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Text follows. University M icrofilm s In ternatio nal INFLUENCE OF CULTIVATION, CROPPING SYSTEMS, AND CROP RESIDUES ON THE CONTENT AND DISTRIBUTION OF NITROGEN FORMS IN SOILS By Ebinimi F. A. B u ru to lu A DISSERTATION Submi t t e d to Michigan S t a t e U n i v e r s i t y in p a r t i a l f u l f i l l m e n t o f t h e r e q u ir e m e n t s f o r t h e de gr ee of DOCTOR OF PHILOSOPHY Department o f Crop and Soil Sc ie n ce s 1985 ABSTRACT INFLUENCE OF CULTIVATION, CROPPING SYSTEMS, AND CROP RESIDUES ON THE CONTENT AND DISTRIBUTION OF NITROGEN FORMS IN SOILS By Ebinimi F. A. B ur uto lu Changes in o r g a n i c C and t o t a l N, and in t h e d i s t r i b u t i o n o f N in f r a c t i o n s o b t a i n e d by a c i d h y d r o l y s i s were used t o e v a l u a t e e f f e c t s o f t i l l a g e , c r o p p i n g systems and t y p e s o f cr o p r e s i d u e s on N s t a t u s in s o i l s . Under cash cr o p systems on C h a r i t y c l a y and Hodunk sandy loam, t o t a l N in t h e plow l a y e r was lower by layers of adjacent v irgin s o i ls . o r g a n i c C were 62% in c l a y and 6 6 % than in s u r f a c e The c o r r e s p o n d i n g d e c r e a s e s in 80% in t h e sandy loam. In a l i v e s t o c k o p e r a t i o n on Kalamazoo sandy loam, t o t a l N was lower by 23% and o r g a n i c C by 12% th an in t h e v i r g i n s o i l . At a n o t h e r l o c a t i o n onC h a r i t y c l a y , seven cash crop sys­ tems i n v o l v i n g d i f f e r e n t sequences and p r o p o r t i o n s o f c o r n , navy b e a n s , s u g a r b e e t s , o a t s and a l f a l f a were compared. A f t e r 11 y e a r s , t o t a l N had d e c l i n e d by 2 t o 11% from l e v e l s found a t t h e b e g i n n in g of th e experiment. Organic C had d e c l i n e d by 13 t o 17%. At a l l f i e l d l o c a t i o n s , d e c r e a s e s in t h e p r o p o r t i o n of no n h y d ro ly za b le N and i n c r e a s e s in t h e p r o p o r t i o n of h y d r o l y z a b l e Ebinimi F. A. B ur uto lu unknown forms (HUN f r a c t i o n ) i n d i c a t e d t h a t a l o n g - t e r m e f f e c t o f t i l l a g e was t o i n c r e a s e e x po s ur e and d e c r e a s e s t a b i l i t y o f p h y s i c a l l y p r o t e c t e d humic complexes. This i n c r e a s e d t h e p r o p o r t i o n o f lower m o l e c u l a r w ei g h t f ra g m e n ts and p r e c u r s o r s . An i n c r e a s e in exposed s u r f a c e was i n d i c a t e d a l s o by i n c r e a s e s in h y d r o l y z a b l e ammonium. V a r i a b l e changes in t h e p r o p o r t i o n o f h y d r o l y z a b l e amino a c i d and amino s u ga r f r a c t i o n s app ea re d r e l a t e d t o c u r r e n t cr o p c o v e r . A Hodunk sandy loam amended w it h r e s i d u e s o f c o r n , navy b e a n s , s u g a r b e e t s o r a l f a l f a was i n c u b a t e d f o r 63 d a y s . Both chemical and b i o l o g i c a l t r a n s f o r m a t i o n s may have c o n t r i b u t e d t o ob se rv ed p a tte rn s of m in e ra liz a tio n - immobilization. The HUN f r a c t i o n seemed t o be a key i n t e r m e d i a t e in t r a n s f e r s o f N among o r g a n i c f r a c t i o n s and in exchanges with t h e mineral N p o o l. Amino a c i d and amino s u g a r f r a c t i o n s peaked a f t e r ma jor r e s p i r a t o r y l o s s e s o f C has o c c u r r e d and ap p e a r e d r e l a t e d t o s i z e o r a c t i v i t y o f m i c r o b i a l p o p u l a t i o n s . L e s s e r p a r a l l e l changes i n h y d r o l y z a b l e ammonium i n d i c a t e d i t s a s s o c i a t i o n with a c t i v e s u r f a c e s i t e s . DEDICATION Thi s d i s s e r t a t i o n i s d e d i c a t e d t o my w if e Comfort and our c h i l d r e n , T a r i p r e y e , E b i t a r i and T a r i t o n y e f o r t h e i r en co u ra g em en t, s a c r i f i c e , p a t i e n c e and ACKNOWLEDGMENTS The a u t h o r would l i k e t o e x p r e s s s i n c e r e a p p r e c i a t i o n to Drs. D. R. C h r i s t e n s o n and A. R. Wo lco tt f o r t h e i r v er y u s e f u l g u id a nc e and s u p p o r t in t h e r e s e a r c h and p r e p a r a t i o n o f t h i s d i s s e r ­ tation. I am a l s o g r a t e f u l t o o t h e r members o f my g u id a nc e co m m it te e, D r s . B . G . E l l i s , S. A. Boyd and 0. D. Meaders f o r t h e i r a d v i c e and u s e f u l s u g g e s t i o n s t h r o u g h o u t my program. My t ha nk s a r e due t o Dr. C. Cr es s f o r h i s a d v i c e in t h e s ta tis tic a l analysis. I am a l s o g r a t e f u l t o Mr. C al v in B r i c k e r f o r h i s rew ar d in g a s s i s t a n c e in t h e f i e l d and l a b o r a t o r y work d u r i n g my program. A s s i s t a n c e from o t h e r f a c u l t y , s t a f f and g r a d u a t e s t u d e n t s i s g r a t e f u l l y acknowledged. The a u t h o r a l s o w is h es t o tha nk t h e R iv e r s S t a t e U n i v e r s i t y o f S ci e n c e and Tec hno log y, P o r t H a r c o u r t , N i g e r i a , f o r t h e i r f i n a n c i a l support. S p e c i a l th a n k s and p r a i s e s t o God t h e F a t h e r , t h e Son and t h e Holy S p i r i t f o r making me " l i k e a t r e e p l a n t e d by t h e r i v e r s o f w a t e r , t h a t b r i n g e t h f o r t h h i s f r u i t in h i s s e a s o n ; h i s l e a f s h a l l n o t w i t h e r ; and w h a ts o e v e r he doeth s h a l l p r o s p e r " ( p s . 1:3 KJV). TABLE OF CONTENTS Page LIST OF TABLES....................................................................................................... vi LIST OF F I G U R E S ................................................................................................ x C ha pt er I. II. INTRODUCTION .......................................................................................... 1 LITERATURE CITED 3 ............................................................................ EFFECT OF CULTIVATION ON THE CONTENTAND DISTRIBUTION OF NITROGEN FORMS IN SOME MICHIGAN SOILS . . . . 5 E f f e c t o f C u l t i v a t i o n on Organic M a t t e r and Total N .......................................................................................... C u l t i v a t i o n and C o n t e n t o f Organic-N Forms . . . C u l t i v a t i o n and P r o f i l e D i s t r i b u t i o n of Organic N F o r m s ................................................................................................ O b j e c t i v e s o f P r e s e n t Research ......................................... 9 11 MATERIALS AND METHODS ..................................................................... 13 Experimental S i t e s ..................................................................... S o il S a m p l i n g ................................................................................... L a b o r a t o r y A nal ys es ..................................................................... 13 13 13 RESULTS AND DISCUSSION .............................................................. D i s t r i b u t i o n s o f N in V ir g in and C u l t i v a t e d P r o f i l e s .......................................................................................... Total K je ld ah l N and Organic C a r b o n ............................ F r a c t i o n a l Forms o f N ....................................................... E f f e c t s o f C u l t i v a t i o n on D i s t r i b u t i o n of N in S u r f a c e S oil L a y e r s .............................................................. ......................................... Changes in T o ta l K je ld ah l N Changes in F r a c t i o n a l Forms o f N ................................... F r a c t i o n a l C o n t r i b u t i o n s t o Total Kjel dah l N Loss . SUMMARY AND CONCLUSIONS LITERATURE CITED 5 8 16 16 16 18 27 27 30 35 .............................................................. 40 ............................................................................ 42 iv C h ap ter III. Page INFLUENCE OF CROPPING SYSTEMS ON FORMS OF NITROGEN IN A CLAY S O I L ................................................................................... 47 MATERIALS AND METHODS ..................................................................... 53 F i e l d E x p e r i m e n t ............................................................................ So il T y p e .......................................................................................... So il S a m p l i n g ................................................................................... L a b o r a to r y Analy se s ..................................................................... S t a t i s t i c a l A na ly s es ..................................................................... 53 54 54 56 56 RESULTS AND DISCUSSION .............................................................. 57 E f f e c t o f Cropping System on t h e D i s t r i b u t i o n o f N Over T i m e ................................................................................... Changes in Total K je ld ah l N and Organic Carbon . Changes in F r a c t i o n a l Forms o f N ................................... 57 57 59 SUMMARY AND CONCLUSIONS IV. .............................................................. 65 LITERATURE CITED ................................................................................... 67 EFFECT OF TYPE AND RATE OF CROP RESIDUES ON THE CONCENTRATION AND DISTRIBUTION OF NITROGEN FORMS DURING INCUBATION ............................................................................ 72 MATERIALS AND METHODS ..................................................................... 76 La b o r a to r y Analy se s ..................................................................... S t a t i s t i c a l Analy se s .............................................................. 77 77 RESULTS AND DISCUSSION ..................................................................... 78 Apparent Gains and Loss es o f N .......................................... Changes in Exchangeable Ammonium .......................................... Changes in N i t r i f i e d N .............................................................. Changes in Organic N F r a c t i o n s ......................................... Total Hy dr o ly za bl e N and Non hy dro lyz abl e N Changes Among H yd ro ly za b l e Forms o f N ............................ 78 86 88 90 90 95 SUMMARY....................................................................................................... 106 CONCLUSIONS.......................................................................................... 110 LITERATURE CITED ............................................................................ 112 APPENDICES.............................................................................................................. 115 v LIST OF TABLES T ab le 1. 2. 3. 4. 5. 6 . 7. 8 . 9. 10. 11. 1. 2. C h ap ter II Page L o c a ti o n and management o f s o i l s , d e s c r i p t i o n of p r o f i l e s , and pH and carb on c o n t e n t o f sampled s o i l d e p t h s ................................................................................................. 14 Organic carb on and t o t a l K je ld ah l n i t r o g e n in c u l t i ­ v a t e d and v i r g i n s o i l p r o f i l e s ............................................... 17 C o n te n t and d i s t r i b u t i o n o f t o t a l h y d r o l y z a b l e N in c u l t i v a t e d and v i r g i n s o i l p r o f i l e s ........................................ 19 C o n te n t and d i s t r i b u t i o n o f h y d r o l y z a b l e ammonium N in c u l t i v a t e d and v i r g i n s o i l p r o f i l e s ........................................ 20 C o nt e nt and d i s t r i b u t i o n o f a-amino a c i d N in c u l t i ­ v a t e d and v i r g i n s o i l p r o f i l e s ............................................... 21 C o n te n t and d i s t r i b u t i o n o f s e r i n e plus t h r e o n i n e N in c u l t i v a t e d and v i r g i n s o i l p r o f i l e s ................................... 22 C o nt e n t and d i s t r i b u t i o n o f amino s u g a r N in c u l t i ­ v a t e d and v i r g i n s o i l p r o f i l e s ................................................ 23 C o nt e n t and d i s t r i b u t i o n o f h y d r o l y z a b l e unknown N(HUN) in c u l t i v a t e d and v i r g i n s o i l p r o f i l e s ................................... 24 Co nt e nt and d i s t r i b u t i o n o f n o n h y d r o ly z a b le N in c u l t i v a t e d and v i r g i n s o i l p r o f i l e s .......................................... 25 D i s t r i b u t i o n o f o r g a n i c N f r a c t i o n s in c u l t i v a t e d and v i r g i n s u r f a c e s o i l s ............................................................................ 29 E f f e c t o f c u l t i v a t i o n on NH4 and u n i d e n t i f i e d N in a c i d h y d r o l y s a t e s in r e l a t i o n t o n o n h y d r o ly z a b le N . C ha pt er I I I 36 Crops grown and supple me nta l N a p p l i e d t o cr o p p in g systems from 1972 t o 1983 55 E f f e c t o f c r o p p i n g system on t o t a l Kjel dah l N and o r g a n i c car b on l e v e l s and c a r b o n - n i t r o g e n r a t i o in a C h a r i t y c l a y s o i l ..................................................................... 58 vi T a b le Page 3. E f f e c t o f c r o p p i n g system on t h e c o n c e n t r a t i o n o f n i t r o ................................................ gen forms and p e r c e n t a g e change 4. E f f e c t o f c r o p p i n g system on t h e d i s t r i b u t i o n of to ta l K je l d a h l N among o r g a n i c N f r a c t i o n s and p e r c e n t chang e. 61 E f f e c t o f c r o p p i n g system on t o t a l h y d r o l y z a b l e N(THN), h y d r o l y z a b l e ammonium (AN), and h y d r o l y z a b l e unknown N(HUN) in r e l a t i o n t o no nh y d r o ly za b le N(NHN) . . . . 62 5. 60 . E f f e c t o f c r o p p i n g system on h y d r o l y z a b l e NH4 (AN), amino a c i d N (AAN), amino s u g a r N (ASN) and h y d r o l y z a b l e unknown N (HUN) in r e l a t i o n t o t h e t o t a l h y d r o l y z a b l e N (T H N) .............................................................................................................. 6 64 Cha pt er IV 1. 2. 3. 4. 5. 6 . 7. 8 . 9. 10. Composition o f cr o p r e s i d u e s used in t h e i n c u b a t i o n s t u d y .............................................................................................................. 78 E f f e c t o f t y p e and r a t e o f cr op r e s i d u e and time of i n c u b a t i o n on o r g a n i c carbon ...................................................... 84 E f f e c t o f t y p e and r a t e o f r e s i d u e and time o f in c u b a ­ t i o n on ex ch a n g ea b le ammonium N ............................................... 87 E f f e c t o f t y p e and r a t e o f cr op r e s i d u e s and time of i n c u b a t i o n on t h e c o n c e n t r a t i o n of n i t r a t e p l u s n i t r a t e . 89 E f f e c t o f t y p e and r a t e o f cr o p r e s i d u e s and time of i n c u b a t i o n on t h e c o n c e n t r a t i o n o f t o t a l N .............................. 96 E f f e c t o f t y p e and r a t e o f cr op r e s i d u e s and t h e time o f i n c u b a t i o n on t h e c o n c e n t r a t i o n o f t o t a l h y d r o l y z a b l e n i t r o g e n ....................................................................................................... 97 E f f e c t o f t y p e and r a t e o f cr op r e s i d u e s and time o f i n c u b a t i o n on t h e c o n c e n t r a t i o n o f no nh y d r o ly za b le N . 98 E f f e c t o f ty pe and r a t e o f cr op r e s i d u e s and time of i n c u b a t i o n on t h e c o n c e n t r a t i o n of h y d r o l y z a b l e unknown N ................................................................................................ 99 E f f e c t o f t y p e and r a t e o f crop r e s i d u e s and ti m e o f i n c u b a t i o n on t h e c o n c e n t r a t i o n o f h y d r o l y z a b l e ammonium N ................................................................................................ 100 E f f e c t o f ty p e and r a t e o f cr op r e s i d u e s and time o f i n c u b a t i o n on t h e c o n c e n t r a t i o n o f amino a c i d N . . vi i . 101 Page E f f e c t o f ty pe and r a t e o f cr op r e s i d u e s and time o f i n c u b a t i o n on t h e c o n c e n t r a t i o n of amino s u g ar N 102 APPENDIX A P r o b a b i l i t i e s f o r s i g n i f i c a n c e o f main e f f e c t s and i n t e r a c t i o n s o f r e s i d u e s , r a t e s , and time of a n a l y s e s f o r car b on and forms o f n i t r o g e n ......................................... 117 P r o b a b i l i t i e s f o r s i g n i f i c a n c e o f main e f f e c t s and i n t e r a c t i o n s o f r e s i d u e s , r a t e s , and ti m es on t h e p r o p o r t i o n o f f r a c t i o n a l forms o f N ......................................... 118 E f f e c t o f t y p e and r a t e of crop r e s i d u e s and time o f i n c u b a t i o n on t h e c o n c e n t r a t i o n o f t o t a l o r g a n i c n i t r o g e n ....................................................................................................... 119 E f f e c t o f cr op r e s i d u e t y p e and time o f i n c u b a t i o n on t h e p r o p o r t i o n o f t o t a l N as t o t a l h y d r o l y z a b l e N . . 120 E f f e c t o f t y p e and r a t e o f c r o p r e s i d u e s on t h e p r o p o r ­ tio n of to ta l N as to t a l hydrolyzable N ............................ 121 E f f e c t o f cr o p r e s i d u e r a t e and time o f i n c u b a t i o n on the proportion of t o t a l N as t o t a l hydrolyzable N . 122 E f f e c t o f ty pe and r a t e o f cr o p r e s i d u e on t h e conc en ­ t r a t i o n o f n o n h y d r o l y z a b l e N ....................................................... 123 E f f e c t o f r e s i d u e r a t e and time o f i n c u b a t i o n on th e c o n c e n t r a t i o n o f n o n h y d r o l y z a b l e N ......................................... 124 E f f e c t o f ty p e and r a t e o f c r o p r e s i d u e on t h e p r o p o r ­ t i o n o f t o t a l N a s n o n h y d r o ly z a b le N ................................... 125 E f f e c t o f r e s i d u e r a t e and time of i n c u b a t i o n on th e p r o p r o t i o n o f t o t a l N a s n o n h y d r o ly z a b le N . . 126 E f f e c t o f r e s i d u e t y p e and time o f i n c u b a t i o n on t h e c o n c e n t r a t i o n o f h y d r o l y z a b l e ammonium N ............................ 127 E f f e c t o f t y p e and r a t e o f crop r e s i d u e s on t h e c o n c e n t r a t i o n o f h y d r o l y z a b l e ammonium N ............................ 128 E f f e c t o f r e s i d u e r a t e and time o f i n c u b a t i o n on t h e c o n c e n t r a t i o n o f h y d r o l y z a b l e ammonium N ............................ 129 E f f e c t o f r e s i d u e ty p e and time o f i n c u b a t i o n on th e p r o p o r t i o n o f t o t a l N as h y d r o l y z a b l e ammonium N . 130 vi i i . T a b le 15. 16. 17. 18. Page E f f e c t o f t y p e and r a t e o f cr o p r e s i d u e s on t h e p r o p o r ­ t i o n o f t o t a l N a s h y d r o l y z a b l e ammonium N. . . . 131 E f f e c t o f r e s i d u e r a t e and time o f i n c u b a t i o n on t h e p r o p o r t i o n o f t o t a l N a s h y d r o l y z a b l e ammonium N . 132 . E f f e c t o f t y p e and r a t e o f cr o p r e s i d u e s and time o f i n c u b a t i o n on t h e p r o p o r t i o n o f t o t a l N a s amino acid N ............................................................................................... 133 Simple e f f e c t o f t y p e o f cr o p r e s i d u e s and time of i n c u b a t i o n on t h e c o n c e n t r a t i o n and p r o p o r t i o n of t o t a l N a s amino s u g a r N ..................................................... 134 19. E f f e c t o f ty p e and r a t e o f r e s i d u e on t h e p r o p o r t i o n o f ..................................................... 135 t o t a l N a s amino s u g a r N 20. Simple e f f e c t o f ti m e o f i n c u b a t i o n on t h e p r o p o r t i o n o f t o t a l N a s h y d r o l y z a b l e unknown N .......................... ix 136 LIST OF FIGURES fig u re 1. 2. 3. 4. 1. 2. 3. 4. 5. 6 . 7. 8 . C h ap ter II C o n te n t o f o r g a n i c N f r a c t i o n s in c u l t i v a t e d (C) and v i r g i n (V) s u r f a c e ( 0 - 0 . 15m) in a C h a r i t y c l a y s o i l . Page . 31 C o nt e n t o f o r g a n i c N f r a c t i o n s in c u l t i v a t e d (C) and v i r g i n (V) s u r f a c e ( 0 - 0 . 15m) in a Kalamazoo sandy loam s t u d y .............................................................................................................. 32 C on te nt o f o r g a n i c N f r a c t i o n s in c u l t i v a t e d (C) and v i r g i n (V) s u r f a c e ( 0 - 0 . 15m) in a Hodunk sandy loam s o i l .............................................................................................................. 33 De crease in c o n t e n t o f o r g a n i c N f r a c t i o n s e x p r e s s e d as p e r c e n t o f t o t a l N l o s s due t o c u l t i v a t i o n ........................... C h a p t e r IV 37 E f f e c t o f ty p e and r a t e o f a l f a l f a r e s i d u e s and time of i n c u b a t i o n on t h e c o n c e n t r a t i o n o f t o t a l n i t r o g e n . . 80 E f f e c t o f ty pe and r a t e o f s u g a r b e e t r e s i d u e s and time o f i n c u b a t i o n on t h e c o n c e n t r a t i o n o f t o t a l n i t r o g e n . 81 E f f e c t o f ty p e and r a t e o f co rn r e s i d u e s and time of i n c u b a t i o n on t h e c o n c e n t r a t i o n o f t o t a l n i t r o g e n . . 82 E f f e c t o f ty p e and r a t e o f navy bean r e s i d u e s and time o f i n c u b a t i o n on t h e c o n c e n t r a t i o n o f t o t a l n i t r o g e n . 83 Concentration of n itro g e n f r a c t i o n s during incubation a t 50 g/kg a l f a l f a r e s i d u e a d d i t i o n .................................................. 91 Concentration of n itro g en f r a c t i o n s during incubation a t 50 g/kg s u g a r b e e t r e s i d u e a d d i t i o n .................................... 92 Concentration of nitro g en f r a c t i o n s during incubation a t 50 g/kg navy bean r e s i d u e a d d i t i o n .................................... 93 Concentration of n itro g en f r a c t i o n s during incubation a t 50 g/kg corn r e s i d u e a d d i t i o n .................................................. 94 x CHAPTER I INTRODUCTION The n a t u r e and s t a t u s o f s o i l o r g a n i c m a t t e r and n i t r o g e n a r e im p o r t a n t f a c t o r s in crop p r o d u c t i o n . Organic m a t t e r c o n t r i b u t e s im p o r t a n t p h y s i c a l , c h e m i c a l , and b i o l o g i c a l p r o p e r t i e s t o s o i l s . N it ro g e n i s an e s s e n t i a l el em en t in p l a n t n u t r i t i o n . When s o i l i s c u l t i v a t e d , s o i l o r g a n i c m a t t e r and t o t a l N d e c l i n e w ith t i m e . The d e c l i n e i s r a p i d and a p p e a r s l i n e a r in t h e e a r l i e r y e a r s a f t e r v i r g i n s o i l s a r e b r o u g h t un de r c u l t i v a t i o n , b u t g r a d u a l l y slows and u l t i m a t e l y r e a c h e s a new e q u i l i b r i u m a f t e r 50 t o 100 y e a r s o f c u l t i v a t i o n . The r a t e and magnitude o f o r g a n i c m a t t e r and t o t a l N l o s s i s i n f l u e n c e d by t h e c r o p p i n g system and sequence ( 4 , 5, 7, 8 , 15, 17, 1 8 ) , c r o p s grown ( 7 , 2 0 ) , s p e c i f i c management p r a c t i c e s ( 4 , 5, 14, 15, 16, 2 ) , t h e o r i g i n a l s o i l N c o n t e n t ( 3 , 5, 6 , 7, 17, 18 ) , c l i m a t e ( 9 , 10 ), s o i l ty p e ( 1 , 1 5 ) , and l e n g t h o f c u l t i v a t i o n . The r a t e o f e s t a b l i s h m e n t o f e q u i l i b r i u m i s p r o v id e d by change and t h e magnitude A o f t h e term (NQ - —) e x p ( - r t ) in t h e e q u a t i o n of Bartholomew and Kirkham ( 2 ) : N=A . r where (N o V < -t r NQ i s t h e i n i t i a l N c o n t e n t r i s t h e annual r a t e of N lo ss A i s t h e annual r a te of addition 2 More th an 90% o f t h e t o t a l N in most s u r f a c e s o i l s i s in o r g a n i c form. About o n e - h a l f o f t h e o r g a n i c N has n o t been a d e q u a t e l y characterized. I n o r g a n i c N p l a y s a prim ary and d i r e c t r o l e in p l a n t nutrition. The in vo lv em ent o f o r g a n i c N in p l a n t n u t r i t i o n i s a t b e s t r e g a r d e d a s s eco nd ary and i n d i r e c t , t h a t i s , th ro ug h t h e p r o c e s s of m ineralization. D i f f e r e n t k in d s o f N compounds and complexes d i f f e r in t h e i r s u s c e p t i b i l i t y to m i n e r a l i z a t i o n . I t might be ex p ec te d t h a t t h e i r im portance a s s o u r c e s o f N f o r p l a n t s w i l l v ar y a c c o r d i n g l y . The c o n t e n t and p r o p o r t i o n s of v a r i o u s o r g a n i c N f r a c t i o n s have been i n f l u e n c e d by t h e management sy st em . These o r g a n i c N f a c t i o n s s h i f t from one form t o a n o t h e r d u r i n g c u l t i v a t i o n and o t h e r management practices. Many r e s e a r c h e r s have a t t e m p t e d t o i d e n t i f y t h e forms of o r g a n i c N t h a t might be u s e f u l a s p r e d i c t i v e s o i l t e s t s (1 1 , 12, 13, 19). The p r e s e n t s tu dy was u n d e r t a k e n t o d e t e r m i n e t h e n a t u r e and magnitude o f changes in c o n t e n t and d i s t r i b u t i o n o f N forms under t h e f o l l o w i n g t h r e e systems: 1. V ir g in s o i l s and t h e i r c u l t i v a t e d a n a l o g u e s under t h r e e t y p e s o f management 2. R o t a t i o n a l cr o p p in g f o r e l e v e n y e a r s 3. I n c u b a t i o n systems i n v o l v i n g v a r i o u s r e s i d u e ty p e s and r a t e s f o r a 63-day p e r i o d . LITERATURE CITED 1. 2. Anderson, M. A . , and G. M. Browning. 1950. Some p h y s i c a l and chemical p r o p e r t i e s o f s i x v i r g i n and s i x c u l t i v a t e d Iowa s o i l s . S o i l S c i . Soc. Arner. Pro c. 14: 370364. Bartholomew, W. t i o n s and ch an g e s. W is.), II: V . , and D. Kirkham. 1960. Mathematical d e s c r i p ­ i n t e r p r e t a t i o n s o f c u l t u r e induced s o i l n i t r o g e n I n t . Congr. S oil S c i . T r a n s . 7th (Madison, 471-477. 3: F r i t s c h e n , L. J . , and J . A. Hobbs. 1958. E f f e c t o f cr op r o t a t i o n and f e r t i l i z e r t r e a t m e n t on t h e n i t r o g e n and o r g a n i c carbon c o n t e n t s o f a p r a i r i e s o i l . S oil S c i . Soc. Amer. Proc. 22:439 -4 41 . 4. Gosdin, G. W., M. S t e l l y , and W. E. Adams. 1950. The o r g a n i c m a t t e r and n i t r o g e n c o n t e n t and c a r b o n - n i t r o g e n r a t i o o f Ceci l s o i l a s i n f l u e n c e d by d i f f e r e n t c r o p p in g systems on c l a s s e s I I , I I I , and IV l a n d . So il S c i . Soc. Amer. Proc. ( 1 9 49 ). 14 :203-208. 5. Haas, H. J . , C. E. Evans, and E. F. M i l e s . 1957. N it ro g en and carb on changes in G re a t P l a i n s s o i l s as i n f l u e n c e d by c r o p p i n g and s o i l t r e a t m e n t s . Te ch nic al B u l l e t i n No. 164. USDA. 6 . 7. 8 . 9. Hi de, J . C . , and W. H. Metzger. 1939. The e f f e c t o f c u l t i v a t i o n and e r o s i o n on t h e n i t r o g e n and carbon o f some Kansas s o i l s . Agron. J . 31 :6 2 5- 6 32 . Hobbs, J . A . , and P. L. Brown. 1957. N i tr o g e n and o r g a n i c carbon changes in c u l t i v a t e d Western Kansas s o i l s . Kansas Agr. Exp. S t a . B u l l . 89. Hobbs, J . A ., and P. L. Brown. 1965. E f f e c t s o f cr o p p in g and management on n i t r o g e n and o r g a n i c carbon c o n t e n t s o f a w e s te r n Kansas s o i l . Kansas Agr. Exp. S t a . Tech. B u l l . 144. J e n n y , H. 1941. F a c t o r s o f s o i l f o r m a t i o n . Company, New York. 3 McGraw-Hill Book 4 10. J e n n y , H. 1960. Comparison o f s o i l n i t r o g e n and ca rb o n in t r o p i c a l and t e m p e r a t e r e g i o n s . Miss ouri A g r i c . Exp. S t a . Res. B u l l . 7 6 5 :1 - 3 0 . 11. Kai, H ., Z. Ahmad, and T. Harada. 1973. F a c t o r s a f f e c t i n g im m o b i l i z a t i o n and r e l e a s e o f n i t r o g e n in s o i l and chemical c h a r a c t e r i s t i c s o f t h e n i t r o g e n newly im mo bil ize d. III. T r a n s f o r m a t i o n o f t h e n i t r o g e n immobilized in s o i l and i t s chemical c h a r a c t e r i s t i c s . Soil S c i . P l a n t N u t r . 19:275 -2 86 . 12. Keeney, D. R . , and J . M. Bremner. 1964. t h e n i t r o g e n d i s t r i b u t i o n in s o i l s . Pr oc. 28 :65 3-6 56 . E f f e c t o f c u l t i v a t i o n on S o il S c i . Soc. Amer. 13. Keeney, D. R . , and J . M. Bremner. 1966. C h aracterization of m i n e r a l i z e d n i t r o g e n in s o i l s . Soil S c i . Soc. Amer. Proc. 30 :71 4- 719 . 14. Lee, C . , and R. H. Bray. 1949. Organic m a t t e r and n i t r o g e n c o n t e n t s o f s o i l s a s i n f l u e n c e d by management. So il S c i . 68 :2 03 -2 1 2. 15. Mazurak, A. P . , and E. C. Conrad. 1966. Changes in c o n t e n t o f t o t a l n i t r o g e n and o r g a n i c m a t t e r in t h r e e Nebraska s o i l s a f t e r seven y e a r s o f cr o p p in g t r e a t m e n t s . Agron. J . 58:8 5 -8 8 . 16. M e i n t s , V. W., L. T. K u r t z , S. W. M e ls te d , and T. R. Peck. 1977. Long-term t r e n d s in t o t a l s o i l N as i n f l u e n c e d by c e r t a i n management p r a c t i c e s . So il S c i . 124:110-116. 17. M etger, W. H. 1939. N itr og en and o r g a n i c ca rb o n o f s o i l s as i n f l u e n c e d by cr o p p in g systems and s o i l t r e a t m e n t s . Kansas Agr. Exp. S t a . Tech. B u l l . 56. 18. Myers, H. E . , A. L. H a l l s t e d , J . B. Kuska, and H. J . Haas. 1943. N it ro g en and ca r b o n changes in s o i l s unde r low r a i n f a l l a s i n f l u e n c e d by cr o p p in g systems and s o i l t r e a t m e n t . Kansas Agr. Exp. S t a . Tech. B u l l . 45. 19. S t e w a r t , B. A . , L. K. P o r t e r , and D. D. Joh n so n. 1963. I m m o b i l i z a t i o n and m i n e r a l i z a t i o n of n i t r o g e n in s e v e r a l organic f r a c t io n s of s o i l . Soil S c i . Soc. Amer. P ro c . 27:302 -3 04 . 20. Van B a v e l , C. H. M., and F. W. S c h a l l e r . 1951. S oil a g g r e g a t i o n s , o r g a n i c m a t t e r and y i e l d s in a l o n g - t e r m e x p e r i m e n t as a f f e c t e d by c ro p management. Soil S c i . Soc. Amer. P r o c. (1 95 0) . 15:399 -4 04. CHAPTER I I EFFECT OF CULTIVATION ON THE CONTENT AND DISTRIBUTION OF NITROGEN FORMS IN SOME MICHIGAN SOILS The r o l e o f o r g a n i c m a t t e r and n i t r o g e n in s o i l f o r m a t i o n , f e r t i l i t y , and c r o p p r o d u c t i o n has been t r e a t e d e x t e n s i v e l y in pub­ lished l i t e r a t u r e . S u r f a c e o r g a n i c m a t t e r and n i t r o g e n d i s t r i b u t i o n vary t r e ­ mendously among and w i t h i n t h e ma jor s o i l o r d e r s o f t h e w or ld . The magnitude o f v a r i a t i o n depends t o a g r e a t e x t e n t on s o i l forming f a c t o r s such a s c l i m a t e , v e g e t a t i o n , t o p o g r a p h y , p a r e n t m a t e r i a l and ag e. According t o Jenny ( 2 2 , 2 3 ) , t h e impo rta nce of t h e f a c t o r s d e t e r m i n i n g t h e o r g a n i c m a t t e r and n i t r o g e n c o n t e n t s o f medium t e x t u r e d s o i l s o f t h e U n it e d S t a t e s d e c r e a s e d in t h e o r d e r : c l i m a t e > v e g e t a t i o n > to po gr ap hy = p a r e n t m a t e r i a l > age E f f e c t o f C u l t i v a t i o n on Organic M a tt e r and Tot al N Within a s o i l o r d e r , management f a c t o r s , such a s c u l t i v a t i o n and f e r t i l i z a t i o n b r i n g a b o u t s i g n i f i c a n t changes in o r g a n i c m a t t e r and n i t r o g e n d i s t r i b u t i o n in s u r f a c e and p r o f i l e s o i l s . C ultivation a f f e c t s t h e d i s t r i b u t i o n o f o r g a n i c m a t t e r and n i t r o g e n th r ou gh i t s i n f l u e n c e on t h e o r g a n i c carbon e q u i l i b r i u m in s o i l s . 5 6 Some work has been done on t h e e f f e c t o f c u l t i v a t i o n on t h e o r g a n i c m a t t e r and n i t r o g e n c o n t e n t s o f s o i l s in t h e t e m p e r a t e , t r o p i c a l , and s u b t r o p i c a l r e g i o n s . In t h e i r l o n g - t e r m st udy on t h e e f f e c t o f c r o p p i n g on t h e s u r f a c e s o i l n i t r o g e n and o r g a n i c carbon c o n t e n t o f t h e s o i l s a t 14 l o c a t i o n s in t h e G r ea t P l a i n s , Haas and Evans (15) r e p o r t e d t h a t n i t r o g e n d e c l i n e d by 39% on t h e av e r a g e over a 36-year period. Th is r e p r e s e n t s 1.07% l o s s o f s o i l n i t r o g e n f o r each y e a r o f c r o p p r o d u c t i o n . The a v e r a g e o r g a n i c carbon l o s s over a 3 7 - y e a r cr o p p in g p e r i o d was 42% w it h an annual l o s s of 1.15%. In a s i m i l a r s t u d y in w e s te r n Kansas s o i l s under low r a i n ­ f a l l c o n d i t i o n s , Hobbs and Brown (18) r e p o r t e d t h a t cr o p p in g had marked e f f e c t on n i t r o g e n and o r g a n i c carbon l o s s e s . The N l o s s e s were r a p i d a f t e r c u l t i v a t i o n o f t h e v i r g i n s o i l began and t h e r a t e g r a d u a l l y d e c r e a s e d w it h t i m e . N i tr o g e n and o r g a n i c C l o s s e s av era ged 23.3% and 36.2%, r e s p e c t i v e l y , from 1916 t o 1958. However, l o s s e s slowed down t o 2.2% f o r n i t r o g e n and 2.1% f o r o r g a n i c C in t h e l a s t eig h t years (19). In t h e i r p r e l i m i n a r y s t u d i e s on t h e s t a t u s o f o r g a n i c m a t t e r and n i t r o g e n in s o i l s unde r s h i f t i n g c u l t i v a t i o n in t h e t r o p i c s , I s i r i m a h e t a l . (20) found t h a t c u l t i v a t i o n d e c r e a s e d o r g a n i c m a t t e r by 55% and t o t a l N c o n t e n t by 60% in a l l s o i l t y p e s . They a l s o o b s er ve d t h a t t h e long f a l l o w p e r i o d had n o t i n c r e a s e d t h e l e v e l o f n i t r o g e n and o r g a n i c m a t t e r markedly. loam P r a i r i e s o i l On a Greary s i l t in Kansas, F r i t s c h e n and Hobbs (13) worked on t h e e f f e c t o f cr op r o t a t i o n on t h e N and o r g a n i c carbon c o n t e n t s and found l o s s e s o f both o v e r t h e p e r i o d . S i m i l a r l y , Hide and Metzger (16) r e p o r t e d a d e c l i n e in carb on and n i t r o g e n o f Kansas s u r f a c e s o i l s of 7 37% and 32%, r e s p e c t i v e l y , due t o c u l t i v a t i o n . s o i l s in t h e G r e a t P l a i n s , P o r t e r e t a l . Working w ith s u r f a c e (33) r e p o r t e d t h a t cr o p p in g o f v i r g i n s o i l s d e c r e a s e d t h e t o t a l N and t h e o t h e r forms o f N. In a n o t h e r s t u d y , Smith and Young (36) showed t h a t t h e t o t a l N and o r g a n i c C o f s u r f a c e s o i l s d e c l i n e d on t h e a v e r a g e by 42% and 33%, r e s p e c t i v e l y , due t o c u l t i v a t i o n . There i s l i t t l e on t h e mi n er al N forms. i n f o r m a t i o n on t h e e f f e c t o f c u l t i v a t i o n I t was ob se rv ed in some s t u d i e s t h a t ex c h a n g e a b le NH^ and n i t r a t e N c o n t e n t s were n o r m a l ly s m a l l , and both f r a c t i o n s may n o t a c c o u n t f o r more th a n 2% o f t h e t o t a l s o i l N. N i t r i t e s do n o t ac cu mu la te in s o i l s t o a g r e a t e x t e n t , e x c e p t in a l k a l i n e c o n d i t i o n s , h e n c e , l a r g e amounts a r e r a r e l y d e t e c t e d in soil an aly sis. + Mineral n i t r o g e n a l s o o c c u r s a s f i x e d NH^ and t h i s f r a c t i o n i s very s i g n i f i c a n t in some s o i l p r o f i l e s . The a v e r a g e amount o f f i x e d ammonium N remained un changed, i n d i c a t i n g t h a t c u l t i ­ v a t i o n had made no e f f e c t on t h e f i x e d ammonium c o n t e n t o f t h e s u r ­ f a c e s o i l s o f Canada ( 1 7 ) . The s t u d i e s c i t e d above have g e n e r a l l y i n d i c a t e d a l o s s of o r g a n i c m a t t e r and t o t a l N with c u l t i v a t i o n . Some i n v e s t i g a t i o n s have r e p o r t e d t h a t c u l t i v a t i o n i n c r e a s e d o r g a n i c m a t t e r ( 1 , 14, 27 ). In t h e i r s t u d i e s , G r i g o r ' y e v (14) and Konovalonva (27) r e p o r t e d t h a t humus and N c o n t e n t i n c r e a s e d w ith c u l t i v a t i o n on s o d - p o d z o l i c f o r e s t s o i l s in t h e o r d e r : well cultivated m o d e ra te l y > s l i g h t l y cultivated cultivated > f Q r e s t SQi ls 8 I t i s a p p r o p r i a t e t o i n d i c a t e t h a t most o f t h e s e s t u d i e s d i s c u s s e d t h e e f f e c t o f c u l t i v a t i o n on o r g a n i c m a t t e r and t o t a l N contents of surface s o i l s . E ffect of c u l tiv a t io n is not r e s t r i c t e d to su rface horizons alo n e. The impact g r a d u a l l y moves t o s u b s u r f a c e horizons. F u r t h e r m o r e , i t i s i m p o r t a n t t o compare c u l t i v a t e d and v i r g i n s o i l s t o a p p r e c i a t e t h e impact o f c u l t i v a t i o n in a g r i c u l t u r a l s o il s. Se v e r a l s t u d i e s have shown t h a t o r g a n i c m a t t e r and t o t a l n i t r o g e n d e c l i n e d w i t h d e p t h in both v i r g i n and c u l t i v a t e d s o i l s (2 9 , 3 6 ) . The magnitude and r a t e o f d e c l i n e was g e n e r a l l y g r e a t e r in t h e c u l t i v a t e d than in t h e v i r g i n s o i l . C u l t i v a t i o n and Co n te nt o f Organic-N Forms C u l t i v a t i o n d e c r e a s e d t h e c o n t e n t o f a l l N forms m a rk e dl y, e x c e p t nonexchangeable ( f i x e d ) NH^ N in s u r f a c e s o i l s . The p r o p o r - t i o n o f t o t a l N a s nonexch an gea ble ( f i x e d ) NH^ N i n c r e a s e d s l i g h t l y , a s d i d t o t a l h y d r o l y z a b l e N and o t h e r h y d r o l y z a b l e f r a c t i o n s such as ammonium N, hexosamine N, and u n i d e n t i f i e d N. The p e r c e n t a g e o f h y d r o l y z a b l e amino a c i d N and n o n h y d r o ly z a b le N d e c r e a s e d due to cultivation. The a v e r a g e p e r c e n t l o s s o f d i f f e r e n t forms o f N on c u l t i v a t i o n d e c r e a s e d in t h e o r d e r ( 24 ): amino a c i d N (43.0%) > n o n h y d r o l y z a b l e N (39.4% > Total N (36.2%) > t o t a l h y d r o l y z a b l e N (35.2%) > u n i d e n t i f i e d h y d r o l y z a b l e N (34.5%) > h y d r o l y z a b l e ammonium N (28.6%) > hexosamine N (27.6%) > nonexchanga b l e ammonium N (0.2%). 9 In a n o t h e r s t u d y , n o n d i s t i l l a b l e a c i d - s o l u b l e N showed t h e g r e a t e s t d e c l i n e w i t h c r o p p i n g , fo ll o w ed by d i s t i l l a b l e a c i d - s o l u b l e ammonium N and a c i d - i n s o l u b l e N ( 1 2 ) . These s t u d i e s t e n d to show t h a t t h e p r o p o r t i o n o f i n d i v i d u a l o r g a n i c N f r a c t i o n s in t h e s u r f a c e h o r iz o n may n o t be g r e a t l y changed by c u l t i v a t i o n , b u t t h e r e no rm al ly i s q u a n t i t a t i v e r e d u c t i o n in amounts o f most f r a c t i o n a l forms. C u l t i v a t i o n and P r o f i l e D i s t r i b u t i o n o f Organic N Forms In many t e m p e r a t e s o i l s , t h e p r o p o r t i o n o f t h e t o t a l N p r e s e n t a s amino a c i d N, amino s u g a r N, and a c i d i n s o l u b l e N range from 30-50%, 5-24%, and 20-30%, r e s p e c t i v e l y . Hy d ro ly za bl e ammonium N and h y d r o l y z a b l e unknown N (HUN) o c c u r a s 20-35% and 10-20%, r e s p e c t i v e l y , o f t h e t o t a l N. With d e p t h , t h e c o n t e n t s and p e r c e n t ­ ages o f th e s o i l N may i n c r e a s e , d e c r e a s e , o r remain t h e same, depending on t h e management o r c u l t u r a l p r a c t i c e s , b i o t i c , c l i m a t i c , o r ed ap hi c f a c t o r s o r t h e s t a t u s o f decom po sit io n o f c e r t a i n o r g a n i c compounds in t h e s o i l e n v ir on m en t. Re p o r t s have i n d i c a t e d t h a t t h e p r o p o r t i o n o f s o i l N as amino a c i d N d e c r e a s e d w i t h dept h in d i f f e r e n t s o i l s (2 6, 3 0 , 3 7 , 4 1 ) . The d e c r e a s e o f amino a c i d N w ith de pt h may be r e l a t e d to the d e c lin e w ith d ep th o f t h e m i c r o b i a l p o p u l a t i o n whose c e l l s c o n t a i n amino acids. S ev er al s t u d i e s have r e p o r t e d t h a t t h e p e r c e n t a g e o f amino s u g a r N d e c r e a s e d with d e p t h (2 6, 35, 39 , 4 0 , 4 2 ) . O ther s t u d i e s 10 showed t h a t amino s u g a r N i n c r e a s e d w it h de pt h ( 3 0 , 4 1 , 5 0 ) . n o t c l e a r why amino s u g ar N would i n c r e a s e w ith d e p t h . I t is Thi s p a t t e r n may be r e l a t e d t o t h e h i g h e r c a l c iu m c o n t e n t in t h e lo w er h o r i z o n s . Some s o i l s in s u b t r o p i c a l r e g i o n s showed a d e c l i n e o f amino s u g a r N w it h a d e c r e a s e in p e r c e n t c a l c iu m in t h e lower h o r i z o n s ( 4 0 ) . A f a i r l y r e a s o n a b l e e x p l a n a t i o n f o r t h e i n c r e a s e in amino s u g a r N with depth may be due t o e x t e n s i v e d ec om p os i ti on and t u r n o v e r which may l e a d t o s e l e c t i v e p r e s e r v a t i o n o f amino s u g a r N ( 4 7 , 5 0 ) . The s e l e c t i v e p r e s e r v a t i o n may be due t o p r o t e c t i o n by a d s o r p t i o n o r c om pl ex at io n w it h o r g a n i c and mi ne ra l c o l l o i d s . Although amino a c i d N and amino s u g a r N a r e t h e main i d e n t i ­ f i a b l e o r g a n i c N compounds in s o i l h y d r o l y s a t e s , i t i s i m p o r t a n t to know t h e d i s t r i b u t i o n p a t t e r n s o f t h e o t h e r N fo r m s . The p r o p o r t i o n o f s o i l N a s h y d r o l y z a b l e ammonium N i n c r e a s e d w it h de pt h in s o i l p r o f i l e s o f t h e U s t o l l s u b o r d e r in w e s t e r n Nebraska (29) and a p o d z o l i c s o i l in c e n t r a l Sweden ( 3 0 ) . An e a r l i e r s t u d y i n d i c a t e d t h e same t r e n d in a wide v a r i e t y o f s o i l s in t h e n o r t h - c e n t r a l U.S. ( 4 1 ) . The r a t e o f h y d r o l y z a b l e ammonium N i n c r e a s e w i t h d e p t h v a r i e d with the s o il type. The i n c r e a s e o f h y d r o l y z a b l e ammonium N w ith depth c o u l d be du e, in p a r t , t o th e l i b e r a t i o n o f NHg from c l a y - f i x e d NH^ by a c i d h y d r o l y s i s , r a t h e r tha n from o r g a n i c compounds ( 4 , 26, 39 , 41, 44, 48). The d i s t r i b u t i o n p a t t e r n s o f o r g a n i c N forms can va r y con­ s i d e r a b l y with t h e s o i l t y p e . In min era l s o i l s o f t h e t r o p i c a l and s u b t r o p i c a l r e g i o n , t o t a l h y d r o l y z a b l e N and u n i d e n t i f i e d N i n c r e a s e d 11 w ith d e p t h . Acid i n s o l u b l e N d e c r e a s e d with d e p t h . There was no c o n s i s t e n t p a t t e r n in p r o f i l e d i s t r i b u t i o n in o t h e r o r g a n i c N forms. A nother s t u d y showed t h a t t o t a l h y d r o l y z a b l e N, amino a c i d N, and ammonium N d e c r e a s e d , b u t amino s u g a r N i n c r e a s e d w ith d ep th in a l l b u t one p r o f i l e ( 1 2 ). Few s t u d i e s have compared s o i l p r o f i l e d i s t r i b u t i o n p a t t e r n s o f o r g a n i c N forms in c u l t i v a t e d and t h e i r v i r g i n a n a l o g u e s . In t h e i r s t u d i e s on some s o i l p r o f i l e s , Meints and P e t e r s o n (29) r e p o r t e d t h a t t h e c o n c e n t r a t i o n o f t h e o r g a n i c f r a c t i o n s in both c u l t i v a t e d and v i r g i n s o i l p r o f i l e s d e c l i n e d w it h d e p t h . However, c u l t i v a t i o n d e c r e a s e d t h e p r o p o r t i o n o f t o t a l N a s n o n h y d r o ly z a b le N and amino a c i d N. I t increased th e proportion of hydrolyzable ammonium N, compared t o t h e v i r g i n s o i l p r o f i l e s . Thi s i n d i c a t e s t h a t re g u la r a d d itio n s of organic m a te ria ls w ithout s o il d isturbance ov er a p e r i o d o f t i m e , a s in v i r g i n c o n d i t i o n s , r e s u l t s in a c h a r ­ a c t e r i s t i c d i s t r i b u t i o n o f o r g a n i c N f r a c t i o n s , and t h a t t h i s d i s ­ t r i b u t i o n can be a l t e r e d by d i f f e r e n t i a l d ec o m p os it io n when c u l t i v a t e d c o n d i t i o n s a r e imposed. The r a t e and magnitude o f change w i l l be i n f l u e n c e d by t h e t y p e , q u a n t i t y , and fr e q u e n c y o r o r g a n i c amend­ ments added o r c r o p r e s i d u e r e t u r n e d and t h e l e n g t h o f time t h a t a give n s y st em o f management i s imposed. O b j e c t i v e s o f P r e s e n t Research The n a t u r e and p a t t e r n o f p r o f i l e d i s t r i b u t i o n o f o r g a n i c N components in Michigan s o i l s has n o t been c o n s i d e r e d in p u b l i s h e d literatu re. The p r e s e n t i n v e s t i g a t i o n was u n d e r ta k e n a s p a r t o f a cr o p p in g systems stu d y t o : 12 1 . d e t e r m in e t h e e f f e c t o f c u l t i v a t i o n on t h e c o n t e n t and p r o p o r t i o n o f h y d r o l y z a b l e and n o n hy dr o ly za bl e forms o f N 2 . determine the p a t te r n o f p r o f i l e d i s t r i b u t i o n of o r g a n i c m a t t e r , t o t a l N, and f r a c t i o n a l forms o f N in some s o i l t y p e s . MATERIALS AND METHODS Experimental S i t e s Three p a i r s o f s o i l p r o f i l e s from c u l t i v a t e d s o i l s and t h e i r v i r g i n a n a l o g u e s were sampled. Each p a i r o f p r o f i l e s was l o c a t e d s i d e by s i d e on t h e same s o i l t y p e . The c u l t i v a t e d s o i l p r o f i l e s had been unde r one ty p e o f management o r a n o t h e r c o n t i n u o u s l y f o r a t l e a s t ten y e a rs . The v i r g i n - f o r e s t e d s o i l p r o f i l e s had mixed v e g e t a t i o n f o r upwards o f 50 y e a r s . L o c a ti o n and d e s c r i p t i o n o f p r o f i l e p a i r s a r e given in Table 1. So il Sampling Twenty c o r e s were comp osi ted f o r t h e s u r f a c e h o r i z o n s ( 0 - 0 . 15m) from c u l t i v a t e d and v i r g i n p r o f i l e s . co m po sit ed f o r each s u b s o i l h o r i z o n . V ir g in and c u l t i v a t e d members o f each p a i r were sampled on t h e same day. in Tabl e 1. Twelve c o r e s were Depths sampled a r e shown All samples were s c r e e n e d t o remove most undecayed and p a r t l y decayed p l a n t r e s i d u e s , a i r - d r i e d , g r oun d, and s t o r e d f o r analysis. La b o r a to r y Analyses So il pH was measured with pH m e te r u s i n g a g l a s s e l e c t r o d e on a 1 :1 s o i l - t o - w a t e r suspension. 13 14 Tabl e 1. Lo c a ti o n L o ca tio n and management o f s o i l s , d e s c r i p t i o n o f p r o f i l e s , and pH and ca r b o n c o n t e n t o f sampled s o i l d e p t h s . So il Type Management Depth pH m Cultivated (corn-beansugar beet rotation) 0 . 00-0 .15 7. 8 14 0 . 15-0 .23 7.8 6 0 . .38 7. 8 8 0 . 00-0 .08 6.5 49 0 . 08-0 .15 6 .6 24 0 . 15-0 .23 6.5 20 0 . 23-0 .30 6.5 17 0 . 30-0 .38 6 .8 12 C ultivated (A lfalfa-grass sod) 0 . 00-0 .15 5.6 26 0 . 15-0 .23 6 .8 20 V ir g in (Forest) 0 . 00-0 .08 5.3 28 0 . 08-0 .15 5. 0 30 0 . 15-0 .23 4.9 25 0 . 23-0 .30 6 .8 23 0 o 1 o o Charity clay . .15 6.5 5 0 . 15-0 .23 6.4 1 0.00-0.15 5. 2 29 0.15-0.23 4.8 9. 9 0.23-0.41 4.8 4.3 V ir g in (Forest) Barry County Ingham County Kalamazoo sandy loam Hodunk sandy loam g/k g O 1 CO CM Saginaw County Organic C C ultivated (Potatocornc or n) V ir g in (Forest) 15 Tot al K je ld ah l N was det erm ine d by t h e semimicro K je l d ah l methods d e s c r i b e d by Bremner ( 6 ) , Bundy and Bremner ( 4 ) , and Bremner and Mulvaney ( 7 ) . E a s i l y o x i d i z e d o r g a n i c C was det er m in e d by c o l o r i m e t r i c method d e s c r i b e d by S c h u l t e ( 3 4 ) . This method i n v o l v e s chromic a c i d o x i d a t i o n f o r d e t e r m i n a t i o n o f e a s i l y o x i d i z e d m a t e r i a l th ro ug h s po n ta n eo us h e a t . The method was s t a n d a r d i z e d a g a i n s t t h e Walkley- Black method (5 2 , 5 3 ) . C/N r a t i o was ta ke n a s t h e r a t i o o f t o t a l N t o o r g a n i c C. T o t a l h y d r o l y z a b l e N, no nh y d r o ly za b le N, and h y d r o l y z a b l e N f r a c t i o n s , t o i n c l u d e ammonium N, a-amino a c i d N, hydroxyamino a c i d ( s e r i n e + t h r e o n i n e ) N and h y d r o l y z a b l e unknown N were de t e r m in e d by t h e methods d e s c r i b e d by Bremner (5) and Stevenson ( 4 2 , 4 5 , 4 6 , 4 7 , 49). All a n a l y s e s were done in d u p l i c a t e and t h e v a l u e s r e p o r t e d a r e t h e means. more th a n 5%. Analy se s were r e p e a t e d where t h e d u p l i c a t e s v a r i e d RESULTS AND DISCUSSION D i s t r i b u t i o n s o f N in V ir g in and C u l t i v a t e d P r o f i l e s Tot al K je ld ah l N and Organic Carbon Organic carbon and t o t a l K jel dah l N c o n t e n t s and t h e i r d i s ­ t r i b u t i o n s in t h r e e Michigan s o i l p r o f i l e s a r e shown in Ta bl e ?.. At a l l t h r e e l o c a t i o n s , q u a n t i t i e s p r e s e n t a t each sampling dept h were s u b s t a n t i a l l y lower in c u l t i v a t e d th an in v i r g i n s o i l . The d e c l i n e s in t o t a l N and o r g a n i c carb on were r e l a t i v e l y g r e a t e r in t h e C h a r i t y and Hodunk s o i l s th a n in t h e Kalamazoo. These d i f f e r e n c e s would a p p e a r t o r e f l e c t d i f f e r e n c e s in management, r a t h e r th an d i f f e r e n c e s in g e n e t i c p r o p e r t i e s o f s o i l s (T ab l e 1 ) . The Kalamazoo had been p r o t e c t e d by a c o v e r o f a l f a l f a and g r a s s p a s t u r e f o r 7 y e a r s p l u s manure in t h e r e c e n t p a s t — 1980, whereas t h e C h a r i t y was s u b j e c t t o t i l l a g e each y e a r o f t h e r o t a t i o n and a l s o t h e Hodunk during th e th r e e years of the r o t a t i o n . The pH d a t a in Tabl e 1 i n d i c a t e t h a t t h e c u l t i v a t e d Hodunk s o i l may have been limed more h e a v i l y o r r e c e n t l y th a n t h e Kalamazoo soil. The h i g h e r pH o f c u l t i v a t e d C h a r i t y and Hodunk s o i l s would have been more f a v o r a b l e f o r m i c r o b i a l p o p u l a t i o n s t h a t decompose crop r e s id u e s . A l a r g e r p r o p o r t i o n o f annual carb on a d d i t i o n s would have been l o s t a s COg, and t h e n e t m i n e r a l i z a t i o n o f N would have been greater. Losses o f N from t h e s o i l s would have o c c u r r e d ma inly through 17 T a b l e 2. D O r g a n i c c a r b o n and t o t a l K j e l d a h l n i t r o g e n i n c u l t i v a t e d and v i r g i n s o i l p r o f i l e s . Charity clay Kalamazoo sandy loam e p t h ----------------------------- --------------------------------------N+ OC C/N N OC C/N m — g/kg- — — g/kg — Hodunk sandy loam ----------------------------N OC C/N — g/kg— C ultivated 0.00-0.15 1.3 0.15-0.23 0. 87 6.7 8 0.23-0.38 0.53 8.4 16 14 11 2.4 26 11 0.8 4 5.6 7 1 .6 20 13 0.46 1.7 4 — — — 3.4 29 9 2.4 2. 9 30 10 0.74 9.9 13 0 .4 2 4.3 10 — — — — V ir g in 0.00-0.08 4.9 49 0.08-0.15 2. 7 24 0.15-0.23 1.9 20 11 2. 4 25 10 0.23-0.30 1.5 17 11 1.9 23 12 0.30-0.38 1. 4 12 — — — 10 9 9 — 28 12 = Tot al K je ld ah l n i t r o g e n ; OC = Organic c a r b o n ; C/N = Carbonnitrogen r a ti o 13 removal in h a r v e s t e d c r o p s , a l t h o u g h l o s s e s by v o l a t i l i z a t i o n d e n i t r i f i c a t i o n , e r o s i o n o r l e a c h i n g may have o c c u r r e d a l s o . The C/N r a t i o o f t h e c u l t i v a t e d Hodunk 0 - 0 . 15m and 0 . 1 5 0.23m de pt h counterpart. was much lowe r tha n a t t h e same d e p t h s in i t s v i r g i n This d i f f e r e n c e may r e f l e c t t h e f a c t t h a t t h e p r o f i l e s were sampled in l a t e f a l l a f t e r h a r v e s t o f corn and b e f o r e i n c o r ­ p o r a t i o n o f any s u r f a c e r e s i d u e s . Changes in C/N w ith depth s u g g e s t t h a t d i f f e r e n t g e n e t i c h o r i z o n s may have i n t e r c e p t e d d i f f e r e n t p r o p o r t i o n s o f n i t r o g e n o u s t o ca r b o n a ce o u s compounds o r complexes moving downward in p e r c o l a t i n g water. There a r e n o t enough d a t a t o g e n e r a l i z e on t h i s p o i n t , however. F r a c t i o n a l Forms o f N F r a c t i o n a l d i s t r i b u t i o n s o f N in v i r g i n and c u l t i v a t e d p r o f i l e s a r e p r e s e n t e d in Ta bl es 3 thr ough 9. In a l l c a s e s , t h e q u a n t i t i e s found a t a l l d e p t h s were markedly lower in c u l t i v a t e d th a n in v i r g i n s o i l s . In a l l p r o f i l e s , t h e q u a n t i t i e s d e c r e a s e d with each in c re m en t o f d e p t h , e x c e p t f o r t h e d e e p e s t samples in t h e v irg in Charity clay. At t h i s s i t e , s i m i l a r q u a n t i t i e s o f a-amino a c i d N ( T ab l e 5 ) , amino s u g a r N (Tab le 7 ) , and n o n h y d r o l y z a b l e N ( Ta bl e 9) were found in t h e 0 . 2 3 - 0 . 30m and 0 . 3 0 - 0 . 38m d e p t h s . Thus, t h e d e p l e t i n g e f f e c t s o f c u l t i v a t i o n e x t e n d e d down­ ward f o r c o n s i d e r a b l e d e p t h s in t h e s e p r o f i l e s and a f f e c t e d a l l N fractions. However, d i f f e r e n t f r a c t i o n a l forms d e c r e a s e d a t d i f ­ f e r e n t r a t e s , r e s u l t i n g in wide v a r i a t i o n in p e r c e n t a g e d i s t r i b u t i o n o f N forms in t h e d i f f e r e n t d e p t h s . 19 T a b l e 3. C o n t e n t and d i s t r i b u t i o n o f t o t a l h y d r o l y z a b l e N in c u l t i v a t e d and v i r g i n s o il p r o f i l e s . Depth Charity clay m Kalamazoo sandy loam pgN/g ugN/gt % Hodunk sandy loam ygN/g % C ultivated 0.00-0.15 llll 87.9 2167 89.9 699 83 .1 0.15-0.23 674 77.5 1273 80.6 366 79.0 0.23-0.38 531 82.4 V ir g in 0.00-0.08 3728 7 4 .8 2735 80.4 1895 77.9 0.08-0.15 2307 87.0 2253 77. 7 541 72.8 0.15-0.23 1663 86.3 1898 80.4 306 71.3 0.23-0.30 1359 8 8 .8 1549 81.5 — — 0.30-0.38 1159 85.8 — — — — + ugN/g s o i l . t Percent of to ta l K j e l d a h l N. 20 Table 4. C o n t e n t and d i s t r i b u t i o n o f h y d r o l y z a b l e ammonium N in c u l t i v a t e d and v i r g i n s o i l p r o f i l e s Depth Charity clay ugN/gt m % \ Kalamazoo sandy loam ugN/g % Hodunk sandy loam u gN/g % C ultivated 0.00-0.15 343 27.1 517 21.4 0.15-0.23 248 28.5 335 2 1 .2 0.23-0.38 216 33.5 188 22.3 97 20.9 Vi rg in 0.00-0.08 811 16 .2 597 17.5 375 15.4 0.08-0.15 668 25.2 577 19.9 149 2 0 .0 0.15-0.23 525 27.2 521 2 2 .0 57 13.3 0.23-0.30 462 30.2 383 2 0 .1 -- — 0.30-0.38 426 31.5 — — — — ^ygN/g s o i l . t Percent of to ta l Kjeldahl N 21 T a b l e 5. C o n t e n t and d i s t r i b u t i o n o f a - a m i n o a c i d N in c u l t i v a t e d and v i r g i n s o i l p r o f i l e s Depth Charity clay MgN/g+ m Kalamazoo sandy loam ugN/g % Hodunk sandy loam ugN/g % Cultivated 0.00-0.15 349 27.6 832 34.5 182 2 1 .6 0.15-0.23 230 26 .4 484 3 0. 6 150 32.3 0.23-0.38 214 33.2 Virgin 0.00-0.08 1586 31.8 1149 33.7 785 32.3 0.08-0.15 904 34. 1 809 27 .9 246 33 .1 0.15-0.23 682 3 5. 3 634 26.9 127 29.6 0.23-0.30 452 2 9. 5 555 29. 2 — — 0.30-0.38 507 3 7. 5 — — — — ^ugN/g s o i l . Percent of to ta l K j e l d a h l N. 22 Table 6. C o n t e n t and d i s t r i b u t i o n o f s e r i n e and t h r e o n i n e (hy d ro x y am in o a c i d ) N in c u l t i v a t e d and v i r g i n s o i l profiles Depth Charity clay u g N /g t m ** Kalamazoo sandy loam ygN/g Hodunk sandy loam ygN/g % 7. 0 59 7.0 6 .0 40 8 .6 151 6 .2 % Cultivated 0.00-0.15 156 12.3 170 0.15-0.23 55 6.3 95 0.23-0.38 59 9.2 Vi rg in 0.00-0.08 324 6.5 246 7. 2 0.08-0.15 202 7. 6 198 6 .8 59 7.9 0.15-0.23 143 7. 4 147 6 .2 44 1 0 .2 0.23-0.30 107 6.9 127 6 .6 — — 0.30-0.38 79 5. 8 — — — ty g N /g s o i l . ^ P e r c e n t o f t o t a l Kjeldahl N. — 23 T a b l e 7. C o n t e n t and d i s t r i b u t i o n o f amino s u g a r N in c u l t i v a t e d and v i r g i n s o i l p r o f i l e s Charity clay Depth m u g N /g t Kalamazoo sandy loam ugN/g % Hodunk sandy loam pgN/g % C ultivated 0.00-0.15 144 11.4 233 9.7 67 7. 9 0.15-0.23 94 1 0 .8 134 8.5 55 1 1 .8 0.23-0.38 94 14.6 V ir g in 0.00-0.08 444 8.9 383 11.3 194 7.9 0.08-0.15 228 8 .6 272 9.3 50 6.7 0.15-0.23 178 9.2 255 1 0 .8 55 1 2 .8 0.23-0.30 144 9.4 211 1 1 .1 — — 0.30-0.38 155 11.5 — — — — fp gN /g s o i l . | Percent of to ta l K j e l d a h l N. 24 Table 8. C o n t e n t and d i s t r i b u t i o n o f h y d r o l y z a b l e unknown N(HUN)+ i n c u l t i v a t e d and v i r g i n s o i l p r o f i l e s Depth Charity clay m MgN/g* % Kalamazoo sandy loam § ygN/g % Hodunk sandy loam ugN/g % C ultivated 0.00-0.15 275 2 1 .7 585 24.3 262 31.1 0.15-0.23 102 11.7 320 2 0 .2 64 1 2 .8 2 2 .2 0.23-0.38 7 1 .1 V ir g in 0.00-0.08 887 17. 8 606 17.8 541 0.08-0.15 507 19.1 595 20. 5 96 12.9 0.15-0.23 278 14.4 488 2 0 .6 67 15.6 0.23-0.30 301 19.6 400 2 1 .0 — -- 0.30-0.38 71 5.2 — - - — — *HUN = T o t a l h y d r o l y z a b l e N minus (ammonium N + a-amino a c i d + hydroxyamino a c i d N + amino s u g a r N). JrygN/g s o i l . £ P e r c e n t o f t o t a l K je ld ah l N. 25 Table 9. Depth + C ontent and d i s t r i b u t i o n o f no n h y d ro ly zab le N v a t e d and v i r g i n s o i l p r o f i l e s C harity clay m ugN/gt % § Kalamazoo sandy loam ugN/g % in c u l t i ­ Hodunk sandy loam ygN/g % Cultivated 0.00-0.15 153 1 2 .1 243 1 0 .0 142 16.8 0.15-0.23 196 2 2. 5 307 19.4 97 20.9 0.23-0.38 113 17.5 V irgin 0.00-0.08 1256 25.2 665 19.5 537 2 2 .0 0.08-0.15 343 12.9 647 22.3 202 2 7 .2 0.15-0.23 264 13.7 462 19.6 123 23. 7 0.23-0.30 171 1 1 .2 351 18.6 — — 0.30-0.38 191 14.1 — — — — ^ N o n h y d r o ly z a b le N - Total Kjel dah l N minus t o t a l h y d r o l y z a b l e N. $ pgN/g s o i l . § P e r c e n t o f t o t a l K je ld ah l N. 26 In t h e c u l t i v a t e d p r o f i l e s , t o t a l h y d r o l y z a b l e N a s p e r c e n t o f t o t a l Kjel dah l N in each d ep th d e c r e a s e d below t h e 0.0.15m la y e r (Table 3). A s i m i l a r r e d u c t i o n o c c u r r e d below t h e 0 - 0 . 08m l a y e r in t h e v i r g i n Kalamazoo and Hodunk s o i l s , whereas an i n c r e a s e o c c u r r e d below t h e 0 . 0 8 - 0 . 15m l a y e r in t h e C h a r i t y . Changes in t h e p r o p o r t i o n o f n o n h y d r o ly z a b le N (Ta bl e 9) w e r e , o f c o u r s e , r e l a t e d i n v e r s e l y t o t h e s e changes in t h e t o t a l f o r h y d r o l y z a b l e for ms. Sharp i n c r e a s e in i l l u v i a l (subsurface) l a y e r p r o b ab ly r e p r e s e n t n i t r o g e n o u s m a t e r i a l s i n t e r c e p t e d and r e t a i n e d a s r e s i s t a n t polymers and complexes. The p r o p o r t i o n o f h y d r o l y z a b l e NH^ (Tab le 4) i n c r e a s e d w ith d e p t h in t h e C h a r i t y p r o f i l e s and t h e v i r g i n Kalamazoo. Such i n c r e a s e s have been r e p o r t e d f r e q u e n t l y (2 9, 30) and o f t e n a t t r i b u t e d t o r e l e a s e d u r i n g a c i d h y d r o l y s i s o f c l a y - f i x e d NH^ ( 4 , 17, 26 , 29, 30 , 38 , 4 1 , 44, 4 8 ) . R e l e a s e o f NhJ d u r i n g h y d r o l y s i s from l a b i l e am id e s , imino compounds, and c e r t a i n a-am ino a c i d s a s t r y p t o p h a n e mi ght a l s o be e x p e c t e d t o i n c r e a s e w ith dep th ( 2 , 6 , 26, 3 8 ) . Except in t h e v i r g i n C h a r i t y s o i l , h y d r o l y z a b l e NH^ te nded t o va r y d i r e c t l y w it h C/N r a t i o . Th is r e s u l t would a g r e e w it h r e p o r t s t h a t f i x e d Nh J and C/N both i n c r e a s e w ith d ep th ( 1 7 ) , b u t i s a t v a r i a n c e w ith o t h e r s where t h e p e r c e n t a g e o f t o t a l N as h y d r o l y z a b l e NH^ v a r i e d i n v e r s e l y w it h C/N r a t i o ( 1 0 ) . No c o n s i s t e n t p a t t e r n s o f change w ith dept h were o b s er v ed f o r a-amino a c i d s ( T a b l e 5) o r hydroxyamino a c i d s ( Ta bl e 6 ). There was some t e n de n cy f o r amino s u g a r s t o i n c r e a s e r e l a t i v e t o TKN in t h e 27 de e p e r h o r i z o n s , a s has been r e p o r t e d by o t h e r s (3 0 , 41 , 5 0 ) . p r o p o r t i o n o f h y d r o l y z a b l e unknown N (HUN) (Table 8 The ) te n d e d to d e c r e a s e with d ep th in a l l b u t t h e v i r g i n Kalamazoo p r o f i l e . This d e c r e a s e was s h ar p in t h e lower d e p t h s o f t h e C h a r i t y c l a y . I t would a p p e a r t h a t t h e l e v e l o f TKN, a s well a s t h e d i s ­ t r i b u t i o n o f f r a c t i o n a l forms in t h e s e p r o f i l e s r e p r e s e n t s a dynamic e q u i l i b r i u m a t each de p th between t h e r a t e o f a d d i t i o n o f C and N ( a s p l a n t d e b r i s o r mo bi le m a t e r i a l s e l u v i a t e d from above) and t h e r a t e of removal (by m i n e r a l i z a t i o n and l e a c h i n g o r by c o n v e r s i o n o f one f r a c t i o n a l form t o a n o t h e r ) . E f f e c t s o f C u l t i v a t i o n on D i s t r i b u t i o n o f N in S u r f a c e S oil Layers Changes in Tot al K je l d a h l N D i s t u r b a n c e o f s o i l s by t i l l a g e i n c r e a s e d p o r o s i t y and a e r a t i o n , t h e r e b y i n c r e a s i n g t h e r a t e o f dec o m p os it io n o f p l a n t residues. Breakdown o f a g g r e g a t e s by s o i l - w o r k i n g equipment a l s o exposes p r e v i o u s l y p r o t e c t e d m a t r i x s u r f a c e s to i n t e r a c t i o n w it h t h e m i c r o b i a l biomass and w i t h chemical systems in p e r c o l a t i n g s o i l water. As a r e s u l t , a l a r g e r p r o p o r t i o n o f t h e n a t i v e s o i l o r g a n i c m a t t e r can e n t e r i n t o a c t i v e c y c l e s of m o b i l i z a t i o n - i m m o b i l i z a t i o n t u r n o v e r ( 2 1 , 28, 3 2 ) . The r a t e o f r e c y c l i n g and e x t e n t t o which t h e r e l e a s e o f m i n e r a l i z e d N can oc cu r may be enhanced f u r t h e r when m i c r o b i a l a c t i v i t y i s s t i m u l a t e d by a d d i t i o n s o f lime t o u n f a v o r a b l y acid s o ils . The above im pa ct s o f c u l t i v a t i o n a r e e x p r e s s e d d i r e c t l y on s u r f a c e l a y e r s t h a t a r e a c t u a l l y d i s t u r b e d by t i l l a g e o p e r a t i o n s . 28 In Tabl e 10, r e c o v e r i e s of N and p e r c e n t a g e d i s t r i b u t i o n s o f f r a c ­ t i o n a l f o rm s, as t h e means f o r s u r f a c e l a y e r s t o 0.15m in v i r g i n s o i l s , a r e compared with v a l u e s found in t h e plow l a y e r ( 0 - 0 . 15m) of th e ir c u ltiv a te d counterparts. I t can be c a l c u l a t e d from t h e s e d a t a t h a t t h e magnitude o f t o t a l Kjeldahl N l o s s e s a t t r i b u t a b l e t o c u l t i v a t i o n was above 67% in t h e C h a r i t y c l a y and 65% in t h e Hodunk sandy loam. These v a l u e s compare w ith d e c l i n e s o f 60 t o 70% o b s e r v e d a f t e r 80 t o 100 y e a r s under m od e ra te l y i n t e n s i v e t o i n t e n s i v e management systems in t h e p r a i r i e s and g r e a t p l a i n s o f midwestern U.S.A. ( 1 3 , 15, 16, 18). In t h e c i t e d s t u d i e s , o r g a n i c m a t t e r and N in s u r f a c e s o i l s d e c r e a s e d a t a d e c l i n i n g r a t e o v e r a p e r i o d o f 60 t o 80 y e a r s , a f t e r which a new e q u i l i b r i u m was e s t a b l i s h e d between annual i n p u t s and l o s s e s o f C and N. The p e r c e n t a g e d e p l e t i o n o f s o i l o r g a n i c m a t t e r and N ( t o t h e p o i n t where redu ce d l e v e l s became s t a b l e ) v a r i e d d i r e c t l y with c u l t i v a t i o n i n t e n s i t y and i n v e r s e l y with such f a c t o r s as t h e p r o p o r t i o n o f legumes in t h e r o t a t i o n , t h e l e v e l o f amendment w ith animal manures and f e r t i l i z e r s and t h e l e v e l o f cr o p y i e l d s maintained. The c u l t i v a t e d s o i l s a t a l l t h r e e s i t e s in t h e p r e s e n t s tud y had pr o b ab ly been c l e a r e d and b r o u g h t un d er c u l t i v a t i o n a t l e a s t 75 y e a r s ago. The f a c t t h a t t w o - t h i r d s o f t h e N i n i t i a l l y p r e s e n t had a p p a r e n t l y d i s a p p e a r e d from t h e plow l a y e r s o f C h a r i t y and Hodunk s o i l s i n d i c a t e t h a t t h e s e two s o i l s had a t t a i n e d s t a b l e e q u i l i b r i u m un d er d e p l e t i v e r o t a t i o n s i n v o l v i n g ma inly c u l t i v a t e d T a b l e 10. D i s t r i b u t i o n o f o r g a n i c N f r a c t i o n s in c u l t i v a t e d and v i r g i n s u r f a c e ( 0 . 0 0 - 0 . 15m) s o i l s Soil Type » TKNf H yd ro iyz abl e N________________________ Management THn AN AAN ASN yg/gt yg / g % yg /g 3817 1264 3016 1111 79.0 87.9 738 343 19.3 27.1 1245 349 32.6 27.6 336 144 3150 2410 2493 2167 79.1 89 .9 587 517 18.6 21.4 979 832 31 .0 34 .5 Vi rg i n Cultivated 2432 841 1895 679 77.9 8 0 .7 375 188 15.4 22.3 785 162 Means V irg in 3133 2468 78.8 567 17.8 Means C u l t i v a t e d 1505 1319 87.6 349 23.6 % NHN ™ / HUN NHN yg /g 8 .8 697 275 18.4 21.7 801 153 20.9 11.4 327 233 10.3 9.7 600 585 19.0 24.3 657 243 20.9 32. 3 19.3 194 67 7.9 7.9 541 262 2 2 .2 537 162 2 2 .0 31.1 19.3 3.5 4.2 1003 3 2. 0 286 9.0 613 19.6 665 2 1 .2 3. 7 448 27.1 148 9.7 374 25.7 186 13.8 7.1 % yg /g % % % yg/g yg / g Charity clay V ir gi n 3 Cultivated 12.1 3.8 7.3 Kalamazoo sandy loam Vir gin Cultivated 1 0 .0 3.8 8.9 Hodunk sandy loam TKN = Total Kjeldahl N; THN = Total h y d r o l y z a b l e N; AN = Ammonium N; AAN = a-a m in o a c i d N; ASN = amino s u g a r N; HUN = h y d r o l y z a b l e unknown N; HNH = Nonhydrolyzable N; THN/NHN = Total h y d r o l y z a b l e N:n on hyd ro lyz ab le N r a t i o . ug/g = ygN/g s o i l ; % = p e r c e n t o f t o t a l Kjeldahl N. V ir gi n s o i l , av e r a g e o f 0 . 0 0 - 0 . 08m and 0 . 0 8 - 0 . 15m; C u l t i v a t e d s o i l , 0 . 0 0 - 0 . 15m. 30 c r o p s (Ta bl e 1 ) . on ly 23°/. The c a l c u l a t e d l o s s f o r t h e Kalamazoo s o i l was Management h e r e would a p p e a r t o have been much l e s s d e p l e t i v e , a t l e a s t in r e c e n t y e a r s . I t i s n o t known what c r o p p in g systems may have been used a t t h e s e s i t e s o v e r t h e decades s i n c e th e y were f i r s t c l e a r e d . The a l f a l f a - g r a s s c o v e r had been in p l a c e on t h e Kalamzaoo s o i l f o r 8 y e a r s p l u s manure in t h e r e c e n t p a s t . Normally, annual e q u i l i b r i a und er f o r a g e legumes and g r a s s e s a r e s h i f t e d in t h e d i r e c t i o n o f n e t i n c r e a s e s in s o i l o r g a n i c m a t t e r and N. I t may be i n f e r r e d t h a t t h e c u l t i v a t e d Kalamazoo was in a " s o i l b u i l d i n g " r a t h e r th a n a " s o i l d e p l e t i n g " c y c l e a t t h e time t h e s e samples were t a k e n . Changes in F r a c t i o n a l Forms o f N The q u a n t i t i e s o f t o t a l K jel dah l N and a l l f r a c t i o n a l forms in s u r f a c e l a y e r s ( T ab l e 10) were very much lower in t h e c u l t i v a t e d tha n v i r g i n s o i l s . However, t h e d e c r e a s e s w i t h i n f r a c t i o n a l forms were n o t p r o p o r t i o n a l t o t h e d e c r e a s e s in t o t a l K je l d a h l N. This may be seen in F i g s . 1, 2, and 3 , where t h e p e r c e n t d e c r e a s e w i t h i n f r a c t i o n s i s e n t e r e d b e s i d e each p a i r o f b a r s d e p i c t i n g c o n t e n t . In a l l t h r e e s o i l s , t h e p e r c e n t d e c r e a s e in t h e NHN f r a c t i o n ( n o t h y d r o l y z a b l e in 6 M HC1) was very much g r e a t e r th a n t h e o v e r a l l d e c r e a s e in t o t a l Kjel dah l N, whereas t h e d e c r e a s e in t o t a l hyd ro ­ l y z a b l e N (THN) was l e s s . These d i f f e r e n t i a l d e c r e a s e s in F i g s . 1 t o 3 a r e r e f l e c t e d in t h e p e r c e n t a g e d i s t r i b u t i o n s in Ta bl e 10. p r o p o r t i o n o f t o t a l K jel dah l N s u s c e p t i b l e to h y d r o l y s i s (THN) The SOIL) 5 .0 4 .5 N FORMSCMG/ G 4 .0 CHRRITY CLRY V 3 .5 3 .0 2 .5 OF 1. 5 CONTENT 2.0 1. 0 V 57'. ■ 0.0 TKN THN RN NITROGEN Fig. 1 . ■ ■ IB 0.5 RRN RSN HUN NHN FORMS Conte nt o f o r g a n i c N f r a c t i o n s in c u l t i v a t e d (C) and v i r g i n (V) s u r f a c e ( 0 - 0 . 15m) in a C h a r i t y c l a y s o i l . Numbers b e s i d e each p a i r o f b a r s i n d i c a t e s % d e c r e a s e due t o c u l t i v a t i o n . TKN = t o t a l Kjel dah l N; THN = t o t a l h y d r o l y z a b l e N; AN = h y d r o l y z a b l e ammonium N; AAN = amino a c i d N; ASN = amino s u g a r N; HUN = h y d r o l y z a b l e unknwon N; NHN = n o n h yd r ol y za b le N. KRLRMRZOO SRNDY LORM OF N FORMSCMG/ G SOIL) 5 .0 CO CONTENT V V 23* TKN THN RN RRN NITROGEN Fig . 2 Content o f o r g a n i c N f r a c t i o n s in c u l t i v a t e d a Kalamazoo sandy loam s o i l . Numbers b e s i d e due t o c u l t i v a t i o n . TKN = t o t a l Kjel dah l N; h y d r o l y z a b l e ammonium N; AAN = amino a c i d N; unknown N; NHN = n o n h y dr o ly za bl e N. RSN HUN NHN FORMS (C) and v i r g i n (V) s u r f a c e ( 0 - 0 . 15m) in each p a i r o f b a r s i n d i c a t e % d e c r e a s e THN = t o t a l h y d r o l y z a b l e N; AN = ASN = amino s u ga r N; HUN = h y d r o l y z a b l e SOIL) 4 .5 HODUNK SRNDY LORM 4 .0 FORMS 3 .0 N 2 .0 OF 3 .5 1.5 CONTENT CMG/G 5 .0 1. 0 2 .5 V 65* w CO CO 0 .5 V 0.0 TKN THN RN RRN NITROGEN Fig. 3 65* Co ntent o f o r g a n i c N f r a c t i o n s in c u l t i v a t e d in a Hodunk sandy loam s o i l . Numbers b e s i d e due t o c u l t i v a t i o n . TKN = t o t a l Kjel dah l N; h y d r o l y z a b l e ammonium N; AAN = amino a c i d N; unknown N; NHN = n on hy dr o ly za b le N. RSN HUN NHN FORMS (C) and v i r g i n (V) s u r f a c e ( 0 - 0 . 15m) each p a i r o f b a r s i n d i c a t e % d e c r e a s e THN = t o t a l h y d r o l y z a b l e N; AN = ASN = amino s u g a r N; HUN = h y d r o l y z a b l e 34 i n c r e a s e d , w h i l e t h e p e r c e n t a g e n o t hy d ro ly ze d (NHN) d e c r e a s e d . As a r e s u l t , t h e r a t i o THN/NHN i n c r e a s e d from 3 . 8 in t h e v i r g i n C h a r i t y c l a y t o 7.3 in th e c u l t i v a t e d c o u n t e r p a r t , and from 3 . 8 t o 8 . 9 in t h e Kalamazoo s o i l . The i n c r e a s e from t h e Hodunk sandy loam was l e s s , from 3 . 5 f o r v i r g i n t o 4 . 2 in c u l t i v a t e d s o i l . Among t h e h y d r o l y z a b l e forms in Table 10, t h e p e r c e n t a g e d i s t r i b u t i o n o f h y d r o l y z a b l e NH^ (AN) and t h e h y d r o l y z a b l e unknown (HUN) f r a c t i o n i n c r e a s e d in a l l t h r e e c u l t i v a t e d s u r f a c e s o i l s . The p r o p o r t i o n o f t o t a l K je ld ah l N p r e s e n t as a-amino a c i d s (AAN) in t h e c u l t i v a t e d Kalamazoo had i n c r e a s e d a l s o , b u t had d e c l i n e d s h a r p l y w ith t i l l a g e in t h e C h a r i t y and Hodunk s o i l s . Decreased p r o p o r t i o n s o f amino s u g a r N-(ASN) and s e r i n e + t h r e o n i n e N (STN) were found in t h e c u l t i v a t e d C h a r i t y , b u t t h e i r c o n t r i b u t i o n t o t o t a l K jel dah l N in t h e o t h e r two s o i l s was e s s e n t i a l l y unchanged to t i l l a g e . An im p o r ta n t e f f e c t o f c u l t i v a t i o n i s t h e d i s r u p t i o n o f a g g r e g a t e d s t r u c t u r e s and t h e e x p os u r e o f p r e v i o u s l y p r o t e c t e d humic s u b s t a n c e s t o t h e a c t i o n o f s o i l microbes and chemical sy stems in the so il s o lu tio n (28). Modeling s t u d i e s i n d i c a t e t h a t 50% o f t h e humus in v i r g i n s o i l s may be p r o t e c t e d by a d s o r p t i o n o r en t ra p m e n t in t h e s o i l m a t r i x , whereas t h e de gr ee o f p r o t e c t i o n in s o i l s under c u l t i v a t i o n may be as low as 10% (32). The l a r g e d e c r e a s e s (63 t o 81%) in t h e NHN c o n t e n t o f a l l t h r e e s o i l s (Figs. 1 t o 3) u n do ub te d ly r e f l e c t t h e i n c r e a s e d exp os ur e and d e c r e a s e d s t a b i l i t y o f humic s u b s t a n c e s p r e v i o u s l y s t a b i l i z e d by a d s o r p tio n , p o lym eriza tion, condensation or entrapment. 35 These d e c r e a s e s in NHN were accompanied by r e l a t i v e l y much s m a l l e r d e c r e a s e s in h y d r o l y z a b l e NH^ (AN) and t h e unknown (HUN) fr a c tio n (Figs. 1 to 3). As t h e r e s u l t o f t h e s e d i f f e r e n t i a l d e c r e a s e s in c o n t e n t , t h e AN and HUN f r a c t i o n s a c t u a l l y i n c r e a s e d a s p e r c e n t o f t o t a l K jel dah l N in c u l t i v a t e d s o i l s (Tab le 10 ). I t i s g e n e r a l l y a g r e e d t h a t t h e N t h a t i s no t h y d r o ly z e d by 6 M HC1 (NHN f r a c t i o n ) e x i s t s ma inly in th e form o f s t a b l e humic a c i d s and humin; w h er ea s , t h e h y d r o l y z a b l e AN and HUN f r a c t i o n s o r i g i ­ n a t e in f u l v i c a c i d s and l e s s t i g h t l y bound p e r i p h e r a l g r o u p in g s in humic a c i d s and humin ( 3 2 , 4 7 , 51 ) . As an a v e r a g e f o r a l l t h r e e s o i l s , t h e r a t i o s AN/NHN and HUN/NHN i n c r e a s e d by a f a c t o r o f 2 (Tabl e 11). This a g a i n r e f l e c t s i n c r e a s e d exp os ur e and d e c r e a s e d s t a b i l i t y o f humic s u b s t a n c e s due t o c u l t i v a t i o n . Sim ilar r e l a t i o n ­ s h i p s have n o t been p o i n t e d o u t by o t h e r a u t h o r s , a l t h o u g h i n s t a n c e s can be found in p u b l i s h e d d a t a where l a r g e l o s s e s o f t o t a l N have o c c u r r e d due t o c u l t i v a t i o n ( 2 4) . F r a c t i o n a l C o n t r i b u t i o n s t o Total Kjel dah l N Loss In Fig . 4 , f r a c t i o n a l d e c r e a s e s have been r e p r e s e n t e d as p e r c e n t o f t o t a l Kjeldahl N l o s s . In t h e C h a r i t y and Hodunk s o i l s , t h e a p p a r e n t c o n t r i b u t i o n o f t h e v a r i o u s f r a c t i o n s t o l o s s was r o u g h ly p r o p o r t i o n a l t o t h e q u a n t i t i e s and p r o p o r t i o n s p r e s e n t before c u l tiv a t io n (Ta b le 10 and F i g s . 1 and 3 ) . This r e s u l t is s im ila r to the experience of other in v e stig a tio n s (24, 29). The r e s u l t s with t h e Kalamazoo s o i l were s t r i k i n g l y d i f f e r ­ e n t (Fig. 4 ). The d e c r e a s e in t h e NHN f r a c t i o n a c c o un te d f o r 36 Table 11. E f f e c t o f c u l t i v a t i o n on NH^ and u n i d e n t i f i e d N in a c i d h y d r o l y s a t e s in r e l a t i o n t o n o n h y d r o ly z a b le N. Soil Type AN/NHN' -------------------------------------Virgin C ultivated HUN/NHN -------------------------------------V ir g in C ultivated Charity clay 0.9 2 .2 0.9 1 .8 Kalamazoo sandy loam 0.9 2 .1 0.9 2.4 Hodunk sandy loam 0.7 1.3 1.9 1 .8 Means 0 .8 1.9 0.9 2 .0 +AN = h y d r o l y z a b l e NH^ N, HUN = h y d r o l y z a b l e unknown N, NHN = n o n h y d r o l y z a b l e N. STN ASN CHARITY clay (Corn-bean-sugar beet) HODUNK sandy loam (potato-corn-corn KALAMAZOO sandy loam (alfalfa-grass sod) o * co HYDROLYZABLE N NONHYDROLYZABLE N PERCENT OF TOTAL N LOSS Fig. 4. Decrease in c o n t e n t of o r g a n i c N f r a c t i o n s e x p r e s s e d a s l o s s due t o c u l t i v a t i o n . percent of to ta l N AN = h y d r o l y z a b l e N, AAN = a-amino a c i d N, STN = s e r i n e + t h r e o n i n e N, ASN = amino s ug ar N, HUN = h y d r o l y z a b l e unknown N, NHN = no nh yd ro ly za bl e N. ■vi 38 o n e - h a l f o f t h e t o t a l K je l d ah l N l o s t from t h e v i r g i n s o i l . The a p p a r e n t p e r c e n t c o n t r i b u t i o n s o f AN, AAN, and HUN were much l e s s than in t h e o t h e r two s o i l s and were a l s o much l e s s th an t h e i r o r i g i n a l p r o p o r t i o n o f t o t a l K je l d a h l N ( T ab l e 1 0 ) . as percent of to ta l D ecr eas es in ASN and STN, l o s s in t h e Kalamazoo ( F i g . 4 ) , were s i m i l a r to t h e i r p e r c e n t a g e o f t o t a l K je l d ah l N b e f o r e c u l t i v a t i o n . P atterns of lo ss a t the th ree loc atio n s are c l e a r ly re la te d t o d i f f e r e n c e s in c u r r e n t management a n d , p e r h a p s , a l s o t h e s o i l pH (Tab le 1). I t i s n o t known how long t h e c u l t i v a t e d Kalamazoo s o i l had been in a l f a l f a - g r a s s a t t h e ti m e o f s a m p l in g . I t i s a p p a r e n t in F i g . 2 t h a t un d er t h e p r o t e c t i o n a f f o r d e d by sod c o v e r r e s i d u e s and e x u d a t e s from t h e l e g u m e - g r a s s m i x t u r e were s u p p o r t i n g a sp ectrum of N in h y d r o l y z a b l e forms t h a t was v e ry s i m i l a r t o t h a t in t h e v i r g i n soil. The annual r a t e o f r e t u r n o f N was such t h a t t h e d e g r e e of d e p l e t i o n o f a l l h y d r o l y z a b l e forms was ve r y much l e s s th a n in t h e C h a r i t y c l a y ( F i g . 1) o r t h e Hodunk sandy loam ( F i g . 3 ) . The de gr ee o f d e p l e t i o n o f t h e NHN f r a c t i o n in t h e c u l t i ­ v a t e d Kalamazoo sandy loam was much g r e a t e r than f o r t h e h y d r o l y z a ­ ble f r a c t i o n (Fig. 2). Thi s may be r e s i d u a l e v i d e n c e o f more d e p l e t i v e management in t h e p a s t , in which ca s e t h e l e v e l s found in h y d r o l y z a b l e forms would r e p r e s e n t r e c o v e r i e s from more d e p l e t e d le v e ls p rio r to the establishm ent of the a l f a l f a - g r a s s stand. It would a p p e a r t h a t i n p u t s o f N due t o N £ - f i x a t i o n by t h e a l f a l f a may have e q u i l i b r a t e d q u i c k l y with h y d r o l y z a b l e f r a c t i o n s , whereas 39 f u r t h e r c o n v e r s i o n t o s t a b l e humic complexes may n o t have had time t o proceed to e q u i l i b r i u m a t a l e v e l o f NHN ap p r o a c h in g more c l o s e l y t h a t in t h e v i r g i n s o i l . The a p p a r e n t f r a c t i o n a l c o n t r i b u t i o n s t o t o t a l K jel dah l N l o s s a s c a l c u l a t e d f o r F i g . 4 s e r v e t o f o c u s on changes t h a t can be i n t e r p r e t e d u s e f u l l y in te rm s o f e q u i l i b r i u m s h i f t s due t o d e p l e t i v e v s . c o n s e r v a t i v e management p r a c t i c e s . O b v i o u s l y , th ey do n o t pr o ­ v i d e any b a s i s f o r j u d g i n g w he th er one form o f N i s more s u s c e p t i b l e t o m i n e r a l i z a t i o n th an a n o t h e r , and t h e r e f o r e , more s i g n i f i c a n t a s a s o u r ce o f " a v a i l a b l e N" f o r c r o p s . Comparison o f F i g . 4 with F ig s . 1, 2 , and 3 does i n d i c a t e t h a t t h e h y d r o l y z a b l e f r a c t i o n s respond more q u i c k l y t o chang es in management and a r e t h e r e f o r e more " a c t i v e " th an m a t e r i a l s t h a t a r e n o t h y d r o ly z e d by a c i d . SUMMARY AND CONCLUSIONS E f f e c t s o f c u l t i v a t i o n on o r g a n i c m a t t e r c o n t e n t and on d i s t r i b u t i o n s o f N in h y d r o l y z a b l e and n o n h y d ro ly z a b le forms were a s s e s s e d by comparing d a t a f o r p a i r e d v i r g i n and c u l t i v a t e d p r o f i l e s a t three locations. D ec r ea s es in o r g a n i c carb on and t o t a l Kjel dah l N in c u l t i ­ v a t e d s u r f a c e s o i l s and u n d e r l y i n g s u b s o i l l a y e r s were r e l a t e d t o t h e i n t e n s i t y o f c u r r e n t management. In a co r n - n av y b e a n - s u g a r b e e t r o t a t i o n on C h a r i t y c l a y , o r g a n i c C in t h e plow l a y e r was red u ce d 62% from t h a t in t h e wooded v i r g i n s o i l t o t h e same d e p t h . f o r a p o t a t o - c o r n - c o r n se quence on Hodunk was 80%. The r e d u c t i o n By c o n t r a s t , o r g a n i c C in Kalamazoo sandy loam u n d e r a l f a l f a - g r a s s sod was only 13% l e s s th a n und er f o r e s t c o v e r . C or r es pon din g d e c r e a s e s in t o t a l Kjel dah l N were 67% and 65% f o r t h e C h a r i t y and Hodunk s o i l s and 23% f o r t h e Kalamazoo. D ecr eas es in t h e n o n h y d r o l y z a b l e f r a c t i o n were s u b s t a n t i a l l y g r e a t e r : 81% and 70% f o r t h e two c u r r e n t l y t i l l e d s i t e s and 63% f o r t h e sodded Kalamazoo. As a r e s u l t , t h e p r o p o r t i o n o f n o n h y d r o ly z a b le N t o t o t a l K je ld ah l N in c u l t i v a t e d s o i l s was redu ce d by a p p r o x i m a t e l y 40%. r e d u c t i o n and a c o r r e s p o n d i n g r e l a t i v e i n c r e a s e in t h e p r o p o r t i o n s o f h y d r o l y z a b l e NH^ and u n i d e n t i f i e d N were ta ken a s e v i d e n c e t h a t 40 This 41 t h e s t a b i l i t y o f humic a c i d s and humin had been weakened ( t h e i r h y d r o l y z a b i l i t y i n c r e a s e d ) by i n c r e a s e d ex p os u re a t m a t r i x s u r f a c e s r e s u l t i n g from d i s t u r b a n c e by t i l l a g e o p e r a t i o n s in a l l t h r e e l o c a ­ tions. E f f e c t s o f c u r r e n t management became s t r i k i n g l y a p p a r e n t when f r a c t i o n a l d e c l i n e s were e x p r e s s e d a s p e r c e n t a g e s o f t o t a l Kjel dah l N l o s s . Under d e p l e t i v e cash cr o p systems on C h a r i t y and Hodunk s o i l s , a p p a r e n t c o n t r i b u t i o n s o f t h e v a r i o u s f r a c t i o n a l forms to t o t a l l o s s were r ou gh ly p r o p o r t i o n a l t o q u a n t i t i e s and p r o p o r t i o n s p r e s e n t b e f o r e c u l t i v a t i o n , w i t h t h e major p r o p o r t i o n coming from t h e a-amino a c i d f r a c t i o n . By c o n t r a s t , i n p u t s o f N f i x e d by a l f a l f a in t h e Kalamazoo s o i l had s u p p o r t e d a spec tru m o f N in h y d r o l y z a b l e f r a c t i o n s t h a t was s i m i l a r t o t h a t in t h e v i r g i n s o i l s . The a p p a r e n t p e r c e n t c o n­ t r i b u t i o n s o f a-amino a c i d s , h y d r o l y z a b l e NH^ and u n i d e n t i f i e d N were much l e s s th a n in t h e o t h e r two s o i l s and l e s s a l s o th a n t h e i r o r i g i n a l p r o p o r t i o n o f t o t a l Kjel dah l N. I t i s con cluded t h a t a c i d h y d r o l y z a b l e f r a c t i o n s i n c l u d e " a c t i v e " forms t h a t respond q u i c k l y t o changes in c u r r e n t management. Changes i n v o l v i n g s t a b l e humic s u b s t a n c e s in t h e n o n h y d r o l y z a b l e f r a c t i o n a p p a r e n t l y proceed much l e s s r a p i d l y and may r e f l e c t p a s t management. I t i s u n l i k e l y , however, t h a t s u s c e p t i b i l i t y t o a c i d h y d r o l y s i s can p r o v i d e a b a s i s f o r e s t i m a t i n g t h e a v a i l a b i l i t y o f N forms t o c r o p s w i t h o u t some b a s i s in known management h i s t o r y f o r ju d g i n g w h et h er s o i l s a r e in a d e p l e t i v e o r c o n s e r v a t i v e phase of management. LITERATURE CITED 1. A d e r i k h i n , P. 6 . , Ye P. Ti khova, V. P. Kulahov, and N. Ya D e g ty r areva. 1960. 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An e x am in at io n o f methods f o r d e t e r m i n i n g o r g a n i c carb on and n i t r o g e n in s o i l s . J . Agr. S c i . 25: 598-609. 53. Walkley, A . , and I . A. Bla ck . 1934. An e x a m in a t io n o f t h e D e g t j a r e f f method f o r d e t e r m i n i n g s o i l o r g a n i c m a t t e r and a prop os ed m o d i f i c a t i o n o f t h e chromic a c i d t i t r a t i o n method. So il S c i . 3 7 :2 9 -3 7 . A. R a f t e r . 1981. Chemistry occurring r e s i s t a n t organic A. Paul and J . N. Ladd ( e d s . ) . Marcel Dekker, I n c . , N . J . CHAPTER I I I INFLUENCE OF CROPPING SYSTEMS ON FORMS OF NITROGEN IN A CLAY SOIL Organic m a t t e r and n i t r o g e n c o n t i n u e t o p la y s i g n i f i c a n t r o l e s in s o i l f e r t i l i t y and cr o p p r o d u c t i o n . M a in t a in i n g and improv­ ing t h e f e r t i l e and p r o d u c t i v e s t a t u s o f a g r i c u l t u r a l s o i l s r e q u i r e s t e a d y , b u t a d e q u a t e , r e t u r n o f o r g a n i c m a t t e r as cr o p r e s i d u e s to t h e s o i l th ro ugh a pla nn ed i n t e n s i v e management p r a c t i c e . But i n t e n ­ s i v e c u l t i v a t i o n r e s u l t s in d e t e r i o r a t i o n o f s o i l p r o p e r t i e s which a r e c o s t l y and d i f f i c u l t t o r e p a i r . The d e g r a d a t i o n o f s o i l is often a t t r i b u t e d t o a gradu al d e c l i n e in o r g a n i c m a t t e r which t e n d s towards e q u i l i b r i u m w ith ti m e . and " d e p o s i t o r s . " Moreover, c r o p s a r e a c t u a l n u t r i e n t "miners" They a r e a l s o p o t e n t i a l t o x i n " e x c r e t e r s . " T h e r e f o r e , a planned s e l e c t i o n and s eq uen ci ng o f c r o p s i s d e s i r a b l e in term s o f a d e q u a t e min era l n u t r i t i o n , a l l e l o p a t h i c e f f e c t s of one cr o p s p e c i e s on a n o t h e r and y i e l d s . The e f f e c t i v e n e s s o f a c r o p p in g system in m a i n t a i n i n g o r g a n i c m a t t e r and N depends on t h e crop s p e c i e s in t h e r o t a t i o n , t h e C/N r a t i o o f t h e r e s i d u e s , d u r a t i o n o f r e s i d u e a p p l i c a t i o n , and i n c o r ­ p o r a t i o n method. E f f e c t s o f cr op s p e c i e s and c r o p p in g sequence on o r g a n i c m a t t e r and N a r e due t o d i f f e r e n c e s in r o o t i n g h a b i t s and in q u a n t i t y and q u a l i t y o f r e s i d u e s r e t u r n e d . 47 For example, carbon ac eou s 48 r e s i d u e s low in N a r e decomposed by m ic r oo r ga ni s m s a t t h e expen se o f a v a i l a b l e s o i l N (2 4 ) . Studies of the e f f e c t o f r o t a t i o n s in d ic a te d t h a t organic m a t t e r and t o t a l N l o s s e s were l e a s t in r o t a t i o n s t h a t in c l u d e d small g r a i n s and legumes with l a r g e o r f r e q u e n t amendments w ith l i v e s t o c k manures a n d / o r f e r t i l i z e r s p l u s lime a s needed ( 1 0 , 12, 22, 2 3 ) . Loss es were g r e a t e s t in c o n t i n u o u s row c r o p p i n g w it h l i t t l e o r no a p p l i c a t i o n o f s o i l amendments ( 1 , 8 , 16, 2 7 ) . In a n o t h e r s t u d y , c o n t i n u o u s w hea t, b l u e g r a s s and l a d i n o cl o v e r - o r c h a r d g r a s s p a s t u r e i n c r e a s e d o r g a n i c m a t t e r w hi le c o n t i n u o u s so ybeans and co r n reduced i t o v e r time ( 4 2 ) . All t r e a t m e n t s showed N l o s s e x c e p t where peas were r o t a t e d w ith w i n t e r whe at. In t h e same s t u d y a l l t r e a t m e n t s r e s u l t e d in o r g a n i c m a t t e r g a i n s e x c e p t p l o t s in permanent f a l l o w and t h o s e cropped 2 y e a r s with one i n t e r v e n i n g f a l l o w in r o t a t i o n on a c l a y loam s o i l in Utah ( 1 1 ) . a 25-year S t u d i e s on t h e d r y l a n d s o i l s o f Kansas, from 1916 t o 1956 (9) d e m o n s t r a t e d t h a t small g r a i n s grown c o n t i n u o u s l y o r a l t e r n a t i n g w it h f a l l o w ca us ed t h e s m a l l e s t N and o r g a n i c m a t t e r l o s s e s compared t o c o n t i n u o u s row c r o p , a l t e r n a t e row c r o p , and f a l l o w which showed t h e g r e a t e s t ( 1 5 ) . L ittle infor­ ma tion i s a v a i l a b l e on r o t a t i o n s t h a t i n c l u d e c o r n , navy b e a n s , s u g ar b e e t s in v a r i o u s c o m b in a ti o n s . The t y p e s o f c r o p s grown do a f f e c t t h e d e g re e o f o r g a n i c m a t t e r and N m a in te n a n ce . However, i n v e s t i g a t o r s have a l s o r e p o r t e d t h a t s p e c i f i c management p r a c t i c e s , such as f e r t i l i z a t i o n , t i l l a g e p r a c t i c e s , and r e s i d u e a p p l i c a t i o n , may be more s i g n i f i c a n t in main­ t a i n i n g o r g a n i c m a t t e r and t o t a l N th a n t h e crop s p e c i e s . 49 In t h e i r 54- t o 7 2 - y e a r s t u d y , White e t a l . (46) r e p o r t e d t h a t NPK a p p l i c a t i o n was more e f f e c t i v e in m a i n t a i n i n g o r g a n i c m a t t e r and N l e v e l s o ve r ti m e in t h e c o n t i n u o u s l y c u l t i v a t e d t h a n in the adjacent grassland s o ils . In a l a t e r 1 0 -y e a r s t u d y , Lee and Bray (18) r e p o r t e d t h a t t h e o v e r a l l t r e n d o f a b s o l u t e N l o s s w ith t i m e was e v i d e n t in a l l t r e a t m e n t s , a l t h o u g h PK f e r t i l i z a t i o n a p p e a r e d t o m a i n t a i n t h e o r g a n i c m a t t e r and N c o n t e n t s a t h i g h e r l e v e l s r e l a ­ t i v e to the u n tre a te d p l o t s . They c o nc lu d ed t h a t a p p l i c a t i o n s o f more f e r t i l i z e r might have i n c r e a s e d t h e o r g a n i c m a t t e r and N c o n t e n t s . These f i n d i n g s a p p e a r t o have been conf irm ed by t h e work o f Mazurak and Conrad ( 2 0 ) . They found t h a t a p p l i c a t i o n o f N f e r t i l i z e r s on g r a s s e s , a l f a l f a , and s m a l l - g r a i n s i n c r e a s e d t h e t o t a l N c o n t e n t o f Brunizem, Chernozem, and C h e s t n u t s u r f a c e s o i l s ov er a 7 - y e a r cr o p p in g history. However, l a r g e a p p l i c a t i o n s o f NPK and l i m e , in a n o t h e r l o n g - t e r m s t u d y on 3 s o i l t y p e s , showed c o n t i n u i n g d e c l i n e in t o t a l N w it h time ( 2 1 ) . In a n o t h e r s t u d y , Young e t a l . (47) found t h a t t o t a l N and OM c o n t e n t d e c l i n e d r e g a r d l e s s o f t h e f e r t i l i z e r t r e a t m e n t , b u t t h e r a t e o f d e c l i n e was g r e a t e r in t h e check p l o t s th a n in th o s e t h a t received the f e r t i l i z e r treatm ent. In g e n e r a l , t h e s e s t u d i e s i n d i c a t e t h a t t h e e f f e c t i v e n e s s o f f e r t i l i z a t i o n in m a i n t a i n i n g l e v e l s o f N and o r g a n i c m a t t e r o v e r time may vary w id el y w ith cr o p p in g sy st em , s o i l t y p e , and c l i m a t i c c o n d i ­ tions. O th er i n v e s t i g a t i o n s have examined t h e r o l e o f t i l l a g e p r a c t i c e s in m a i n t a i n i n g o r g a n i c m a t t e r and t o t a l N. In g e n e r a l , l o s s e s o f o r g a n i c m a t t e r and N a r e r e p o r t e d f o r t i l l a g e p r a c t i c e s t h a t g r e a t l y 50 d i s t u r b s o i l s t r u c t u r e o r l e a v e t h e s o i l u n p r o t e c t e d by- v e g e t a t i o n o r r e s i d u e s f o r p e r i o d s o f time ( 1 2 , 14, 23, 4 3 ) . The d e g r e e o f d e p l e t i o n i n c r e a s e s with i n c r e a s i n g i n t e n s i t y and f r e q u e n c y o f t i l l a g e and w it h d e c r e a s i n g p r o p o r t i o n o f sod c r o p s , n o t a b l y legumes, in t h e r o t a t i o n s . C u r r e n t p r a c t i c e s a r e r e - e m p h a s i z i n g t h e need t o a d o p t n o - t i l l o r minimum t i l l a g e p r a c t i c e s a s a measure f o r o r g a n i c m a t t e r and N m a in te n a n ce . In cr op r o t a t i o n s , each crop in t h e seq uen ce a f f e c t s t h e p h y s i c a l , c h e m i c a l , and b i o l o g i c a l p r o p e r t i e s o f t h e s o i l degrees. in v a r y in g Changes in s o i l p r o p e r t i e s a f f e c t t h e growth and y i e l d o f su cc ee d in g c r o p s . An i m p o r t a n t way t h a t c r o p s a f f e c t s o i l p r o p e r t i e s i s t h e r e t u r n o f o r g a n i c m a t t e r a s cr o p r e s i d u e s a f t e r h a r v e s t o f t h e crops. In t h e r o t a t i o n , t h e t y p e and amount o f cr o p r e s i d u e s r e t u r n e d a n n u a l l y a f f e c t t h e c o n t e n t and p r o p o r t i o n o f t h e v a r i o u s o r g a n i c N f r a c t i o n s due t o d i f f e r e n c e s in cr o p c o m p o s i t i o n , decomposi­ t i o n r a t e s and s u i t a b i l i t y a s s u b s t r a t e s f o r t h e m i c r o b i a l p o p u l a t i o n . Cropping se q ue n ce s and management p r a c t i c e s t h a t m a i n t a i n h ig h t u r n o v e r r a t e s th ro ugh f r e q u e n t r e t u r n o f carb o na ce o us r e s i d u e s te n d t o i n c r e a s e t h e c o n t e n t s o f s o i l o r g a n i c m a t t e r and n i t r o g e n and change t h e r e l a t i v e p r o p o r t i o n s and c o m p o s i ti o n o f t h e i r v a r i o u s fractions. In g e n e r a l , changes in o r g a n i c N f r a c t i o n s a r e p r o p o r ­ t i o n a l t o s i g n i f i c a n t changes in s o i l o r g a n i c m a t t e r and t o t a l N. However, v a r i a t i o n s in f r a c t i o n a l d i s t r i b u t i o n can be o b s e r v e d in t h e a b s en ce o f s i g n i f i c a n t d i f f e r e n c e s in o r g a n i c m a t t e r and t o t a l s o i l N. Thi s i s i m p o r t a n t in s h o r t - t e r m s t u d i e s where r e m a r k a b le 51 d i f f e r e n c e s in t o t a l s o i l N due t o c ro pp in g sequence and r e s i d u e a d d i t i o n s may n o t be n o t i c e d , b u t t h e p r o p o r t i o n s o f t h e v a r i o u s o r g a n i c forms may v a r y s i g n i f i c a n t l y . A b so l u te c o n t e n t s o f t h e s e o r g a n i c forms vary w id e l y in s o i l s and v a r i a t i o n s a r e n o t o n ly due t o t h e q u a l i t y and q u a n t i t y o f crop r e s i d u e s , b u t a l s o due t o d i f f e r e n c e s in e x t r a c t i o n , f r a c t i o n a t i o n , and p u r i f i c a t i o n p r o c e d u r e s . Of t h e t o t a l s o i l N, 30 t o 50% o c c u r a s amino a c i d N, 5 t o 24% as amino s u g a r s , and 20 t o 35% a s a c i d i n s o l u b l e N ( 2 , 6 , 3 0 , 34, 35, 36, 4 1 ) . In a l o n g - t i m e r o t a t i o n s tu d y on a Flanagan s i l t loam (Br uni ze m) , t h e c o r n - o a t s - c l o v e r r o t a t i o n with annual a p p l i c a t i o n s o f f ar my ar d manure and c r o p r e s i d u e s had a h i g h e r p r o p o r t i o n o f t h e t o t a l N a s amino a c i d N th an t h e c o n t in u o u s co r n and c o r n - o a t s r o t a t i o n s w i t h o u t manure and r e s i d u e a d d i t i o n s ( 3 3 ) . d i s t r i b t u i o n o f amino a c i d s v a r i e d w ith r o t a t i o n s . The r e l a t i v e However, i t was n o t a p p a r e n t from t h i s s tu d y whe ther t h e o b s er v ed d i f f e r e n c e s were due t o t h e i n c l u s i o n o f c l o v e r in t h e r o t a t i o n , t h e a d d i t i o n o f manure and cr o p r e s i d u e s , o r a com bination o f b o t h . The p r o p o r t i o n s o f t o t a l N as amino a c i d N and amino s u g a r N in s o i l s from a 5 - y e a r r o t a t i o n o f g r a i n s and legumes were s i g n i f i ­ c a n t l y g r e a t e r th a n t h o s e from a w h e a t - f a l l o w system even though t h e r e were no re m a r k a b le d i f f e r e n c e s in t o t a l s o i l N ( 1 7 ) . Thi s st u d y i n d i c a t e d t h a t legumes in a r o t a t i o n make a s i g n i f i c a n t con­ t r i b u t i o n t o t h e f o r m a t i o n o f n i t r o g e n o u s compounds in s o i l s . Cropping syst ems can a l s o have a s i g n i f i c a n t e f f e c t on t h e k i n d s of amino a c i d s in t h e amino a c i d f r a c t i o n o f t h e s o i l (31). On t h e 52 o t h e r han d, i t has been r e p o r t e d t h a t t h e i n c o r p o r a t i o n o f leguminous r e s i d u e s te n d e d t o lower t h e a-amino a c i d N due t o more com plete d e g r a d a t i o n o f t h e amino a c i d s in t h e crop r e s i d u e s compared to c a r b o n a c e o u s r e s i d u e s such a s corn ( 1 3 ) . Under f i e l d c o n d i - t i o n s , in d e p e n d e n t e f f e c t s o f crop r e s i d u e s a r e d i f f i c u l t t o s e p a r a t e from t h e e f f e c t s o f s e v e r a l o t h e r e n v i r o n ­ mental v a r i a b l e s . In r o t a t i o n s t u d i e s , t h e e f f e c t s a t t r i b u t e d to crop r e s i d u e s a r e c u m u l a t i v e f o r p r e v i o u s t r e a t m e n t s in t h e p a r t i c u l a r c r o p p i n g se q u e n c e . F u r th e r m o re , a c c u r a t e measurements o f amounts r e t u r n e d a n n u a l l y by each crop t y p e in t h e se quence a r e ha rd t o come by. Only e s t i m a t e s a r e used t o i n t e r p r e t r e s u l t s in most r e s i d u e s t u d i e s in c r o p p in g syst ems un d er f i e l d c o n d i t i o n s . In t h i s s t u d y , t h e c r o pp in g systems in v o l v e a l f a l f a , navy b e a n s , c o r n , and s u g a r b e e t s , o c c u r r i n g from 25 t o 75% o f t h e time in t h e r o t a t i o n . 1. The o b j e c t i v e s o f t h i s i n v e s t i g a t i o n were: To d e t e r m i n e t h e i n f l u e n c e o f cr o p p in g systems on t h e changes in s o i l o r g a n i c m a t t e r and t o t a l N with ti m e in a C h a r i t y c l a y . 2. To d e t e r m i n e t h e c o n t e n t , p r o p o r t i o n , and r e l a t i v e change o f o r g a n i c N f r a c t i o n s as i n f l u e n c e d by v a r i o u s c r o p p i n g s ys te m s . MATERIALS AND METHODS F i e l d Experiment A c r o p p i n g system r e s e a r c h p r o j e c t was i n i t i a t e d in 1972 on t h e Bean and B eet Research Farm in t h e Saginaw V a ll e y o f Michigan. The o b j e c t i v e s o f t h e s t u d y were: 1. To d e t e r m in e t h e e f f e c t o f r o t a t i o n l e n g t h , c r o p p i n g s y s t e m , and cr o p p in g sequence on p r o ­ d u c t i o n , y i e l d , and q u a l i t y o f navy beans and sugar beets 2. To e v a l u a t e t h e e f f e c t o f t h e s e systems on s p e ­ c i f i c s o il p r o p e r ti e s r e l a t e d to y i e l d . The seven c r o p p in g systems in t h i s i n v e s t i g a t i o n were s e l e c t e d from tw el v e c r o p p i n g systems in t h e whole r e s e a r c h p r o j e c t . in c l u d e d t h e f o l l o w i n g c r o p s : They corn ( Zea mays L . ) , s u g a r b e e t s ( Beta v u l g a r i s L . ) , navy beans ( Phas eol us v u l g a r i s L . ) , o a t s (Avena s a t i v a L . ) , and a l f a l f a (Medicago s a t i v a L . ) . 1. C-Bn-Bn-SB 2. C-C-Bn-SB 3. C-C-C-SB 4. C-SB 5. Bn-SB 6. 0-A-Bn-SB 7. 0-Bn-SB The s e l e c t e d systems were: C = Corn; Bn = Navy b e a n s ; SB = Sugar b e e t s ; 0 = o a t s ; A = A lfalfa 53 54 The co m p lete se quence o f c r o p s in each r o t a t i o n was grown each year. All c r o p s r e c e i v e d a d e q u a t e PgOg and m i c r o n u t r i e n t s bas ed on soil t e s t le v e ls . No a d d i t i o n a l f e r t i l i z e r K was a p p l i e d due t o an adequate so il t e s t K l e v e l . Annual N a p p l i c a t i o n s and c r o p s f o r each y e a r in t h e r o t a t i o n a r e i n d i c a t e d on T ab l e 1. The p l o t s ( 5 . 7 3 x 20.12m) were l a i d o u t on a C h a r i t y c l a y in a randomized c o m p le te bl o c k d e s i g n w it h 4 r e p l i c a t i o n s . S o i l Type The s o i l t y p e was a C h a r i t y c l a y ( A e r i e , H a p le a q u e p t, f i n e , i l l i t i c , c a l c a r e o u s , m e si c ) (Appendix B3). t h e g e n e r a l r e s e a r c h a r e a were: The s o i l t e s t r e s u l t s f o r pH, 7 . 7 ; Bray Pj p h o s p h o r u s , 38 k g /h a ; ex c h a n g e a b le K, 506 k g / h a ; ex ch a n g ea b le Ca, 11,267 k g / h a ; exc ha ng ea b le Mg, 1, 852 k g /h a and p e r c e n t o r g a n i c m a t t e r , 4 . 3 ( 2 6 ) . So il Sampling In J u n e , 1972, 20 c o r e samples were randomly ta k en from t h e plow l a y e r ( 0 - 0 . 2 3 m) o f each p l o t . All p l o t s which had been in t h e c r o p s l i s t e d f o r 1983 Ta b l e 1 were sampled a g a i n in November, 1983. A c o m p os it e sample f o r ea ch p l o t was o b t a i n e d a f t e r p a s s i n g t h e c o r e samples th r o u g h a 5 mm s c r e e n . from t h e sa mp le s. S u r f a c e r e s i d u e s were removed The a i r - d r i e d samples were f i r s t ground t o pass th ro ug h a 2 mm s i e v e and a l i q u o t s were th e n ground t o p as s an 0 .1 8 mm s i e v e b e f o r e be in g u sed f o r t h e v a r i o u s a n a l y s e s . 4* Crops grown and supplem ental N a p p lie d t o crop p in g system s from 1972 t o 1983 Crop o S u p p l. N Crop Su p p l. N Crop k g /h a k g /h a k g /h a C-SB Bn-•SB S u p p l. N Crop k g /h a c 1 S u p p li N -SB 0-A-Bn-SB S u p p l. N Crop S u p p l. N C 150 Bn 30 C 150 C 150 Bn 30 0 56 1973 Bn 28 SB 50 C 168 SB 50 SB 84 A 1974 Bn 28 C 224 C 106 C 224 Bn 28 1975 SB 50 C 140 Sb 50 SB 1976 C 168 Bn 28 C 224 C 224 1977 Bn 28 SB 56 C 168 SB 1978 Bn 28 C 168 C 168 C 1979 SB 56 C 168 SB 56 SB 1980 C 168 Bn 128 C 168 C 1981 Bn 28 SB 56 C 168 SB 1982 Bn 28 C 168 C 168 C 1983 SB 56 C 168 SB 56 SB + SB 1 Each c r o p in e a c h c r o p p in g s y s t e m was grown e a c h y e a r . November 1 9 83. | SOURCE: R ese a rc h R e p o r t s . 1972 t o 1 9 8 3 . MSU, A g r . - Exp. S t n . -SB S u p p l. N k g /h a 0 56 0 Bn 28 Bn 28 SB 50 84 SB 50 0 56 Bn 28 0 56 Bn 28 56 SB 84 A 0 SB 56 224 Bn 28 Bn 28 0 56 56 SB 84 SB 56 Bn 28 224 Bn 28 0 56 SB 56 56 SB 84 A 0 0 56 224 Bn 28 Bn 28 Bn 28 56 SB 84 SB 56 SB 56 S am ples f o r t h i s s t u d y w ere t a k e n in June 1972 and C = Corn; Bn = Navy b e a n s ; SB - s u g a r b e e t s ; 0 = O a t s ; A = § N in b a s a l f e r t i l i z e r a t p l a n t i n g : Crop k g /h a k g /h a 1972 50 CO Crop Year C-C-Bn--SB o C-Bn--Bn-Sb1* 0 1 0 1 Table 1. A lfa lfa C o rn , 4 0 ; b e a n s , 6 0 ; b e e t s , 3 0 ; o a t s , 3 0 ; a l f a l f a , none Saginaw V a l l e y b e a n - b e e t - r e s e a r c h farm and r e l a t e d b e a n - b e e t r e s e a r c h , 56 L a b o r a t o r y Analyses Total K je ld ah l N was de t e r m in e d by semimicro Kjel dah l methods d e s c r i b e d by Bremner ( 3 ) , Bundy and Bremner ( 7 ) , and Bremner and Mulvaney ( 5 ) . E a s i l y o x i d i z e d o r g a n i c C was de te rm in e d by c o l o r i m e t r i c method d e s c r i b e d by S c h u l t e ( 2 8 ) . Thi s method i n v o l v e s chromic a c i d o x i d a t i o n f o r d e t e r m i n a t i o n o f e a s i l y o x i d i z e d m a t e r i a l throug h sp on ta n eo us h e a t . The method was s t a n d a r d i z e d a g a i n s t t h e Walkely- Black method (4 4 , 4 5 ) . O rg an ic m a t t e r was ta ken by m u l t i p l y i n g %C by 1. 724. C/N r a t i o was t a k e n a s t h e r a t i o o f t o t a l N t o C. Tot al h y d r o l y z a b l e N(THN), h y d r o l y z a b l e ammonium N (AN), amino a c i d N (AAN), amino s u g a r N (ASN), h y d r o l y z a b l e unknown N (HUN), and n o n h y d r o ly z a b le N (NHN) were d e t e r m in e d by methods d e s c r i b e d by Bremner (4) and Ste ve ns on ( 3 7 , 3 8 , 4 0 ) . S t a t i s t i c a l Analyses Data were s u b j e c t e d t o a n a l y s i s o f v a r i a n c e and o t h e r e s s e n ­ t i a l a n a l y s e s u s i n g methods d e s c r i b e d by Snedecor and Cochran ( 2 9 ) , S t e e l and T o r r i e (32) and L i t t l e and H i l l s ( 1 9 ) . RESULTS AND DISCUSSION E f f e c t o f Cropping System on t h e D i s t r i b u t i o n o f N Over Time Changes in T ot al K j e l d a h l N and Organic Carbon The c o n t e n t s o f o r g a n i c carb on and t o t a l K je ld ah l N in 1972 and a f t e r 11 y e a r s o f r o t a t i o n a l c r o p p in g a r e shown in Tabl e 2. The q u a n t i t i e s were low er i n 1983 th a n in 1972 in a l l cr o p p in g s y st em s . The d e c l i n e o f t o t a l K je l d a h l N and o r g a n i c ca rb on due t o c ro p pi n g ranged from 5. 9 t o 10.5% and 12.3 t o 17.0%, r e s p e c t i v e l y . This r e p r e s e n t s 0 . 5 t o 1.0% l o s s o f N and 1.1 t o 1.5% l o s s o f o r g a n i c carbon annually over th e 11-year cropping period. This compares w it h 1.07% and 1.15% annual l o s s o f s o i l N and o r g a n i c C, r e s p e c t i v e l y , o ve r a 3 7 - y e a r c r o p p i n g p e r i o d in t h e G r e a t P l a i n s ( 1 2 ) . I n f o r m a t i o n c o n­ c e r n i n g c r o p p in g p r a c t i c e s p r i o r t o 1972 i s n o t a v a i l a b l e . The small d e c l i n e o f s o i l N and o r g a n i c carb on a p p e a r s t o i n d i c a t e t h e e s t a b ­ l i s h m e n t o f e q u i l i b r i u m between t h e r a t e o f annual i n p u t s and l o s s e s . The C/N r a t i o s d e c l i n e d in a l l cr o p p in g systems o ve r t i m e . The av e r a g e C/N change r a t i o o f 0 . 9 0 was very s i m i l a r t o t h e v a l u e s f o r t h e i n d i v i d u a l c r o p p i n g sy ste m s ( T ab l e 2 ) . Although o r g a n i c carb on and s o i l N d e c r e a s e d o v er t i m e , t h e p e r c e n t a g e d e p l e t i o n d i d n o t a p p e a r t o vary s i g n i f i c a n t l y among t h e cr o p p in g s y s t e m s . Th is a p p e a r e d t o i n d i c a t e t h a t a l l t h e c r o pp in g 57 Table 2. Cropping System E f f e c t o f c ro pp in g system on t o t a l Kjeldahl N and o r g a n i c carbon l e v e l s and ca rb o n n i t r o g e n r a t i o in a C h a r i t y c l a y s o i l . C:N 0.C + Change 1972 C:N 1972 1983 C-Bn-Bn-SB 16.8 14.7 -12.5 9.33 8 .4 9 - 9 .0 0 0 .9 0 C-C-Bn-SB 16.5 14.4 - 1 2 .7 9.21 8.6 2 - 6.40 0.9 3 C-C-C-SB 17.6 14.7 -16.5 9. 46 8. 54 - 9.7 2 0 .9 0 C-SB 16.6 14.2 -14.5 9.54 8 .4 0 -1 1. 90 0 .8 8 Bn-SB 16.4 13.6 - 1 7. 1 8 .8 6 8. 29 - 6.43 0.93 0-A-Bn-SB 17.6 14.7 -16.5 9.83 8 .8 5 - 9.96 0.90 0-Bn-SB 16.2 13.9 -14.2 9. 36 8 .2 2 - 1 2 .2 0 0.8 7 Means 16.8 14.3 -1 4 . 9 9.3 8 8. 46 - 9 .8 0 0 .9 0 NS -- NS NS LSD0.05 NS$ 1983 % Change — to .C = E a s i l y o x i d i z a b l e o r g a n i c carbon $ % Change = The p e r c e n t a g e o f mean v a l u e s with c r o p p i n g , based on i n i t i a l va l u e s § NS = Not s i g n i f i c a n t a t 9 5 % p r o b a b i l i t y l e v e l R a t io 83/72 — 59 s ys te m s , r e g a r d l e s s o f t h e p r o p o r t i o n o f corn o r legume in t h e r o t a ­ t i o n s , c o n t r i b u t e d t o a " s o i l d e p l e t i n g , " r a t h e r than a " s o i l b u i l d i n g " cycle. The e l e v e n - y e a r c r o p p i n g p e r i o d seemed s h o r t f o r s i g n i f i c a n t d i f f e r e n c e s t o o c c u r among t h e c r o p p i n g s y s t e m s , though r e a l d i f f e r ­ ences o c c u r r e d . In t h e v i r g i n - c u l t i v a t e d comparisons o f Ch ap te r I I , d e c l i n e s in o r g a n i c ca rb o n and s o i l N were l a r g e and t h e s e r e f l e c t e d d i f f e r e n c e s in i n t e n s i t y o f c u r r e n t management among t h e sampling sites. Changes in F r a c t i o n a l Forms o f N The q u a n t i t i e s and d i s t r i b u t i o n o f f r a c t i o n a l N forms a r e p r e s e n t e d in T ab l e 3. The f r a c t i o n a l forms o f N i n c r e a s e d or decreased a f t e r eleven y e a rs of cropping. The mean v a l u e s show t h a t t h e p r e s e n t d e c r e a s e o f t o t a l Kjel dah l N n o t h y d r o ly z e d by 6M HC1 (NHN) was a bo ut t h r e e times as g r e a t a s t o t a l K je ld ah l N. The p e r c e n t d e c r e a s e in t o t a l h y d r o l y z a b l e N (THN) was l e s s th a n t h a t o f t o t a l Kjel dah l N (Tab le 3 ) . The p r o ­ p o r t i o n o f TKN p r e s e n t a s n o n h y d r o l y z a b l e N d e c r e a s e d by 15%, w h i l e t h a t o f THN i n c r e a s e d by 4% (Ta bl e 4 ) . That gi ve an av er a ge i n c r e a s e in THN/NHN r a t i o from 4 . 0 in 1972 t o 5.1 in 1983 (Table 5 ) . In g e n e r a l , t h e p r o p o r t i o n o f TKN as h y d r o l y z a b l e NH^ (AN) and h y d r o l y z a b l e unknown N (HUN) i n c r e a s e d , w h il e t h a t o f amino a c i d N (AAN) and amino s u g a r N (ASN) d e c r e a s e d in most c ro p pi n g systems (Tab le 4 ) . F u r t h e r m o r e , t h e c o n c e n t r a t i o n of NHN (Tab le 3) d e c r e a se d by 20% on t h e a v e r a g e compared t o d e c r e a s e s o f 2% (THN) and 6% (TKN). Table 3. E ffe c t o f cropping system on th e co n c en tratio n of nitro g en forms and percentage change. H y d r o ly z a b le N TKN C ro p p in g S ystem 1972 C-Bn-Bn-SB THN 5 AN % I AAN Change - 4 .0 — m g/kg— 453 433 + 4 .6 1390 - 0 .8 455 424 - 6 .8 550 492 - 1 0 .5 158 1468 1479 + 0 .7 479 477 - 0 .4 603 497 - 1 7 .6 1 6 9 5 ' - 2 .9 1423 1394 - 2 .0 421 410 - 2 .6 555 467 1851 1648 - 1 0 .9 1398 1429 + 2 .2 428 410 - 4 .2 586 0-A -Bn-SB 1793 1666 - 7 .0 1484 1377 - 7 .2 404 435 + 7 .7 0-Bn-SB 1733 1696 - 2 .1 1425 1401 - 1 .6 453 399 Means 1798 1691 - 5 .8 1439 1412 - 1 .8 439 430 NS NS NS NS 4 3 .5 3 2 .2 Change 1972 1973 Change — m g/kg— 1802 1732 - 3 .9 — m g/kg— 1470 1416 C-C-Bn-SB 1798 1677 - 6 .7 1401 C-C-C-SB 1863 1727 - 7 .3 C-SB 1746 Bn-SB LSD0 .0 5 — — 1972 Change — mg/ kg— 634 449 - 2 9 .2 C hange - -m g /k g — 261 118 - 5 4 .8 — m g/kg— 396 147 152 - 3 .9 238 171 134 - 2 1 .6 - 1 5 .8 189 184 555 - 5 .3 189 577 488 - 1 5 .4 - 1 1 .9 528 510 - 1 .9 576 494 3 9 .7 NS 1972 C hange +169 — m g/kg— 332 316 - 3 .4 322 + 3 5 .3 397 287 - 2 7 .7 215 371 + 7 2 .6 395 248 - 3 7 .2 - 2 .6 258 333 + 2 9 .0 323 301 - 6 .8 155 - 1 8 .0 195 309 + 5 8 .5 453 219 - 5 1 .6 188 140 - 2 5 .5 315 314 - 0 .3 309 289 - 6 .5 - 3 .4 189 134 - 2 9 .1 255 358 + 4 0 .4 307 295 - 4 .5 - 1 3 .9 192 145 - 2 2 .2 232 343 + 5 7 .8 359 279 - 1 9 .6 — 4 5 .5 NS NS — 8 4 .4 1983 NS Change — i"TKN = T o ta l K je ld a h l n i t r o g e n Change = P e r c e n ta g e c h a n g e o f mean v a l u e s w ith c r o p p in g , b a s e d on i n i t i a l % 1983 NS 1972 NHN % % 1983 — 1983 HUN ASN 1983 1983 1972 % v a lu e s . § THN = T o ta l h y d r o ly z a b l e N; AN = h y d r o l y z a b le ammonium N; AAN = am ino a c i d N; ASN = am ino s u g a r N; HUN = h y d r o l y z a b l e unknown N; NHN = n o n h y d r o ly z a b le N. 1972 — Table 4. E ffect of cropping system on the d i s t r i b u t i o n o f to t a l Kjeldahl N among organic N f r a c t i o n s and percent change. Hydrolyzable N THNf AN AAN % % ASN % Cropping System 1972 1983 Change 1972 1983 Change 1972 1983 Change 1972 1983 C-Bn-Bn-SB % 81.6 % 81.8 + 0.2 % 24.0 X 2 6 .1 + 8 .8 % 35.2 % 25.9 -26.4 % 1 4 .5 % 6.8 C-C-Bn-SB 77.9 82.8 + 6.3 2 5 .3 25.3 0.0 30.6 29.3 - 4.2 8.8 C-C-C-SB 7 8 .8 8 5 .6 + 8.6 25.7 27,6 + 7.4 32.4 28.8 -1 1 .1 C-SB 8 1 .5 8 2 .2 + 0.8 2 4 .1 24.2 + 0.4 31.8 27.5 Bn-SB 75.5 86 .7 + 14.8 23.1 24.9 + 7.8 31.6 0-A-Bn-SB 82.7 82.6 - 0.1 22.5 26.1 +16.0 0-Bn-SB 82.2 82.6 - 0.5 2 6 .1 23.5 Means 8 0 .0 8 3 .5 + 4.3 24.4 25.4 NS NS -- NS LSD0 . 0 5 2.08 HUN Change Nonhydrolyzable N (NHN) % 1983 Change 1972 1983 Change -5 3 .1 % 8.2 % 22.8 + 1 7 8 .0 % 1 8 .4 % 1 8 .2 - 1.1 9.1 + 3.4 1 3 .2 19.2 + 45.4 22.0 1 7 .1 -22.3 9.2 7.7 -1 6 .3 11.5 21.5 + 86.9 2 1.2 1 4 .4 -3 2 .1 -1 3 .5 1 0 .8 1 0 .8 0.0 14.7 19.6 + 33.3 1 8 .5 17.8 - 3.8 33.6 + 6.3 10.2 9.4 -7 .8 10.5 18.8 - 79.0 24.5 1 3 .3 -45.7 32.2 29.3 - 9.0 1 0 .4 8.4 -19.2 1 7 .5 1 8 .8 + 7 .4 1 7 .2 1 7 .1 - 0 .6 - 9.9 30.5 30.1 - 1.3 10.9 7.9 -27.5 1 4 .7 2 1 .1 + 4 3 .5 1 7 .7 1 7 .3 - 2 .3 + 4 .3 3 2.0 29.2 8.6 10.7 8.6 -1 7 .2 1 2 .9 20.2 + 67.6 1 9 .9 16.5 -1 5 .4 NS NS — NS 2 .5 4 — 2.73 NS — 3.85 NS — *^THN = T o ta l h y d r o ly z a b le N; AN = h y d r o l y z a b l e ammonium N; AAN = am ino a c i d N; ASN = am ino s u g a r N; HUN - h y d r o l y z a b l e unknown N; NHN = n o n h y d r o l y z a b le N; TKN = t o t a l K je ld a h l N. % c h a n g e in p e r c e n t a g e d i s t i r b u t i o n o f TKN. % 1972 — T a b l e 5. E f f e c t o f c r o p p i n g sy ste m on t o t a l h y d r o l y z a b l e N (THN), h y d r o l y z a b l e ammonium (AN), and h y d r o l y z a b l e unknown N (HUN) i n r e l a t i o n t o n o n h y d r o l y z a b l e N (NHN) AN/NHN THN/NHN HUN/NHN 1972 1983 Rat io 83/72 1972 1983 Ra ti o 83/72 1972 1983 Ra ti o 83/72 C-Bn-Bn-SB 4.51 4 .4 5 0.98 1.32 1.42 1.07 0.45 1.24 1.75 C-C-Bn-SB 3.52 4.84 1.37 1.14 1.47 1.28 0.59 1.12 1.89 C-C-C-SB 3.71 6.0 5 1.63 1.21 1.95 1.61 0.54 1.51 2.79 C-SB 4 .4 0 4.6 2 1.05 1.30 1.36 1.04 0.79 1.10 1.39 Bn-SB 3.08 6.54 2 .1 2 0.94 1.87 1.98 0. 42 1.41 3 .3 5 0-A-Bn-SB 4.78 4.73 0.98 1.30 1.49 1.14 1.01 1.07 1.05 0-Bn-SB 4.62 4.73 1.02 1.46 1.35 0.92 0.82 1.21 1.47 Means 4.01 5.06 1.26 1.22 1.54 1.26 0.65 1.23 1.89 63 These t r e n d s were r e f l e c t e d by i n c r e a s e s in o v e r a l l mean AN/NHN r a t i o from 1.22 in 1972 t o 1.54 in 1983, and HUN/NHN r a t i o from 0 .6 5 in 1972 t o 1.23 in 1983 (Tab le 5 ) . These ch ang es i n d i c a t e t h a t c r o p p i n g te nd ed t o i n c r e a s e ex p os ur e t o t h e a c t i o n o f t h e s o i l b i o ­ mass and d e c r e a s e s t a b i l i t y o f p r e v i o u s l y p r o t e c t e d humic s u b s t a n c e s . The i n c r e a s e in c o n c e n t r a t i o n o f AN and HUN were due t o t h e f a c t t h a t t h e s e f r a c t i o n s may have o r i g i n a t e d in f u l v i c a c i d s and l e s s t i g h t l y bound p e r i p h e r a l gr o u p in g s on humic a c i d s and humic (2 5 , 3 9 ) . With most r o t a t i o n s , t h e d i s t r i b u t i o n among h y d r o l y z a b l e f r a c t i o n s s h i f t e d s h a r p l y towards l a r g e r r a t i o s f o r HUN/THN, whereas t h e AAN/THN and ASN/THN r a t i o s d e c r e a s e d ( T a b l e 6 ) . These changi ng r a t i o s i n d i c a t e t h e " a c t i v e n a t u r e o f t h e h y d r o l y z a b l e N f r a c t i o n s and t h e i r r e s p o n s i v e n e s s t o management." However, t h e p e r c e n t d i s t r i b u t i o n o f t h e o r g a n i c N f r a c t i o n s was n o t a p p r e c i a b l y d i f f e r e n t f o r th e d i f f e r e n t cr o p p in g s ys te m s . The l a c k o f s i g n i f i c a n t d i f f e r e n c e s in c o n c e n t r a t i o n s and p r o p o r t i o n s o f t h e o r g a n i c N forms among c r o p p i n g systems may be due t o t h e f a c t t h a t t h e samples were t a ke n in 1983 f o l l o w e d s u g a r b e e t s in a l l b u t one t r e a t m e n t (Table 1 ) . The e l e v e n - y e a r c r o p p i n g p e r i o d may have been too s h o r t a time t o produce s i g n i f i c a n t d i f f e r e n c e s . However, th e t r e n d s in N c y c l i n g between t h e NHN and THN and t h e f r a c t i o n s w i t h i n THN were s i m i l a r t o t h e f i n d i n g s i n C h a p t e r I I , b u t l e s s dramatic. T a b l e 6. E f f e c t o f c r o p p i n g sys tem on h y d r o l y z a b l e NH* (AN), amino a c i d N (AAN), amino s u g a r N (ASN) and h y d r o l y z a b l e unknown N (HUN) i n r e l a t i o n t o t h e t o t a l h y d r o l y z a b l e N (THN) AN/THN ASN/THN AAN/THN HUN/THN 1972 1983 Rat io 83/72 1972 1983 Ra t io 83/7 2 1972 1983 R at io 83/72 1972 1983 Ratic 83/72 C-Bn-Bn-SB 0.29 0.32 1 .1 0 0.43 0.3 2 0.74 0.18 0.0 8 0.44 0 .1 0 0.23 1.77 C-C-Bn-SB 0.32 0.3 0 0.94 0.39 0.35 0.9 0 0 .1 1 0 .1 1 1 .0 0 0.17 0.23 1.35 C-C-C-SB 0.33 0.32 0.97 0.41 0.34 0.82 0 .1 2 0.0 9 0 .7 5 0.15 0.2 5 1.67 C-SB 0.3 0 0.29 0.9 7 0.39 0.34 0.87 0.13 0.13 1 .0 0 0.18 0.24 1.33 Bn-SB 0.31 0.29 0.94 0.42 0.39 0.93 0.14 0 .1 1 0.79 0.13 0 .2 2 1.38 0-A-Bn-SB 0.27 0.32 1.19 0.38 0 .3 5 0.92 0 .1 2 0 .1 0 0.83 0 .2 1 0.23 1 .0 0 0-Bn-SB 0.31 0.28 0.9 0 0.36 0.36 1 .0 0 0.13 0 .1 0 0. 77 0.17 0.26 1.37 Means 0.30 0.30 1 .0 0 0.40 0.3 5 0 .8 8 0.13 0 .1 0 0.77 0.16 0.24 1.50 SUMMARY AND CONCLUSIONS The e f f e c t s o f c r o p p i n g sy stems on t h e c o n t e n t o f o r g a n i c carbon and d i s t r i b u t i o n o f n i t r o g e n forms o v e r an e l e v e n - y e a r p e r i o d were e v a l u a t e d . Organic carbon and t o t a l K je ld ah l N d e c r e a s e d with cr o p p in g f o r a l l cr o p p in g s ys te m s . T ot al K je l d ah l N l o s s e s ranged from 2.1% f o r t h e 0-Bn-SB r o t a t i o n t o 11.4% f o r t h e Bn-SB r o t a t i o n . Organic C l o s s e s ranged from 13% f o r C-Bn-Bn-SB and C-C-Bn-SB r o t a t i o n s t o 17% f o r t h e Bn-SB r o t a t i o n . The o v e r a l l a v e r a g e d e c r e a s e f o r o r g a n i c C was 14.9%, f o r TKN i t was 5.8%. The 5.8% d e c r e a s e in TKN was co m pri se d o f a 19.6% d e c r e a s e in q u a n t i t y o f n o n h y d r o ly z a b le N (NHN) and a 1.8% d e c r e a s e in t h e quan­ t i t y o f h y d r o l y s a b l e N (THN). These d e c r e a s e s can be compared with d a t a f o r C h a r i t y c l a y in Fig . 1 o f C h a p t e r I I (p . 31) where d e c r e a s e s due t o c u l t i v a t i o n were 67% f o r TKN, 81% f o r NHN and 63% f o r THN. Thus, i t app ea re d t h a t management un d e r a l l seven c ro pp in g systems c o n t i n u e s t o be d e p l e t i v e . The annual d i s t u r b a n c e o f t h e s o i l m a t r i x , due t o t i l l a g e , s e r v e s t o expose s t r u c t u r a l l y p r o t e c t e d c o l l o i d a l s u r f a c e s t o m i c r o b i a l and chemical a c t i v i t i e s t h a t d e c r e a s e t h e s t a b i l i t y of humic complexes. An e x p e c t e d consequence would be t h e d i f f e r e n t i a l l y g r e a t e r d e c l i n e in NHN r e l a t i v e t o THN ob se rv ed h e r e , as well as in t h e p r o f i l e s t u d y o f C h a p t e r I I . 65 66 The a v e r a g e change in co m po si tio n f o r t h e seven c r o p p i n g systems was n o t g r e a t (from THN/NHN = 4 . 0 1 in 1972 t o 5.06 in 1983). Thi s change may be compared w ith t h e p r o f i l e s t u d y , where THN/NHN i n c r e a s e d from 3 . 8 in v i r g i n C h a r i t y c l a y t o 7. 3 in t h e c u l t i v a t e d soil. N e v e r t h e l e s s , t h e r e l a t i v e l y g r e a t e r r e t e n t i o n o f N in a c t i v e forms s u g g e s t s an i n c r e a s e d r a t e o f annual t u r n o v e r . This may be du e, p e r h a p s , t o h i g h e r l e v e l s of y i e l d and r e s i d u e s r e t u r n e d s i n c e 1972. Among t h e h y d r o l y z a b l e N f r a c t i o n s , h y d r o l y z a b l e ammonium (AN) remained c o n s t a n t a t a b o u t 25% o f TKN, whereas i t had i n c r e a s e d from 18% o f TKN in t h e v i r g i n s o i l t o 24% in t h e c u l t i v a t e d a n a l o g . U n i d e n t i f i e d N (HUN) i n c r e a s e d r e l a t i v e t o TKN in both s t u d i e s , b u t t h e f i n a l p r o p o r t i o n s were s i m i l a r (20 t o 22%). The p r o p o r t i o n o f amino a c i d s (AAN) d e c r e a s e d in both s t u d i e s , b u t o v e r a s i m i l a r range (28 t o 32% o f TKN). Amino s u g a r c o m p os it io n d e c r e a s e d from 11% t o 9% o f TKN, a s a mean f o r t h e r o t a t i o n s , b u t remained c o n s t a n t a t a b o u t 9% in t h e p r o f i l e s t u d y . These v a l u e s a r e w i t h i n t h e range r e p o r t e d by o t h e r s , b u t th e y do n o t p o i n t t o any c l e a r t r e n d s . No s i g n i f i c a n t d i f f e r e n c e s f o r c ro p pi n g systems had developed d u r i n g t h e 1 1 - y e a r p e r i o d between 1972 and 1983. D i f f e r e n c e s may dev el o p ov er a l o n g e r p e r i o d o f time as new e q u i l i b r i a between i n p u t s and removals o f N and C a r e app ro ac hed . LITERATURE CITED Bartholomew, W. t i o n s and ch an g e s. W is.), II: V ., and D. Kirkham. 1960. Mathematical d e s c r i p i n t e r p r e t a t i o n s o f c u l t u r e induced s o i l n i t r o g e n I n t . Congr. So il S c i . T r a n s . 7th (Madison, 471-477. Bremner, J . M. 1958. Amino s u g a r s in s o i l s . A g r i c . 9: 5 28 -5 32 . J . S c i . Food Bremner, J . M. 1965. T ot al n i t r o g e n . Jjn C- W. Black ( e d . ) , Methods o f S o il A n a l y s i s , P a r t 2. Agronomy. 9: 1 14 9- 117 8. Bremner, J . M. 1965. Organic forms o f n i t r o g e n , jhi C. A. B la c k , ( E d . ) . Methods o f S o il A n a l y s i s , P a r t 2. Agronomy 9:123 8- 12 55. Bremner, J . M., and C. S. Mulvaney. 1983. N i t r o g e n - - T o t a l . j j i A. L. Page e t a l , ( e d . ) . Methods o f S oil A n a l y s i s , P a r t 2. Agronomy (2nd e d . ) . 9: 595 -6 24 . Bremner, J . M., and K. Shaw. 1954. S t u d i e s on t h e e s t i m a t i o n and d ec om po si ti o n o f amino s u g a r s in s o i l . J . A g r i c . S c i . 4 4: 15 2 - 1 5 9 . Bundy, L. G . , and J . M. Bremner. 1972. A s im pl e t i t r i m e t r i c method f o r d e t e r m i n a t i o n of i n o r g a n i c carb on in s o i l s . S oil S c i . Soc. Amer. Proc. 36 :27 3- 27 5. Campbell, C. A. 1978. So il o r g a n i c c a r b o n , n i t r o g e n , and f e r t i l i t y , pp. 173-271. J j l M. S c h n i t z e r and S. U. Khan (eds.). S oil Organic M a t t e r . E l s e v i e r N o r t h - H o l l a n d , New York. Fahad, A. A ., L. N. Mielke, A. D. Flowerday, and D. S w a r tz e n druber. 1977. So il p h y s i c a l p r o p e r t i e s as a f f e c t e d by soybean and o t h e r cr o p p in g s eq u en ce s. Soil S c i . Soc. Amer. J . 4 6 :3 7 7- 3 81 . Gosdin, G. W., M. S t e l l y , and W. E. Adams. 1950. The o r g a n i c m a t t e r and n i t r o g e n c o n t e n t and c a r b o n - n i t r o g e n r a t i o of C e s il S oil a s i n f l u e n c e d by d i f f e r e n t cr o p p in g systems on C l a s s e s I I , I I I , and IV l a n d . Soil S c i . Soc. Amer. Proc. 14:203-208. 68 11. G r e a v e s , J . E . , and A. F. Bracken. 1946. E f f e c t o f crop p in g on t h e n i t r o g e n , p h o s p h o r u s , and o r g a n i c carb on c o n t e n t o f a d r y - f a r m s o i l and on t h e y e i d l o f whe at. S o il S c i . 62 :35 5- 3 64 . 12. Haas, H. J . , C. E. Evans, and E. F. M i l e s . 1957. Nit ro ge n and carbon changes in G r e a t P lan s s o i l s a s i n f l u e n c e d by c r o p p i n g and s o i l t r e a t m e n t s . Tech. B u l l . 1164 USDA. 13. H a r r i s o n , R. M. 1963. Q u a n t i t a t i v e and q u a l i t a t i v e changes in s o il organic m a tter as r e l a t e d to residue a d d i tio n s , c r o p p i n g squence and management. Ph.D. D i s s e r t a t i o n , Michigan S t a t e U n i v e r s i t y , E a s t L a n s i n g , Michigan. 14. Hobbs, J . A ., and P. L. Brown. 1957. N it r o g e n and o r g a n ic ca rb on changes in c u l t i v a t e d w e s te r n Kansas s o i l s . Kansas Agr. Exp. S t a . B u l l . 89. 15. Hobbs, J . A . , and P. L. Brown. 1965. E f f e c t s o f c r o pp in g and management on n i t r o g e n and o r g a n i c carbon c o n t e n t s o f a w e s t e r n Kansas s o i l . Kansas Agr. Exp. S t n . Tech. B u l l . 144. 16. J o h n s t o n , J . R . , G. M. Browning, and M. B. R u s s e l l . 1942. The e f f e c t o f cr o p p in g p r a c t i c e s o f a g g r e g a t i o n , o r g a n i c m a t t e r c o n t e n t , and l o s s o f s o i l and w a t e r in t h e Marshall s i l t loam. So il S c i . Soc. Amer. Proc. 7:105 -1 07 . 17. Khan, S. U. 1971. N i tr o g e n f r a c t i o n s in a g r ey wooded s o i l a s i n f l u e n c e d by l o n g - t e r m cr o p p in g systems and f e r t i l i ­ zers. Can. J . S o il S c i . 51:431-437. 18. Lee, C. K . , and R. H. Bray. 1949. Organic m a t t e r and n i t r o g e n c o n t e n t s o f s o i l s a s i n f l u e n c e d by management. Soil S c i . 6 8 :2 0 3 - 2 1 2 . 19. L i t t l e , T. M., and F. J . H i l l s . 1978. A g r i c u l t u r a l Experimen­ t a t i o n Design and A n a l y s i s . John Wiley and Sons, New York. 20. Mazurak, A. P . , and E. C. Conard. 1966. Changes in c o n t e n t o f t o t a l n i t r o g e n and o r g a n i c m a t t e r in t h r e e Nebraska s o i l s a f t e r seven y e a r s o f c r o p p i n g t r e a t m e n t s . Agron. J . 58:85-88. 21. M e i n t s , V. W., L. T. K u r t z , S. W. M e ls te d , and T. R. Peck. 1977. Long-term t r e n d s in t o t a l s o i l N as i n f l u e n c e d by c e r t a i n management p r a c t i c e s . S oil S c i . 124:110-116. 69 22. Metzger,W. H. 1939. N it r o g en and o r g a n i c ca rb on o f s o i l s as i n f l u e n c e d by c r o p p in g systems and s o i l t r e a t m e n t s . Kansas Agr. Exp. S t a . Tech. B u l l . 45. 23. Myers, H. E . , A. L. H a l l s t e d , J . B. Kuska, and H. J . Haas. 1943. N it ro g e n and carb on changes in s o i l s un d er low r a i n f a l l as i n f l u e n c e d by cr o p p in g systems and s o i l t r e a t m e n t . Kansas Agr. Exp. S t a . Tech. B u l l . 56. 24. Odland, T. E. and J . B. Smith. 1933. The e f f e c t o f c e r t a i n c r o p s on s u cc ee d in g c r o p s . J . Amer. Soc. Agron. 25: 612-618. 25. P a u l , E. A . , and J . A. van Veen. 1979. The us e o f t r a c e r s t o d e t e r m in e t h e dynamic n a t u r e o f o r g a n i c m a t t e r , p. 75132. ] n J . K. G. G as se r ( e d . ) . Modelling n i t r o g e n from farm w a s t e s . App lied S c ie n c e P u b l i s h e r s , L t d . , London. 26. Research R e p o r t . 1980. Saginaw V al le y b e a n - b e e t r e s e a r c h farm and r e l a t e d b e a n - b e e t r e s e a r c h . Michigan S t a t e Univ. Agr. Exp. S ta . 27. S a l t e r , R. M., and T. C. Green. 1933. F a c t o r s a f f e c t i n g t h e a c c u m u la ti o n and l o s s o f n i t r o g e n and o r g a n i c carbon in cropped s o i l s . J . Amer. Soc. Agron. 25:6 2 2- 6 30 . 28. S c h u l t e , E. E. 1980. Recommended s o i l o r g a n i c m a t t e r t e s t s . ] n W. C. Dahnke, ( e d . ) . Recommended chemical s o i l t e s t p r o c e d u re s f o r t h e North C e n t r a l Region. North Dakota Agr. Exp. S t n . B u l l . 499 ( R e v i s e d ) . N. D. S t a t e U n i v . , Far go, N.D. 29. S ne de co r, G. W., (6 th e d . ) . 30. Sowden, F. J . 1959. I n v e s t i g a t i o n s on t h e amounts of hexosamines found in v a r i o u s s o i l s and methods f o r t h e i r d e t e r m i n a t i o n . Soil S c i . 88 :13 8- 14 3. 31. Sowden, F. J . 1977. D i s t r i b u t i o n o f n i t r o g e n in r e p r e s e n t a t i v e Canadian s o i l s . Can. J . S oil S c i . 57:4 45 -4 5 6. 32. S t e e l , R. G. D., and J . H. T o r r i e . 1980. P r i n c i p l e s and Pro­ c e d u r e s o f S t a t i s t i c s . McGraw-Hill Book Company, New York. 33. S t e v e n s o n , F. J . 1956. E f f e c t o f some l o n g - t i m e r o t a t i o n s on t h e amino a c i d co m p o si ti o n o f t h e s o i l . Soil S c i . Soc. Amer. Proc. 20:204-208. 34. S te v e n so n , F. J . 1957. D i s t r i b u t i o n o f th e forms o f n i t r o g e n in some s o i l p r o f i l e s . S o il S c i . Soc. Amer. Pro c. 21: 283-287. and W. G. Cochran. 1974. S t a t i s t i c a l Methods Iowa S t a t e U n i v e r s i t y P r e s s , Ames, Iowa. 70 35. S t e v e n s o n , F. J . 1957. I n v e s t i g a t i o n s o f a m in o p o ly s a c c h a r id e s in s o i l s : 1. C o l o r i m e t r i c d e t e r m i n a t i o n o f hexosamines in s o i l h y d r o l y s a t e s . S o il S c i . 83 :1 1 3- 1 22 . 36. S t e v e n s o n , F. J . 1957. I n v e s t i g a t i o n s o f a m in o p o ly s a c c h a r id e s in s o i l s : 2. D i s t r i b u t i o n o f hexosamines in some s o i l profiles. S o il S c i . 8 4 :9 9 - 1 0 6 . 37. S t e v e n s o n , F. J . 1965a. Amino a c i d s . J^n C. A. Black e t a l . ( e d s . ) . Methods o f S o il A n a l y s i s , P a r t 2. Agronomy 9: 1437-1451. 38. S t e v e n s o n , F. J . 1965b. ( e d s . ) . Methods o f 9:1429-1436. 39. S t e v e n s o n , F. J . 1982. Organic forms in s o i l n i t r o g e n . J^n F. J . S t e v e n s o n , ( e d . ) . N i tr o g e n in A g r i c u l t u r a l S o i l s . Agronomy 2 2 :6 7- 1 22 . 40. S t e v e n s o n , F. J . 1983. N i t r o g e n - - O r g a n i c f o rm s. Jji A. L. Page e t a l , ( e d s . ) . Methods o f Soil A n a l y s i s . P a r t 2. Agronomy (2nd e d . ) . 9 :6 2 5 - 6 4 1 . 41. Amino s u g a r s . Dl c - A. Black e t a l . S oil A n a l y s i s , P a r t 2. Agronomy S t e v e n s o n , F. J . , and C. N. Cheng. 1970. Amino a c i d s in s e d i ­ ments: r e c o v e r y by a c i d h y d r o l y s i s and q u a n t i t a t i v e e s t i m a t i o n by a c o l o r i m e t r i c p r o c e d u r e . Geochimica e t Cosmochimica A c ta . 3 4 :7 7 - 8 8 . 42. S t r i c k l i n g , E. 1957. E f f e c t o f c r o p p i n g systems and VAMA on s o i l a g g r e g a t i o n , o r g a n i c m a t t e r and cr o p y i e l d s . S o il S c i . 8 4 :4 8 9 - 4 9 8 . 43. Unger, P. W. 1968. Soil o r g a n i c m a t t e r and n i t r o g e n changes d u r in g 24 y e a r s o f d r y l a n d wheat t i l l a g e and crop pi n g p r a c t i c e s . S o i l S c i . Soc. Amer. Pr oc. 32 :42 7-4 29 . 44. Walkley, A. 1935. An e x a m in a t io n o f methods f o r d e t e r m in i n g o r g a n i c carbon and n i t r o g e n in s o i l s . J . Agr. S c i . 25 :598-609. 45. Walkley, A ., and I . A. Bla ck. 1934. An e x a m in at io n o f t h e D e g t j a r e f f method f o r d e t e r m i n i n g s o i l o r g a n i c m a t t e r and a proposed m o d i f i c a t i o n o f t h e chromic a c i d t i t r a t i o n method. S o il S c i . 37:29-37. 46. White, J . W., F. J . Holden, and A. C. R i c h e r . 1945. Mainte­ nance l e v e l o f n i t r o g e n and o r g a n i c m a t t e r in g r a s s l a n d and c u l t i v a t e d s o i l s o v e r p e r i o d s o f 54 and 72 y e a r s . J . Amer. Soc. Agron. 3 7 : 2 1 - 3 1 . 71 47. Young, R. A . , J . C. Z u b r i s k i , and E. B. Norum. 1960. I n f l u e n c e o f l o n g - t i m e f e r t i l i t y management p r a c t i c e s on chemical and p h y s i c a l p r o p e r t i e s o f a Fargo C la y . S oil S c i . Soc. Amer. Pro c. 24 :1 2 4- 1 28 . CHAPTER IV EFFECT OF TYPE AND RATE OF CROP RESIDUES ON THE CONCENTRATION AND DISTRIBUTION OF NITROGEN FORMS DURING INCUBATION An im p o r t a n t way t h a t c r o p s a f f e c t s o i l p r o p e r t i e s i s t h e r e t u r n o f o r g a n i c m a t t e r a s e x u d a t e s and r e s i d u e s produced d u r in g gr ow th, b u t m o s tl y a f t e r h a r v e s t o f t h e c r o p s . The t y p e s and amount o f cr o p r e s i d u e s a f f e c t t h e c o n c e n t r a t i o n and p r o p o r t i o n o f t h e v a r i o u s o r g a n i c N f r a c t i o n s due t o d i f f e r e n c e s in crop c o m p o s i t i o n , de co m po sit io n r a t e s , and s u i t a b i l i t y a s s u b s t r a t e s f o r t h e m i c r o b i a l population. A p p l i c a t i o n o f a l f a l f a , c o r n s t a l k s , s aw d us t , o a t s t r a w and bromegrass a t r a t e s o f 0 t o 16 t o n s / h a / y e a r i n c r e a s e d t h e o r g a n i c C and n i t r o g e n in p r o p o r t i o n t o t h e amount of r e s i d u e s added o v e r a p e r i o d o f 11 y e a r s ( 1 2 ) . These a u t h o r s found no s i g n i f i c a n t d i f f e r ­ enc es among t h e f i v e r e s i d u e s e x c e p t f o r sawdust which produced s i g n i f i c a n t l y lower v a l u e s f o r n i t r o g e n . In o t h e r s t u d i e s , o r g a n i c amendments such as gr ee n r y e , s t r a w , a l f a l f a ha y , dec id u ou s l e a v e s , p e a t , muck, and manure were added t o an Uplands sand and a Rideau c l a y unde r f i e l d c o n d i t i o n s f o r a 2 0 - y e a r p e r i o d . The p r a c t i c e m a i n t a i n e d t h e l e v e l s o f t o t a l N, o r g a n i c m a t t e r and t h e d i s t r i b u t i o n o f t h e v a r i o u s n i t r o g e n o u s compounds (2 3 , 2 4 ) . 72 73 Some i n v e s t i g a t o r s have n o te d a r e l a t i v e c o n s t a n c y in t h e p r o ­ p o r t i o n s o f o r g a n i c N f r a c t i o n s w ith l a r g e d e c r e a s e s in t o t a l N c o n t e n t due t o c u l t i v a t i o n and c r o p p in g ( 5 , 11, 15, 19, 2 8 ) . In s o i l s where l a r g e i n c r e a s e s in t o t a l N have o c c u r r e d unde r f e r t i l i z e d legume p a s t u r e s in t r o p i c a l and t e m p e r a t e a r e a s in A u s t r a l i a , o r g a n i c N f r a c t i o n s p r o p o r t i o n s have remained r e l a t i v e l y c o n s t a n t ( 1 6 ) . This a p p e a r e d t o s u g g e s t t h a t o r g a n i c N f r a c t i o n a t i o n by h y d r o l y s i s u s in g 6 M HC1 produced a p a t t e r n t h a t b or e l i t t l e r e l a t i o n t o t h e b i o l o g i c a l la b ile of soil nitrogen. Some o t h e r s t u d i e s showed t h a t t h e p r o p o r t i o n o f o r g a n i c N f r a c t i o n s would n o t n e c e s s a r i l y remain c o n s t a n t w ith l a r g e changes in t o t a l N. I t was r e p o r t e d t h a t t h e a d d i t i o n o f f r e s h r e s i d u e s was accom­ p an ie d i n i t i a l l y by an i n c r e a s e in h y d r o l y z a b l e a-amino a c i d a r i s ­ ing by p r o t e o l y s i s and m i c r o b i a l s y n t h e s i s ( 6 ) . o bs erv ed f o r o t h e r o r g a n i c N f r a c t i o n s . Changes were a l s o The changes were r e l a t e d more c l o s e l y t o t h e d eg ree o f o x i d a t i o n o f t h e t o t a l o r g a n i c f r a c t i o n tha n t o t h e co m p o si ti o n o f t h e m a t e r i a l s t h a t were added . C o r n s f o r t h (3) r e p o r t e d t h a t c o n s i d e r a b l e r e d i s t r i b u t i o n o f N took p l a c e i n d i c a t i n g changes in th e p r o p o r t i o n s o f t h e or ga ni c -N f r a c t i o n s w it h changes in t h e amounts o f t o t a l N. O th er workers showed t h a t c u l t i v a t i o n and cr o p p in g r e s u l t e d in a marked d e c l i n e in t h e p r o p o r t i o n s o f t o t a l N as organic N f r a c t i o n s (8 , 20). These i n v e s t i g a t o r s did n o t show t h e magnitude o f change in p r o p o r t i o n s o f t o t a l N a s o r g a n i c N f r a c ­ t i o n s i f v a r i o u s ener gy s o u r c e s were added a t v a r y i n g r a t e s w ith no a d d i t i o n a l a p p l i c a t i o n o f f e r t i l i z e r N. 74 The above r e p o r t s have shown t h a t t h e c o n c e n t r a t i o n and p r o p o r ­ t i o n o f t o t a l N a s o r g a n i c N f r a c t i o n s may be s i g n i f i c a n t l y a f f e c t e d by management p r a c t i c e s . That a p p e a r s t o i n d i c a t e t h a t any c u l t u r a l p r a c t i c e t h a t r e t u r n s l a r g e q u a n t i t i e s o f some cr o p r e s i d u e s may i n c r e a s e o r d e c r e a s e t h e r e l a t i v e p r o p o r t i o n s o f t o t a l N p r e s e n t as organic N f r a c t io n s . The r e d i s t r i b u t i o n o f N can o c c u r in s e v e r a l ways. In g e n e r a l , a d e c l i n e in t o t a l N due t o c u l t i v a t i o n o r c r o p p in g i s a s s o c i a t e d with r e d i s t r i b u t i o n o f h y d r o l y z a b l e N and n o n h y d r o l y z a b l e N f r a c t i o n s . However, i t has been r e p o r t e d t h a t a l a r g e d e c r e a s e o f carb on and n i t r o g e n d u r i n g c u l t i v a t i o n did n o t r e s u l t in m e a s u ra b le changes in t h e d i s t r i b u t i o n o f t h e h y d r o l y z a b l e and n o n h y d r o l y z a b l e f r a c t i o n s o f N (14). The a d d i t i o n o f cr o p r e s i d u e s w it h v a r y i n g C/N r a t i o s can a l s o l e a d t o t h e r e d i s t r i b u t i o n o f N from t h e h y d r o l y z a b l e N t o t h e non­ h y d r o l y z a b l e N and v i c e v e r s a , depending on t h e s t a g e o f h u m i f i c a t i o n . During t h e e a r l y s t a g e s o f h u m i c a t i o n , t h e n o n h y d r o l y z a b l e N f r a c t i o n t e n d s t o i n c r e a s e a t t h e expense o f t h e h y d r o l y z a b l e N which comprise the "activ e" m a te ria ls . Within t h e h y d r o l y z a b l e N f r a c t i o n , h y d r o l y z a b l e ammonium N, amino acid N, amino s u g a r N, and t h e h y d r o l y z a b l e unknown N (HUN) change in c o n c e n t r a t i o n and p r o p o r t i o n r e l a t i v e t o change in t h e t o t a l h y d r o l y z a b l e N. Thi s depends on t h e s t a b i l i t y o f t h e s e f r a c t i o n s . Under i n c u b a t e d c o n d i t i o n s , h y d r o l y z a b l e f r a c t i o n s such a s amino a c i d N, hydroxyamino a c i d N and HUN were found t o be more s u s c e p t i b l e t o l o s s th a n t o t a l N ( 9 ) . Thi s means t h a t t h e s e d e c r e a s e s would a c c o u n t f o r t h e o v e r a l l d e c l i n e o f t o t a l h y d r o l y z a b l e N which would a c c o u n t f o r 75 t h e d e c l i n e in t o t a l N. In o t h e r s t u d i e s , t h e d e c r e a s e in t o t a l N was a c c o u n t e d f o r by a d e c r e a s e in n o n h y d ro ly z a b le N and o t h e r h y d r o l y z a b l e f r a c t i o n s such a s hydroxyamino a c i d N ( 3 ) . There i s ve ry l i t t l e t o p s , navy bean information about the e f f e c t of a l f a l f a s t r a w , co r n s t o v e r , and s u g a r b e e t t o p s on t h e c on ­ c e n t r a t i o n and d i s t r i b u t i o n o f N forms in an a c i d s o i l low in s o i l organic m atter. The r e s u l t s can be m e a n in g f u ll y r e l a t e d t o t h e b e h a v i o r and p o t e n t i a l b e h a v i o r o f t o t a l N and o r g a n i c N f r a c t i o n s unde r f i e l d conditions. The o b j e c t i v e o f t h e i n c u b a t i o n s tu d y was: To d e t e r m i n e t h e i n f l u e n c e o f v a r i o u s ty p e s and r a t e s of cr o p r e s i d u e s and time o f i n c u b a t i o n on t h e c o n c e n t r a t i o n and d i s t r i b u t i o n o f N forms. MATERIALS AND METHODS I n c u b a t i o n s t u d i e s were performed on a homogenous l o t o f Hodunk sandy loam s o i l c o l l e c t e d in t h e f a l l o f 1983 a f t e r h a r v e s t o f second y e a r o f corn in a p o t a t o - c o r n - c o r n se que nce . The s o i l was pa s s ed th ro ugh a 4 . 8 mm s c re e n t o remove undecomposed p l a n t m a t e r i a l s , a i r - d r i e d , and th e n s t o r e d in a p l a s t i c bag. Bulk samples o f corn s t o v e r , dry bean s t r a w , s u g a r b e e t to p s and a l f a l f a t o p s were ta k en from t h e f i e l d in O c to b e r . m a t e r i a l s were d r i e d and ground t o p ass a p l a s t i c b ag s . 2 .0 The p l a n t mm s i e v e and s t o r e d in The ground m a t e r i a l s were mixed w ith 500g a l i q u o t s of th e s o il a t r a te s of 0, 2 , 1 0 , and 50 g A g . The amended a l i q u o t s were p l a c e d in p l a s t i c i c e cream c a r t o n s and m o i s t e n e d t o f i e l d c a p a c ­ i t y ( 0 .0 3 mPa) w i t h d e i o n i z e d w a t e r . They were th e n p l a c e d in p o l y ­ e t h y l e n e bags t o re du ce e v a p o r a t i o n d u r i n g i n c u b a t i o n a t 27°C. h o l e p u n c t u r e s were made in each bag f o r gas excha ng e. Pin A t o t a l o f 156 e x p e r i m e n t a l u n i t s were p re p a r e d t o p e r m i t s a c r i f i c i n g t r i p l i c a t e u n i t s o f an unamended c o n t r o l and o f each m a t e r i a l / r a t e c o m bi n at io n a f t e r 9 , 21, 4 2 , and 63 days. Water was added as needed to m a i n t a i n a c o n s t a n t w ei g ht d u r i n g i n c u b a t i o n . S a c r i f i c e d samples were f r o z e n and s t o r e d a t -4°C f o r a n a l y s i s . 76 77 L a b o r a t o r y Analy se s Tot al N was d e t e r m in e d by t h e s a l i c y c l i c a c i d - t h i o s u l f a t e m o d i f i c a t i o n o f t h e K jel dah l method d e s c r i b e d by Bremner and Mulvaney (2). Exchangeable NH^ N and NOg p lu s NOg N were de te rm in e d by t h e methods d e s c r i b e d by Keeney and Nelson ( 1 0 ) . E a s i l y o x i d i z e d o r g a n i c C was de te rm in e d by t h e c o l o r i m a t r i c method d e s c r i b e d by S c h u l t e ( 2 1 ) . Thi s method i n v o l v e s chromic a c i d o x i d a t i o n f o r d e t e r m i n a t i o n o f e a s i l y o x i d i z e d m a t e r i a l thr ough sp on ta n eo us h e a t . The method was s t a n d a r d i z e d a g a i n s t t h e Walkley- Black method (3 1 , 3 2 ) . T ot al h y d r o l y z a b l e N (THN), h y d r o l y z a b l e ammonium N (AN), amino a c i d N (AAN), amino s u g a r N (ASN), h y d r o l y z a b l e unknown N (HUN) and n o n h y d r o l y z a b l e N (NHN) were d e te rm in e d by t h e methods d e s c r i b e d by Bremner (1) and Stev en son ( 2 6 , 27, 29, 30 ). S t a t i s t i c a l An alyses The e x p e r i m e n t was d e s i g n e d in a randomized complete blo ck and t h e d a t a were s u b j e c t e d t o a n a l y s e s o f v a r i a n c e , u s in g methods d e s c r i b e d by Snedecor and Cochran ( 2 2 ) , S t e e l and T o r r i e ( 2 5 ) , and L i t t l e and H i l l s ( 1 3 ) . RESULTS AND DISCUSSION Changes in c o n c e n t r a t i o n and d i s t r i b u t i o n o f N forms were f o ll o w e d o ve r a 63-day i n c u b a t i o n p e r i o d in a sandy loam s o i l amended w ith r e s i d u e s o f a l f a l f a , navy b e a n s , c o r n , o r s u g a r b e e t s a t r a t e s up t o 50 g / k g . A Hodunk sandy loam low in o r g a n i c m a t t e r was used so t h a t r e s i d u e e f f e c t s would be most pronounced f o r measurement. Chemical a n a l y s e s f o r t h e f o u r cr op m a t e r i a l s used a r e given in Tabl e 1. Table 1. Composition o f crop r e s i d u e s used in t h e i n c u b a t i o n s tud y Residue ty p e Total N P K Ca C/Nf ___ 0/ _____ A lfalfa 3 .4 5 0 .2 4 1.53 0.23 14 Navy bean 0 .7 7 0. 07 1.49 0 .3 8 65 Corn 0.7 9 0.09 0.3 8 0 .2 0 63 Sugar b e e t 1.51 0.1 3 1 .1 0 0. 39 33 f E s t i m a t e d C/N r a t i o , assuming 40% C. A pp are nt Gains and Losses o f N Simple e f f e c t s and 2-way and 3-way i n t e r a c t i o n s o f r e s i d u e s , r a t e s and ti m es on t o t a l N were s t a t i s t i c a l l y s i g n i f i c a n t 78 79 ( Ta bl e 1, Appendix A). The d a t a f o r t h e 3-way i n t e r a c t i o n s a r e shown g r a p h i c a l l y in F i g s . 1 t o 4. At ze r o t i m e , t h e c o n c e n t r a t i o n o f t o t a l N r e f l e c t e d t h e d i f f e r e n c e s in N c o n c e n t r a t i o n o f t h e r e s i d u e s (Ta bl e 1) and t h e r a t e s of a d d itio n . Subs equ ent changes d u r i n g i n c u b a t i o n , however, were n o t p a r a l l e l f o r t h e d i f f e r e n t m a t e r i a l s nor d i f f e r e n t r a t e s o f t h e same m aterial. In t h e c a s e o f a l f a l f a a t t h e h i g h e s t r a t e , a s t r i k i n g d e c r e a s e in t o t a l N o c c u r r e d , d u r i n g t h e 63-day i n c u b a t i o n p e r i o d . 10 At t h e g/kg r a t e , a s i m i l a r d e c r e a s e was pr eceded by a s i g n i f i c a n t i n c r e a s e in t h e second s am pl in g . At t h e lo w e s t r a t e (2 g / k g ) , t h e r e was a c o n t i n u i n g i n c r e a s e o v e r t h e e n t i r e i n c u b a t i o n p e r i o d . With t h e o t h e r r e s i d u e s , p a t t e r n s o f change were d i f f e r e n t and v a r i e d w ith ra te of add itio n . The magnitude o f s e v e r a l o f t h e changes o v e r time in F i g . 1 and t h e i r s t a t i s t i c a l s i g n i f i c a n c e , i n d i c a t e t h a t r e a l i n c r e a s e s and r e a l d e c r e a s e s may have o c c u r r e d a t d i f f e r e n t t i m e s . Mechanisms f o r l o s s o f N from s o i l syst ems in c l u d e d v o l a t i l i z a t i o n o f NH3 and d e n i t r i f i c a t i o n o f n i t r a t e and n i t r i t e . Mechanisms f o r adding N i n c l u d e a b s o r p t i o n o f NH3 from t h e atmosphere and N2- f i x a t i o n by nitrogen-fixing b acteria. Energy t o s u p p o r t b i o l o g i c a l d e n i t r i f i c a t i o n a n d / o r Ngf i x a t i o n would have been s u p p l i e d by t h e added r e s i d u e s . The more r e a s i l y a v a i l a b l e carb on s u b s t r a t e s were d i s s i p a t e d r a t h e r q u i c k l y (Tabl e 2 ) . Thus t h e p r o b a b i l i t y t h a t h e t e r o t r o p h i c a c t i v i t i e s were 1500 NITROGENCMG/KG) 1400 1300 1200 1100 1000 300 TOTRL 800 700 800 0 0 10 20 30 I N C U B R T I ON Fig. 1. 40 50 80 70 T IM E (DRYS) E f f e c t o f ty pe and r a t e o f a l f a l f a r e s i d u e s and time o f i n c u b a t i o n on t h e c o n c e n t r a t i o n o f t o t a l n i t r o g e n ( r a t e s = 0 , 2 , 1 0 , and 50 g / k g ) . 1000 SUGRR BEET 50 900 LSD 0. 05 B0 0 700 B 00 0 10 20 30 INCUBATION Fig . 2. 50 G0 T IM E (D A Y S ) E f f e c t o f t y p e and r a t e o f s u g a r b e e t r e s i d u e s and time o f i n c u b a t i o n on t h e c o n c e n t r a t i o n o f t o t a l n i t r o g e n ( r a t e s = 0 , 2 , 10, and 50 g / k g ) . 70 1000 CORN 900 LSD 0.05 50 B0 0 700 6 00 0 0 Fig. 3. 10 20 30 40 50 60 E f f e c t o f ty pe and r a t e o f corn r e s i d u e s and time o f i n c u b a t i o n on t h e c o n c e n t r a t i o n o f t o t a l n i t r o g e n ( r a t e s = 0 , 2 , 1 0 , and 50 g / k g ) . 70 1000 NRVY LSD 0. 900 BERN 05 50 B00 700 B0 0 0 0 F ig. 4. 1 0 20 30 40 50 G0 E f f e c t o f typ e and r a t e o f navy bean r e s i d u e s and time o f i n c u b a t i o n on t h e c o n c e n t r a t i o n o f t o t a l n i t r o g e n ( r a t e s = 0 , 2 , 1 0 , and 50 g / k g ) . 70 84 Table 2. E f f e c t o f ty p e and r a t e o f cr op r e s i d u e and time o f i n c u b a t i o n on o r g a n i c carbo n. Organic carbon I n c u b a t i o n time (day s) Residue Rate 0 + ofc A lfalfa Navy bean Corn Sugar b e e t LSD0 .0 5 42 63 7.7 6 .2 8 .0 7. 8 9.0 8.9 1 1 .0 1 1 .0 7.3 7.3 7. 8 8.4 9.7 ------------ g/kg y/Kg nf\srt Check 21 8 .1 8 .1 8.4 9.3 13.0 2 9.0 10 1 2 .0 50 28.0 2 9.0 10 1 2 .0 50 28.0 8 .6 9.9 16.0 2 9.0 9.2 10 1 2 .0 1 0 .0 50 28.0 17.0 2 9. 0 10 1 2 .0 8.4 8.5 50 28.0 1 2 .0 1 1 .0 7. 4 8.5 14.0 7.8 7.9 9.7 7. 5 8 .6 1 1 .0 7.3 7.5 8 .6 ( 3 - way i n t e r a c t i o n ) Assuming 40% C in Calculated = 8 residues: g C in 1,000 q s o i l + 0 . 4 x g/kg r e s i d u e added 1 ,0 0 0 g s o i l + g kg r e s i d u e added Values a t zero r a t e n o t in c lu d e d in AN0VA 85 r e s p o n s i b l e f o r l o s s e s o r g a i n s o f N would have been g r e a t e s t d u r in g e a r l y s t a g e s o f i n c u b a t i o n and would have d e c l i n e d w ith d e c l i n i n g r a t e o f carbon l o s s . On t h e o t h e r hand, t h e l i k e l i h o o d t h a t l o s s e s o f N might o c c u r by chemical d e n i t r i f i c a t i o n would be e x p e c t e d t o i n c r e a s e a s o x i d a t i o n p r o g r e s s e d and p h e n o l -q u i n o n e systems a p pe a r ed t h a t c o u l d r e a c t with n i t r i t e unde r a c i d c o n d i t i o n s t o produce Ng, ^ 0 , and o t h e r g a s e s (17). In t h e c a s e o f high N m a t e r i a l s , r a p i d d i s s i p a t i o n o f carbon i s accompanied by n e t m i n e r a l i z a t i o n and r a p i d r e l e a s e o f NHg. If NH2 i s r e l e a s e d more r a p i d l y than i t can be a d s o r b e d o r t r a n s f o r m e d by s o i l s y s t e m s , v o l a t i l i z a t i o n l o s s e s w i l l o c c u r . This would a p p e a r t h e most l i k e l y e x p l a n a t i o n f o r t h e d i s a p p e a r a n c e o f N a t t h e h i g h e s t r a te of addition of a l f a l f a . In t h e c a s e o f ca rb ona ceo us m a t e r i a l s , low in N, d ec om p os it io n i s accompanied by im m o b il iz a t io n o f min era l forms o f N i n t o m i c r o ­ bial tis s u e s . The p r e s e n c e o f ca r b on a ce ou s m a t e r i a l s can i n c r e a s e t h e a d s o r p t i v e c a p a c i t y o f t h e s o i l f o r NH3 in t h e am bien t at m o s p h e r e . In t h e p r e s e n t e x p e r i m e n t , i t i s p o s s i b l e t h a t NHg l o s t by v o l a t i l i z a t i o n from high N t r e a t m e n t s may have e q u i l i b r a t e d , throug h t h e c o n f i n e d atmosphere o f t h e growth chamber, w i t h s o i l and r e s i d u e s in low N t r e a t m e n t s . Thus a s i g n i f i c a n t i n c r e a s e in t o t a l N o c c u r r e d d u r i n g t h e f i r s t 21 days a t a l l r a t e s o f corn a d d i t i o n . At t h e 2 g/kg r a t e , t h e i n c r e a s i n g t r e n d was m a i n t a i n e d th r o u g h t h e 63rd day with both corn and a l f a l f a . D i f f e r e n c e s between 2 and 10 g/kg a p p l i c a t i o n s were n o t g r e a t , b u t i t d i d a p p e a r t h a t i n t e r a c t i n g systems which 86 a f f e c t t h e b a l a n c e between g a i n s and l o s s were i n f l u e n c e d d i f f e r ­ e n t l y by t h e r a t e o f a d d i t i o n . Changes in Exchangeable Ammonium V o la tiliz a tio n or adsorption of NHg r e f l e c t s h i f t s in dynamic e q u i l i b r i a t h a t i n v o l v e exc h a ng ea bl e NH^ ( 1 8 ) . The immediate e f f e c t o f added r e s i d u e s a t t i m e z e r o (Tab le 3) was t o redu ce e x ch a ng ea bl e NH^ i n i t i a l l y p r e s e n t in t h e s o i l t o t r a c e l e v e l s . s h a r p l y h i g h e r a t 21 days in a l l sa mples. Lev el s were A d d it i o n o f w a t e r a t t h e b e g i n n in g o f i n c u b a t i o n would have a c t i v a t e d t h e s o i l m i c r o b i a l popu­ lation. The q u a n t i t i e s o f NH^ found r e p r e s e n t t h e b a l a n c e a t t h e time o f sampling between t h e r a t e o f r e l e a s e o f NHg by t h e a c t i v a t e d popu­ l a t i o n and t h e r a t e o f i t s removal by s e v e r a l p r o c e s s e s , i n c l u d i n g i m m o b i l i z a t i o n i n t o m i c r o b i a l t i s s u e s and m e t a b o l i c p r o d u c t s , n i t r i f i c a t i o n , v o l a t i l i z a t i o n , and chemical t r a n s f o r m a t i o n l e a d i n g t o i n c o r p o r a t i o n i n t o humic complexes ( 7 ) . D i f f e r e n c e s in ex ch a n g ea b le NH^ l e v e l s in Tabl e 3 a r e no t r e l a te d c o n s i s te n tl y to th e N content of the resid u es. present a t 21 The 32 mg/kg days w it h t h e h i g h e s t r a t e o f a l f a l f a i s c o n s i s t e n t with t h e e a r l i e r c o n c l u s i o n t h a t l a r g e l o s s o f N from t h i s system may have been due t o v o l a t i z a t i o n o f NHg r e l e a s e d a t r a t e s e x ce ed in g t h e adsorptive capacity of the soil ( F i g . 1). Exchangeable NH^ l e v e l s were lower in t h e l a s t sampling in t h e c o n t r o l th a n in most amended s o i l s . This p r o b ab ly r e f l e c t s a more r a p i d d e c r e a s e in s i z e and a c t i v i t y o f t h e m i c r o b ia l p o p u l a t i o n due to e a r l i e r d ep letion of a v a ila b l e s u b s t r a te s . 87 Tabl e 3. E f f e c t o f t y p e and r a t e o f r e s i d u e and time o f i n c u b a t i o n on ex c h a n g e a b le ammonium N. Exchangeable ammonium N I n c u b a t i o n time (day s) Residue Rate 9 Check A lfalfa ot 2 50 2 10 50 Corn 2 10 50 Sugar b e e t 2 10 50 LSDn nc 0 .0 5 42 63 15.0 9.9 4.2 19.0 4.2 32.0 16.0 19.0 7.1 7.1 7.1 9.9 7.1 9. 9 9.9 9.9 7.2 7.1 9.9 7. 2 21 ---------------- mg/kg /kg 10 Navy bean 0 2 .8 Tracet Trac e Trace Trace Trace Trace 1 1 .0 Trace Trace Trace 19.0 7. 1 8.5 1 1 .0 8.5 Trace Trace Trace 18.0 7.1 18.0 9.9 5. 7 23 .0 5. 7 8.5 9.9 (3-way i n t e r a c t i o n ) 9.9 7. 5 1 0 .0 3.2 t v a l ues a t ze r o r a t e n o t i n c l u d e d ' i n ANOVA. I Trace = A v a l u e o f 1. 0 mg/kg was a s s i g n e d f o r s t a t i s t i c a l a n a l y s i s . 88 Changes i n N i t r i f i e d N Normally n i t r i f i c a t i o n r e p r e s e n t s an i m p o r t a n t s i n k f o r NH^ in s o i l s . N i t r i f i c a t i o n r a t e s and t h e q u a n t i t i e s o f n i t r a t e p l u s n i t r i t e produced w it h a l f a l f a and s u ga r b e e t (Tab le 4) r e f l e c t e d both t h e d i f f e r e n c e s in n i t r o g e n c o n t e n t o f t h e s e two r e s i d u e s and t h e r a te s of a d d i tio n . The t r a n s f o r m a t i o n was most r a p i d and e x t e n s i v e w ith a l f a l f a , which c o n t a i n e d 3.45% N, fo ll o w ed by s u g a r b e e t to p s which c o n t a i n e d 1.51% N and l e a s t w ith co r n and navy b ean s. In t h e c a s e o f navy bean r e s i d u e s (0.77% N) and corn (0.80% N) t h e a d d i t i o n o f 2 g/Kg had no e f f e c t on n i t r i f i c a t i o n as compared w it h t h e c o n t r o l . At h i g h e r r a t e s , n i t r i f i c a t i o n was s e v e r e l y d e l a y e d . These d e l a y s o c c u r r e d even though l e v e l s o f ex ch an gea ble NhJ ( T ab l e 3) were no lower th a n many o f t h o s e a s s o c i a t e d w ith high n i t r i f i c a t i o n r a t e s in s o i l s amended w i t h a l f a l f a o r s u g a r b e e t s . Thus, t h e f a i l u r e o f n i t r a t e t o acc um ula te nor ma ll y a t h i g h e r r a t e s o f wide C/N r a t i o r e s i d u e s in t h i s s tu d y does no t a p p e a r t o have been due t o c o m p e t i t i v e i m m o b i l i z a t i o n o f NH^, t h e s u b s t r a t e f o r t h e f i r s t s t e p in n i t r i f i c a t i o n . R a t h e r , i t would a p p e a r t h a t NO2 a n d / o r NO^ were removed by o t h e r t r a n s f o r m a t i o n s as r a p i d l y as formed. P r o c e s s e s t h a t u t i l i z e NOg a n d / o r NO^ i n c l u d e m i c r o b i a l a s s i m i l a t i o n , m i c r o b i a l d e n i t r i f i c a t i o n and r e a c t i o n o f N0 ^ with o r g a n i c compounds a t a c i d pH. These r e a c t i o n s o f NO^ can r e s u l t in both chemical i m m o b i l i z a t i o n and chemical d e n i t r i f i c a t i o n (1 7 ) . 89 Table 4. E f f e c t o f t y p e and r a t e o f cr o p r e s i d u e s and time o f i n c u b a t i o n on t h e c o n c e n t r a t i o n o f n i t r a t e p l u s n i t r i t e N itr a te plus n i t r i t e nitrogen I n c u b a t i o n time (day s) Residue Rate N added in r e s i d u e 0 21 0 A lfalfa 2 10 50 Navy bean 2 10 50 Corn 2 10 50 Sugar b e e t 2 10 50 LSD0.0 5 * 63 mg/kg — g/kg Check 42 — 0.9 16.5 26.1 30 .8 69 345 1725 1. 5 3.1 6.4 26.2 66 .4 207.0 3 9. 5 81.4 241.0 50.6 8 3 .9 277.0 15 79 387 1. 5 1.5 1.5 17.1 1.3 1. 5 18.8 1.3 1. 5 30 .9 16 80 400 1. 5 1.5 1.5 1 1 .2 3 1. 4 1 .1 26.1 6.7 0.9 30 151 755 1.3 1.5 1.5 15.5 13.5 19.0 30. 9 33.1 95. 8 37.1 41.7 99 .8 ( 3 - way i n t e r a c t i o n ) 1.3 1 1 .6 Values a t ze r o r a t e n o t in c l u d e d in ANOVA 8 .6 44.5 1 1 .0 0. 9 90 Changes i n O r g a n ic N F r a c t i o n s In F i g s . 5 t o 3 , d a t a f o r n i t r a t e p lu s n i t r i t e a r e compared g r a p h i c a l l y w ith r e c o v e r i e s o f N in o r g a n i c forms a t t h e 50 g/kg r a t e of a d d itio n . I t s h ou ld be no te d t h a t NHg r e c o v e r e d in t h e h y d r o l y z a ­ b l e f r a c t i o n (AN) would have i n c l u d e d t h e ex ch an gea ble NH^ in Table 3. Because t h e v a l u e s were low, ex ch a n g ea b le NHjJ was n o t broken o u t s e p a r a t e l y in t h e f i g u r e s . P a t t e r n s o f change in t h e AN f r a c t i o n o r in t o t a l o r g a n i c N (TON) would n o t have been a l t e r e d a p p r e c i a b l y i f •J* t h i s mineral f r a c t i o n had been e x c l u d e d . I f p r e s e n t , NH^ f i x e d by c l a y m i n e r a l s would have a l s o c o n t r i b u t e d t o AN. However, i t i s u n l i k e l y t h a t much f i x e d NH^ would have been p r e s e n t in t h i s sandy loam s o i l . Changing l e v e l s o f o r g a n i c N (TON) in F i g s . 5 t o 7 r e f l e c t e d n e t m i n e r a l i z a t i o n t o NOg a n d / o r NO3 . In t h e c a s e o f corn ( F i g . 8 ), TON ac c o u n te d f o r t o t a l N (TN) in t h e system b ec a u se n e t n i t r i f i c a t i o n d id n o t o c c u r . Total H yd ro ly za b l e N and No nh ydrolyzable N In t h e c a s e o f a l f a l f a ( F i g . 5) and s u g a r b e e t t o p s ( F i g . 6 ), changes in TON were due mainly t o changes in t o t a l h y d r o l y z a b l e N (THN). Changes in t h e n o n h y d r o ly z a b le f r a c t i o n (NHN) were s m a l l . By c o n t r a s t , changes in TN and TON with t h e two low N r e s i ­ dues ( F i g s . 7 and 8 h y d r o l y z a b l e for ms. ) r e f l e c t e d changes in both h y d r o l y z a b l e and non­ With b ot h navy beans and c o r n , i n c r e a s e s in NHN c o n t r i b u t e d t o t h e e a r l y i n c r e a s e s in TN and TON a t 21 day s. N FRRCTIO N S( MG/KG) 15 0 0 14 0 0 1300 * TN 1200 00 1 100 .. -0 - 1000 300 THN- 800 700 600 OF 500 400 RRN' CONC. 300 2 0 0 i 100 <>— NN NHN’ HUN. RSN 0 0 10 20 30 I N C U B R T I ON Fig. 5. 40 50 60 70 T IM E ( DRYS) C o n c e n t r a t i o n o f n i t r o g e n f r a c t i o n s d u r i n g i n c u b a t i o n a t 50 g/kg a l f a l f a r e s i d u e a d d i t i o n . TN = t o t a l N; TON = t o t a l o r g a n i c N; THN = t o t a l h y d r o l y z a b l e N; AN = h y d r o l y z a b l e ammonium N; AAN = amino a c i d N; ASN = amino s u g a r N; HUN = h y d r o l y z a b l e unknown N; NHN = n o n hy dr o ly za bl e N; NN = n i t r a t e + n i t r i t e N. ( R e f e r t o Ta bl es 4 t o 11 f o r s t a t i s t i c a l t e s t s . ) N FRflCTIONS( MG/KG) 1200 1 100 SUGAR BEET 1 0 0 0 TN 900 B0 0 THN- 700 B0 0 500 CONC. OF 400 300 200 00 0 0 10 20 30 INCUBRTION Fig. 6 . 40 50 B0 70 TIM E( DRYS) C o n c e n t r a t i o n o f n i t r o g e n f r a c t i o n s d u r in g i n c u b a t i o n a t 50 g/kg s u g a r b e e t r e s i d u e a d d i t i o n . TN = t o t a l N; TON = t o t a l o r g a n i c N; THN = t o t a l h y d r o l y z a b l e N; AN = h y d r o l y z a b l e ammonium N; AAN = amino a c i d N; ASN = amino s u g a r N; HUN = h y d r o l y z a b l e unknown N; NHN = n o n h yd r ol y za b le N; NN = n i t r a t e + n i t r i t e N. (R ef er t o Tabl es 4 t o 11 f o r s t a t i s t i c a l t e s t s . ) N FR RC TIO N S( MG/KG) OF 1000 NRVY 300 BERN B0 0 ■ TN TON 700 THN B0 0 500 400 300 • RAN CONC. 200 ••□ AN A NHN 100 HUN FzrrRSN NN 0 0 10 20 30 40 50 G0 70 I N C U B R T I ON T I M E ( D R Y 5 ) Fig. 7. Concentration of nitrogen f r a c t i o n s during incubation a d d i t i o n . TN = t o t a l N; TON = t o t a l o r g a n i c N; THN = AN = h y d r o l y z a b l e ammonium N; AAN = amino a c i d N; ASN h y d r o l y z a b l e unknown N; NHN = n o n h yd ro ly za bl e N; NN = (R ef er t o Tab le s 4 t o 11 f o r s t a t i s t i c a l t e s t s . ) a t 50 g/kg navy bean r e s i d u e t o t a l h y d r o l y z a b l e N; = amino s uga r N; HUN = n i t r a t e + n i t r i t e N. N FRRCTIONSCMG/KG) 1000 CORN 300 TN 800 TON' 700 THN 800 500 400 OF 300 CONC. 200 100 (>— ----- 0 0 10 20 30 40 50 80 70 I N C U B F I T I ON T I M E ( DRYS ) Fig. 8 . C o n c e n t r a t i o n o f n i t r o g e n f r a c t i o n s d u r in g i n c u b a t i o n a t 50 g/kg corn r e s i d u e a d d i t i o n . TN = t o t a l N; TON = t o t a l o r g a n i c N; THN = t o t a l h y d r o l y z a b l e N; AN = h y d r o l y z a b l e ammonium N; AAN = amino a c i d N; ASN = amino s u g ar N; HUN = h y d r o l y z a b l e unknown N; NHN = n o nh yd ro ly za b le N; NN = n i t r a t e + n i t r i t e N. ( R e f e r t o Ta bl es 4 t o 11 f o r statistical tests.) 95 In t h e c a s e o f navy beans ( F i g . 7) s i g n i f i c a n t lo s s e s of N from t h e system d u r i n g t h e l a s t 21 days (Ta bl e 5) were due t o d e c r e a s e s in both THN ( T ab l e 6 ) and NHN (Ta b le 7 ) . An a d d i t i o n a l d e c r e a s e in o r g a n i c N (TON) was due t o n e t n i t r i f i c a t i o n . With corn ( F i g . occurred. 8 ) no a c c u m u l a t i o n o f n i t r a t e o r n i t r i t e I n s t e a d , i t a p p e a r e d t h a t a l a r g e t r a n s f e r o f N from h y d r o l y z a b l e t o n o n h y d r o l y z a b l e f r a c t i o n o c c u r r e d d u ri n g t h e l a s t day s. 21 As a r e s u l t , b ot h TN and TON remained e s s e n t i a l l y unchanged. Changes Among H y d r o ly z a b l e Forms o f N The 3 - way i n t e r a c t i o n p l o t t e d in F i g s . 5 forms o f N in t h e a c i d h y d r o l y s a t e a r e t a b u l a t e d to 8 f o r the d if f e r e n t in Table P r o b a b i l i t i e s f o r main e f f e c t s and i n t e r a c t i o n s a r e 8 t o 11. give n in Tables 1 and 2 , Appendix A. A l f a l f a s y st e m : In F i g . 5 , i t a p p e a r s t h a t much o f t h e N t h a t was l o s t from a l f a l f a - a m e n d e d s o i l a t t h e h i g h e s t r a t e must have o r i g i n a t e d in t h e h y d r o l y z a b l e unknown f r a c t i o n (HUN). A ls o , much o f t h e N t h a t a p p e a r e d as NOg p l u s NOg must have o r i g i n a t e d in t h e HUN f r a c t i o n . A l a r g e i n c r e a s e in t h e h y d r o l y z a b l e ammonium f r a c t i o n (AN) d ur in g t h e f i r s t 21 days i n d i c a t e s t h a t u n i d e n t i f i e d HUN m a t e r i a l s were f i r s t c o n v e r t e d to h y d r o l y z a b l e NH^ a n d / o r e xc ha ng ea b le NH^ b e f o r e en tering into f u r t h e r tra n sfo rm a tio n . Gradual d e c r e a s e s in amino a c i d s (AAN) may r e f l e c t t h e r e c y c l ­ ing o f a l f a l f a p r o t e i n s i n t o a d e c l i n i n g m i c r o b i a l p o p u l a t i o n . A 96 Table 5. E f f e c t o f t y p e and r a t e o f c r o p r e s i d u e s and time o f i n c u b a t i o n on t h e c o n c e n t r a t i o n o f t o t a l N To ta l n i t r o g e n (TN) I n c u b a t i o n time (d ay s) Residue Rate 9 0 A lfalfa Corn Sugar b e e t LSD0 .0 5 21 42 63 - - - - - - - my/ *.y - - - - - - - - - - - /kg Check Navy bean 0 565 605 619 604 2 711 731 751 799 10 811 855 790 760 50 1483 1334 1299 1271 2 648 612 694 644 10 695 692 709 676 50 808 856 855 795 666 693 722 728 10 697 745 707 697 50 767 851 816 826 2 697 657 653 637 10 712 719 704 701 50 965 924 986 930 2 + (3-way i n t e r a c t i o n ) 38 4* ' Values a t ze ro r a t e n o t i n c l u d e d in ANOVA. 97 Table 6 . E f f e c t o f t y p e and r a t e o f cr o p r e s i d u e s and t h e time of i n c u b a t i o n on t h e c o n c e n t r a t i o n o f t o t a l h y d r o l y z a b l e nitrogen T ot al h y d r o l y z a b l e n i t r o g e n (THN) I n c u b a t i o n time (d ay s) Residue Rat e 0 ---------------U|y/ n9// K9 \tn Check A lfalfa 0 + 2 10 50 Navy bean 2 10 50 Corn 2 10 50 Sugar b e e t s 2 10 50 LSD0 .0 5 42 21 63 - 498 531 552 521 557 699 1276 526 607 948 542 628 901 534 594 804 550 576 698 540 572 627 523 592 696 488 524 631 471 553 652 505 547 704 521 588 709 504 546 625 557 591 839 546 577 774 506 577 732 519 570 697 ( 3 - way i n t e r a c t i o n ) ^ V a l u e s f o r zero r a t e n o t i n c l u d e d in AN0VA. 64 98 T a b l e 7. E f f e c t o f t y p e and r a t e o f c r o p r e s i d u e s and t i m e o f i n c u b a t i o n on t h e c o n c e n t r a t i o n o f n o n h y d r o l y z a b l e N Nonhydrolyzable N (NHN)^* I n c u b a t i o n ti m e ( d a y s ) Residue Rate 0 Navy bean 74 67 83 10 153 109 50 200 179 182 179 169 80 157 214 82 191 97 117 157 55 119 228 152 115 158 126 147 119 194 142 114 177 197 146 175 113 106 192 140 200 140 119 125 95 128 132 116 114 137 81 89 133 2 2 10 50 Corn 2 10 50 Sugar b e e t 2 10 50 LSDn nt; 63 67 0 A lfalfa 42 .......... mg/kg g/kg Check 21 $ (3-way i n t e r a c t i o n ) NS *^NHN = Nonh yd ro lyz abl e N = TN - THN ^ V a l u e s a t z e r o r a t e n o t in c l u d e d in ANOVA 99 Tabl e 8 . E f f e c t o f t y p e and r a t e o f crop r e s i d u e s and ti m e o f i n c u b a t i o n on t h e c o n c e n t r a t i o n o f h y d r o l y z a b l e unknown N H y dr o ly za bl e unknown n i t r o g e n (HUN)' I n c u b a t i o n time (d ay s ) Residue Rate 0 42 21 n9/*9 / kn Check 0 A lfalfa 2 10 50 Navy bean 2 10 50 Corn 2 10 50 Sugar b e e t 2 10 50 LSD0 .0 5 $ 63 mn/lsn _- -_ _- _- _- _- _- _- _my/*y 79 150 131 181 207 578 114 116 233 84.0 89 .1 195 67.2 88.5 128 151 119 184 135 182 152 73.8 9 8. 2 143 62.9 7 0 .5 9 3. 4 152 164 198 51.2 119 251 101 92.0 76.9 84.4 141 132 188 8 0. 7 82.3 103.2 211 243 351 (3-way i n t e r a c t i o n ) 110 8 8 - 166. .6 * HUN = H y d r o ly z a b l e unknown N = Tot al h y d r o l y z a b l e N (Ammonium N + amino a c i d N + amino s u g a r N) t V a l u e s : a t ze r o r a t e i n o t i n c l u d e d in AN0VA 103 9 5. 3 100 149 100 Table 9. E f f e c t o f t y p e and r a t e o f c r o p r e s i d u e s and t i m e o f i n c u ­ b a t i o n on t h e c o n c e n t r a t i o n o f h y d r o l y z a b l e ammonium N H yd ro lyz abl e ammonium n i t r o g e n (AN)* I n c u b a t i o n time (day s) Residue Rate 0 141 165 168 172 10 113 133 50 201 168 198 306 162 192 271 166 184 287 2 121 157 129 156 159 170 167 161 176 162 168 171 97 132 137 160 148 164 180 166 180 159 166 176 133 137 145 170 167 217 179 188 232 160 183 215 0 A lfalfa Navy beans 2 10 50 Corn 2 10 50 Sugar b e e t 2 10 50 LSD0 .0 5 63 - mg/kg ---------------- 9/kg Check 42 21 * (3-way i n t e r a c t i o n ) 24, . 6 *AN = h y d r o l y z a b l e ammonium N i n c l u d i n g ex ch an gea ble NH^ 3*Values a t ze r o r a t e n o t i n c l u d e d in ANOVA 101 Table 10. E f f e c t o f t y p e and r a t e o f cr o p r e s i d u e s and time of i n c u b a t i o n on t h e c o n c e n t r a t i o n o f amino a c i d N. Amino a c i d n i t r o g e n (AAN) I n c u b a t i o n time (day s) Residue Rate 0 21 9/ K9 Alfalfa -0 + 2 10 50 Navy beans 2 10 50 Corn 2 10 50 Sugar b e e t s 2 10 50 LSDq q 5 (any com parison) 63 mn f V n ____________ •'iy/Ny ---------- r» / |/n Check 42 186 158 136 136 155 274 396 180 225 349 194 242 328 218 321 226 242 236 188 185 249 205 234 291 147 194 242 179 226 235 222 155 178 274 184 227 305 4 6 .3 Values a t ze r o r a t e n o t in c l u d e d in ANOVA. 236 292 202 236 321 202 192 200 279 194 242 287 192 223 272 102 Table 11. E f f e c t o f t y p e and r a t e o f cr o p r e s i d u e s and time o f i n c u b a t i o n on t h e c o n c e n t r a t i o n o f amino s ug ar N. Amino su g a r n i t r o g e n (ASN) I n c u b a t i o n time (days) Residue Rate 0 21 0 A lfalfa + 2 10 50 Navy bean 2 10 50 Corn 2 10 50 Sugar b e e t 2 10 50 lsdo . o 5 ( 3-way i n t e r a c t ! on) 63 m g / k g ..................... g/kg Check 42 119.0 108 8 6 .0 58. 0 65.3 6 8 .1 67.0 102 105 107 60.0 98. 9 104.0 69 .3 102 70.8 52.7 58 .2 103 6 1 .9 46.5 55.3 8 6 .1 71.0 85 .1 87.8 74.9 6 3 .8 74.9 56.4 54.2 53.5 6 8 .4 85.0 71.6 58.4 61 .9 77.6 58.2 6 3 .8 69.4 51.9 51.9 6 4. 3 44 .3 70.3 75.8 71.2 6 3 .8 61. 9 27.4 "^Values a t ze ro r a t e n o t i n c l u d e d i n ANOVA. 77.7 99. 8 103 s i g n i f i c a n t i n c r e a s e in amino s u g a r s (ASN) from 21 days t o 42 days would be c o n s i s t e n t w i t h n e t s y n t h e s i s by t h e m i c r o b i a l p o p u l a t i o n . Sugar b e e t s y s t e m : I t would a p p e a r t h a t w ith s u g a r b e e t s as with a l f a l f a , N l o s t d u r i n g t h e f i r s t 21 days and N n i t r i f i e d d u r in g t h e f i r s t 42 days must have o r i g i n a t e d in t h e HUN f r a c t i o n ( F i g . 6 ). A ls o , i t would a p p e a r t h a t HUN m a t e r i a l s were f i r s t c o n v e r t e d t o h y d r o l y z a b l e NH^ a n d / o r ex c h a n g e a b le NH^ b e f o r e be in g t r a n s f o r m e d further. The e v i d e n c e t h a t N may have been added t o t h e system between 21 and 42 days may r e f l e c t t h e lo w er N c o n t e n t and w id er C/N r a t i o o f s u g a r b e e t s as compared w it h a l f a l f a . The a p p a r e n t i n c r e a s e a t t h i s time and t h e a p p a r e n t l o s s o f N d u r i n g t h e l a s t 21 days a f f e c t e d a l l f r a c t i o n s e x c e p t HUN. The r a t e o f n i t r i f i c a t i o n l e v e l e d o f f a f t e r 42 d a y s . This would be c o n s i s t e n t w ith d e n i t r i f i c a t i o n a s t h e mechanism f o r N l o s s a t t h i s ti m e . Navy bean s y s t e m : The i n i t i a l F i g . 7 was r e f l e c t e d m a in ly in i n c r e a s e in TN and TON in NHN and t h e AN f r a c t i o n s . Thi s would seem t o s u p p o r t t h e view t h a t a d d i t i o n s o f N t o t h e system were due to adsorption of NHg from t h e at m o s p h e re . The added NHg would be ex p e c te d to ac c u m u la te f i r s t a t a c t i v e s u r f a c e s i t e s in t h e AN f r a c t i o n b e f o r e b ei ng f i x e d in more s t a b l e co m b in at i o n s in t h e fraction. NHN I f b i o l o g i c a l N g - f i x a t i o n had o c c u r r e d i t would be ex p ec te d t o ap p e a r f i r s t in r e c o g n i z e d m e t a b o l i c p r o d u c t s such a s amino a c i d s and amino s u g a r s . In f a c t , i n c r e a s e s in AAN and ASN o c c u r r e d 104 l a t e r and a t t h e expense o f N t h a t p r e v i o u s l y ac c um ula ted i n t h e NHN fraction. Apparent l o s s e s o f N from t h e system d u r in g t h e l a s t 21 days i n vo l v ed mainly d e c r e a s e s in NHN and HUN. However, i t i s l i k e l y t h a t t h i s n i t r o g e n was f i r s t n i t r i f i e d and then l o s t by e i t h e r b i o l o g i c a l o r chemical d e n i t r i f i c a t i o n . The low pH o f t h e s o i l (pH 5 . 5 ) would have f a v o r e d chemical d e n i t r i f i c a t i o n . Corn s ys te m : I n c r e a s e s in TN d u r in g t h e f i r s t 21 days ( F i g . in v o l v e d i n c r e a s e s in b o th AN and NHN, b u t a l s o in HUN. 8 ) I n c r e a s e s in i d e n t i f i a b l e m e t a b o l i c p r o d u c t s (AAN and ASN) d id n o t o c c u r u n t i l later. Again, t h i s i s e v i d e n c e t h a t a d s o r p t i o n o f NH-j, r a t h e r th an N2 " f i x a t i o n , was r e s p o n s i b l e f o r i n c r e a s e d N in t h e syst em. As in t h e o t h e r t h r e e s y st e m s , t h e h y d r o l y z a b l e NH^ f r a c t i o n (AN) a p p e a r s t o r e p r e s e n t N h e l d t r a n s i t i o n a l l y by a c t i v e s u r f a c e groups. I t s e q u i l i b r i u m l e v e l did n o t f l u c t u a t e w i d e l y , b u t t h e f l u x o f N th ro ug h t h i s s t a g e was und ou bte dly hi g h . The HUN f r a c t i o n may r e p r e s e n t a n o t h e r t r a n s i t i o n a l phase th r o ug h which N compounds and complexes o f i n t e r m e d i a t e w ei g h t pas s en r o u t e t o and from l a r g e r and more s t a b l e complexes in t h e NHN fraction. Thus, d u r i n g t h e l a s t 21 days of i n c u b a t i o n , i t a p p e a r s t h a t NHN i n c r e a s e d d i r e c t l y a t t h e expense of t h e HUN f r a c t i o n ( F i g . 8 ). The same t h i n g happened a t t h i s time in t h e a l f a l f a system ( F i g . 5 ) . S i m i l a r r e c i p r o c a l changes between t h e s e two f a c t i o n s had o c c u r r e d d u r in g t h e f i r s t 21 days w ith navy beans ( F i g . 4) and d u r i n g l a t e r s t a g e s o f i n c u b a t i o n with s u g a r b e e t s ( F i g . 3 ) . 105 N i t r i t e o r n i t r a t e d i d n o t a cc u m u la te a t any time in t h e corn system ( F i g . 8 ). I t must be assumed t h a t a c t i v e n i t r i f y i n g p o p u l a t i o n s were p r e s e n t bec a us e t r a c e l e v e l s were m a i n t a i n e d ( T ab l e 4 ) . I t i s p o s s i b l e t h a t n i t r i t e may have been s i d e t r a c k e d i n t o r e a c t i o n s l e a d i n g t o s t a b l e o r g a n i c co m b in at i o n s and t h a t t h e s e r e a c t i o n s may have been i n v o l v e d in t h e t r a n s f e r o f N from t h e HUN f r a c t i o n t o NHN d u r i n g t h e l a s t 21 day s. SUMMARY A l f a l f a t o p s , navy bean s t r a w , corn s t o v e r and s u g a r b e e t t o p s a t 0 , 2, 10, and 50 g/kg were i n c o r p o r a t e d in a Hodunk sandy loam soil. Changes in c o n c e n t r a t i o n and d i s t r i b u t i o n o f N forms were f o l l o w e d o v e r a 63-day i n c u b a t i o n p e r i o d . P a t t e r n s o f n i t r o g e n t r a n s f o r m a t i o n and d i s t r i b u t i o n s o f N in d i f f e r e n t forms were e s s e n t i a l l y u n a f f e c t e d by t h e a d d i t i o n s o f t h e d i f f e r e n t r e s i d u e s a t t h e 2 g/kg r a t e . N i t r i f i c a t i o n r a t e s and t h e q u a n t i t i e s o f NOg p lu s NO^ produced i n c r e a s e d with t h e r a t e o f a d d i ­ t i o n o f r e s i d u e s high in N ( a l f a l f a t o p s , 3.45% N, and s u g a r b e e t t o p s , 1.51% N). In t h e c a s e o f low N m a t e r i a l s (navy bean s t r a w and corn s t o v e r , both a b o u t 0.8% N), n e t n i t r i f i c a t i o n was d e l a y e d a t higher r a te s of a d d itio n . At 50 g / k g , no more th an t r a c e q u a n t i t i e s o f NO3 p l u s N0 g were e n c o u n t e r e d a t any time w ith t h e corn amendment. Some r e c o v e r i n g o f n i t r i f y i n g c a p a c i t y in t h e high r a t e bean system was a p p a r e n t in t h e l a s t sampling (63 d a y s ) . These d i f f e r e n t p a t t e r n s o f n i t r a t e a c c u m u la ti o n d e m o n s t r a t e t h e e f f e c t o f C/N r a t i o on t h e b a l a n c e between n e t m i n e r a l i z a t i o n and n e t i m m o b i l i z a t i o n c f N a s p l a n t r e s i d u e carbon i s c o n v e r t e d t o CO2 and m i c r o b i a l c e l l s and p r o d u c t s . during th e f i r s t 21 Major l o s s e s o f carbon o c c u r r e d days o f i n c u b a t i o n , b u t c o n t i n u e d a t d e c r e a s i n g r a t e s th rou gh t h e 63rd day. Changes in t o t a l N (TN) and d i f f e r e n t i a l 106 107 e f f e c t s on f r a c t i o n a l for ms o f N were most pronounced a t t h e h i g h e s t r a t e o f r e s i d u e a d d i t i o n (50 g / k g ) . Large l o s s e s o f N o c c u r r e d d u r i n g t h e f i r s t 42 days from t h e h i g h e s t r a t e o f a l f a l f a and s u g a r b e e t t o p s . narrow Losses o f N from t h e s e C/N systems were a s c r i b e d t o v o l a t i l i z a t i o n o f NHg. in h y d r o l y z a b l e ammonium Increases (AN), i n c l u d i n g t r a n s i e n t l y high l e v e l s o f e x ch a ng ea bl e NH^ were c o n s i s t e n t w it h t h e i n t e r p r e t a t i o n t h a t r a p i d C was accompanied by n e t m i n e r a l i z a t i o n o f N, resp irato ry loss o f a t r a t e s t h a t exceeded t h e s o i l ' s c a p a c i t y t o ad s or b and s t a b i l i z e th e r e l e a s e d fo r losses of NHg. D e n i t r i f i c a t i o n d i d n o t a p p e a r t o be r e s p o n s i b l e N d u r i n g t h e f i r s t 42 days in t h e s e two s y s t e m s , s i n c e NOg ac c um ula ted a t r a p i d and u ni f or m r a t e s o v e r t h i s p e r i o d . On t h e o t h e r h an d, t h e a d d i t i o n o f wide C/N m a t e r i a l s (navy beans and c o rn ) a t high r a t e s r e s u l t e d in s i g n i f i c a n t i n c r e a s e s in t o t a l N d u r i n g t h e f i r s t 21 d a y s . These i n c r e a s e s were a s c r i b e d to a d s o r p t i o n o f NHg v o l a t i l i z e d from a l f a l f a and s u g a r b e e t systems and t r a n s f e r r e d by d i f f u s i o n th ro u gh t h e c o n f i n e d atmosphere o f t h e growth chamber. The i n c r e a s e s in TN were ac c o u n te d f o r by i n c r e a s e s in t h e n o n h y d r o ly z a b le f r a c t i o n (NHN), h y d r o l y z a b l e ammonium (AN), and u n i d e n t i f i e d h y d r o l y z a b l e forms (HUN). I n c r e a s e s in r e c o g n i z a b l e m e t a b o l i c p r o d u c t s - - a m i n o a c i d s (AAN) and amino s u g a r s (ASN)--did no t o cc u r u n t i l l a t e r . This was ta ken a s e v i d e n c e t h a t t h e i n i t i a l i n c r e a s e s in TN were due t o a d s o r p t i o n o f NHg r a t h e r tha n t o b i o ­ l o g i c a l N2 f i x a t i o n . S i g n i f i c a n t l o s s e s o f N o c c u r r e d d u r in g t h e l a s t 21 t o 42 days from t h e high r a t e s y s t e m s . These a p pe a r ed t o have been due 108 to d e n i t r i f i c a t i o n , s i n c e t h e r a t e o f n i t r a t e a c c u m ul a tio n was s h a r p l y c u r t a i l e d w ith a l f a l f a and s u g a r b e e t s and c o n t i n u e d t o be s t r o n g l y r e p r e s s e d in t h e p r e s e n c e o f beans and c o r n . of the soil The low pH (pH 5 . 5 ) would have f a v o r e d chemical d e n i t r i f i c a t i o n by s i d e t r a c k i n g r e a c t i o n s o f n i t r i t e . A l s o , t h e more r e a d i l y a v a i l a b l e energy s u b s t r a t e s t o s u p p o r t b i o l o g i c a l d e n i t r i f i c a t i o n would have been l a r g e l y d i s s i p a t e d d u r i n g t h e f i r s t s e v e r a l days o f i n c u b a t i o n . S i g n i f i c a n t i n c r e a s e s and d e c r e a s e s in amino a c i d s and amino s u g a r s s u g g e s t t h a t m i c r o b i a l p o p u l a t i o n s may have rea ched peak numbers sometime between t h e 2 1 s t and 42nd day o f i n c u b a t i o n . How­ e v e r , i t app ea re d t h a t much l a r g e r q u a n t i t i e s o f N were a c t i v e l y c y c l e d o v e r t h e e n t i r e i n c u b a t i o n p e r i o d by t r a n s f o r m a t i o n s in v o l v i n g t h e HUN and NHN f r a c t i o n s . R ec i p r o ca l chang es in t h e HUN and NHN f r a c t i o n s s u g g e s t t h a t HUN m a t e r i a l s r e p r e s e n t a t r a n s i t i o n a l phase th rou gh which N i n com­ pounds o f i n t e r m e d i a t e m o l e c u l a r w ei g h t p a s s e s en r o u t e t o and from l a r g e r a n d / o r more s t a b l e complexes in t h e NHN f r a c t i o n . The AN f r a c t i o n + (which in c l u d e d exc h a ng ea bl e NH^) p ro b ab ly r e p r e s e n t s N h e l d t r a n s i e n t l y by a c t i v e s u r f a c e g r o u p s . I t s equilibrium l e v e l d i d n o t f l u c t u a t e w i d e l y , as i s t o be e x p e c te d i f q u a n t i t i e s p r e s e n t depend p r i m a r i l y on a c t i v e s u r f a c e a r e a . f l u x o f N throug h t h i s phase was und o ub te d ly h i g h . N e v e r t h e l e s s , th e Ammonia e n t e r i n g t h e system from t h e e x t e r n a l at mo sp her e o r r e l e a s e d w i t h i n t h e systems by m i n e r a l i z a t i o n would l i k e l y a p p e a r f i r s t a t s u r f a c e s i t e s b e f o r e en terin g into f u r t h e r tran sfo rm atio n s such as m i c r o b i a l im m o bi li za ­ t i o n , n i t r i f i c a t i o n , v o l a t i l i z a t i o n and chemical c o n d e n s a t i o n t o form 109 humic complexes o f v a r y i n g s t a b i l i t y t o be found in t h e HUN and NHN fractions. CONCLUSIONS The ob s er ve d d i s t r i b u t i o n s o f N may have r e s u l t e d , in p a r t , from a r t i f a c t s o f a c i d h y d r o l y s i s - N evertheless, the data in d icate t h a t f r a c t i o n a l a n a l y s e s bas ed on a c i d h y d r o l y s i s can be used t o d i f f e r e n t i a t e a number o f c h e m i c a l l y d i s t i n c t c a t e g o r i e s o f N com­ pounds t h a t ap p e a r t o e x i s t in dynamic s e q u e n t i a l r e l a t i o n s h i p s , one to another. The b a s i c t r a n s f o r m a t i o n l e a d i n g t o changi ng d i s t r i b u t i o n s o f N was un do ub te d ly t h e r e s p i r a t o r y disengagement o f COg by t h e s o i l heterotrophic population. The most a c t i v e l y f l u c t u a t i n g f r a c t i o n s were r e c o v e r e d in t h e h y d r o l y s a t e . O n e - h a l f o r l e s s o f t h e h y d r o l y z a b l e N was in r e c o g n i z a b l e products of microbial s y n th e s is . Thus, much o f t h e a c t i v e c y c l i n g o f N may have in v o l v e d s t r i c t l y chemical a n d / o r p h y s i c a l t r a n s f o r m a t i o n s in t h e e x t r a c e l l u l a r en vi ro n m en t. Nonenzymatic p r o c e s s e s i n f e r r e d from t h e d a t a i n c l u d e d v o l a t i l i z a t i o n and a d s o r p t i o n o f NHg, sequences o f p o l y m e r i z a t i o n and d e p o l y m e r i z a t i o n i n v o l v i n g p r e c u r s o r s and components o f f u l v i c and humic a c i d s , and r e a c t i o n s of n i t r o u s a c i d l e a d i n g to both chemical im m o b il iz a t io n and chemical d e n i t r i f i c a t i o n . These c o n c l u s i o n s were based mainly on r e s u l t s a t t h e 50 g/kg r a t e o f amendment. S e q u e n t i a l changes were no t c l e a r l y e x p r e s s e d a t 110 Ill more p r a c t i c a l lower r a t e s . 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P r o b a b i l i t i e s f o r s i g n i f i c a n c e o f main e f f e c t s and i n t e r a c t i o n s o f r e s i d u e s , r a t e s , and t i m e s on a n a l y s e s f o r c a r b o n and forms o f n i t r o g e n . Source o f v a r i a n c e Parameter Measured Residence (R) Rate (A) Time (T) R x A R x T A x T Rx A x T Degrees of Freedom 3 2 3 6 9 6 18 n = 36 48 36 12 9 12 3 Total N 0 .0 1 0 .0 1 0.0 5 0 .0 1 0 .0 1 0 .0 1 0 .0 1 Total h y d r o l y z a b l e N 0 .0 1 0 .0 1 0 .0 1 0 .0 1 0 .0 1 0 .0 1 0 .0 1 Hyd rolyzable ammonimum N 0 .0 1 0 .0 1 0 .0 1 0 .0 1 0 .0 1 0.05 NS Amino a c i d N 0 .0 1 0 .0 1 0.05 0 .0 1 NS NS 0.05 Amino s u g ar N 0 .0 1 NS 0 .0 1 NS NS NS NS Hyd rolyzable unknown N 0 .0 1 0 .0 1 0 .0 1 0.05 0 .0 1 0.0 5 0. 05 Nonhydrolyzable N 0 .0 1 0 .0 1 NS 0 .0 1 NS 0.0 5 NS Exchangeable NH^ 0 .0 1 0 .0 1 0 .0 1 0 .0 1 0 .0 1 0 .0 1 0 .0 1 N itrate + n i t r i t e N 0 .0 1 0 .0 1 0 .0 1 0 .0 1 0 .0 1 0 .0 1 0 .0 1 Organic C 0 .0 1 0 .0 1 0 .0 1 NS 0 .0 1 NS NS T a b l e 2. P r o b a b i l i t i e s f o r s i g n i f i c a n c e o f main e f f e c t s and i n t e r a c t i o n s o f r e s i d u e s , r a t e s , and t i m e s on t h e p r o p o r t i o n { % o f t o t a l N) o f f r a c t i o n a l form s o f N. Source of v a r i a n c e P arameter measured Residue (R) Rate (A) Time (T) R x A R x T A x T R x A x T Degrees o f Freedom 3 2 3 6 9 6 n = 36 48 36 12 9 12 Total h y d r o l y z a b l e N 0.0 1 0.0 5 0 .0 1 0 .0 1 0. 05 0.05 NS Hydrol yza bl e ammonium N 0 .0 1 0.01 0 .0 1 0. 05 0.0 5 0.0 5 NS Amino a c i d N 0 .0 1 0.0 1 0 .0 1 0.05 0.05 NS 0.05 Amino su ga r N 0.01 0.0 1 0 .0 1 0.01 NS NS NS NS NS 0.01 NS NS NS NS 0 .0 1 0.01 0.05 NS Hydrolyzable unknown N Nonhydrolyzable N N.S. 0 .0 1 N.S. 18 3 119 Table 3. E f f e c t o f t y p e and r a t e o f c r o p r e s i d u e s and t i m e o f i n c u b a t i o n on t h e c o n c e n t r a t i o n o f t o t a l o r g a n i c n i t r o g e n . T ot al o r g a n i c n i t r o g e n (TON)^ I n c u b a t i o n time (d ay s) Residue Rate 0 oi 42 63 ------------------- mg/kg - g/kg Check 21 564 589 593 573 A lfalfa 2 10 50 710 808 1477 705 789 1127 712 709 1058 748 676 994 Navy bean 2 10 50 647 694 807 595 691 855 675 707 854 613 667 751 Corn 2 10 50 665 696 766 682 745 850 696 700 815 697 686 825 Sugar b e e t 2 10 50 696 711 964 642 706 905 622 671 890 600 659 830 LSD0 . 0 5 (3-way i n t e r a c t i o n ) NS 1 TON = T o ta l Org anic N = Tot al N - C ( N i t r a t e + n i t r i t e N) t Values a t z e r o ti m e n o t i n c l u d e d in ANOVA 120 Table 4. E f f e c t o f c r o p r e s i d u e t y p e and time o f i n c u b a t i o n on t h e p r o p o r t i o n o f t o t a l N a s t o t a l h y d r o l y z a b l e N. To ta l h y d r o l y z a b l e N ( e x p r e s s e d a s % o f t o t a l N) I n c u b a t i o n time (d ay s) Residue 0 21 42 % 63 Res idue M< ------------ A lfalfa 8 3. 6 71.3 73.7 69.5 74.5 Navy bean 84.6 81.5 80.2 71.5 8 0 .9 Corn 78.3 76.7 8 0. 6 74.5 77.5 Sugar b e e t 83. 3 82.5 78.6 79.2 80.9 Time mean 82.5 77.9 78.3 75.2 LSD0 .0 5 ( 2-way i n t e r a c t i o n ) 4.8 121 T a b l e 5. E f f e c t o f t y p e and r a t e o f c r o p r e s i d u e s on t h e p r o p o r t i o n o f t o t a l N a s t o t a l h y d r o l y z a b l e N. Total h y d r o l y z a b l e N ( e x p r e s s e d as % o f t o t a l N) Residue r a t e ( g /k g ) Residue 0* 2 10 50 Re sid ue Mean ................. ............. % A lfalfa 87.7 72.4 78.7 72.4 77 .8 Navy bean 87.7 81 .1 81.7 8 0. 1 82.6 Corn 87.7 71.6 78.7 8 2 .4 8 0. 1 Sugar b e e t 87.7 80.5 8 1 .7 80.5 82.6 Rate mean 87.7 76.4 8 0 .2 78.8 LSD0 .0 5 (2-way i n t e r a c t i o n ) 4.2 ^ V a l u e s a t ze ro r a t e n o t in c l u d e d in ANOVA. 122 Table 6. E f f e c t o f c r o p r e s i d u e r a t e and tim e o f i n c u b a t i o n on t h e p r o p o r t i o n o f t o t a l N a s t o t a l h y d r o l y z a b l e N. To ta l h y d r o l y z a b l e N ( e x p r e s s e d a s % o f t o t a l N) I n c u b a t i o n time (days) 0 Rate 21 9/k g 42 % 63 Rate Mean -------------- ot 77.4 76.6 75.6 74.7 76.1 2 78.4 79.4 74.3 73.4 76.4 10 8 2. 9 76.6 8 2. 1 78.8 80.2 50 8 6 .0 77.7 78.3 73.3 78.8 Time mean 81 .2 77.6 77.6 75.1 LSD0 .0 5 ( 2-way i n t e r a c t i o n ) 4.2 1"Values a t z e r o r a t e n o t in c l u d e d in ANOVA 123 T a b l e 7. E f f e c t o f t y p e and r a t e o f c r o p r e s i d u e on t h e c o n c e n t r a ­ t i o n o f n o n h y d r o l y z a b l e N. Nonhydrolyzable N ^ Residue r a t e ( g /k g ) Residue 0^ 2 10 50 Residue Mean mg/kg A lfalfa 70. 0 178.8 113.2 181.7 135.9 Navy bean 70.0 107.2 124.6 153.7 113.9 Corn 70.0 184.4 147.7 141.7 135.9 Sugar b e e t 70.0 107.8 107.5 131.7 104.2 Rate mean 70.0 144.6 123.2 152.2 LSD0.0 5 (2-way i n t e r a c t i o n ) ^ N on hyd ro lyz abl e N = Total N $ 34 .7 Tot al h y d r o l y z a b l e N Values a t ze ro r a t e n o t in c l u d e d in ANOVA 124 Table 8. E f f e c t o f r e s i d u e r a t e and t i m e o f i n c u b a t i o n on t h e c o n c e n t r a t i o n o f n o n h y d r o l y z a b l e N. Nonhydrolyzabl e N1" I n c u b a t i o n time (day s) 0 Rate 21 42 63 Rate Mean mg/kg .......... g/kg O -H - 7 0. 0 154.0 55 .0 167.0 111.5 2 145.3 126.0 152.8 153.3 144.6 10 121.6 156.5 100.4 114.3 123.2 50 137.5 171.2 139.3 160.8 152.2 118.7 152.0 111.9 148.9 Time mean LSD0 . 0 5 ( 2-way i n t e r a c t i o n ) 3 4. 7 ^ N o nh yd ro ly za bl e N = Tot al N - T o ta l h y d r o l y z a b l e N $ V a l u e s a t z e r o r a t e n o t i n c l u d e d in ANOVA 125 T a b l e 9. E f f e c t o f t y p e and r a t e o f c r o p r e s i d u e on t h e p r o p o r t i o n o f t o t a l N a s n o n h y d r o l y z a b l e N. Nonhy dro lyza ble N* ( e x p r e s s e d a s 5I o f t o t a l N) Residue r a t e (g/tcg) Residue 0* 2 10 50 Residue Mean ...................% -----------------A lfalfa 12.3 23.7 13.9 13.5 15.9 Navy bean 12.3 16.2 17.9 18.3 16.2 Corn 12.3 26.2 20. 6 17.1 19.1 Sugar b e e t 12.3 16.1 15.1 13.8 14.3 Rate mean 12.3 2 0 .6 16.9 15.7 LSD0.0 5 (2-way i n t e r a c t i o n ) 4.2 ^ N o n h y d r o ly z a b le N = T o ta l N - Tot al h y d r o l y z a b l e N ^ V a l u e s a t z e r o r a t e n o t i n c l u d e d in ANOVA 126 T a b l e 10. E f f e c t o f r e s i d u e r a t e and t i m e o f i n c u b a t i o n on t h e p r o p o r t i o n o f t o t a l N a s n o n h y d r o l y z a b l e N- Nonhydrolyzabl e NT ( e x p r e s s e d a s 5I o f t o t a l N) I n c u b a t i o n t i m e ( day s) 0 Rate 21 42 63 Rate Mean -------------% g/kg 0* 12.3 2 2 .5 19.1 24.3 19.6 2 21.3 18.2 21 .5 21.3 2 0 .6 10 16.8 2 0 .6 13.8 16.3 16.9 50 13.7 17.8 14.2 17.1 15.7 Time mean 16.0 19.8 17.1 19.8 LSD0.0 5 (2-way i n t e r a c t i o n ) 4.2 ^N o n h y d r o ly z a b le N = Tot al N - Total h y d r o l y z a b l e N $ V a l u e s a t z e r o r a t e n o t i n c l u d e d i n ANOVA 127 T a b l e 11. E f f e c t o f r e s i d u e t y p e and t i m e o f i n c u b a t i o n on t h e c o n c e n t r a t i o n o f h y d r o l y z a b l e ammonium N. H ydr oly zab le ammonium N (AN)^ I n c u b a t i o n time (day s) Residue 0 21 42 63 Residue Mean ............ mg/kg ----------A lfalfa 148.6 223.8 208.2 2 1 1 .8 198.1 Navy bean 135.4 161.7 167.9 166.9 158.0 Corn 121.8 157.2 175.1 161.1 155.3 Sugar b e e t 138.0 184.4 199.6 186.0 177.0 Time mean 135.9 181.8 187.7 182.9 172.1 LSD0.0 5 ( 2-way i n t e r a c t i o n ) 14.2 ^ AN = Hydro lyz abl e ammonium N i n c l u d i n g ex ch . NH^ 128 T a b l e 12. E f f e c t o f t y p e and r a t e o f c r o p r e s i d u e s on t h e c o n c e n t r a t i o n o f h y d r o l y z a b l e ammonium N. Hy d ro ly za bl e ammonium N (AN)^" Residue r a t e ( g /k g ) Residue 0^ 2 10 50 Residue Mean mg/kg A lfalfa 141.0 151.9 176.6 265.6 183.8 Navy bean 141.0 151.5 161.0 161.6 153.8 Corn 141.0 149.2 152.7 164.1 151.8 Sugar b e e t 141.0 160.5 168.6 201.9 168.0 Rate mean 141.0 153.3 164.7 198.3 LSD0 .0 5 (2-way i n t e r a c t i o n ) 12.3 tAN = H y dr o ly za bl e ammonium N i n c l u d i n g ex ch . NH^ ■^Values a t ze r o r a t e n o t in c l u d e d in ANOVA 129 T a b l e 13. E f f e c t o f r e s i d u e r a t e and t i m e o f i n c u b a t i o n on t h e c o n c e n t r a t i o n o f h y d r o l y z a b l e ammoniijm N. Hydrolyzabl e ammonium N (AN)1" I n c u b a t i o n time (d ay s) Rate 0 42 63 Rate Mean •.......... m g / k g ------------- g/kg * 21 141.0 165.0 168.0 172.0 161.5 2 115.9 163.4 171.9 161.9 153.3 10 139.4 167.9 176.6 175.0 164.7 50 152.6 214.0 214.7 21 2 .0 198.3 137.2 177.6 182.8 180.2 0 Time mean LSD0 .0 5 ( 2 - way i n t e r a c t i o n ) 12.3 t AN = Hy d ro ly za b le ammonium N i n c l u d i n g exch . NH^ 1rValues a t z e r o r a t e n o t i n c l u d e d in ANOVA 130 T a b l e 14. E f f e c t o f r e s i d u e t y p e and ti m e o f i n c u b a t i o n on t h e p r o p o r t i o n o f t o t a l N a s h y d r o l y z a b l e ammonium N. Hyd rolyzable ammonium N (AN)^ I n c u b a t i o n time (days) Residue 0 42 21 63 Residue 1 %*■.......... A lfalfa 15.2 22.9 2 2 .2 22.4 20.7 Navy bean 19.0 2 2 .8 22.5 23.8 2 2 .0 Corn 17.2 20. 7 23 .5 22.3 2 0 .9 S uga r b e e t 17.8 24 .2 25.7 24.8 23.1 Time mean 17.3 22.7 23.5 23.3 LSD0 .0 5 (2-way i n t e r a c t i o n ) 1.7 t AN = H yd ro ly za b le ammonium i n c l u d i n g exch . NH^ X Ex pressed as % of t o t a l N 131 T a b l e 15. E f f e c t o f t y p e and r a t e o f c r o p r e s i d u e s on t h e p r o p o r ­ t i o n o f t o t a l N a s h y d r o l y z a b l e ammonium N. Hy d ro ly za bl e ammonium N (AN)1" Res i d u e r a t e ( g / k g ) 0* Residue 2 10 50 Residue Mean .......... — % A lfalfa 24 .8 20.3 2 2 .0 19.9 2 1 .8 Navy bean 24.8 23.3 23.3 19.5 22 .7 Corn 2 4 .8 2 1 .2 2 1 .5 2 0 .2 21.9 Sugar b e e t 24 .8 24.4 23.8 21.3 23.6 Rate mean 24 .8 2 2 .3 2 2 .6 2 0 .2 LSD0 . 0 5 ( 2-way i n t e r a c t i on) 1. 5 t AN = H y d r o l y z a b l e ammonium N i n c l u d i n g exch . NH^ ^ Value a t z e r o r a t e n o t in c l u d e d in ANOVA § Ex p res sed a s % o f t o t a l N 132 T a b l e 16. E f f e c t o f r e s i d u e r a t e and t im e o f i n c u b a t i o n on t h e p r o p o r t i o n o f t o t a l N a s h y d r o l y z a b l e ammonium N. Hyd ro ly za bl e ammonium N (AN)t I n c u b a t i o n ( day s) 0 21 42 63 Rate Mean %x..... 9 / kg oS 24.8 26.4 27.6 25 .0 25.9 2 17.0 24.4 24. 5 23.3 22.3 10 19.3 22.3 24.3 24.7 2 2 .6 50 15.6 21.4 2 1 .8 22.1 2 0 .2 19.2 23.6 24.6 23.8 22 .8 Time mean LSD0 .0 5 (2-way i n t e r a c t i on) 1.5 t AN = H y d r o ly z a b l e ammonium N i n c l u d i n g exch . NH^ ■f Ex pr es se d a s % o f t o t a l N 5 Values a t z e r o r a t e n o t in c l u d e d in ANOVA 133 T a b l e 17. E f f e c t o f t y p e and r a t e o f c r o p r e s i d u e s and tim e o f i n c u b a t i o n on t h e p r o p o r t i o n o f t o t a l N a s amino a c i d N. Amino a c i d n i t r o g e n (AAN) I n c u b a t i o n time (days) Residue Rate 0 21 42 63 _ *10 t _— —..................... ————————— 9/ kg Check 0* 32 .9 26.1 30 .0 30.8 A lfalfa 2 21 .7 24.5 25.9 25.3 10 33 .7 26.3 30. 5 28.6 50 26.7 26.0 25.2 25.2 2 3 4 .8 30 .6 29.5 29.7 10 34 .8 26.6 33 .0 29.6 50 29.2 28.9 34.1 35.1 2 22.1 25.7 30 .7 26.8 10 27.9 30.3 33. 4 34.6 50 3 1 .6 27.8 35. 7 34.7 2 2 2 .1 27.9 30.9 30.1 10 25.0 25.8 33. 5 31.8 50 28.3 28.5 32.5 29.2 Navy bean Corn Sugar b e e t (3-way i n t e r a c t i o n ) LSD0 . 0 5 t 4.7 Ex p res se d a s % o f t o t a l N ^ Values a t z e r o r a t e n o t i n c l u d e d in ANOVA 134 Tabl e 18. Simple e f f e c t o f ty pe o f c r o p r e s i d u e s and time o f i n c u b a t i o n on t h e c o n c e n t r a t i o n and p r o p o r t i o n o f t o t a l N a s amino s u g a r N. Amino s ug ar N Residue mg/kg Time o f incubation Amino s u g a r N (ASN) day mg/kg ** A lfalfa 9 0. 5 0 76 .2 9.7 Beans 73.7 21 58 .4 7. 4 Corn 6 6 .7 42 82.8 10.4 Sugar b e e t 6 2 .2 63 75.9 9.9 7. 9 1 ,1 LSD0 . 0 5 7.9 t Expressed a s % o f t o t a l N 135 Table 19. E f f e c t o f t y p e and r a t e o f r e s i d u e on t h e p r o p o r t i o n o f t o t a l N a s amino s u g ar N • Amino s ug ar N (ASN) Residue r a t e ( g/ k g) ot Residue 2 10 50 Residue 1 %X------------- A lfalfa 16.2 12.5 11.4 6.5 1 1 .6 Navy bean 16.2 10.1 10.5 10.1 11.7 Corn 16.2 9.2 9. 3 8 .6 10.8 Sugar b e e t 16.2 8 .6 8 .8 7.1 10.2 Rate mean 16.2 10.1 9.9 8 .1 (2-way i n t e r a c t i o n ) LSD0 .0 5 1 .8 ' Values a t z e r o r a t e n o t in c l u d e d in ANOVA X Exp ressed a s % o f t o t a l N 136 T a b l e 20. S i m p l e e f f e c t o f t i m e o f i n c u b a t i o n on t h e p r o p o r t i o n o f t o t a l N a s h y d r o l y z a b l e unknown N. I n c u b a t i o n time Day ...................................... — f ..... Hy d ro ly za bl e unknown N (HUN) %* 0 27 .2 21 20:5 42 13.1 63 13.4 1.1 LSD0 . 0 5 + 1 HUN = H y d r o ly z a b l e unknown N = Total h y d r o l y z a b l e N - (ammonium N + amino a c i d N + amino s u g a r N) $ Ex p res se d a s % o f t o t a l N APPENDIX B SOIL SERIES 137 APPENDIX B1 HODUNK SERIES The Hodunk s e r i e s c o n s i s t s o f m o d e ra tl e y well d r a i n e d GrayBrown P o d z o l i c ( O c h r e p t i c f r a g u d a l f ) s o i l s w ith f r a g i p a n s which de v el op ed on c a l c a r e o u s sandy loam g l a c i a l t i l l . Hodunk s o i l s a r e found i n a s s o c i a t i o n w i t h t h e well d r a i n e d H i l l s d a l e and m o d e r a te l y well d r a i n e d Elmdale s e r i e s which a l s o dev eloped on c a l c a r e o u s sandy loam t i l 1. S o il Profile: Hodunk sandy loam AP 0 - 0 . 18m Dark g r a y i s h brown (10 YR 4 / 2 ) t o very dark g r a y i s h brown (10 YR 3 / 2 ) ; sandy loam; m o d e ra te l y f i n e , g r a n u l a r s t r u c t u r e ; f r i a b l e when m o i s t and s o f t when d r y ; medium c o n t e n t o f o r g a n i c m a t t e r ; medium t o s l i g h t l y a c i d ; a b r u p t smooth boundary. 0 . 1 0 t o 0.28m t h i c k Ap 0 . 1 8 - 0 . 41m Y ell ow ish brown (10 YR 5 / 4 ) ; p a l e brown (10 YR 6 / 3 ) o r l i g h t y e l l o w i s h brown (10 YR 6 / 4 ) ; sandy loam; weak, f i n e , g r a n u l a r t o weak, f i n d s u b a n g u l a r blo ck y s t r u c t u r e ; very f r i a b l e when m oi st and s o f t when d r y ; medium a c i d ; a b r u p t wavy boundary. 0 . 1 5 t o 0 .5 1 m t h i c k . B. 0 . 4 1 - 0 . 64m 1111 Brown (10 YR 5 /3 ) t o p a l e brown (10 YR 6 / 3 ) ; sandy loam t o l i g h t sandy c l a y loam; massive t o weak, t h i c k , p l a t y s t r u c t u r e ; f i r m when m o i s t and b r i t t l e when d r y ; weak t o m o d e ra te l y developed f r a g i p a n ; few th e n c l a y f l o w s ; medium t o s t r o n g l y a c i d ; c l e a r wavy boundary. 0 .1 0 t o 0.3 0 m t h i c k . 138 139 B2g 0 . 6 4 - 1 17m Brown (10 YR 5 /3 ) t o y e l l o w i s h brown (10 YR 5/4) m o t t l e d w it h y e l l o w i s h brown (10 YR 5/ 8 ) and dark brown ( 7 . 5 YR 4 . 4 ) , m o t t l e s a r e common, medium, d i s t i n c t ; sandy c l a y loam, heavy sandy loam, or l i g h t c l a y loam; few t h i n c l a y f l o w s ; weak, medium, s u b a n g u l a r blo ck y s t r u c t u r e ; f i r m when m o i s t , s t r o n g l y t o medium a c i d in t h e upper p a r t and s l i g h t l y a c i d in t h e lower p a r t ; a b r u p t i r r e g u l a r bo un dar y. 0 .3 8 t o 0.7 6 m t h i c k . Cg 1.18 m + L i g h t y e l l o w i s h brown (10 YR 6 / 4 ) t o brown (10 YR 5 / 3 ) m o t t l e d w i t h y e l l o w i s h brown (10 YR 5 / 6 - 5 / 8 ) , m o t t l e s a r e common, medium, d i s t i n c t ; sandy loam; m a ss iv e t o ve ry weak, c o a r s e , s u b a n g u l a r blocky s t r u c t u r e ; f r i a b l e when m oi st and ha r d when d r y ; calcareous. Topography: G e n tl y t o m o d e ra te l y s l o p i n g t i l l moraines. p l a i n s and Drainage and Perm eability: M od er at e ly well d r a i n e d . S u r f a c e r u n o f f i s slow t o m o d e ra te . P e r m e a b i l i t y i s moderate t o slow depe ndi ng upon t h e d e g r e e o f development o f t h e fragipan. N atu ral V egetation: Deciduous f o r e s t c o n s i s t i n g o f s u g a r maple, b e e c h , oa k , and h i c k o r i e s . Source: S c h n e i d e r , I . F . , R. W. Joh ns on , and E. P. W h i te s id e . 1967. T e n t a t i v e placement o f Michigan s e r i e s in t h e new s o i l c l a s s i f i c a t i o n syst em . Dept, of Crop and So il S c i . , Michigan S t a t e U n i v e r s i t y , E a s t L a n s i n g , Michigan. APPENDIX B2 KALAMAZOO SERIES The Kalamazoo s e r i e s c o n s i s t s o f d e e p , well d r a i n e d s o i l s , formed in loamy outwash o v e r l y i n g s a n d , loamy s a n d , o r sand and gra ve l on outwash p l a i n s , t e r r a c e s , v a l l e y t r a i n s , and low l y i n g m o r a i n e s . These s o i l s have mode rate p e r m e a b i l i t y in t h e A and B h o r i z o n s and r a p i d p e r m e a b i l i t y in t h e 11B and 11C h o r i z o n s . 0 t o 12 p e r c e n t . S lo p e s range from Mean annual p r e c i p i t a t i o n i s a b o u t 34 i n c h e s , and mean annual t e m p e r a t u r e i s a b o u t 49 d e g r e e s F. TAXONOMIC CLASS: Typical Pedon: F in e- lo am y , mixed, mesic Typic H a p l u d a l f s . Kalamazoo loam—on a 1 p e r c e n t s l o p e in a c u l t i v a t e d field. (C o lo r s a r e f o r m o i s t s o i l u n l e s s o t h e r w i s e stated .) So il P rofile Ap 0 - 0 . 28m Dark g r a y i s h brown (10 YR 4 / 2 ) loam; weak medium g r a n u l a r s t r u c t u r e ; f r i a b l e ; common f i n e r o o t s ; n e u t r a l ; a b r u p t smooth boun dar y. 0 . 1 5 t o 0.2 8 m thick. B1 0 . 2 8 - 0 . 41m Dark y e l l o w i s h brown (10 YR 4 / 4 ) loam; weak medium s u b a n g u l a r blo ck y s t r u c t u r e ; f r i a b l e ; common f i n e r o o t s ; worm c h a n n e l s f i l l e d w ith Ap m a t e r i a l ; n e u t r a l ; gradu al wavy b ou nda ry . 0 t o 0 . 1 5 m t h i c k . B21t 0 . 4 1 - 0 . 51m Dark y e l l o w i s h brown (10 YR 4 / 4 ) c l a y loam; moderate medium s u b a n g u l a r bloc ky s t r u c t u r e ; f i r m ; t h i n c o n t in u o u s dark y e l l o w i s h borwn (10 YR 3 / 4 ) c l a y f i l m s on f a c e s o f p e d s ; few f i n e r o o t s ; 1 p e r c e n t p e b b l e s ; n e u t r a l ; gr adu al wavy boundary. B22t 0 . 5 1 - 0 . 76m Dark brown ( 7 . 5 YR 4 / 4 ) c l a y loam; moderate medium s u b a n g u l a r bloc ky s t r u c t u r e ; f i r m ; t h i n c o n t i n u o u s dark y e l l o w i s h brown (10 YR 3 / 4 ) c l a y f i l m s on f a c e s o f peds ; few f i n e r o o t s ; 1 p e r c e n t p e b b l e s ; n e u t r a l ; gradu al wavy boundary. The combined t h i c k ­ n ess o f th e B21t and B22t h o r i z o n s 0 .2 0 t o 0 .7 6 m. 140 141 B23t 0 . 7 6 - 0 . 96m Dark y e l l o w i s h brown (10 YR 4 / 4 ) sandy loam; weak medium s u b a n g u l a r blocky s t r u c t u r e ; f r i a b l e ; t h i n d i s c o n t i n u o u s dark y e l l o w i s h brown (10 YR 3 /4 ) c l a y f i l m s on f a c e s o f p e d s ; 5 p e r c e n t p e b b l e s ; medium a c i d ; g r a d u a l wavy boundary. 0 .1 5 t o 0 .3 8 m thick. IIb31 0 . 9 6 - 1 . 07m Dark y e l l o w i s h brown (10 YR 4 / 6 ) loamy c o a r s e sand; m a s s i v e ; f r i a b l e ; 10 p e r c e n t p e b b l e s ; medium a c i d ; g r a d u a l wavy boun dar y, t t o 0 .5 1 m t h i c k . II b 32 1 . 1 - 1 . 39m Dark y e l l o w i s h brown (10 YR 4 / 4 ) g r a v e l l y loamy s a n d ; m a s s iv e ; f r i a b l e ; 20 p e r c e n t p e b b l e s ; n e u t r a l ; g r a d u a l wavy boundary. 0 to 0 .3 8 t h i c k . IIC Dark y e l l o w i s h brown (19 YR 4 / 4 ) g r a v e l l y c o a r s e san d; s i n g l e g r a i n e d ; l o o s e ; 20 p e r c e n t p e b b l e s ; s l i g h t effe rv e sc e n c e ; mildly a l k a lin e . 1 . 4 - 1 . 63m D rainage and Permeability: Well d r a i n e d . Runoff i s slow on t h e l e v e l a r e a s and r a p i d on t h e s t e e p e r s l o p e s . P e r m e a b i l i t y i s mode rate in t h e A and B h o r i z o n s and r p a i d in t h e IIB3 and IIC h o r i z o n s . Use and Vegetation: A l a r g e p a r t i s cropped t o c o r n , w hea t, s o yb ea ns , and hay. A small p a r t i s in p a s t u r e . Some a r e a s a d ja c e n t to the la r g e r c i t i e s are id le cropland. The n a t i v e v e g e t a t i o n was oak and h i c k o r y f o r e s t . Source: N a t i o n a l C o o p e r a t i v e S o il Surv ey, U .S .A . , 1978. APPENDIX B3 CHARITY SERIES The c h a r i t y s e r i e s c o n s i s t s o f p o o r l y d r a i n e d t o ve r y p o o r ly d r a i n e d and limy s o i l s which d ev el o p ed from h i g h l y c a l c a r e o u s s t r a t i f i e d l a c u s t r i n e c l a y and s i l t y c l a y m a t e r i a l s (management group l c - c ) . They a r e g e n e r a l l y l o c a t e d in n e a r l y l e v e l t i l l and l a k e p l a i n a r e a s . Rep res ent ati on p r o f i l e o f C h a r i t y s i l t y c l a y loam in a c u l t i v a t e d field: 0.0.15m Very d a r k g r a y , f r i a b l e , limy s i l t y c l a y loam; strong g ra n u la r s t r u c t u r e . 0 . 1 5 - 0 . 28m G ra y is h - b r o w n , f i r m , 0 . 2 8 - 0 . 51m L i g h t b r o w n i s h - g r a y , very f i r m , limy s i l t y c l a y ; f a i n t l y m o t t l e d w it h p a l e brown. 0 . 5 1 - 1 . 07m + L i g h t b r o w n i s h - g r a y , Taxonomic l a s s f o r t h e C h a r i t y Clay: limy s i l t y c l a y . very f i r m , limy c l a y . A e r i e , H a p le a q u e p t, f i n e , illitic ( c a l c a r e o u s , mesic) Source: Soil Survey Arenac County, Michigan. USDA Soil C o n s e r v a ti o n S e r v i c e in C o o p e r a t io n w ith Michigan A g r i c . Exp. S t a . and Michigan Dept, o f C o n s e r v a t i o n , May 1967. 142