Biological Nitrogen Fixation Through Grain Legumes in Different Cropping Systems of the

Semi-Arid Tropics

J. V . D. K. Kumar Rao , S. P. an^'. and K. K ~ e e '

1 I(;HISAT As1,i Center Patancheru 502 324. Andllra Pladesh Ind!,i

Biological Nitrogen Fixation Through Grain Legumes in Different Cropping Systems of the

Semi-Arid Tropics

J. V. D. K. Kumar ~ a o ' , S. P. ~ a n i ' , and K. K. ~ e e '

Abstract

- . - -- -- -

1 ICRISAT Asla Center Patancheru 502 324 Andhra Pradesh Indla

J. V. D. K. Kumar Rao et al. -- - -. -- -- - -

Introduction

One-sixth of tlie \vorld's pop~~la t ion lives in thc semi-,wid tropics (SAT), including p'irts of

48 c lc~\~c~loping coun t r i e s in Alricci, i l s i , ~ , 'lnd L ,~ t in A m c r i c c ~ . The SAT region is

cli,ir'ictt.ri/t~d by t~nprcdictable \vc'itlicr, limited cintl orrntic rainf,~ll, ,ind nutriftit-poor

soils. Mtl,>n ,~nnu,ll tc*nipc~r,it~~rei in the SAT ,Ire > 18°C; and r,iinf,lll c~xce~ccls potential c~\~apotr,inspir,ltion for only 2 to 4.5 months in the dry SAT, ancl for -1.5 to 7 months in thc

wet dr\ , SAT (Troll IL)h5). 'l'lle soils of the SAT ,Irt> gener,~ll\. l o~v in both tot'ql ,ind plant- ,~\~,iil,iblt~ N. Crop yicblds in tlica SA i ,ire often limited 11y N-supply. Fertili/c~rs arc ~lst.cl only

to ,I limited cxttlnt h t ~ c ~ i t ~ s t ~ ot Io\v per-c'ipita incomes, liniitc~~i crcdit t'icilitics tor most i,irmcrs, L l ~ ~ c l Idck of inirastructirrc.; lor fcrtili/er procluction ,incl Jistrihution. Unclcr st~cti

situ,itions thc opportl~~li t i t 's ,lrc> grc>,~test tor c.uploit,ltion of thc I cg~~rne ' s ,qhilitv to fix ,~tmosplicric-N: in s ~ ~ m b i o i s with rlii70bic~. Tlie suCcesstt~l forni,ltion of a funct io~i ,~l

s\.mhiosis is ~1t.pc~ndc~nt o n rn~lny physicail, e n \ ~ i r o n m i ~ n t c ~ l , ,itid t~iologicnl factors 'ind c;lnnot be assurnrd t o occur ,IS '3 routine. Nitrogen fix'ltion hy Icg~rlncs is ifery i n i p ~ r t ~ i n t i t1

m,iint,iining soil tt,rtility and iust,~itiing 1,111~1 productivitv in the SAT (Wani t l t '11. 199-lb).

Bccc~~ustb the rel,ltionsl~ip bcltwc,c~n N:-fix'ltion ,111ci Icgutiir gro\vth or p rod~~c t ion is not .3lw,jys direct and o b v i o ~ ~ \ , considerable etfort h,ls bccn put into the t l t ~ \ ~ ~ l ~ t ~ ~ ~ i e ~ i t of

mctliocis for nie,lsuring N2-fix'ltion (ll,jrdy et al. 1C173; t'ritlti ,ind Broc.;li,irt 1975; M'iriotti ct

al. 1983; Bergcrst,n t.t '11. 1989). Accuratt) measurement of N,-fixation t~nder field conelitions

a l l ~ w s re,llistic nsscss~i i~nt sf legume ' contribution to ,I system's N-bal,lncr (1nd pro\,idt.s a

b'isis tor c I t ~ \ ~ ~ l o p i ~ i g s ~ ~ s t ~ ~ ~ n a b l c strategies to ma nag^ the soil crop s v s t ~ ~ i i s . I ' ig~onpea (C:[1lorrlr.: i'111(111), chickpc~,i (C~(.l>r i i r I ~ ~ t i ~ ~ ~ l r ~ / ) , , ~ n d g r o u n c i n ~ ~ t (Ar'i1c-lli.; Ir~pcr,yili~i~) art, tht,

important legumes of StZ'P, ,itid 'ire grown '1s components of crop rotCitions in c lo~~b lo

cropping, intt'rcropping, and niixrd cropping. W e discuss the) merits of the difiercnt techniques for cluantitying N2-tixdtion 'ind review then importancr of svmbiotic UNI; in the

N-ccononlics of tlic many gr'liti legun~v-based production 5ystcms ot the S/I'T. Fin'illy,

strdtegics will be reviewed that may Ic,id to increased N?-fix,~tion of thc legume> in tlic system.

Methods of evaluating N,-fixation of grain legumes

A l t h o ~ ~ g h there arc sc~ver,il nicthodologies for n ~ c ~ ~ s u r i n g N!-fix'~tion in plants, none of

them measures N2-fixed with cibsolute accurac\r. The ad\~atitages ,111ci disadv,~nt,~ges of difft,rent mcthocis av,~ilablc for me'isuring nitrogcn fix'ltion are presented briefly.

Rate of N,-fixation activity

Acetylene reduction assay -. I l ~ e acetylene reduction ,Issay (ARA) arose from the observations that the N2-fixing enzyme

complex, nitrogenasc, ctit;llyzcs the reduction of acctylcne (c2F-12) to etliylcnc (C,l I,). This method is indirect and has only one tirnc assay of tile N,-fixing 'lctivity of the plants, and

Biological N, Fixation through Grain Legumes -

unless flow-through systems 'ire employed, reliable cstim,-Itcs cannot bt. obtaincd (Wittj. and blinchin 1988). In ni'iny legume species, substanti,~l decline in tiitrogen,ise activity occurs after exposurc to C,li?. This nicthod is q ~ ~ ~ i l i t a t i v r in nature ancl the ARA grt',ltlv

undercstimatcci N?-fixing '~ctivity uncier field conditions in cornpciriso~i witli the c,stim,ltcs from ntlicr niethocis ( e . ~ . , HoJdev ct al. 1981; Kirm,ir Rao anel l.)drt 1987).

N-solute method Xylem s ~ ~ p c'irrirs N-containing compounds from the root\ to thc shoots of field-grown legumes origin'~ling from ('1) nodules '1s assimilation products of N2-tix,ltion arid ( h ) soil mineral-N taken u p by the roots. Procl~~cts of N2-fiu'ltion ,irtJ transportcci t i , other p'irts ot

the plClnt in thcb svlern ,is urcidcs or ,~mides, ivhcreas N ,~bsorbrd frorn tlicb soil ,is NO, is cithcr tr,~nsported dircctly to the shoot or reduccci to ,jmides bctorr transpc~rt,ltion. hl,ln). legumes, primarily those of the tribes I'h,iseolccit~ ,lr~ci DosrnoeIit~,ic~ (c.g. , pigeonpr'l), tr,~nsport most of their fiscd-N in thr form of irrei~ies (I'coples r>t al. 1980~) . 111 most 'urvidt' cxxporters' thcre is little nitrate re~luctase rlctivity in the roots, ,-Incl thtrs the proportion of N in tlic xyle~ii s'ip ,IS urcides is directly proportional to the amount of N-fixcld. In thost1 Irgtlmes tli'it do not tr,-Insyort fixed nitrogen 'is ureidcs, it is possiblr to iorrel,-~tc nitrogen l i ~ ~ l t i o n with thr proportio~i of ,imitlc-N in the xylcni s'lp onl?. in some species (cl.g., ;\t'iiilrii / I , I / ~ J O ~ U ~ ' I I r ~ r i t f C i c ~ , , 11r.rc~tirrrrttr) ~ ' r~ l i c r (~ thcrc. is littltl nitr,ite reduct'isr ,~cti\rity in thc roots (I'coplewt al., 1987).

' I he urcide method pro\,idc.; c~rilv a short-term mc~lsurc ot s \ nibiotic d e p ~ ~ d t ~ n c c , ,jnd tlie time delay bct\vecn decLipit,ltilig the shoot ancl \.acuunI c.xtr,iction of uvlcni sap ,~fft>cts tlie ureidc content. I his rlicthod c ~ i n bc used tor coniparirig treatments for IINF b y

collecting thr sap within 4 min ot strm dc'tachnit.nt (l'coplcs et al. 1c)HQb).

Integrated measurements of N,-fixation

N-difference method

Total N-uptako by d non-fixing rcfcrcnct7 crclp is subtr;lctccl from the tot,jl N-uptahc by legume, which thim gives C) mc>asurt1 of the amount of N-fixed in the, legume c r o p rht' rn'lin ' i ss i~~~ipt icm is th'it both the crops t3xploit simil,lr soil vnlumc~ witli simil'lr rooting ~ r l d ,lbsorb tlic s'ime c l rno~~n t ot soil-N. 'This c~ln only be \~rrificcl by using "N-l,lbelc.d ft.rtili/t>r. Comparisons of N,-fix'ltion c,~lculatrd by N-diffcrencr ivitli cstini,3tc's by "~-c l i lu t~on h,it t>

often shown good agreement for soils low in h or wlit.re recover\' oi "N-lahcl is cqucil in the legume and non-fixing control (Chalk 1985). Conip,lrcci tvith tlic "h-n'lturnl , ibund~ir~ct~ method the N-diffrrenctl mctliod tpnded to ~~ndercstim,ite thc t)t pigconpcc~ ( T ~ b l c 1 ) .

This is 1-7artic~1larly wit11 extra-sh(>rt-d11ration 'lnd short-clur'1tion pigtxonpea in both Altiiol

arid Vcrtisol fields. With meciium duration pigeonpca (gruivn '1s sole crop) tli,~t arc generally intercropped with ccretlls such JS sorghi1111 or millet, the N-clifferencc '~ncl ' < N - natural-abundance methods gave siniil,~r values ot ",<,NLI,,,. Use of thr. N-clitfercnct. nicthocl is complicated when clealing witli intercropped legumes bccaure the intercrop competition may affect the ability of the legume dnci non-fixing rt,fercmce crops to access soil-N.

J. V. D. K. Kumar Rao et al.

Table 1. lot,il N-ttpt'lkc .lrld per i.c,rit ri~trogt'n d t > r ~ \ t , ~ l Irom the ,itmosphcrc ( ' I , , N,,,,) I i ~ r pigeotlpd gfl ioty~eh i ~ t

~ i t l f t ~ r t a n t n i , ~ t u r ~ t ~ srclllps , I> ~ i c ~ t ~ ~ r r n t r i c ~ l b!, the 'U I~,I~LI~~II-,II~LI,I~~~I~~~~ ~ ~ i c ~ t h o d ;11id 1 1 ~ tlic h-d~ftcrencr 111c>tIiod ( K I I I T ~ , I ~ l < ~ t > , I.\' 1 ) A , I O ~ ~ I I ~ \ C * I I , C' , Y O I I ~ V ~ I I I I ~ I , T, I t o , 0 , R J O , 1. I ? . , J I ~ L ~ A ~ i ~ ~ - < C y a n i f i , J J ~ i n l - r u l ~ l ~ s h t ~ d )

~~c'IlcltYt7~', r ~ i * ~ t ~ t r ~ t \

lCI'l> 4 (ESLl) IC I'L R4O??(l~SL)) ICI'L 57 (SL))

1'1. l i l (SL)J IC[' I - h (hl l ) l IC'I ' I 871 l q (h7 l ) l 1 i17L ?(>(, (1-11) T 7 (1.D)

1 (-51) c L \ t r , i > h n ~ - t - ~ i ~ i r , l t ~ o ~ l , SD o r - ~ i t r ~ t ~ t i , I ~ L ~ L ~ I L I I ~ - ~ ~ L I ! - , ~ ~ I ~ I ~ , I I I - - I ~ ~ n ~ - d ~ ~ r a t t o n ?. i'clr t!sL) ,Itid 51) ~~Igt'ollpt'.' \ivgI1~1111 h \ b r ~ d C'Sti '1 (,lbout I ? O - i l , r ~ dLlr,ltion) 1 ~ ~ 1 s uccil; IS liS70, .I long

d l~r , i t l i )n wrglium i . i h ~ l ~ t 1 H O d,irs) IVJ\ t r \ t ~ l as .i n o n - l ~ x ~ n g cirntrol l o r \ , T I ) nnd ILL) p1geonpc.d.

15 N-isotope dilution method

The test Icgumc ancl the non-fixing rctt~renctl crop art. grown o n a 17~-e r i r i ched soil for I ; isotope dilution mcasuremcnt of N,-lix,ition. Tlic N-t.nrichmcnt of thc non-fixing

refcrenccl crop will reflect that of the soil on which i t is grown, wlicrcas that of thc legume \ \ r i l l bc rrduccd in proportion to the amount of ,qtn~ospheric ("N,) nitrogrn tixed. The main cissumption of tlie method is that both the legumc '~nci tlie reference crop take LIP soil-N

("N:"N) in the s,Ime ratio (Fried nncl Brocshart 1075). Tlic single most important factor affecting the) ,iccuracy of thi5 niethod is fincling ,qn a p p r ~ p r i ~ i t e referenct~ crop that matches the legurnc in its rooting, N-ilptakc p,ittern, and cluration. As tlic l'N-cnric:liment of thr

availahlt. soil-N tends to decline ,~f ter tlie "N-fertilizer is ndcicci, and because of the

diffic~~lties of mixing the I'N-enriched fertilizer tliroughout the soil horirons exploitcci by thc plants, ,In! misniatchirig of reference and test crops will result in '~lbsorption of different I .> h-rnrichmcnt froni soil (Witty 1983). Tlicsc problems arc considered in detail by Chalk

(IYH5), Danso (lYXS), and Wittv ~ n c i Giller (1991).

~atural-"N-abundance method 'l'hr N-traiisforniatiuns in soil result in isotopic fr,lctionation resulting in a small increase in

thc "N-abundance of soil-N coniycired with ,~tmosphcric-N, (Shearer and Kohl 1986). I t is possiblt, to c ~ ~ r r y out isotope dilution nieCisurt~nients of N,-fix,~tion on such soils without tlie

I I) need to ,apply N-enriched fertilizers. The problenis outlined with the use of "N-enriched fert i l i~er clo not seem to be as great when using the "N-natural-abundance method becc~use

the enrichment of plant-available-N is relatively constant and varies little with depth (Ledgard and I'eoples 1988). This method has the added advantage of not requiring the addition of ' i ~ -en r i ched fertilizer, and thus measurements of N,-fixation ciln be made in

established experinicnts or farmers fields where suitable reference plants are present.

Biological N, Fixation through Grain Legumes

Recent reports indicate that the " ~ - n ~ ~ t u r ~ i l - a b u ~ i d a ~ i c e method is an c>xtrcmely useful method for measuring Nz-fix'ltion in d wide \-arivty of f'lrming systcnls (I't~ot~les et '11. 1991), but is less likely to be of itse in following the fate of tised N. It is important to note

that the accuracy of tht. technique, will dcpt3nd on the 1cvt.l of n'itur'll-' 'N dbunii,lncr of the soil. The 6 " ~ units for most soils are be t~vccn -3 ,,nil +15. Lcvcls of 6 " ~ > 6.0 arc

prcfcr,~blc, ~ l thoi lgh values AS l o ~ v as might still bc i~sc l~ t l , d tbpenJi~~g on the level ut I'fix (Unkovich et '11. 1994). Soils with \.cry low or varinblc 6 " ~ \,cilues will be unsuitable

tor assessing N,-tixc%tion. Furthermore, the niethod rcnc1uirt.s prc,cisc mass spectrometc1r (cdpdblc of mc,isuring accuratclv differences of U . l ' l ( ' ) <ind mrticuloi~s ,incllyticLil procedures (We'lver 'incl D'lnso 1993).

Estimates of N,-fixation by grain legumes

The estiti~;ltt~s of N,-fixed bv thc food legumes grown in tho SAT \,,iricd grc'ltlv ~trith crop spt'cies dnd loc~t ion ( l'clt71e~ 2 ) . The Icvcls o f fixcltinri depend on water s~tpply, inocul,ltion, crop t ~ i a n ~ ~ g e t i i r ~ i t p ~ ~ l i t i c c s , i t ic l~ding ,ippIicdti~)n of fcrtilizcr-N 'ind soil-h fertility. 111

,ilmost ,ill cast.s, "IIN,,,,, WAS rcduccd in the presence of higher con1binc.d-'l'.

Food legumes <irtx not olily g r o ~ ~ t i it1 p i ~ r c stdnds but thry ,Ire oftcn intt~rpl~lntecl ~vitli other species. Mixed i.ropping is pr<icticcd trC~ditir)ncllly in manv parts ot Atrii,~, Asi,l, ,lnd

1,'ltin Anleric'i. Thc combin,itic>n oi crops is dctcrniint~cl hy the length ot growing se~lson

and cnvironnicntal ad,iptcitiori, hut usuclll!~ c,lrlv- and lattx-maturing crops ~ i r c combineii to ensure efficient utili~ntion ot Ihc resources during the growing se'ison. In trc)pic,il regions the legumes such '1s cn\vpe,i, pigronpc,j, grounclnut, and chickpe,l a r r usi1,111\. intcrcropprd

\vitli riiaize, si>rgliu~ii, millet, safflo\t~t.r, or rice. I'he qu'it~titc of N: fixed 17): the legume in

an intcrcrop depends on tlic spccic.s, plant nicx-phology , ~ n d legume density in the intc3rcrup

mixturc atid crop m,inagement pr,jcticcs ( T ~ h l c 3 ) . I)ifft~rcnces in the compc>titi\,u abilities of the component crops for soil-N can result in stirni~l~ltioti of N,-fixation (I<c~rkdst.rn r t '11.

1988). I lowrver , N2-fixdtion by climbing typvs of common bean was i ~ n ~ ~ f f t > c t e d b!,

intercropping with nic>i;le ((;r,~h,lm , ~ n d liosas 1978), it~hcreas stlacling by tall cereal crops can reduce both yicld and N2-fixation of shor tw s t ~ t u r c ~ Icgumes such as grounclnut (Nambiar et '11. 1983).

Beneficial effects of legumes

In intercropping

It is generally assumed that ,I portion of N2-fixed hy an inti,rcroppeil legume is mcjclc

available to the associated nonlegunir during thc grotving se'lson. Dec'lving roots nodules are important in this transfer of N, ,qlttiough these organs generally contain only CI

small fraction of the total plant-N, e.g,, 3-40 kg N ha ' (Kumar Kao and Dart 1987; Bcrgcrscn

et al. 1989). The possibility of exudation of N from living roots should not be ignored (Poth

J. V. D. K. Kumar Rao et al. - - -. -- - --

'T-able 2. I ' r r c~~nt~ ige K,,, , ot stimc tooil Irgumes grown 111 t rop~cs (I'coplcs and Herr~ifgc, 1 L ) Y O ) .. - - -- .- - . - . -. .. . - - 'jprcres Range

Table 3. Eltcit c ~ t Iritt,rcropplng grdill Icxunics \v~tll c e r r ~ l s o n ~ . rop- i i d r r ~ v e d troll~ N - t ~ x , ~ t ~ o n ~ .-- - ~. -- - - .

I{tit. bc.,irr I'hd11~111tj IOO'O 0 ih 4'1 1 Zi.75 I] Hh 4 1

C'{>wpea ) l ~ ~ b t r ~ j l ~ ~ i 1011.0 0. h4 K7 2 71 ,?y li.hh 54

I r i~ i~a 1IlCl:ll 0 51 04 1

hh.33 1) i S 48 ~ ~ d \ ~ d l l 100.11 0 30 1 8 4

75 75 0.31 10 K~gt-rt,~ 100.0 11.7'1 I IS T

0: 38 0 51) 7: I ' I ~ C O I I ~ ~ L ~ ~ I Ind1.3 1i10 0 0.SH 8t( h

I O ( I . 1(1l\ I1 'Ih ,.- I ?

lnciia I 00 . O 0.h3 150 7 100: 1(111 0 Xh 165 - - -- - -. -. - .. . . - . .

1 I< t~rh ,~~rn ct ,11. (IYSS). 2 Clttirt rt a1 ( lYH7), 3 I'c~tr,i ct d l . ( IYXh), 4 . va11 Kebscl and Kt~shusk~ (IYSX), 5 . EagIissham t, t < > I . lIO81) (>. K L I ~ I I ~ I ~ Ii'io t>t '31 (lYS7), 7, IoL~tt~i ct c ~ l ( l L I Y 1 )

et d l . 14186). Evidence uf IV-transfer frorn legume to cereal has been obt'lineri i r i

intercropping studies (Eaglesham et al. 1981; 13andopadl1yny and De 1986; and I'c~trci et '31. 198b), including genotypic difftlrences in thc extent of 5-39'%, of lcgurne fixed-N transferred to ceredl in intcrcropping (Senaratne and Ratnasinghe 1993), although not confirmed in other investigations (Kumar liao et al. 1987; Ofori et '11. 1987; Rerkasem and Rerkasem 1988; van Kcssel 'ind Roskoski 1988). This suggests that cliwct transfer of N from legume to nclnlt.gumt. cornponcrit crop during thc season may he ~n in im~i l (Chdlk 1996 in this proceedings)

On cereals following legumes

The total amount of N in a legumc crop comes either from N2-fixation or from uptake of mineral-N from the soil. In food legumes, total-N is partitioned into either the harvested seed or the vegetative parts that generally remain as crop residues. When the quantities of N involved in plant growth, in N2-fixation and in the seed are calculated for food legume crops i t is apparent that the net N-balance is often low and in some cases negative. Positive

Biological N, Fixation through Grain Legumes . . -- -

net N-bc31anccs of up to 13h kg ha ' tor se\rvr,tl legunies following sevd hCtrvt7st h,lve bcen

reported ('Tcjble 4). tlowcvcr, Wdni ct '11. (IYY-lb) recalc~rlated the N-bal,~nccs trorn these

datd assuming that crop residues arc renio~.cd from tlie f i t ~ l c l '1s p1.r the coninlot1 pr,lc.tiic in tlie SAT, and sliowrd negClti\,e net N-bal'itices (kg 11'3 I ) froni -27 to -95 for groundnut, -28

to -101 for sovbe,in, -28 lor the colnriion bean, -24 to -h5 tor grccngr'lr~, ,lnc+ -25 to -60 for comrpecl.

Llcspite the vari,ihlc N-b'il;tnc.t.s the bcnefits reported in tropii,ll crop legunies to

subscyuent cereal crops ~ I r r consistent and s i~bstant i~i l (Wdni ,incl Lce 1992) , in~i rn '~). 1.7vrsist for sever,il sc,>sons (M,ic.Coll 198c)), reg,1rclless rv11etht3r or not the, Irgunie rv'is

grown in r n o n o r u l t ~ ~ r r or rvas i n t e r i r o p ~ ~ c d . Krsponst~s to prc\'inusl: intcrcroppcd I c g t ~ n ~ t ~ \ ,lrc mort, moclcst ( T j h l c 5 ) t l ~ ~ i r i tht' e ~ t ) r r ~ ~ p l ) r i ~ i i t ~ g ri1011~)crop. When the

contributit)n of tllcl I c g ~ ~ m c \v,~s qlrantitit,~l ,is fc~rtilizt~r-N t~quii ,ilc,nl, '1s much ,is (78 kg N ha ' r\r,~s rccluirt~ii in tlw cc~rc~,iI-ct~re,~l stlqtrrnce to ,ichic\,c simil,ir yield inipro\.ements.

'I'hr o\,tbrall benefits of 1cgunlt.s ,ircb not ii~lly cxpl,lineci cvhcn only thrir BNI: i'ltt,cts ,3rc

consieierccl. I he other likclv benefits includt~ ir~crc~tscd c~~riil'ibility of nutrients other than

N , improved soil structure, c~nh,inced Ivvcl of growth-promoting stlbst,lnccs, and rrduceei

pcst 'irid ~ i i s ~ ~ , i s e iticidenct. (Wani t.t '11. 199-lb). Thr extent of t l~csc bcnefits are ~tict~ited by

site, scason, and crop scqLrenctL.

Improving the contribution of legumes in cropping systems

Although Icgurnes hnvcl tlic 'ibility to fix N2, i t cannot be ,~ssumcd tIi'1t the inclusion of m y legilme in a cropping system will t>nsurt> significant contributions to tht> N cycle. As is

txvicient from published reports most legumes dcplc t r soil-N when plant rn'ltcrial i i

remos~t~d troln the iicld (CV'lni et ,iI. lLIY-l n,b). '1'0 derive m,~xirnum b~rwfits froni Iegurilt~s,

we must take ,I holistic ,ipyru,icIi c ~ ~ i c l ~rndcrst;rnJ the cntirtl 13NF ,ind N-cycling systcm.

Table 1. Nc.t I\'-l1,1latiit, Ior gr.1111 I L ' ~ ~ I I I I C < t o l l o w ~ ~ i g \ t ' ivl I i d r \ . ~ s t . - - . . . . .-- -- - .... . . .~ -

U t l \ l Y i 4

J. V. D. K. Kumar Rao et al.

Table 5. I<rs~du,il ettect ut Icgunic~s grown '1s sole '~nci ~n tc r t rop \\,tth '1 ccri.aI o n a fol lorvln~ trrr,il yirld in trrms ot tc.rl~i~?i,r-h c q u ~ v , i l c ~ i t ~ .

I el.t1l17cr-N t ~ q u ~ v , i l t ~ ~ i l I'recc.tl ing ltbg~~r~rc, Folh>rv~ng ~-t*rcs,~l (kg hcl ' 1 Rcf

Host-plant improvement

Variabilitv exists in legumes for the ,Irnount of N, fixed and for the proportion of plmt-N derived from HNF. We need to identify legumes , ~ n d genotvpes that yield more, and derive ,i Inrge part of their N-requirement from fix'ition. For ex'imple, cornpcired with chickpca, pigronpe'l returned '-1 I'lrgr ,inlount of fixt,cI-N to the soil through nodul ,~te~I roots and fcjllcn Ic,~\~cs. Siniil,lrly, tlicrr is '1 need to identity genotypes tti,lt can tix well under ,ld\,erst>

soil conditions, such as high soil-N, soil 'icidity ,lnd ,ilk,ilinitv, Al 'itici Mn toxicitv, ~vatrrl~)gging, high- , ~ n d low-soil tcwpcraturc. I h c natural occiIrrcncc of non-nodulating plants ~ i t h i n chickpca gcnotvpes indiecite '1 need to ensure t h ~ t their prop)rtion in the

relensecl genotypes docs not increase. Most pl'int brccding and ti)sting work is done on

research stntions where soil-mineral-N is invariably liiglier than that in farmcrs' fields. Nonnodulating and low-~iodulating plants are therefore not detected during selection dnd testing of improved genotypes. This has been demonstrated in chickpca and pigeonpea

(Kupela 1994) and may also be t rue for other legumes. To avoid this, appropr ia te procedurt-s must be ,jdopted in breeding dnci testing progr~jnis. Herridge and Danso (1995)

in a r twnt review si~ggested rnethocls for concurrrtitly nieasuririg N2-fix'qtion 'ind cissessing

lieritabilitv and repeatability of N2-fixation for breeding and selection programs with pc~rticular emphasis on common bean ( l - ' / i i i s~~ol~/s z ~ ~ / / , y ( i ~ . i s ) and soybean ( C j l , ~ l i i i ~ ~ ' t l l (~ .x ) .

Improved crop management

Appropriate crop and soil management practiccs sliould be followcci to ensure maximum HNF contributivn by legumes. For rxaniple, high mineral-N in soil that reduces HNF can bt. mariclgc~i either by irnniobilization of thc soil-N through addition of org'inic n ~ ~ ~ t e r i a l with a

high C / N ratio or through reduced tillage. In intercropping situations in which application of fertilizer-N is esscnti'~l for obtaining high cereal yields, an appropriate form of fertilizer,

e.g., slow-releasing formulations or organic-N, should be used. Also, suitable methods of f e r t i l i ~ e r 'lpplication, e .g . , placement of fertilizer in cereal crop rows rather than broadcasting and mixing in soil, must be followed (Wnni et a1. 1YY4b). Appropriate amendments with nutrients other than N that might limit legume growth-and in turn BNF-should be applied.

Biological N, Fixation through Grain Legumes

Rhizobial inoculation Under ficlcl conclitions, response to rhirobial inijc~~l,ition in tr,-ldition,il Icg~irne-gro~%,ing 'lrcas lids not beer1 consistent. Situ,ltions that need inocul,itiun should be identified ,ind

efforts must br. focused o n such arc'is. Rcscarcli for soltlction of tbfficic'nt \tr,iins ,inel iclentific,ition of spccifiz host-bnctcri,i combinations must continut' . The i n ~ p o r t ~ i t i t constr,iints limiting the exploitation of inocu1,ition tt~chnc>logy ‘ire,: ( J ) poor 11~1,ilit!' of thv inocul,~nts; (b) I'~ck of ktiowledgc '1bo11t inocul'ltiorl tcclinology aniong extension pc,rsunncl

m c i t'irmers; (c) inctfecti\r~ inoi i~l~int delivery systc>ms; Lind (d) I'ick of appropri'ltc policv silpport hy go\s i~r~ir~ic i~i ts tli,it W O ~ I I L ~ favor L I S ~ . of inoc~~l ' i~ i t s b), t,lrmtars.

Conclusion

l~eguiiics h ,~ \~c l 'in import'int rolv '1s intc~rcrops ,lnci sequcnti,il crops in sust'iining the

prod~~ct iv i ty of different cropping systems i t 1 the SAT. 11 holistic v s t r m ,lppro,ich is ,I niust

for mLixirni~ing thc bilnefits lrom BNI: in legunics. High N2-fixing Icgumes 'incl cultt\.ars shoulcl be scalt~-tt~i tor inclusioti in the cropping systvms. i\ppropri,itc~ soil ,lnd L \ ~ , ~ ~ L ~ I -

~ i i an~ igen~en t pr,lcticcs supportitig gooel pl,i~it growth, for tl.g., sowing or] ric1gc.s or broad

beds tor protecting fro111 w,~tcrIogging, using scoops tor liglit texturcd soils to incrcs,iscn

tv,itc~r stclr,igc, need to be followed. ' I o rnsilrc good nodul'3tion 'inel N,-fixation by Icgumcs in cropping systrms, I,irrnrrs rnl~st ('1) usc3 .i}pprc)~ri.it~~ c r o ~ i ~ ~ i ~ ~ t i ~ i g ~ ' t ~ i c ~ i t pr'~cticx's, such '15

'ipplication ot pliospIi'~tic f ~ ~ r t i l i ~ ~ ~ r s or other deficietit plcilit nutrients; (L,) control pests ,l~ici

d i s r ,~scs th<it ma) ,iffeet p l ~ n t c~110py '11nd in turn yhotosynthatc s i ~ p p l y to roots; ( c ) prCic-tic~~ N - ~ i i ' l ~ i ~ i g e ~ ~ i c \ t ~ t in soil (t'.g., use ot slow r~lt,,3sing tormul,ltions, ,~pplying N to cerc,lls only bl. pl,icelnet~t, i~s t> of organic sourcc>s); ,mcl (d) use need-b,~scd inoculations

with good ilu,ilit!, rIii7obi,ll i i i o c i ~ l ~ i ~ i t ~ . If r c t ~ ~ r n c d to tli? soil, p h n t residues ~voulcl help in

incrc,>sing the soil org,inic rn'3ttc.r content, and thcrclb~. incrc'isc thcl soil fertilitv. rhrougli such a n ,3pproC~cIi, bt.netit5 irom Icgi~nies DNt: z,ln bc m,lxirnized for impro\, ing or

~ust~i i i i ing producti\.ity ot SAT croppitig s),stenis.

References

l3,11iclopadhydy, S.K., ancl Dc, R. 1986. Nitrogen relationships and residual cttects ot

intercropping sorghum with legumes. Journal ot Agricultural Science 107:h39-632.

Ucrgersen, F.J., Brvckwcll, J., C;'iuIt, R.R., Morthorpe, L., I'ec>plcs, kl.H., d ~ i d 'Turner, (;.I.. 1989. F.ffects of a \ ~ ~ i i l ~ ~ b l e soil nitrogen 'ind ratcls of inocul,ition on nitrogen tix,ltiotl b y

i lr igatcd soybedns and evaluation of 6"N methods for n ~ e ~ ~ s u r e r n c n t . A ~ ~ s t r , i l i ~ l n Journal of Agriculturc Research 10:763-780.

Hudcley, K.M., Chalk, IJ.M., Victoria, R.I.., anel Matsui, E. 1984. Nitrogc,n tixcltion tl)'

nodula ted soybean under tropical field condit ions estimateel by the "N isotoyc dilution technique. Soil Biology and Biochemistry lh:583-588.

Chalk, P.M. 1985. Estinintion of N, fixation by isotopt> dilution: A n apprais,il of tt.chniqucs

involving IiN e n r i c h c n t and their application. Soil Biology and Bic~hcmistry 17:3XY-4ll~.

331

J. V. D. K. Kumar Rao et al.

CIi,111\, P.M. 19%. Nitrogvn tr'insfer from Icgunics to cereals in intercropping (in this \,olurnc).

D,iriso, S.K.A. 1983. Methods of cstini'lting biologic,~l nitrogen fix'itic)ri. P,igt's 223-244 irl (Ssdli, ti., ,inti Kt>y,i, S.O., ecls.). B i o l o g i ~ ~ ~ l nitrogen lixation in Africa. lilrizot~irr~~r MIRCEN, N,~iroL>i, Kvnyd.

F.;lgleshclni, A.R.J., Ay'i~i~ib'i, A., Ii~rig'i R'io, V., 'ind ]:skew, 11.1.. lC)81. Imprcn-ing the nitr0gt.n nutri t ion of n i a i ~ c by i~ i t c rc ropp ing with cowpea. Soil Biology and Biochc.rnistr!' 13: 16'1-171.

l :r~c~I, hl., 'ind Brocsli,irt, H. 1975. i ln independent mcasurcmcnt of the ,imount of 11itrogc.n tivcci L7!. '1 l~~g111~ie crop. I 'ld~~t '11iei S ~ i l 43:707-71 1.

(;r,lti,~nl, ['.I I . , ,i11<1 lios'l.;, J.C. IC)78. I'lcint and nodulr dr\~t~lopnient ,>ncl nitrogen tix'ition in cliriihing ci~ltiv~irs of / ' / ~ ~ ~ s L ~ o / I ~ ~ il1/l,y17/.i.s grown i l l I I ~ O I I I ) C L I ~ ~ L I ~ C or r i ~ ~ o ~ i r i t e d tvitli Z('t/

III~III . ; L. Journ,~l of Agrisultur,jl Science 90:311-317. H,lrd>,, R.W.F., Uurns, II.C., , i~ id Holstcn, R.D. 1973. ilpplic,~tions of the ,~cctylene-cttiylcnc

,iss~i!~ tor ml~,isuremt~nt of nitrogcn fix'ltion. Soil Hiolog!, ancl HioChemistry .4:47-81. I-lcrricigc, D.F., ,~nei Di~nso, S.K.A. 1995. Enli,~ncing crop legume N: fix'ltion through

selection ,ind breecling. I'l'jnt ,ind Soil 173:Sl-82. Kum'ir Ii,io, J.V.I).K., and Dart, I ' .J . Ie)87. Nocl~rl~ition, nitrogcr? fixation 'inel nitrogen ~ i p t ~ k c

in pigconpc~'1 (Ci~jililils 1~11ji111 (L.) Millsp.) of different maturity groups. Pl,~nt ,11id Soil ')V:2h55-2t~0,

Kurn'ir li,io, J.L'.I).K., Dart, I>.)., '2nd S'istry, I'.V.S.S. 1YH3. Iiesidual cffcct of pigconpc'~ (Clrjirr~rr.; i.1rji111) on !zit,lcl arid nitrogcn ri1sponsc, of maize. Expcriniclit,il Agriculture Icj:131-141.

Kum'ir R'io, J.V.II.K., l'liornpson, J .A . , Sastry, P.V.S.S., I;illcr, K.E., ancl Day, J.M. 1987. hleasurt.rncnt ot N2-fixation in field grown pigconpea (Ciljtii~rls i . t i ; t~ t l (L . ) Millst?.) using l'N-l,~bcllccl fertilizer. Plant and Soil 101:107-113.

Lcdg'lrd, S.F., 'incl I'csples, M.B. 1C)HX. Measurement of nitrogcn fixntion in the field. I'agcs 351-367 ill ~ I d v ~ i n c r s in nitrogen cycling in agricultural ecosystcliis (Wilson, J.R., c.d.).

Wallingforcl, UK: CAB Int~rnational. M,~cC'oll, D. 1989. Studit,s on maim (Zcil IIIII!/S) 'lt I ~ L I ~ L I , ~ , MCiIc1wi. 11. Yit,ld in short rot<itions

tvith legumes. Expt.rirnetitcil Agriculture 25.367-374. M'lriotti, A.J. , Mariotti, I:., 'inel Aniarger, N. 1983. Use of natural "N abundancca in the

niensuremt.nt ot symbiotic fixation. I'ages 61-77 111 Il'uclear tcchniqucs in in~pro\ping t7'1stt"re management. IAEA, Vienn'l.

N,lmhi,~r, P.T.C., Rao, M.R., Reddy, M.S., Floyd, C., Dart, P.J., and Willey, R.W. 1983. Effcct

of in tercropping on nodul,ition , ~ n d N2-fix,~tion by g r o u n d n u t . Experimental Agriculture 19:79-86.

Ofori, F., Pdte, J.S., 'lnd Stern, W.R. 1987. 1:valuation of Nz fixation and nitrogai economy of 1'1

'I ni,~ire/cowpe,-I intercrop system using N dilution methods. Plant and Soil 102:139- 160.

I'atra, D.D., Saclidev, M.S., and Subbaiah, B.V. 1986. ' 5 ~ studies on the transfer of legumr- fixed nitrogen to ,~ssociated cereals in intercropping systems. Biology and Fertility of Soils 2:165-171.

I'eoples, M.H., and Herridge, D.F. 1990. Nitrogen fixation by legumes in tropical and

Biological N, Fixation through Grain Legumes -- -- pp -- - -. - - - - --

subtropical agrii-ulturc. Adv,inccs in Agrononiv 14:155-223.

Pcoples, M.U., Sudin , M.N., ancl Ilcrriclge, D.F. 1987. Tr, i l~sloc~it ion of n i t rogtnous

compot~nc j s in symbiotic 'lnci nitr,ltc~-ti~cl cirnidt~-cuporting Icgt1rncl5. Iourn,il ot

Expcrimentcll Hotciriv 3K:Jh7-579.

I'coples, M.H., Tai7dh, A.W., Rt~kascnl , R. , 'ind Herridge, L).I*. ( t ~ i s . ) 19XCl,~. ILlctl1o~ls for

c ~ d l u ~ l t i n g nitrogen fixation by ~ lodu l , l t t~ l legumet. in thc lield. klonojir,lpli no. 1 1 , ACIAII, C,inbcrr,i 76 pp.

Pcoplrs, M.B., Hc>bh, Il.M., Gibson, i\.ti . , ,lnd I lerriclgt., I1.F. lCMC)b. I>cvc~loprlicnt ot tlie

xylem ureidc JSSCIY tor tlit, n ier isure~~ic~~i t of nitrogen flxcition b!. pij ie~npit~i ( C i i / i i ~ l / ~ i

c-iljilrr ( I . . ) Millst>.). Journ,il of E x t ~ ~ ~ r i ~ i l e n t ~ i l l%otc~n\. 40:535-413.

Peoylcs, M.B., I3ergcrscn, F . J . , ' I ' I I ~ ~ L ~ ~ , (;.I,. , S, impt~t, C ' . , lit,rkast,m, D . , Blirorns~ri, I\.,

NurliClv,lti, i).I'., I:,~iz,ili, A.W., Suciin, M.N. , Norh,iv,lti, Ll., , ~ n d ttr~rricigc, 1j.F. l ' J c l l .

Use of n'iti~r'll ~1nriihmc.nt of "N in pl,lnt ,i\~,lil,tblt~ soil N tor tllr ~nr. , js i~renit~nt ot

symbiotic N, fivciti~xi. 1';ig~~i 117-130 irl St,lblc isotoyt'.; it1 yl,lnt nutrition, soil fcrtilitl.

'tnd cn\'ironrnrnt,ll s t~ldies, IAEA, Vicnn,~. Potli, M., La l.avrt~, j.S., ,lnJ I;ocht, D.D. 1086. C)u,intiti~.,~tioti try ~ i ~ r c c t 'h' dilutioli of tivcd

N2 inc~)rpor,itiori into soil by ii7ji711t1.s ~ i l j i711 (pigi~otiped), Soil Uiologi. ,3nd Bioctieniistr\,

18:135-127. Rerk,lsem, K., ,lnd Rcrk,istbn~, U . IC)H8. L'iclcis 'jnd nitrogen ~ i~~ t r i t i o r i of irltercroppt~~i ni ' i i~e

anci ricebe'1n [Vl , yrr i l ~rrn l l c ' l l i i t i~ (Tlit~rnb.) Ohuri , ~ n d Oh,lshi). i'l'l~l t 'lnci 5oiI 108: 141- 1h2.

I<crk,jscm, I < . , licrk,isem, I(. , I ' cop l~~s , iLI.B., I I rrr i~lgt . , I).F., 'ind f3c~r,qcrsen, I : . ! . IWS.

Me,isurt~rrlrnt of N! fix'ition in nlaizc. ( / I U r~rirr~.; I .) - rict.he,ln [ l / i , y r l i i ~ r r r r l ~ i ~ l l i l l i i (Tll l~mh.)

Oli~vi ,inel COh~shi] intcrcrops. Pl,int . I I ~ L ~ Soil 108:1?.5-l?5.

Iiupel,j, 0 . 1 ' . 1994. Screening tor the intr,icultivaral \~,iri,ibilitc. of nodul'ltion in zhickpc~,i

~ n d t7igeonye'1. I'agt>s775-3 3 i 1 l ,inking triologic'll nitrogcll tixation rc>sc,lrch In :\s1,1:

Rt~port of a mt~r t ing nf the, Asi'i bLJurking (;rout7 on Biologi~~ll N~troge)n I-ix'ltlon i n

l . t>g~~rncs , 0-8 Dcc 1993, ICKISAT i 2 s i ~ Ccntc>r, India ( R i ~ p c l a , C).I' . , Kum,ir I i ~ o ,

J.V.1I.K.. W'ini, S.lJ., ,qncl Iohci~isen, C., cds.) . I ' ,~t,~nchc~ri~ 502 334, Andlira I'radesll,

Indi'i: Intcrnation.il C'rops Rc~e~ i rch Institute tor tlie Semi-ilriti Trop~cs.

Sen,~r,~tnc, I<., ,~n t i Katn,jsinglie, D.S. 1C)C13. N supply by groun~inuts to maize In LI n>'li/c' plirs grounclnt~t intt.rcropping s y s t ~ ~ l t i , '1s ,itfcctt~cl I>\, tlie g c ~ ~ ~ o t \ , p c . liiolog!. 'inel

1:ertility of Soils 15:215-219.

She,~rer, G., ,311~1 Kohl, D . H 1986. N, fiu'ltion in field settings: ctim.ltions luscd o n n,ltul-,ll "N abuncl,incr. A u s t r ~ l i ~ n lo~~rn , t l of IJlci~it I'hysiology 13:tiClc)-7Sh.

Suwanarit, 12., Su\v~ni, lr ,~t , C., and Chott.ch,iungni,~nir,it, S. I c )Hh . (I)i~'llltities ot tivc'cl N nil c f t t ~ t s of grain legunies 011 iolloiving n i , ~ i ~ t l , ,in4 h' ,)nil 1' s t ~ t u s of soil in~iic'ltcil Ll!.

isotopes. I'l,-lnt anci Soil 93:24Cl-2L58.

'Tobita, S., Ito, O., M,ltsunaga, I<., R,ln, 'I'.I'., Reg(], I'.!., joh,lnst~n, C., 'lncl L'oncyCim,l, I ' . lc)Y-1. Ficld evclluatic>n of ~iitrogcbn tix'ition ,~nc l ~1st . of rlitrogtln fcr t i l i / t l r

s o r g h ~ l m / p ~ g e o ~ i ~ ~ e ~ t intercropping on ,In Aliisol in the, Ir1ciiCln St'rlli-Arid rropics. Hiology and Fertility of Soils 17:241-248.

7'roll, C. 1965. Seasonal climcitt's of thc e,jrth. 1'~gtl 28 r r r World ni.lps of c l in~~ i to lng)

(Rodrnwalt, E., 'ind J i~s tk~i tz , H., cds.). Ikrlin, Springcr Vcr l~g .

Unkovitch, M.J., I'atc, J.S., S'lnforcl, I]., ,117d Arunstrong, E.I.. lLlC14. I'otcnti,ll prtscisiorl of tllr'

333

J. V. D. K. Kumar Rao et al.

I + N n,>tural ,>bund,lncc method in field estimates of nitrogen fixation by crop and pcjsturc Icgumes in ssutti-west Ai~stralin. Australian Journ,~l of Agriculture Research

45:119-132. Van Kesscl, C., and Roskoski, 1.1'. lC)H8. Row sp'lcing effects on N: fixation, N-yield and soil

N uptdke of intercropped cowyea and niai~c., Plant and Soil 1 I I : 17-23. Wani, S.IJ., 'ind Idre, K.K. 1992. liole of biofertilizers in irpland crop production. Pagcs 91-

112 i r ~ Fcrtilizcrs, organic nianurcs, recvclablc wastcs and biofertilizers (Tanclon, I-I.L.S., ed.). Fertilizer Development and C o r i s ~ ~ l t ~ ~ t i o n C)rgcinization, New Delhi, India.

Wani, S.I'., licgo, I . J . , and Kuni'lr liclo, J.V.D.K. lL)Y4,i. Contributioli of legumes in cropping systems: ,I long-terrn perspective. Pages H4-Y(1 irl Linking biological nitrogcn fixation resecircli in Asia: report of a mee t i~ ig of thc Asi'i Working C;roi~p 011 Biologicdl Nitrogen Fixatiori in 1,egumes. (I<upela, 0.1'., Kumar Rae, J.V.D.K., Wani, S.I'., rid Joliansen, C'., eds.). 1'~tancheru 502 324, Andhra Prndesh, Indi'i: International Crops

Kesec~rcli Institutt. for tlic Semi-Arid Tropics. W'lni, S.I'., l i ~ ~ p e l a , O.P., and Lrr, K.K. 1994h. BNF tt~chnology for sustainable '~griculturc

Pages 215-62 i r r Tr,~nsactions of thc 15th World Congress uf Soil Science. 10-16 luly 1994. Acapulco, Mexico. Syniposi,> I'aper Conimission Ill, Vol. 12, Internation,~l Society of Soil Science and the Mexican Society of Soil Scicwcc.

Wc,~vcr, K.W., and Ddnso, S.K.A. 1994. Ilinitrogcn Fixation.P'~ges 1019-1015 irl Methods of soil clncllysis, I'art 2. Microbiologi~~ll anti biocheniicdl propt.rtics - SSSA Book Series h0.5, USA.

I ') Wittv, J.F. 1983. Estimdting N2 fixation in tlic field using N I,jbellrd tertili7t.r: some problems and sulutions. Soil Biology dnd Biochemistry 15:631-63').

Witty, J.F., '~ncl Giller, K.E. 1991. E~~i luat ior i of errors ill the mcc~surt.nient of biological I i nitrogc~n fixation using IV fertilizer. Pages 59-72 irr The use of stahlt. isotopes in plant

nutrition, soil fertility and enviro~~nientnl studies. IAEA, Vienna. Witty, J.F., ancl Minchin, F.R. 1988. MeCisurerncnt of nitrogen fixation by the dcetylene

reduction 'jssay; myths atid mysteries. Pdges 331-344 ill Nitrogen fixation by legumes in mediterr,ine~in cigriculture (Beck, L>.I'., 'ind Materon, I..A., rds . ) . Dordrccht,

Netherlands: Martinus Nijhoff Publishers.