Pe do s phe r e 15( 6) : 7 07 -71 5, 2 0 0 5 I SS N 1 0 0 2 - 01 6 0/ CN 3 2 - 1 31 5 / P ⑥ 2005 SCI ENCE PRESS, BEI JI NG Ef f ects of Accel erated Soi l Erosi on on Soi l Nutri ent Loss Af t er Def or es t ati on on t he Loes s Pl at eau* 1 ZHENG Fen- Li St at e Ke y Lab o r at or y o f Soi l Er o s i o n and Dr yl and Far mi ng i n Lo e s s Pl at e au, I ns t i t ut e o f So i l and Wat e r Cons e r v at i on, Ch i ne s e Ac ade my o f Sc i e nc e s a nd Mi ni s t r y o f Wa t e r Re s o ur c e s , Ya n g l i n g 7 1 21 0 0 ( Ch i na ) . E- ma i l : f l z h@i s wc . a c . c n ( Re c e i v e d Ma y 1 1 , 2 0 0 5 ; r e v i s e d S e pt e mbe r 2 5, 2 0 0 5 ) ABSTRACT S oi l e r os i on and nut r i e nt l o s s e s on ne wl y- de f or e s t e d l ands i n t he Zi wul i ng Re gi on on t he Loe s s Pl at e au of Chi na we r e moni t o r e d t o qua nt i t a t i ve l y e v al uat e t he e fe c t s of ac c e l e r a t e d s oi l e r os i on, c aus e d by de f or e s t at i on, on or gani c ma t t e r , ni t r o g e n a nd ph o s pho r u s l o s s e s . Ei g h t n a t ur a l r uno fp l o t s we r e e s t a bl i s h e d o n t h e l o e s s i a l h i l l s l o pe s r e pr e s e n t i ng di fe r e n t e r o s i on pa t t e r ns of do mi na n t e r o s i o n pr oc e s s e s i n c l u di n g s he e t , r i l l a n d s ha l l o w gul l y ( s i mi l a r t o e ph e me r a l gul l y) . S e di me n t s ampl e s we r e c ol l e c t e d af t e r e ac h e r os i ve r ai nf al l e ve nt . Re s ul t s s ho we d t hat s oi l nut r i ent s l os s e s i nc r e a s e d wi t h an i nc r e as e of e r os i on i nt e ns i t y. Li ne a r r e l at i ons be t we e n t he l os s e s of or gani c ma t t e r , t ot al N, NH4 - N, and a v ai l abl e P and e r os i o n i n t e ns i t y we r e f ound. Nu t r i e n t c on t e nt pe r un i t a moun t o f e r o de d s e di me n t de c r e a s e d f r o m t he s he e t t o t he s ha l l o w gul l y e r os i on z one s , whe r e a s t ot al nut r i e nt l o s s i nc r e a s e d. Compar e d wi t h t ops oi l , nut r i en t s i n e r ode d s e di me nt we r e e nr i c he d, e s pe c i al l y a v ai l abl e P and NH4 - N. The i nt e ns i t y of s oi l nut r i e nt l os s e s was al s o c l os e l y r e l a t e d t o s oi l e r os i on i nt e ns i t y and pa t t e r n wi t h t he mos t s e v e r e s o i l e r o s i o n a nd n ut r i e n t l os s oc c u r r i ng i n t he s h a l l o w gul l y c ha n ne l s o n l o e s s i a l hi l l s l o pe s . Th e s e r e s e a r c h indi f ng s wi l l he l p t o i mpr o v e t he und e r s t a n di ng o f t he r e l a t i o n be t we e n a c c e l e r a t e d e r o s i on pr o c e s s a f t e r de f or e s t a t i on and s oi l qual i t y de gr a da t i on and t o de s i gn be t t e r e c -en o vi r onme nt al r e habi l i t a t i on s c he me s f or t he Lo e s s Pl at eau. Ke y Wo r d s : a c c e l e r a t e d s oi l e r os i on, de f or e s t at i on, e r os i on i nt e ns i t y, Loe s s Pl a t e au, nut r i e nt l os s I NTRODUCTI ON S o i l nut r i e nt l o s s c a us e d饰 a c c e l e r a t e d s o i l e r o s i o n a f t e r de f o r e s t a t i o n i s be c o mi ng mo r e o f a c o nc e r n i n t he wo r l d. A l a r g e numbe r o f s t udi e s ha v e be e n de s i gne d t o i n ve s t i g a t e s o i l nut r i e nt l os s wi t h e r o de d s e d i me n t s . F o r i ns t a nc e , Fl a na g a n a n d Fo s t e r ( 1 9 8 9 ) f o und t h a t n u t r i e n t s i n e r o de d s e di me n t we r e s i g n i ic f a n t l y e n r i c he d; Mo n k e e t a l . ( 1 9 7 7 ) s ho we d t ha t n u t r i e n t e n r i c h me n t r a t i o s i n s e d i me n t r a n g e d f r o m 1 . 2 t o 2 . 3 ; Yo u n g e t a l . ( 1 9 8 6 ) s h o we d t ha t n u t r i e n t e n r i c hme n t i n e r o d e d s e d i me n t d e c r e a s e d wi t h a n i n c r e a s i n g r u no fr a t e a nd s us pe n de d s e di me n t c o nc e n t r a t i o n; a nd J o h ns o n a n d Ba k e r ( 1 9 8 3 , 1 9 8 4 ) a f t e r a n a l yz i n g o v e r 6 5 0 i n di v i dua l r u no fs a mpl e s f r o m c o r n a nd s o y be a n ie f l d s d i s c o v e r e d t ha t Kj e l da h l - N a nd t o t a l P c o n t e n t s i n s e di me n t we r e c l o s e l y r e l a t e d t o s e di me n t c o n c e n t r a t i o n i n r u no f. I n a dd i t i o n, S h a r p l e y e t a l . ( 1 9 9 1 ) me a s u r e d e r o s i o n a n d a s s o c i a t e d N a n d P l o s s e s wi t h s e d i me n t u n d e r na t ur a l r a i nf a l l a s a fe c t e d b y ma na g e me nt a nd f o und t ha t bo t h N a nd P c o nt e n t s i n s e di me nt we r e s t r ongl y r e l at e d t o s e di me nt c onc e nt r at i on of i ndi vi dua l r unofe ve nt s . D ur i ng t he pa s t 1 0 y e a r s i n t he Uni t e d St at e s muc h e fo r t ha s be e n de v ot e d t o s t udyi ng t he e fe c t s o n s o i l qua l i t y whe n c on ve r t i ng v e g e t a t i o n t o c ul t i v a t i on, s uc h a s t he Co ns e r v a t i o n Re s e r v e Pr o g r a m ( CRP) . Th e r e s u l t s s h o we d t h a t c o n v e r t i n g CRP l a n d s t o c u l t i v a t i o n s i g n i ic f a n t l y i n c r e a s e d r u n o fa n d e r o s i o n a nd a c c e l e r a t e d s o i l q ua l i t y d e g r a da t i o n ( Da v i e a nd La n t , 1 9 9 4 ; Gi l l e y e t a l . , 1 9 9 6, 1 9 9 7 a, b) . I n Chi na, s t udi e s o f s o i l e r o s i o n a nd s o i l de g r a da t i o n ha v e be e n mo s t l y c o nduc t e d i n s e ve r e l y e r ode d r e g i o ns , s u c h a s t h e r e d - s o i l r e g i o n ( Ti a n e t a l . , 2 0 0 3 ; Zh a n g e t a l . , 2 0 0 4 ) a nd t h e Lo e s s Pl a t e a u ( Ta n g e t a l . , 1 9 8 7 ; Ba i e t a l . , 1 9 9 1 ; Li , 1 9 9 0; Pe ng a nd Wa n g, 1 9 9 5 ) . Ho we v e r , l i t t l e a t t e n t i o n ha s be e n pa i d t o qua n t i f yi ng s o i l nut r i e nt l os s a nd s o i l qua l i t y de t e r i o r a t i o n a f t e r de f o r e s t a t i on, e s pe c i a l l y o n t he Loe s s * ' Pr o j e c t s u pp o r t e d b y t h e Na t i o n a l Na t u r a l Sc i e n c e F o u n da t i o n o f Chi n a ( No. 9 0 3 0 2 0 0 1 ) a n d t h e Na t i o n a l Ke y Ba si c Re s e a r c h Suppor t Fou nda t i o n ( NKBRS F) o f Chi na ( No. 2 0 0 2 CB1 1 1 5 0 2 ) 万方数据 708 F. L. M ENG Pl a t e a u whe r e s o i l qua l i t y de t e r i o r a t i o n c a us e d by a c c e l e r a t e d s oi l e r o s i o n a f t e r de f o r e s t a t i o n ha s be c o me one of t he mai n envi r onment al i s s ues. T he Zi wul i ng Se c o nda r y Fo r e s t Ar e a o n t he Loe s s Pl a t e a u, whe r e v e g e t a t i o n ha s e xpe r i e nc e d c o m- pl e t e de s t r uc t i o n, na t ur a l r e s t o r a t i on, a nd de s t r uc t i o n a ga i n dur i ng t he pa s t 1 4 0 y e a r s o r s o, pr o v i de d a na t ur a l r e s e a r c h s i t e t o e v a l ua t e i mpa c t s o f v e g e t a t i o n c ha ng e on r e g i o nal e nvi r o nme nt a l qua l i t y. The o bj e c t i v e o f t hi s r e s e a r c h wa s t o q ua nt i f y t he e fe c t s o f a c c e l e r a t e d s o i l e r o s i o n c a us e d by de f o r e s t a t i o n o n s o i l o r g a n i c ma t t e r ( OM) , t o t a l n i t r o g e n ( TN) , a mmo n i a n i t r o g e n ( NH4 - N) a n d a v a i l a b l e p h o s p h o r u s ( P) l o s s e s , b y mo ni t o r i ng s o i l e r o s i o n a nd n ut r i e n t l o s s i n n e wl y - d e f o r e s t e d l a n ds i n t he Zi wu l i n g Re g i o n. Thi s i nf o r ma t i o n wi l l he l p t o i mpr o v e unde r s t a ndi ng o f t he r e l a t i o ns hi p be t we e n a c c e l e r a t e d s oi l e r o s i o n a f t e r de f o r e s t a t i o n a nd s o i l qua l i t y de g r a da t i o n. M ATERI ALS AND M ETHODS St ud y s i t e d e s c r i pt i o n D ur i ng t he pa s t 1 40 y e a r s , e xc e pt i n t he Zi wul i ng Ar e a, na t ur a l ve g e t a t i o n i n mo s t o f t he r e g i o ns o n t he Loe s s Pl a t e a u ha s be e n c o mpl e t e l y de s t r o ye d. The Zi wul i ng Fo r e s t Ar e a, whi c h oc c upi e s a bo ut 2 3 0 0 0 km2 , i s t he s o l e s e c o n da r y f o r e s t r e g i o n o n t h e Lo e s s Pl a t e a u. I t i s s i t ua t e d i n t he hi l l y r e g i o n be t we e n t h e Do n g z hi a nd Luo c h ua n Pl a t e a us ( La t i t ud e 3 3 0 5 0 ' - 3 6 0 5 0 ' N a nd Lo ng i t ud e 1 0 7 0 3 0 ' -1 0 9 0 4 0 ' E) . Abo ut 1 4 0 y e a r s a g o, t h e e c o - e n v i r o nme n t o f t h e Zi wul i ng Re g i o n wa s s i mi l a r t o mo s t hi l l y - g ul l y r e g i o ns on t he Lo e s s Pl a t e a u t oda y , i . e . v e g e t a t i o n wa s c o mpl e t e l y de s t r o y e d; s o i l e r os i o n was s e v e r e ; a n d t o p s o i l ( h u mi c h o r i z o n ) wa s wa s h e d a wa y . At t h a t t i me , a wa r b e t we e n t h e Ha n a n d Hu i na t i o na l i t i e s o c c ur r e d, l e a di ng t o a po pul a t i o n e xodus . Si nc e t he n s e c o nda r y f o r e s t v e g e t a t i o n ha s be e n de v e l o pi ng. The ie f l d e xpe r i me nt wa s c o nduc t e d a t t he Fuxi an Obs e r v a t o r y f o r So i l Er o s i o n a nd Ec o - e nvi r o nme nt , whi c h wa s e s t a bl i s he d i n 1 9 8 9 ( Ta ng e t a l . , 1 9 9 3 ) . Thi s o bs e r v a t o r y i s l o c a t e d o n t h e e a s t e r n s l o pe o f t he Zi wul i ng Se c o nda r y Fo r e s t Re gi o n. Loe s s c o v e r e d l o w mount a i ns a nd hi l l s , e l e v a t i o ns r a ng i ng f r o m 9 2 0 t o 16 8 3 m wi t h a r e l a t i v e h e i g h t o f 1 0 0 t o 1 5 0 m, a n d a g u l l y d e n s i t y o f 4 . 5 k m k m-2 c h a r a c t e r i z e t h e l a ndf o r ms . The a nnua l a v e r a g e t e mpe r a t ur e i s 6 t o 1 0 ' C, whi l e pr e c i pi t a t i o n r a ng e s f r o m 6 0 0 t o 7 0 0 mm, i n whi c h 6 0% f a l l s f r om J une t o Se pt e mbe r . The ma xi mum pr e c i pi t a t i on i n a mo nt h c a n a c c o unt f o r 2 5 % t o 4 0% o f t he t o t a l a nnua l r a i nf a l l , a nd t he ma xi mum da i l y r a i nf a l l i s 87 mm. I n t h e f o r e s t a r e a , t he ma i n t r e e s pe c i e s we r e o a k ( Qu e r c u s l i a o t u n g e ns i s Ko i d z umi ) , po p l a r ( Po pu l u s d a v i d i a n a Do d e ) a n d b i r c h ( Be t u l a pl a t y p h y l l a S u k a c z e v) . Th e c a n o p y d e n s i t y o f t h e t i mbe r f o r e s t wa s mo r e t ha n 7 0%, a nd a2 t o 5 c m de e p l i t t e r l a ye r c o v e r e d t he s o i l s ur f a c e . Thi s s o i l had a n o bvi ous o r g a ni c hor i z o n wi t h we l l - de v e l o pe d s o i l a g g r e ga t e s a nd de ns e r oo t i ng s ys t e m. Ho we ve r , a r g i l l i c ho r i z o ns wer e not obvi ous. Si t e sel ect i on and dat a col l ect i on T o po g r a p场 i n t he hi l l y- g ul l y r e g i o n o f t he Loe s s Pl a t e a u i s c ompl e x. Al o ng wi t h s l o pe l e ng t h, s l o pe g r a di e nt i nc r e a s e d, i . e . , t he s l o pe s ha pe wa s c o nv e x. Sl o pe s we r e v e r y s t e e p r a ng i ng f r o m 30 -1 20 i n t he s h e e t e r o s i o n d o mi n a n t z o n e ( t o p s l o pe ) , 1 2 0 - 2 5 0 i n t h e r i l l e r o s i o n d o mi n a n t z o n e ( mi dd l e s l o pe ) , t o 1 8 0 - 3 5 0 i n t h e s ha l l o w g u l l y e r o s i o n d o mi n a n t z o n e ( d o wn s l o pe ) . To i f nd r e p l i c a b l e s l o pe s e c t i o n s a i f e l d s ur ve y wa s unde r t a ke n t o s e l e c t a r e pr e s e nt a t i v e hi l l s l o pe t o e s t a bl i s h r unofp l o t s a c c o r di ng t o t ypi c a l t o po g r a phi c a l f e a t u r e s . Ei g h t r u no fp l o t s , i nc l udi ng t wo c o n t r o l pl o t s ( wo od l a nd) a nd s i x de f o r e s t e d pl o t s , we r e c o ns t r uc t e d o n hi l l s l o pe s a s s ho wn i n Ta bl e I . Fo r t he s e r uno fp l ot s , t he s a me do mi na n t e r o s i o n z o ne ha s t he s i mi l a r g e o mo r phi c a nd e r o s i v e c o ndi t i o ns . Ea c h pl o t wa s s ur r o unde d wi t h c o nc r e t e bl o c k bo r de r s ( e xt e ndi ng 1 0 c m a bo v e t he s u r f a c e a nd 1 0 c m be l o w t he s u r f a c e ) f o r r uno fp l o t i s o l a t i o n. A t r o ug h f o r r uno fc o l l e c t i o n wa s i ns t a l l e d a t t he o ut l e t . Fo r e a c h r uno fe v e nt s t o r a g e c o nt a i ne r s we r e us e d t o c o l l e c t r uno fv o l ume f r o m e a c h r uno fp l o t . M ul ti - sl ot di vi sors were i nstal l ed i n case one col l ect i on contai ner coul d not hol d al l of the r unof i n an 万方数据 709 SOI L EROSI ON EFFECT ON SOI L NUTRI ENT LOSS TABLE I Ar r ange ment of nat ur al r unof pl ot s Runofp l ot Loc a t i on Dom i nated erosi on zone 4 Bare and f al l ow 101 5-32 5 100 5-26 5 100 5-26 11. 7 424 26-35 13. 6 995. 2 5-35 14. 2 965. 8 5-35 6 8 1 了 2. 5 6 3 6 Bar e and f al l ow 2. 5 3 7石 5-12 64 12-26 2. 5 0 2 5 Bar e and f al l ow Veget at i on l and Bar e and f al l ow 门} 0 4 2 3 Bare and f al l ow m m2 .6 A 2 Bar e and f al l ow Lengt h Wi dt h Ar e a Sl ope gr adi ent 5 5 1一 2 一 1 Top s l ope She e t e r os i on Mi ddl e s l ope Ri l l e r os i on z one Top - mi ddl e s l ope She e t+ r i l l e r os i on z one Top- mi ddl e s l ope Shee t+ r i l l er os i on z one Top- mi ddl e s l ope Cont r ol Do wn- s l ope Shal l o w gul l y e r os i on Whol e hi l l s l ope She e t+ r i l l+s hal l ow Land use ( t o p t o bo t t o m) gu l l y e r o s i on Whol e hi l l s l ope Cont r ol Ve ge t at i on l and 80. 2 ( t o p t o bo t t o m) e x t r e me r a i nf a l l e v e n t . Du r i ng o bs e r v a t i o n pe r i o ds f r o m 1 9 8 9 t o 2 0 0 3 , pr i o r t o t he r a i n y s e a s o n ( i n Ap r i l ) , a s ho v e l wa s us e d t o t ur n t h e s o i l i n t he r uno fp l o t s t o a d e pt h o f 2 0 c m a c c o r di n g t o l o c a l l y t r a d i t i o n a l c u l t i v a t i o n pr a c t i c e s . Twi c e a y e a r c o r e s a mp l e r s we r e us e d t o t a k e t o ps o i l s a mpl e s ( 2 0 c m d e e p) f o r n u t r i e n t t e s t s , i . e . , t hr e e da y s a f t e r t i l l a g e i n Ap r i l a nd a f t e r r a i n s a t t h e e n d o f Oc t o be r . Ac c o r di ng t o t he t o po g r a p帅 a nd e r o s i o n pa t t e r ns , iv f e s a mpl i ng s i t e s a l o ng t he s l o pe l e ng t h i n t he s he e t e r o s i o n do mi na nt z o ne , s e v e n s a mpl i ng s i t e s i n t he r i l l e r o s i o n do mi na nt z o ne , a nd 1 8 s a mpl i ng s i t e s i n t he s ha l l o w g u l l y e r o s i o n do mi na n t z o ne ( s i x i n t h e s ha l l o w g ul l y c ha nne l a nd 1 2 a t bo t h s i de s o f t he s ha l l o w g u l l y c ha nn e l ) we r e c ho s e n. I n a dd i t i o n, s o i l s a mp l e s f r o m wo o d l a nds ( Pl o t s 5 a n d 8 , Ta b l e I ) t h a t c o r r e s p o n d e d t o t h e s a mp l e l o c a t i o n s o f d e f o r e s t e d p l o t s we r e c o l l e c t e d . A f t e r e a c h r uno f f e v e n t , t he wa t e r l e v e l i n e a c h c o n t a i ne r wa s me a s ur e d t o c a l c ul at e r uno fv o l ume , a nd a f t e r mi xi ng r o und wi t h am uddl e r , s e di me nt s a mpl e s we r e c o l l e c t e d f r o m e a c h c o nt a i ne r . Af t e r 2 4 h o f s e di me nt a t i o n, t he c l e a r wa t e r wa s po ur e d o ut o f t he bo t t l e s . The n t he s e di me nt wa s dr i e d饰 a i r o r s u nl i g h t a nd t h e a i r - dr i e d s o i l s a mpl e s we r e u s e d f o r l a bo r a t o r y a na l ys i s . Or g a n i c ma t t e r ( OM) wa s d e t e r mi n e d u s i n g t h e me t h o d o f Wa l k l e y a n d Bl a c k ( Bi g h a m, 1 9 9 6 ) , t o t a l n i t r o g e n ( TN) ( Kj e l d a h l d i g e s t ) a n d NH4 - N ( 2 . 0 mo l L一 1 KCl e x t r a c t a n t ) we r e e s t a b l i s h e d u s i n g a n a u t o ma t e d i o n a n a l y z e r , a n d a v a i l a bl e ph o s p h o r us ( 0. 5 mo l L一1 Na HC03 e x t r a c t a n t ) wa s a n a l y z e d wi t h c o l o r i me t r y . Cal cul at i ons A nnual l y i n Apr i l f or e a c h r uno fp l o t s o i l OM, t o t a l N, NH4 - N a nd a v a i l a bl e P c o nt e nt s we r e t a k e n a s r e f e r e nc e v a l ue s t o c a l c ul a t e t he nut r i e nt e nr i c hme n t r a t i o o f t he s e di me n t f o r t ha t y e a r . The di fe r e nc e s i n annua l v a l ue s be t we e n Apr i l a nd Oc t o be r o f e a c h y e a r f o r e a c h r uno fp l o t we r e c a l c ul a t e d t o a s s e s s nutri ent l oss es. I n t hi s s t udy , t he nut r i e nt e nr i c hme n t r a t i o i n e r ode d s e di me nt f r o m e a c h r uno fp l o t i n e a c h o bs e r - v a t i o n y e a r wa s de ine f d a s a s pe c i a l nut r i e nt c o nt e nt i n e r ode d s e di me nt s c o mpa r e d t o t he c o r r e s po ndi ng s o i l r e f e r e nc e v a l ue i n Apr i l o f t ha t y e a r f o r t he s a me pl o t . The s e nut r i e nt e nr i c hme n t r a t i o s we r e us e d t o qua nt i f y nut r i e nt l o s s a s s oc i a t e d wi t h di fe r e nt e r o s i o n i nt e ns i t i e s a nd pa t t e r ns . LSD Te s t wa s pe r f o r me d t o de t e r mi ne whe t he r s i g ni ic f a n t di fe r e nc e s i n t he nut r i e n t l o s s a nd nut r i e nt e nr i c hme n t r a t i os i n e r ode d s e di me nt a mo ng s he e t e r o s i o n do mi na n t z one , r i l l e r o s i o n do mi na nt z o ne , a nd e phe me r a l gul l y e r o s i o n do mi nan t z o ne . RESULTS AND DI SCUSSION Re l at i ons h咖 b e t we e n s oi l e r os i on and nut r i e nt l os s One m ajor c t o f e r os i o n i s l o s s of s oi l nut r i e nt s al ong wi t h e r ode d s e di me nt s . By a na l yz i ng i m pa 万方数据 F. L. ZHEN G 710 r ai nf a l l e ve nt s , t he r e l at i ons hi p be t we e n Loess Pl ateau of quant i ied. Al f s o,i n t he ne wl y de f o r e s t e d l a nds on the n eroded sedi m ents af nut ri ent cont ent si t er erosive and nutri ent l oss m ay t o ps o i l v a r i e d g r e a t l y wi t h e r os i v e e v e n t s a nd t i me due t o s e v e r e s o i l l os s . a t e s a nd e r o s i o n pa t t e r ns t he r uno fp l o t s wi t h di fe r e n t s i z e s Addi t i ona l l y, due t o di fe r e nc e sm erosion r had di ferent nutri ent contents. I n t hi s s t udy , nut r i e nt l os s e s c a us e d饰 s he e t , r i l l a nd s ha l l o w gul l y we r e me a s ur e d s e pa r a t e l y . Chi na, nut r i e nt c ont ent amount decreased f r om Tabl e II showed that f or rai nf al l eventsnutri ent cont e无 tpe u t s e me t Per rU un li n l 毛s ed Qi l m en l l ta i ncreas ed. Thi s z one s , whi l e t hepr o por t i on of nut r i e ntloss s he e t t o s ha l l o w g ul l y do mi na nt Data i n Tabl e wa s c a us e d by t he i nc r e a s e d s e di me nt yi e l d f r o m s he e t t o s ha l l o w g ul l yerosion zones. c o nt r i but e d a ppr o x i ma t e l y 7 0 % o f t he I I I r e v e al e d t ha t nut r i e nt l os s e s f r om r i l l and s hal l ow gul l y TABLE II Nut r i ent s i n e r oded s edi ment s f r om s he et , r i l l , and s hal l ow gul l y e r os i on zones under s eve r al r ai nf al l e vent s Da t e Ra i n - 1 3 0 a ) f al l Dom i nant Er o s i o n Ra t i o b l OM Reduc- Total duc - P' l Reduc - NH4- N Re erosion rate t i onb ) N t i onbl t i onb) pattern t km一2 ti mes m m m m g kg-1% g kg-1% 6 . 8 0 2 . OJ 4 8 . 5 1} 3 0 4 … 21. 96 4 … 129. 2 1 1 7 . 8 97. 4 7 23. 08 8 20. 51 4 5 3 99. 2 7 5 1工 0 1 l l ee 9 8 『 1 9 11. 85 112. 9 12. 62 27. 41 92. 4 28. 48 l a 5 5 0 阿‘ Ql q山 1上 . 18 31. 99 4 . 11 11 11 11 1工 11 飞1 ,工 n 自 6 峭 I . 48 18. 92 5  ̄ 0 脚了 9 11 2 0 2 . 26 3 . … 9 4 11 9 11 9 6 2 1立 2 . 19 38. 14 22. 38 4 5 2. 35 124. 8 27. 7 5 Shal l o w gul l y 1 757 36. 46 18. 93 … 2003 100. 9 3 6 1. 67 40. 59 6 4 Ri l l 1252 25. 82 5 5 29, 22. 47 44. 10 … Sheet erosi on 748 27. 43 117. 8 6 5 2 0. 34 Jul . 14. 36. 78 29. 41 . Shal l o w gul l y 1 443 0 32. 82 9 5 1996 158. 8 . Ri l l 9637 18. 32 34. 49 6 6 29, 92. 7 43. 09 . She et er osi on 526 36. 77 2 8 1. 15 Jul . 108 4. 48 19. 86 . Shal l o w gul l y 11 66 113. 4 4 4 1996 18. 06 . 1. 63 Ri l l 424 5 4 13, 31. 54 141. 5 . Sheet er osi on 260 9 7 0. 17 Jul . 10 0 7 15. 77 39. 72 7. 63 片1 8 2 9 Shal l ow gul l y 1 220 22. 29 14. 79 mg kg-1% 5 5 1995 . 26. 16 25, Sheet er osi on 160 Ri l l 302 1. 89 0. 45 Aug. 13.6 ,土 一 1 mi n-1 mg kg-1% 9. 31 14. 04 ' ) Ma x i mu m 3 0 - mi n r a i n f a l l i n t e n s i t y . b ) Co mp a r e d t o s h e e t e r o s i o n . ` ) Av a i l a b l e p h o s p h o r o u s . TABLE II I Nut r i ent l os s es f r om di fe r ent er os i on zones f or s el ec t ed year s Year Erosi on zone Soi l nutri ent OM Total N NH4- N % 1995 Sheet erosi on domi nant zone Ri l l er osi on domi nant zone Shal l o w gul l y e r os i on domi nant z one 1996 28. 6 27. 8 24. 1 Ri l l erosi on domi nant zone 33. 1 31. 2 31. 4 32. 6 Shal l o w gul l y e r os i on domi nant z one 36. 1 40. 2 40. 8 43. 3 25. 4 25. 8 23. 8 32. 2 32. 6 4 . QD . 1上 4 3 4 6 … S 3 4 八 0 5 2 3 几‘ 3 … 8 2 4 2 6 4 ,工 3 q‘ q‘ 八 0 8 片t . 1 匕 5 … … 8 1上 3 … 33. 3 6 . 1主 4 】0 8 2 3 8 } 1 4 1 丫 万方数据 . Shal l ow gul l y er os i on domi nant z one 0 4 Ri l l erosi on domi nant zone 8 Sheet erosi on domi nant zone 4 3 M ean . Shal l ow gul l y e r os i on domi nant zone 23. 9 5 2 Ri l l erosi on domi nant zone 42. 4 3 1上 OJ 4 Sheet erosi on domi nant zone 4 2 2003 力 0 Shal l ow gul l y er os i on domi nant z one . Ri l l erosi on domi nant zone q‘ 0 3 4 Sheet erosi on domi nant zone 6 30. 8 6 2 1997 Sheet erosi on dom i nant zone 22. 1 24. 1 34. 3 32. 4 43. 6 43. 5 SOI L EROSI ON EFFECT ON SOI L NUTRI ENT LOSS 711 t o t a l nut r i e nt l o s s o n hi l l y s l o pe s . A l i ne ar r e l at i ons hi p be t we e n nut r i e nt l os s and i nt e ns i t y f o r t he l oe s s i a l hi l l s l o pe s c o ul d be expresses as: ( 1 ) NL= aEa nt ens i t y whe r e NL i s nut r i e nt l os s( a i s t he pr o po r t i o na l c oe f ic f i e n t ; a nd Ea i s t heerosion i k g k m- 2 ) ; ( t k m- 2 ) . The pr o po r t i o na l c o e ic f i e n t , a, be t we e n n ut r i e n t l o s s i n t e ns i t y a nd e r o s i o n i n t e ns i t y f o r a ) t he s he e t erosi on zone,b nd c ) t he c o mbi ne d s he e t , r i l l a nd s ha l l o w ) t he - , c o mbi ne d s he e t a nd r i l lerosion zones,a ues wer e f ound f or di ferent nutr i ents f rom e I V. Di ferent 。 val gul l yerosi on zones was gi ven i n Tabl di ssi mi l ar eros i on domi nant zones. TA BLE IV Pr opor t i o nal c ons t ant ,“,be t we e n nut r i ent l os s and s oi l e r os i on and t he c or r e l at i on c oe fi c i e nt r Erosi on zone Soi l nutri ent Q r 食 r 仪 r Sheet erosi on zone Combi ned s heet+ r i l l . erosio n zones on + Combi ned sheet+ r i l lerosi s hal l ow gul l y e r os i on zone s OM Total N NH4- N P 24. 332 1. 3307 0. 1163 0. 0056 0. 9979 0. 9674 0. 9090 0. 9726 20. 026 1. 1057 0. 0975 0. 0051 0. 9999 0. 9997 0. 9996 0. 9997 17. 114 1. 1838 0. 1195 0. 0053 0. 9574 0. 9864 0. 9794 0. 9875 Nut ri ent enri chment i n eroded sedi ment Se v e r a l r e s e a r c he r s ha v e r e po r t e d t ha t N a nd P i n e r ode d s e di me nt we r e s i g ni ic f a nt l y e nr i c he d ( Mo n k e e t a l . , 1 9 7 7 ; Fl a n a g a n a n d F o s t e r , 1 9 8 9 ; Yo u n g e t a l . , 1 9 8 6 ) . Da t a f r o m t h i s s t ud y a l s o s ho we d t ha t OM, t o t a l N, a v a i l a bl e P and NH4 - N we r e g r e a t l y e nr i c he d i n e r ode d s e di me nt s . The e n r i c hme nt r a t i o s f o r OM, t ot a l N, NH4 - N a nd a v a i l a bl e P f r o m t he s he e t e r o s i o n z o ne , t he c o mbi ne d s he e t a nd r i l l e r o s i o n z o ne s , a nd t he c o mbi ne d s he e t , r i l l and s ha l l o w g ul l y e r o s i o n z o ne s we r e t a bul a t e d i n Ta bl e s V, VI , a nd VI I , r e s pe c t i v e l y. The s e da t a i ndi c a t e d t ha t a v a i l a bl e P ha d t he hi g he s t e nr i c hme nt r a t i o wi t h v a l ue s r a ng i ng f r o m 1 . 4 2 t o 3. 6, f o l l o we d饰 NH4 - N wi t h v a l ue s r a ng i ng f r o m 1 . 1 3 t o 1 . 9 4. The e nr i c h- me nt r a t i o s o f OM a nd t o t a l N i n s e di me n t we r e f r o m 0. 97 t o 1 . 4 3 a nd 0. 8 9 t o 1 . 2 9, r e s pe c t i v e l y . The e n r i c hme nt r a t i os , r e g a r dl e s s o f di f f e r e nt g e o g r a phi c a l l o c a t i o ns , we r e s i mi l a r t o t he r e s ul t s o f Mo nk e e t a l . ( 1 9 7 7 ) . Ho we v e r , t h e e n r i c hme n t r a t i o s i n t h e s he e t e r o s i o n z o ne f r o m t hi s s t u dy we r e h i g he r t W t ho s e o bt a i ne d f r o m l o ng - t e r m c u l t i v a t e d a r e a s i n t h e s e v e r e l y e r o d e d r e g i o n o f Lo e s s Pl a t e a u ( Li , 1 9 9 0 ) , i nd i c a t i ng a c c e l e r a t e d n ut r i e n t l o s s i n t h e be g i nn i ng s t a g e s a f t e r d e f o r e s t a t i o n. I n a dd i t i o n, t h e TA BLE V Nutri ent cont ents i n er oded sedi ments and thei r enri chment rati os f r om the sheet er osi on zone Erosi on rate Nutri ent content i n sedi m ent Nutri ent enri chm ent rati o i n sedi m ent NH4- N Avai l abl e P OM Total N — mg k g-1_ NH4- N Avai l abl e P 2 3 2 3 3 4 9 7 ‘ 6 0 . 1土 2 q‘ 6 3 6 2 1上 9 4 6 7 4 2 … … 91 2 7 3 一 .上 1上 11 . . 3 … 0 6 3 一 上 0 1 ll C ) 11 2. 13 . . 2. 37 OM 11 1上 11 ,1 西 1 . 上 只 Qd 3 4 11 2 q山 7 1 .1 : 11 8 1上 9 6 23. 36 一 1 21. 48 3 26. 19 … 八‘ 0 3 一 1 31. 54 3 24. 08 ,1 0 5 6 114. 8 110. 4 4 3 5 124. 8 5 万方数据 158. 8 … . 255 4 1 了 q自 2 690 3 4 7 526 L L L 95 133. 8 8 24 4 26. 16 1土 11 0 5. 45 4 133. 5 2 1. 37 9 160 … 23. 99 . 7. 17 0 2 128. 2 } 了 3 1. 55 11 2 418 一 .上 g k g -1 11 1上 1工 一 1 g k g-1 t km-2 Total N F. L. ZHENG 712 TABLE VI Nut r i ent c ont ent s i n er oded s edi ment s and thei r enri chment r at i os f r om the combi ned s heet and r i l l er osi on zones Erosi on r ate Nutri ent content i n sedi ment Nutri ent enri chment rati o i n sedi ment Tot al N NH4- N 3 3 曰 1 工 t 0 11 2 1上 2 5 1. 79 … . 4 1. 57 OM ,1 2 0 6 , . 8 3 9 2 曰 土 门 ‘ 6 11 0 … 一 .上 4 1上 8 0 曰 土 口J 4 11 2 : 2 4 1土 3 一 1 】 勺 6 … CO 刁 ee l} 1 0 ; . 0 0 一 ee 1上 0 4 2 0 3 1 1 1上 1上 一 .上 1上 1一 4 可 悦1 2 11 0 0 0 … 16. 43 … . 18. 13 ,1 户 95. 4 20. 04 9 8 . 05 94. 5 4 . 03 11 213 11 1 169 21. 50 11 97. 4 19. 30 1上 1. 10 18. 92 1 .上 11218 21. 47 一 .1 108. 6 g kg-1 T〕 七 al N NH4- N Avai l abl e P ,1 21 424 OM 1上 127. 2 Q口 4 C洲 2 11 3 37 5. 11 4 103. 5 } 匕 21 - 5 9 1 … 134. 2 7 15 20 … 359 k g-1 1上 1上 1土 671 9 t km-2 Avai l abl e P TABLE VII Nut r i e nt c ont e nt s i n e r ode d s e di me nt s and t he i r e nr i c hme nt r at i os f r om t he c ombi ne d s he e t+ r i l l+s hal l o w gul l y e r os i on zo n es Nutri ent enri chm ent rati o i n sedi m ent Erosi on rate Nutri ent content i n sedi m ent Z bt al N NH4- N 6 2 3 5 2 91 4 1土 2 … 4 9 1上 2 3 1 2 6 4 知 1 一 11 1上 3 1上 ,1 11 2 3 5 … 9 ,上 5 } 1 9 9J 5 1上 一 .上 1上 } 土 11 一 ee . 一 .1 ll q‘ 3 . 0口 阿了 } 0 3 1上 0 . 5 一 1 7 9 … 11 7 3 ,1 6 1上 2 0 11 2 1上 1工 1上 0 3 2 67 77 16 32 42 17 22 63 55 16 45 69 24 54 21 . 11 ,1 2 4 1上 8 2 1土 . 1 . 4 0 17. 86 NH4- N Avai l abl e P OM 1上 11 9 0 0 9. 94 0 113. 9 8 23 0 6. 93 ,上 121. 7 ,土 10 10. 11 0 107. 2 : 97 1 7. 61 1 114. 8 0 23 … 7. 65 ,1 1上 0 124. 6 … 11 . 11. 35 . 106. 2 1上 1土 11 1上 } 土 07 . 13. 41 . 181. 3 1书 0 35 8. 56 4 9 5 142. 8 … 21 4 7 1‘ 5 7 5 11. 65 4 3 9 135. 7 … 21 TotalN . 12. 65 . 138. 0 . 43 8. 29 . 127. 1 . 20 1 13. 53 1上 1上 1l ll J .上 136. 1 1 了 6 0 5 ,1 9 35 1上 2 97 12. 59 8 7 7 776 130. 8 2 1981 29 0 9 2 7235 13. 77 2 4589 217. 4 21. 59 八‘ 7853 17 L L L L L 已 L L 161 11 3310 一 .1 1182 12. 99 0 4 3 q‘ 11 9 1土 州 1 2 3735 1033 177. 1 g kg -I 11 2 4271 33 OM 2 4 9 2060 mg kg I_ k g一I L L L 工 8337 1土 2049 9 t km-2 Avai l abl e P 1. 12 1. 08 1. 13 1. 12 1. 22 1. 22 1. 11 1. 32 1. 22 1. 21 1. 07 1. 26 1. 29 1, :; 3 enri chment rati os were di ferent i nt he s he e t e r os i on z one, t he c ombi ne d s he e t and r i l l e r os i on z one s , a nd t he c ombi ne d s he e t , r i l l and s ha l l o w g ul l yerosion zones,s ho wi ng g r e a t i mpa c t o f e r o s i o n pa t t e r ns on s oi l nutri ent l os s. Av a i l a bl e P i n s o i l de c r e a s e d wi t h t he de f o r e s t e d y e a r f r o m 1 9 89 t o 1 9 9 5, whe r e a s t hei n creasi ng buted t r e nd o f a v a i l a bl e P e n r i c hme n t r a t i o wa s o bs e r v e d i n e r o de d s e di me n t ( Fi g. 1 ) . Thi s c o ul d beattri to theerosion r a t e c a us e d b y pe r un i t o f r a i nf a l l e r o s i v i t y t ha t i n c r e a s e d wi t h t h e de f o r e s t e d y e a r ( Fi g. 1 ) . Soi l nut r i e nt var i at i on wi t h t he de f or e s t e d ye ar S he e t , r i l l a nd s ha l l o w g ul l y e r o s i o n ha v e di f f e r e n t s o i l d e t a c hme n t a n d t r a n s po r t c a pa c i t i e s ; t h e r e f o r e , t he y po t e nt i a l l y ha v e di f f e r e nt i mpa c t s on s oi l nut r i e nt l o s s . Due t o a n i nc r e a s e of s o i l e r odi bi l i t y, t he e r o s i o n r a t e c a us e d by pe r uni t o f r a i nf a l l e r o s i vi t y i nc r e a s e d o v e r t i me a s s ho wn i n Fi g. 1 , i . e . , t he e r o s i o n r a t e i n c r e a s e d f r o m 1 . 9 1 t k m- ' / J m- 2 mm- 1 i n 1 9 8 9 t o 1 2 . 3 5 t k m - 2 / j M- 2 Mi n一1 i n 1 9 9 6 ; whi l e a v a i l a bl e P i n e r o de d s e di me nt de c r e a s e d wi t h t he de f o r e s t e d y e a r e xc e pt i n 1 99 6 a nd i t de c r e a s e d f r o m 2 3 . 8 mg k g -1 i n t h e i f r s t y e a r ( 1 9 8 9 ) t o 8 . 2 mg k g -1 i n 1 9 9 5 . Ta b l e VI I I s ho ws t h e r e duc t i o n o f n ut r i e n t s i n t he t o p s o i l ( 2 0 c m) i n s he e t , r i l l a nd s ha l l o w g u l l y z o ne s t hr e e ye a r s a nd s e v e n ye a r s a f t e r de f o r e s t a t i o n c o mpa r e d t o aw ood l a nd c o nt r o l . I n t he s he e t 万方数据 SOI L EROSION EFFECT ON SOI L NUTRI ENT LOSS 713 e r o s i o n z o n e , a v e r a g e a n n u a l s o i l e r o s i o n r a t e wa s 6 7 7 5 t k m-2 ( Ta b l e I X) . Co n s e q u e n t l y , f o rsheet by do mi na nt e r o s i o n pa t t e r ns a f t e r t hr e e y e a r s o f de f o r e s t a t i o n OM d e c r e a s e d by 8 . 5 %-1 3. 9 %, t o t alN 5 2 0一 和门」利 UOE 二0一 」Ued O一 q怕- 一 mA< 0 2 卜 。利 一 un」 gd^qPen.oe妇 佗Juo一 soJ 山 ( ! 口义。) 尸 u。 妇 uoud。l q.1 一 门> V 犷EuJ,E早. E戈忿之一 >一 s o J 。1 1 . 卜 u一 佗」 : 25 20 15 1. 5 10 1. 0 Avai l abl e P cont ent 0. 5 Er osi on r at e per uni t of r ai nf al l er osi vi t y Avai l abl e P enr i chment r at i o 0 ` 1988 1990 1996 1992 1994 - 1 0 1998 Def or est ed year Fi g. 1 Change s of a v ai l abl e P i n e r ode d s e di me nt s , e r os i on r at e c aus e d by pe r uni t of r ai nf a l l e r os i vi t y, and av ai l a bl e P e nr i c hme nt r at i os f r om t he c ombi ne d s he e t , r i l l , and s hal l o w gul l y e r o s i on z one s f or t he de f o r e s t e d ye ar s . Avai l abl e P e nr i c hme nt r a t i o means t he r a t i o of av ai l abl e P i n s e di me nt t o av ai l abl e P i n t ops oi l ; and e r os i on r a t e pe r uni t of r ai nf al l e r os i vi t y me ans t ha t 1 mm of r ai nf a l l pr oduc e s e r os i ve e ne r g y pe r uni t ar e a c aus i ng s oi l l os s . TA BLE VIII erosion z ones and the combi ned Nut r i e n t s t a t u s i n t he t o ps oi l ( 2 0 c m) o f t he s he e t e r os i o n z on e , t he c o mbi ne d s he e t a nd r i l l s he et , r i l l and s hal l ow gul l y e r os i on zone s be f or e and af t e r def or es t at i on Erosi on Domi nant zo n e erosion Cont r ol ( woodl and) Years af ter def orestati on 3 7 pattern OM Tot a l N NH4 - N pa ) OM Tot al N NH4 - N P OM Tot al N NH4 - N P 11 : 1上 8 1占 3 } 1 6 3 0 2 15. 71 4 3 15. 94 : 2 3 206. 4 8 7 17. 99 8 2 ,1 2 188. 6 11 l 28. 25 1. 61 s he e t , r i l l and Ril l and 40. 46 1. 80 s hal l o w gul l y Ril s hal l ow gul l y 3 26. 70  ̄ 日} 176. 3 9 Sheet 29. 74 1. 47 Combi ned 114. 0 19. 02 1. 14 118. 3 4. 58 0 28 79 1. 47 L L L 192. 3 1上 37. 74 1. 130. 4 5 s he e t and r i l l Ri l l 20. 28 1 5 8. 45 131. 0 … 181. 9 门 n 23. 55 1. 1 匕 Combi ned Sheet 11 8. 78 21. 46 1 9 2 7 183. 6 mg k g-1 一一 g k g-1一 一mg吨-I- 5 23. 45 1. g k g-1 ,上 Sheet I__ 一 一 mg kg一 2 Sheet 1上 - 3 1 一 gkg 116. 0 4. 64 103. 8 5.14 116. 0 2. 60 18. 76 1. 22 105. 2 2. 36 105. 4 2. 53 15. 25 1. 28 93. 6 2. 26 103. 6 2. 71 12. 56 0. 96 71. 0 2. 13 ' ) Av a i l a b l e p h o s ph o r o u s . TABLE I X Me a n e r o s i o n r a t e s a nd s t a n da r d de vi a t i o ns ( SD) f r o m s he e t e r o s i o n z on e , t h e c ombi ne d e r o s i o n z one s o f s he e t a nd r i l l , and t he c ombi ned e r os i on z ones of s he et , r i l l and s hal l ow gul l y er os i on dur i ng t he obs er vat i on per i ods Erosi on zone Domi nant erosi on M ean er osi on Rati o of erosi on rate to that i n pat t er n r a t e ( S D) the sheet erosi on zone t k m-2 y e a r -1 Sheet Sheet Combi ned sheet and r i l l Ri l l Combi ne d s he et , r i l l and s hal l ow gul l y Ri l l and Sha l l ow gul l y 万方数据 6 7 7 5 ( 1 3 4 5 ) 1 3 2 2 1 ( 2 3 6 9 ) 1 8 5 7 9 ( 3 8 2 6 ) 1. 0 1. 95 2. 74 F. L. M ENG 714 7 . 6 %-1 0. 2 %, NH4 - N b y 2 8. 3 %- 3 4. 2 %, a nd a v a i l a bl e P b y 4 0. 5 %-6 1 . 9 %. S e v e n y e a r s a f t e r d e f o r e s t a t i o n OM de c r e a s e d by 1 8. 9%-3 6. 9%, t o t a l N饰 1 3. 0%-1 7. 0%, NH4 - N b y 3 5. 6 %-4 0. 3 %, a nd a v a i l a bl e P by 45. 1 %-65. 4%. A s t h e e r o s i o n r a t e i nc r e a s e d t o 1 3 2 2 1 t k m-2 y e a r -' i n t h e c o mb i n e d s h e e t a n d r i l l e r o s i o n z o n e s a nd t o 1 8 5 7 9 t k m-2 y e a r -' i n t he c o mbi n e d s h e e t , r i l l a n d s h a l l o w g u l l y e r o s i o n z o n e s ( Ta b l e I X) , s o i l n u t r i e n t c o n t e n t s o f OM, t o t a l N, NH4 - N a n d a v a i l a b l e P d e c r e a s e d a c c o r d i n g l y ( Ta bl e VI I I ) . F o r r i l l d o mi na n t e r o s i o n pa t t e r n a f t e r t hr e e y e a r s o f de f o r e s t a t i o n, OM de c r e a s e d b y 2 3. 7 %- 2 9 . 2 %, t o t a l N b y 1 6. 0 %-1 6. 8 %, NH4 - N b y 4 0. 7 %- 4 4. 1 %, a nd a v a i l a bl e P b y 6 2. 1 %-7 4 . 0 %. Af t e r s e v e n y e a r s o f de f o r e s t a t i o n, OM de c r e a s e d b y 4 0. 8 -4 6. 0%, t o t a l N b y 2 0. 5 %-2 1. 1 %, NH4 - N by 46. 0 %-5 0. 4%, a nd a v a i l a bl e P b y 6 7 . 1 %-7 6 . 8 %. I n t he mo s t s e v e r e l y e r o d e d s ha l l o w g ul l y c ha nne l s , s o i l n u t r i e n t l o s s wa s t he mo s t s e v e r e . Wi t h r i l l a nd s ha l l o w g ul l y do mi na nt e r o s i o n pa t t e r ns t hr e e y e a r s a f t e r de f o r e s t a t i o n, reduct i ons i n OM , e s pe c t i v e l y , a nd TN, NH4 - N a nd a v a i l a bl e P we r e 61. 2 %, 3 3. 3%, 4 9. 8% a nd 8 3. 0 %,r i ndi cated af t e r s e ve n ye a r st he y we r e 6 9. 0 %, 4 6. 7 %, 6 5. 6 % a nd 8 6. 6 %, c o r r e s pondi ng l y . The s eresults that nutr i ent l oss o c c ur r e d r a pi dl y a f t e r de f o r e s t a t i o n. The i nt e ns i t y of nut r i e nt l o s son hi l l s l ope s erosi on i ncreas ed as s heeterosion s hi f t e d t o r i l l e r os i o n o r s ha l l o w g ul l y e r o s i o n due t o a n i nc r e a s eof f t e r d e f o r e s t a t i o n a v a i l a bl e P ha d t he g r e a t e s t r e d uc t i o n, f o l l o we d i nt e ns i t y. Fo r a l lerosion pat t e r nsa Thi sc oul d bea t t r i but e d t o pho s pho r o us , a mmo ni a - ni t r o g e n a nd o r g ani c ma t t e r 饰 NH4 - N a n dOM . by c l a y i n t hes o i l a nd t r a ns po r t e d wi t h e r ode d s e di me nt s , whe r e a s t o t a l N wa s be i ng s t r o ng l ybound a s s o c i a t e d wi t h OM ( Pe n g , 1 9 9 9 ) . CONCLUSIONS I n t he ne wl y- de f o r e s t e d l a nds o f t he Loe s s Pl a t e a u, Chi na, di f f e r e nc e s i n e r o s i on a nd s e di me nt t r a ns po r t pr oc e s s e s i n s he e t , r i l l a nd s ha l l o w g ul l y e r o s i o n z o ne s c a us e d di f f e r e nt i n t e ns i t i e s o f nut r i e nt l o s s e s . Nut r i e nt c o n t e nt pe r uni t s e di me nt de c r e a s e d f r o m s he e t t o s ha l l o w g ul l y e r o s i o n z o ne s , whe r e a s t he t o t a l a mo unt o f nut r i e nt l os s i nc r e a s e d. A ma j o r i t y o f nut r i e nt l o s s e s c a me f r om r i l l a nd s ha l l o w g ul l y e r o s i on z o ne s , c o nt r i but i ng a ppr o xi ma t e l y 7 0 % of t he t ot a l nut r i e nt l o s s i n hi l l y s l o pe a r e a s . So i l nut r i e nt l os s i nc r e a s e d l i ne a r l y wi t h i nc r e a s i ng s o i l e r o s i o n i n t e ns i t y. A g e ne r a l mode l f o r nut r i e nt l os s , NL, a nd s o i l e r o s i o n i nt e ns i t y , E, , , c o ul d be e xpr e s s e d a s NL=aEo, whe r e a i s t he pr o po r t i o na l c oe f f i c i e nt . Ac c o r di ng t o t he di f f e r e nc e o f a v a l ue s f r o m di f f e r e n t e r o s i o n do mi na nt z one s , f ut ur e r e s e a r c h o n nut r i e n t l o s s s ho ul d be c o nduc t e d a c c or di ng t o do mi na nt e r o s i o n z o ne s a nd e r os i o n pa t t e r ns o n t he Loe s s Pl a t e a u. Al s o, t he r e we r e di fe r e nt n ut r i e nt e nr i c hme nt r a t i o s f o r t o t a l N, OM, NH4 - N, a nd a v a i l a bl e P wi t h a v ai l a bl e P a nd NH4 - N be i ng hi g he r . Addi t i o na l l y , s o i l nut r i e nt l o s s wa s c l o s e l y r e l a t e d t o di fe r e nt e r o s i o n pa t t e r ns , i . e . , s he e t , r i l l a nd s ha l l o w g ul l y e r o s i o n. The mo s t s e v e r e s o i l e r o s i o n a nd nut r i e n t l o s s e s oc c ur r e d i n t he s ha l l o w g ul l y c hanne l s o n l o e s s i a l hi l l s l o pe s a nd ne xt i n r i l l e r o s i o n a r e a s I n t he s hal l o w g ul l y c ha nne l s e v e n y e a r s af t e r de f o r e s t a t i o n, OM, t o t a l N, NH4 - N, a nd a v a i l a bl e P we r e r e du c e d b y 6 9 %, 4 6. 7 %, 6 5. 6 % a n d 8 6 . 6 %, r e s pe c t i v e l y . T he s e r e s e a r c h indi f ng s wi l l he l p i mpr o v e t he unde r s t a ndi ng o n e fe c t s o f e r o s i on pr oc e s s e s o n s o i l qua l i t y de g r a da t i on, a nd ma y pr o vi de r e f e r e nc e da t a f o r e c o - e n vi r o nme n t a l r e ha bi l i t a t i o n o n t he Loe s s Pl at eau of Chi na. REFERENCES Bai , H. Y. , Tang, K. L. , Che n, W . L. and Cha, X. 1 991. Soi l e r os i on and nut r i e nt l os s pr oc e s s e s on s l ope f a r mi ng l and. 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