lo s e approxim ation o f e q u ilib riu m o v e r a p e rio d o f s e v e r a l months i n a c lo se d system (B aker, 1967; K i t t r i c k, 1969; and Huang and K e lle r, 1973a, 1973b). I n te r p r e ta tio n s o f m in e ra l s t a b i l i t y may be made from s o lu b i l it y d a ta o b tain ed from t h i s " te m p o ra rily c lo se d " system. Such in fe r e n c e can be a p p lie d to s o i l s a s open system s because r a t e s of gains o r lo s s e s of c o n s titu e n ts in s o ils a re slow. Since i t norm ally ta k e s h u n d red s of y e a rs to e f f e c t a p p re c ia b le changes in s o i l s, the i n t e r p r e t a ti o n s may be a p p lic a b le f o r long p e rio d s. A lso, sin ce g e n e ra l m in e ra l s t a b i l i t y sequences have b een e s ta b lis h e d, th e s e d a ta may be used f o r p r e d ic tiv e p u rp o ses. Many in v e s t ig a t o r s have en co u n te re d d i f f i c u l t i e s in ap p ly in g th e s e techniques to s o i l s. For exam ple, G a rre ls and C h ris t (1965) r e p o r te d t h a t therm odynam ic d a ta f o r s i l i c a t e s a r e sc a rc e and i n c o n s is t e n t, and M arion e t a l. (1976) re p o rte d t h a t c h a ra c te r iz in g Al and Si io n ic s p e c ie s i s d i f f i c u l t. Huang and K e lle r (1973b) found t h a t c la y m in e ra ls have a wide ran g e o f s t a b i l i t i e s, and sta n d a rd f r e e e n e rg ie s of fo rm a tio n o f th e m in e ra ls vary w ith t h e i r com position. S o ils a re f u r th e r co m p licated b ecau se in d iv id u a l s o i l p a r t i c l e s may have th in la y e rs on t h e i r s u rfa c e s t h a t re p r e s e n t a l t e r a t i o n p ro d u c ts o f th e m in e ral. N e v e rth e le s s, i t i s p o s s ib le to d ev elo p q u a l i t a t i v e

10 diagram s t h a t a re u s e f u l in d e te rm in in g w hich m in e ra ls may be c o n t r o l l i n g th e c h e m is try o f th e s o i l s o lu tio n, and in p r o v id in g m in e ra l sequences t h a t m ight be e x p e c te d i f e q u ilib riu m w ere a tt a in e d (G a rre ls and C h r i s t, 1965). T here h a s been much c o n je c tu r e c o n c e rn in g which Al and S i io n ic s p e c ie s a r e p r e s e n t a t g iv en ph l e v e l s (Huang and K e lle r, 1972, 1973a; K i t t r i c k, 1969; and M arion e t a l., 1976). K i t t r i c k (1969) r a t i o n a l i z e d 3+ t h a t s in c e th e Al io n i s dom inant in th e ph range w here m ost w e a th e r in g o c c u rs, namely 2.0-6.0, i t i s th e o n ly Al s p e c ie s o f concern. However, Huang and K e lle r (1 9 7 2 ), and M arion e t a l. (1976) showed t h a t th e p r o p o rtio n s o f Al s p e c ie s i n aqueous s o lu tio n a re h ig h ly ph- d ep en d en t and sh o u ld be c o n s id e re d. Thus, c a lc u la tio n s from aqueous s o l u b i l i t y d a ta on a lu m in o s i li c a te m in e ra ls should be b a se d on the p r o p o r tio n o f d i f f e r e n t Al s p e c ie s in th e c a lc u la t io n (Huang and K e l le r, 1972). K i t t r i c k (1969) examined some s o i l m in e ra ls in th e A ^ f ^ - S ic ^ - ^ O system. He em phasized t h a t t h e r e a r e too many m in e ra ls i n s o i l s to c o n s id e r them a l l a t once. T h e re fo re, th e id e a i s to c o n s id e r only th o se m in e ra ls t h a t seem m ost im p o rta n t in com peting f o r a lim ite d group o f e le m e n ts. He chose t h i s sy stem f o r two r e a s o n s, (1) i t i s a r e l a t i v e l y sim ple system y e t i t c o n ta in s m in e ra ls t h a t make up la rg e p e rc e n ta g e s o f many s o i l s, and ( 2 ) and m ost im p o rta n t, s t a b i l i t y i n fo rm a tio n i s a v a i l a b l e fo r th e m in e r a ls t h a t need to be c o n s id e re d. He p re s e n te d com posite m in e ra l s t a b i l i t y diagram s o f am orphous S i, m o n tm o rillo n ite, k a o l i n i t e, and g i b b s i t e t h a t a re in good agreem ent w ith n a t u r a l sy ste m s. He a ls o d e m o n stra ted t h a t c r y s t a l l i z a t i o n of hydroxy-a l compounds i s h in d e re d by o rg a n ic a c id s.

11 Huang and K e lle r (1973b) c o n s tr u c te d s t a b i l i t y diagram s o f some p h y l l o s i l i c a t e s (K -m ica, k a o l i n i t e and h a l l o y s i t e ) in th e S i 0 2 -A l 2 C>3- K2 O-H2 O system. They c o n sid e re d th e v a r i a t i o n o f Al and S i io n ic s p e c ie s w ith ph in c o n s tr u c tin g th e d iag ram s. The i n t e r p r e t a t i o n s o f t h e i r s t a b i l i t y diagram s a re c o n s is t e n t w ith d a ta from n a tu r a l w a te rs of p r e s e n t-d a y l o c a l i t i e s where k a o l i n i t e i s b e in g form ed. They found th e s t a b i l i t y of k a o l i n i t e to be s tr o n g ly d ep en d en t on ph below th e i s o e l e c t r i c p o in t of Al in aqueous s o lu tio n (ph 6. 7 ), b u t in d ep en d en t of ph i n more a lk a l in e e n v iro n m en ts. Huang (1973) n o ted s im ila r ph- dependence w ith N a -m o n tm o rillo n ite, K -m ica, k a o l i n i t e, and h a l l o y s i t e. He r e p o r te d t h a t s t a b i l i t y diagram s w hich in c lu d e Al in a d d itio n to Na, K, H, and IfySiO^ a r e more r e p r e s e n t a t i v e of n a t u r a l g e o lo g ic system s th a n th o se w hich om it A l. M arion e t a l. (1976) exam ined th e a p p l i c a b i l i t y o f e q u ilib r iu m r e l a t i o n s h i p s to th e m o b ility o f Al and S i in open sy stem s, s o i l colum ns, u sin g n in e s o i l s r e p r e s e n tin g s i x d i f f e r e n t s o i l o r d e r s. They showed t h a t g i b b s i t e, h a l l o y s i t e, k a o l i n i t e, and m o n tm o rillo n ite a p p eared to c o n tr o l th e s o l u b i l i t y o f Al and S i. In m ost o f th e s o i l s in t h e i r s tu d y, th e s o l u b i l i t y o f Al ap p e are d to be c o n tr o lle d by a s o li d ph ase compound le s s s o lu b le th a n g i b b s i t e. They concluded t h a t compounds which govern Al and S i s o l u b i l i t y v a ry from s o i l to s o i l. G ib b s ite was found to be im p o rta n t in c o n t r o l l i n g Al s o l u b i l i t i e s o n ly in h ig h ly w e a th ere d s o i l s. In more m o d erate w e a th e rin g re g im e s, a lu m in o s ilic a te m in e r a ls w ere more l i k e l y to c o n tr o l Al s o l u b i l i t i e s. There was cons id e r a b le d if f e r e n c e in th e t o t a l s o lu b le Al t h a t e x is te d in e q u ilib r iu m w ith th e d i f f e r e n t Al compounds ( th r e e o r d e r s of m ag n itu d e ); t h i s a lo n e can r e s u l t in a p p re c ia b le d i f f e r e n c e s in th e Al s t a t u s of s o i l s.

12 Reesman and K e lle r (1968) s tu d ie d th e low b u f f e r in g c a p a c ity o f s o lu tio n s e q u il ib r a te d w ith h ig h alu m in a and a lu m in o s ilic a te m in e r a ls. They r e p o r te d t h a t v a r i a t i o n in ph c o n tr o l le d by o th e r m in e ra ls may be a m ajor f a c t o r in c r e a ti n g th e c o n d itio n s n e c e s s a ry f o r fo rm atio n o f m in e ra l p h ases such as b o eh m ite, a llo p h a n e, and e n d e l l i t e. Thomas (1974) a rg u ed t h a t knowledge o f th e Al io n a c t i v i t y in s o i l s o lu tio n s w i l l n o t become p r e c i s e u n t i l th e h y d r o ly tic r e a c ti o n s o f Al and H2 O have been m ore c l e a r l y d e fin e d. He do es ag ree t h a t e x i s t i n g m ethods p ro v id e a re a s o n a b le ap p ro x im atio n o f s o i l s o lu tio n Al a c t i v i t y. C la rk (1966) s ta t e d t h a t th e r e l a t i o n s h i p betw een s o i l ph and c o n c e n tr a tio n o f w a te r s o lu b le Al can be p lac e d on a p h y sic o c h e m ic a lly c o n s is te n t b a s is only by ta k in g in to a c c o u n t th e a c tu a l v a lu e o f th e io n p ro d u c t o f Al (011)3 i n s o i l s. He f u r t h e r re p o rte d t h a t because th e v a lu e o f pal + 3pOH may v a ry from 3 3-3 6, d if f e r e n c e s i n th e s o l u b i l i t y o f A l( 0 H) 3 compounds may have a g r e a t e r r e l a t i v e e f f e c t on Al concent r a t i o n s i n s o i l s o lu tio n th a n d i f f e r e n c e s in ph. A number o f common m in e ra ls in c lu d in g k a o l i n i t e, h a l l o y s i t e and m o n tm o rillo n ite can p ro d u ce a g i b b s i t e - l i k e C a 1 ( 0H) 3 3 s o l u b i l i t y p ro d u c t (M arion e t a l. } 1976). The c a lc u la t e d p A l( 0 H> 3 v a lu e s sh o u ld f a l l in th e o rd e r o f m o n tm o rillo n ite ^ k a o li n it e s* g ib b s ite a t H^SiO^ a c t i v i t i e s o f th e s e m in e ra ls c o n s is t e n t w ith th e s o lid p h a s e s. The p A l( 0 H) 3 v a lu e s g r e a t e r th an t h a t o f g ib b s ite i n d ic a te th a t m ore in s o lu b le compounds a r e governing Al s o l u b i l i t y. The f a c t t h a t th e p A l( 0 H) 3 v a lu e f o r g i b b s i t e in s o i l su sp e n sio n s c h a r a c t e r i s t i c a l l y d e c re a s e s w ith in c r e a s in g ph su g g e sts t h a t s o il s c o n ta in amorphous and more s o lu b le A l( 0 H) 3 a t h ig h e r p H 's (F rin k and P eech, 1963a;

13 and R ichburg and Adams; 1970). L indsay and Moreno (1960) re p o rte d t h a t u n d er m ost c o n d itio n s Al^"*~ a c t i v i t y in s o i l s o lu t i o n s w i l l exceed t h a t o f th e more s t a b l e g i b b s i t e b ecau se o f c o n tin u e d w e ttin g and d r y in g, ch an g in g o f o x id iz in g and re d u c in g c o n d itio n s, a c t i v i t y of m ic ro b e s, and o t h e r f a c t o r s w hich fa v o r th e p e r s i s te n c e o f some of th e more s o lu b le o r amorphous fo rm s. O ther m ethods have been u sed f o r e v a lu a tin g th e Al s t a t u s o f s o i l s o l u t i o n s. F or exam ple, M isra e t a l. (1974) p re s e n te d an e q u a tio n f o r e s ti m a t in g th e Al c o n c e n tr a tio n i n s o lu t i o n from ph and i o n ic s tr e n g th o f a s o i l e x t r a c t. B renes and P e a rso n (1973) d ev elo p ed an e q u a tio n to d e te rm in e s o i l s o lu tio n Al c o n c e n tr a tio n by u s in g ph and e l e c t r i c a l c o n d u c tiv ity o f a s a tu r a te d p a s te e x t r a c t. D a la i (1975) c h a r a c te r iz e d th e h y d r o ly s is p ro d u c ts o f Al io n s from " s o l u t io n " Al and " ex c h a n g e ab le " Al e x tr a c te d from a c id s o i l s w ith 0.01M CaCl2 and N KCl, r e s p e c t i v e l y. He a g reed w ith B lanchar and S c riv n e r (1972) th a t th e d e g re e o f h y d r o ly s is o f "ex c h a n g e ab le " Al was low er th a n " s o lu tio n " A l. However, he d is a g re e d w ith Ragland and Coleman (1959) who su g g e ste d t h a t Al io n s h y d ro ly z e more e x te n s i v e l y in a c id s o i l s and c la y system s th a n i n aqueous s o lu tio n s a t th e same ph. In contrast to these techniques, Chesworth (1975) believes that the application of Gibbs phase rule and topological techniques of Schreinemaker are more applicable to studies of mineral stability in soil systems. In summary, th e th e o ry and m ethodology o f therm odynam ics has been a p p lie d to s o i l s and g e o c h em istry by many s c i e n t i s t s. They have:

14 ( 1 ) d eveloped q u a l i t a t i v e diagram s t h a t a re u s e f u l in d e te rm in in g w hich m in e ra ls may be c o n tr o l li n g th e s o i l s o lu tio n c h e m istry and i n p ro v id in g p o s s ib le m in e ra l s t a b i l i t y seq u en ces, ( 2 )- shown t h a t c a lc u la tio n s from aqueous s o l u b i l i t y d a ta c o n cern in g a lu m in o s ilic a te m in e ra ls sh ould ta k e in to acco u n t th e p r o p o rtio n o f th e d i f f e r e n t Al io n s p e c ie s i n th e s o lu tio n, (3) shown t h a t th e s t a b i l i t y o f some m in e ra ls a re ph -dependent below th e i s o e l e c t r i c p o in t of Al in aqueous s o lu t i o n (ph 6.7 ) b u t in d ep en d en t of ph in more a lk a l in e e n v iro n m en ts, and (4) shown t h a t th e compounds w hich c o n tr o l Al and S i s o l u b i l i t y may v ary from s o i l to s o i l. P o s s ib le problem s e n c o u n te re d i n stu d y in g Al c o n c e n tra tio n s in th e s o i l s o lu tio n a re : ( 1 ) th e low s o l u b i l i t y of some compounds, ( 2 ) th e s tro n g tendency 3+ o f Al to h y d ro ly z e in aqueous s o lu t i o n, and (3) th e com plexing of Al w ith o rg a n ic m a tte r. The Role o f Aluminum i n S o il A c id ity As e a r l y a s 1904, V e itc h r e p o r te d t h a t s o i l a c i d i t y i s dependent on th e p re se n c e o f Al and i n some in s ta n c e s Fe and Mn. However, l i t t l e a t t e n t i o n was g iv en to t h i s and s im ila r r e s u l t s f o r a number o f y e a rs. P e a rso n (1975) and P r a t t (1966) c i t e M ag istad, who, in 1925, r e l a t e d ph to th e l e v e l o f Al in s o lu tio n. P r a t t d em o n strated t h a t as ph i s r a i s e d th e l e v e ls o f Al i n s o i l and c u ltu r e s o lu tio n s d e c re a s e r a p i d l y to l e s s th a n 1 ppm a t about ph 5.0 and above. In 1934, P aver and M a rsh a ll r e p o r te d t h a t b o th Al and H ta k e p a r t in s o i l a c i d i t y r e a c t i o n s. T h e ir work w ith ex changeable Al and H showed t h a t s o - c a lle d " H -s a tu ra te d c la y s " were p red o m in an tly " A l- s a tu r a te d c l a y s," and t h a t a m ajor p o r tio n o f th e Al came from