Green Gram Rotation Effects on Maize Growth Parameters and Soil Quality in Myanmar

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1 Journl of Agriculture nd Rurl Development in the Tropics nd Sutropics Volume 109, No. 2, 2008, pges Green Grm Rottion Effects on Mize Growth Prmeters nd Soil Qulity in Mynmr M. Kywe 1, M. R. Finckh 2 nd A. Buerkert 3 Astrct At present mize green grm crop rottions re not widely prcticed mong frmers in Mynmr. However, this cropping system might ecome more populr in the future given rising prices for green grm nd mize grin nd scrcity of minerl nitrogen (N) fertilizers in this Asin country. The results of cropping systems experiment with continuous mize versus green grm-mize rottion, mnure ppliction (0 nd 2 t h 1 ) nd phosphorus (P) fertiliztion (0 nd 15 kg P h 1 ) in ech of five consecutive sesons reveled strong decline in totl dry mtter nd grins yields for oth crops irrespective of the tretment. Tretment effects on yield components, nutrient concentrtions, mycorrhizl infection nd nemtode infesttion were smll or negligile. The dt show tht in ddition to mnure used t 2 t h 1, ppliction of minerl N fertilizers is essentil to mintin prticulrly mize yields. A comprison of different green grm cultivrs did not indicte genotype specific effects on mize growth. The incorportion of legume residues, unless they re used s niml feed, is recommended to increse the recycling of N nd to lnce N fluxes when green grm is cultivted for seed. Keywords: Mize, Green grm, Rottion, Mnure, Nitrogen, Phosphorus, Mynmr 1 Introduction Among the 60 different crop species grown in Mynmr, mize (Ze mys L.), grown for domestic use nd export, is the second most importnt cerel fter rice (Oryz stiv L.). In 2003, the totl mize re in Mynmr ws 300,000 h with n verge grin yield of 2,500 kg h 1 (FAO, 2004). Given fvourle terms of trde on export mrkets, mize cultivtion is ecoming incresingly populr nd frmers re using more nd more hyrid vrieties. However, soil fertility in continuously cropped mize fields is deteriorting rpidly leding to declining yields during the riny (My-Septemer) nd dry (Octoer-Decemer) seson (MOAI, 2005). To supply nitrogen (N) to the crop, frmers often use minerl fertilizers t rtes of up to 100 kg N h 1 rther thn legume 1 Dr. Myo Kywe, Deprtm. of Agronomy, Yezin Agriculturl University, Yezin, 05282, Mynmr 2 Prof. Dr. Mri R. Finckh, Ecologicl Crop Protection, University of Kssel, D Witzenhusen, Germny corresponding uthor 3 Prof. Dr. Andres Buerkert, Orgnic Plnt Production nd Agroecosystems Reserch in the Tropics nd Sutropics, University of Kssel, D Witzenhusen, Germny 123

2 rottions. However, imports of minerl fertilizers re severely hmpered y shortges of foreign exchnge nd therefore their use is low. Similrly, mnure ppliction is restricted due to scrcity-induced high prices. With productive frmlnd fcing incresed pressure from growing popultion, cerellegume rottions hve een proposed s n effective mens to increse the productivity of nutrient-depleted soils in low-externl input systems (Buerkert et l., 2001,). On cid sndy soils of semi-rid West Afric where crop yields re strongly limited y P vilility (Btiono et l., 1992), cerel/legume rottions sed on mize, sorghum (Sorghum icolor L. Moench), cowpe (Vign unguicult L.) nd groundnut (Archis hypoge L.) hve een shown to cuse lrge increses in cerel yields (Bgyoko et l., 2000,c). Similrly, soil productivity in SE Asi including Mynmr is limited y low ph, low CEC, low se sturtion nd high P-fixtion cpcity (Pushprjh nd Bchik, 1987). Highly wethered tropicl soils (Oxisols, Ultisols) re typiclly chrcterized y low totl nd ville P nd n often high P retention cpcity (Friesen et l., 1997). Moreover, P use efficiency is usully low nd rrely exceeds 20% of pplied P in the yer of ppliction depending on the nture of the soils nd crops concerned (Su Ro et l., 1995). However, when mnure nd fertilizer P re pplied together, synergistic effects often led to ville P eing higher thn expected from the sum of oth mendments lone (Reddy et l., 1999). While the ddition of niml mnure my improve P-vilility, it is unlikely to hve much impct on other yield limiting fctors such s pests nd diseses, which re fvoured y continuous cropping, ut it my slow down the deteriortion of soil structure. While yield increses in cerels following rottion with legumes hve een reported from Mynmr (Hn et l., 2001), solid experimentl dt from cropping systems experiments re necessry to sustntite these reports. So fr, the few ville dt refer to rice-sed systems nd were collected on cid Vertisols (Fris, 1992). Given the scrcity of dt on legume rottion effects for mize in Mynmr, the ojectives of this study were to exmine to wht degree n expected N-relted yield decline in mize monocropping system under the low externl input conditions of locl frmers could e slowed down y rottion with green grm nd to explore the cuses of possile yield-enhncing effects of green grm on mize. The following reserch hypotheses were therefore tested in field experiments: (i) rottion with green grm (Vign rdit), frm yrd mnure nd P fertilizer will slow down the expected yield decline in continuous mize system, (ii) incorportion of green grm shoot residues will further enhnce mize growth. Different green grm cultivrs were used to determine possile cultivr-system interctions. 2 Methodology 2.1 Experimentl detils The experiment ws conducted from 2002 to 2004 on Gleysol soil with ph wter of 5.6; 50 mg totl N kg 1 soil nd 6.8 mg Bry-1 P kg 1 soil t the frm of Yezin 124

3 Agriculturl University ( N ltitude, E longitude, 102 m ltitude). The lyout consisted of split-split plot design with four replictions. Tretment fctors were two cropping systems s min plots. The suplot fctor ws mnure ppliction t 0 nd 2 t h 1 cttle compost, with N concentrtions of 1.15, 0.78, 0.67, 1.01 nd 0.89% nd P concentrtions of 0.51, 0.97, 1.15, 0.91 nd 0.78% for the five experimentl sesons, respectively. The su-su plot fctors consisted of 0 nd 15 kg P h 1 s sl triple-super phosphte (TSP with 21% P). In the first seson, three introduced green grm cultivrs (V-3726, VC-5205 nd Knti) nd one mize cultivr (Yezin Hyrid-3) were used. In seson two nd three, the three green grm cultivrs V-3726, Knti nd the lndrce Pkhoku were grown. Becuse of its high yield, V-3726 ws lso chosen for the 4 th nd 5 th seson. Annul rinfll, distriuted imodlly etween My nd Novemer, totlled 1369 mm in 2002, 727 mm in 2003 nd 1279 mm in Lnd preprtion ws done once y n niml-drwn plough followed y two hrrowing opertions. Plnt spcing ws 0.5 m etween nd 0.1 m within rows for green grm nd 0.5 m etween nd within rows with one plnt per hill for mize. Weed nd pest control ws done s necessry. To exmine the effects of legume residue mngement, tretments of shoot incorportion nd removl were dded in the 5 th seson s further split of legume plots. 2.2 Plnt smpling nd nlysis At flowering smples for tissue nlysis of oth crops were tken, dried t 70 C toweight constncy nd nlysed for N nd P t the Agriculturl Chemistry Division Lortory, Deprtment of Agriculturl Reserch in Yezin nd t the Institute of Crop Science Lortory, University of Kssel, Germny. Totl N ws determined with Mcro-N- Anlyser (Hereus, Bremen, Germny). For P nlysis, shoot nd seed smples were shed for 4 hrs in muffle furnce t 500 C nd the sh ws dissolved in 1:30 (v/v) HCl. Phosphorus ws determined clorimetriclly (Hitchi U-2000 spectrophotometer). At finl hrvest totl dry mtter (TDM, kg h 1 ) ws mesured nd the Hrvest Index (HI) ws determined. For root nlyses soil smples (0 to 0.2 m) were collected t five loctions within ech plot in ll locks t flowering. All smples were wshed over 0.5 mm sieve to remove dherent soil nd nlysed for root length density ccording to Tennnt (1975) in 10 mm grid line petri dish with inoculr t 40. After counting, root smples were dried t 60 C for 12 h. Dry weight, totl root length (TRL), specific root length (SRL) nd root length density (RLD) were determined using the following equtions: Z mesh (cm) 11/14 SRL = (1) X (g) TRL = SRL y (g) (2) where: Z = totl numers of intersects; X = dry weight of counted smple; y = dry weight of entire root; nd RLD = TRL(cm) soil volume (cm 3 ) (3) 125

4 2.3 Mesurements of mycorrhize nd nemtodes Mycorrhiz nd nemtode incidence were ssessed in the 4 th nd 5 th growing seson. For mesurement of mycorrhize, 100 g of wshed mize roots were cut into segments of mm nd clered with 10% KOH t 60 C for 1 h. Susequently, roots were rinsed three times in deionized wter nd cidified for 30 minutes in 2 N HCl. Then, roots were stined with 0.05% trypn lue in lctic cid over night followed y destining in lctic cid. Percent mycorrhiz coloniztion of roots ws determined y the line intersection method (Kormnik nd McGrw, 1982). A modified Bermn funnel method s descried y Hooper (1984) ws used for the extrction of nemtodes from 200 g soil nd root smples prior to counting. 2.4 Dt nlysis Dt of TDM, grin yield nd nutrient concentrtions were nlysed for ll sesons together wherey tretments were split into sesons nd susequently nlysed for ech seson seprtely y Anlysis of Vrince (ANOVA) using the Restricted Mximum Likelihood procedure (REML) nd time series nlysis of GENSTAT (Lwes Agriculturl Trust, 2000). Sesonl dt of grin yield nd plnt nutrient concentrtions were lso sujected to ANOVA. The dt of nemtode popultions otined in the finl seson ws trnsformed s log se 10 nd nlysed s ove. 3 Results 3.1 Green grm Regrdless of the tretment level TDM nd grin yield of green grm decresed over the course of the experiment y n verge of 41% nd 52% (Fig. 1 nd 2). Across sesons mnure ppliction led to consistently higher TDM wheres P ppliction ws only enhncing growth in seson 2 nd 5 without mnure (Fig. 1). Significnt effects of mnure on grin yield were noted in seson 4 nd 5 (Fig. 2). Effects of mnure nd P on grin yield vried gretly with the seson. No effects were oserved in seson 1, wheres in seson 2 P nd mnure ddition resulted in significnt yield increses with no synergistic effects eing oserved etween oth types of mendments (Tle 1). While men grin yield declined y out hlf over the durtion of the experiments (from 600 kg h 1 in seson 1 to 310 kg h 1 in seson 5) during the sme period, RLD ws reduced y 75% (from 4.5 cm cm 3 to 0.9 cm cm 3 ). The LAI of green grm ws lso reduced y 59% cross sesons (from 3.3 to 1.9), ut the HI remined with vlues of nd unchnged. Pod numers per plnt declined from 12.9 to 12.3 over the course of the experiment. Of the cultivrs tested in some, ut not ll sesons grin yields were highest for cultivr V-3726 which is very populr in Mynmr ecuse of its lrge grin size nd susequent high mrket price. Although not significnt, N nd P concentrtions in green grm shoots of ll tretments incresed over the durtion of the experiment from round 23 to 42 mg g 1 nd from 2.2to3.6mgg 1, respectively (Tle 2). In untreted controls shoot N concentrtion 126

5 ws higher thn with mnure nd shoot P incresed from 3.9 to 4.6 mg P g 1. No correltions were found etween N nd P concentrtions nd green grm grin yield (r = 0.37, r = 0.34). Figure 1: Effects of mnure nd phosphorus (P) ppliction on totl dry mtter of green grm (cv. V-3726) in field tril in Mynmr ( ) M 0 P 0 M 0 P 1 M 1 P 0 M 1 P 1 Totl dry mtter (kg h -1 ) st 2nd 3rd 4th 5th Riny 2002 Riny 2003 Dry 2003 Riny 2004 Dry 2004 Seson M0P0 = no mnure, no minerl P; M0P1 = no mnure, 15 kg P h 1 ;M1P0=2th 1 mnure, no minerl P; M1P1=2th 1 mnure, 15 kg P h 1. The lsd0.05 vlues cross tretments re 1650, 1208, 720, 1175 nd 480, in seson 1-5, respectively. Columns within seson mrked with different letters re significntly different t P < Tle 1: Comined nlysis of vrince (ANOVA) of mnure (M) nd phosphorus (P) ppliction effects in green grm grown in cropping systems (CS) experiment with continuous mize nd mize in rottion with green grm t Yezin, Mynmr (five sesons from ). Source of vrition Prmeter Totl dry mtter (kg h 1 ) Pr > F Grin yield (kg h 1 ) RLD (cm cm 1 ) Seson Mnure Seson Mnure P Seson P Mnure P Seson Mnure P Proility of tretment effect (significnce level), Root length density, 2002 riny, 2003 riny, 2003 dry, 2004 riny, 2004 dry 127

6 Figure 2: Effects of mnure nd phosphorus (P) ppliction on grin yield of green grm (cv. V-3726) in field tril t Yezin, Mynmr ( ) Grin yield (kg h -1 ) M 0 P 0 M 0 P 1 M 1 P 0 M 1 P st 2nd 3rd 4th 5th Riny 2002 Riny 2003 Dry 2003 Riny 2004 Dry 2004 Seson M0P0 = no mnure, no minerl P; M0P1 = no mnure, 15 kg P h 1 ;M1P0=2th 1 mnure, no minerl P; M1P1=2th 1 mnure, 15 kg P h 1. The lsd0.05 vlues re 201, 143, 199, 95 nd 80, in seson 1-5, respectively. Columns within sesons mrked with different letters re significntly different t P < Tle 2: Nitrogen (N) nd phosphorus (P) concentrtions in green grm nd mize shoots in cropping system field experiment t Yezin, Mynmr cross five sesons ( ). Dt show tretments mens. Concentrtion (mg g 1 )inseson Green grm Shoot N n Shoot P n Mize Shoot N n Shoot P n n.. not ville 128

7 3.2 Mize With 93% nd 97% the respective decline of mize TDM nd grin yield over the durtion of the experiment ws lrger thn similr effects in green grm (Fig. 3 nd 4). The overll ANOVA showed significnt F-vlue for seson, cropping system, mnure nd P ppliction (Tle 3). For individul yers, F-vlues did not show significnt rottion effects from seson 2 onwrds, lthough yields from rottion plots tended to e higher thn those from continuous mize plots. Root length density decresed over time nd there were only mrginl effects of P fertilizer nd no effects of rottion on RLD. Although cross yers rottion effects on mize growth were inconsistent, crop rottion incresed TDM, grin yield, RLD nd the numer of ers per plnt compred to continuous mize in sesons 2, 3 nd 4. Mnure ppliction led to incresed lef re, plnt height, TDM nd grin yield. Phosphorus ppliction lso incresed LAI nd plnt height, therey contriuting to incresed TDM nd grin yield. In seson 5, incorportion of legume residues significntly enhnced grin yield reltive to residue removl only without P ppliction (Fig. 5). However, compred to mize growth in previous sesons, grin yield nd TDM of mize in ll tretments shrply declined. By seson 3, legume rottion-induced increses in mize growth were lrger thn those cused y mnure- nd P-ppliction (Fig. 4). From seson 2 onwrds, rottion effects were little ffected y mnure nd P ppliction. In the 4 th nd 5 th cropping seson mnure ppliction tended to increse mycorrhizl infection ut effects on plnt-prsitic nemtodes were inconsistent cross cropping systems (Fig. 6 nd 7). The verge LAI of mize decresed from 4.0 to 0.3 nd there ws no significnt effect of mnure nd P ppliction on er numer per plot. Mnure incresed er numers from 12 to 15. From seson 2 to 5 plnt height nd stem dimeter declined from 143 nd 5.7 cm to 48 nd 3.9 cm. Across sesons, the HI remined lmost constnt. Recycling / incorportion of legume strw led to sustntil yield increses ut ws not enough to llevite N constrints. Over sesons the rpid yield decline overtime ws reflected in strong decrese of N concentrtions in mize shoots from 19 to 13 mg g 1 nd concomitnt increse in P concentrtions from 1.6 to 4.6 mg g 1 (Tle 2). In the 5 th seson incorportion of legume residues led to slight increse in mize N concentrtion. From seson one to seson five, N removl of the mize field declined from 54 kg N to 30 kg N. The soil minerl N concentrtion in the top 15 cm of the profile tended to e higher in rottion plots with residue incorportion up to six weeks fter plnting compred to rottion plots with legume residue removl or continuous mize cultivtion. However, these differences were not sttisticlly significnt. 129

8 Figure 3: Effects of cropping system, mnure nd phosphorus (P) ppliction on totl dry mtter of mize in field tril t Yezin, Mynmr ( ). Totl dry mtter (kg h -1 ) d c 1st 2nd C 2nd R c c 3rd C 3rd R Riny 2003 Dry 2003 Riny 2004 Dry 2004 Seson 4th C 4th R M 0 P 0 M 0 P 1 M 1 P 0 M 1 P 1 5th C C = continuous mize, R = mize-green grm rottion, M0P0 = no mnure, no minerl P; M0P1 = no mnure, 15 kg P h 1 ;M1P0=2th 1 mnure, no minerl P; M1P1 = 2 t h 1 mnure, 15 kg P h 1. The lsd0.05 vlues re 1040, 503, 643, 582 nd 107, respectively. Columns within sesons mrked with different letters re significntly different t P < th R Tle 3: Anlysis of vrince (ANOVA) for the time dependent effects (five sesons from ) of cropping system (continuous mize versus green grm-mize rottion), mnure ppliction (0 nd 2000 kg h 1 ) nd nded phosphorus (P) fertiliztion (0 nd 15 kg P h 1 ) on totl dry mtter (TDM), grin yield nd root length density (RLD) of mize (Ze mys L.) t Yezin, Mynmr. Source of vrition Prmeter Totl dry mtter (kg h 1 ) Pr > F Grin yield (kg h 1 ) RLD (cm cm 1 ) Seson System Seson System Mnure Seson Mnure System Mnure Seson System Mnure P Seson P System P Mnure P Seson System P Seson Mnure P System Mnure P Seson System Mnure P Proility of tretment effect (significnce level), Root length density, 2002 riny, 2003 riny, 2003 dry, 2004 riny, 2004 dry 130

9 Figure 4: Effects of cropping system, mnure nd phosphorus (P) ppliction on grin yield of mize in field tril t Yezin, Mynmr ( ) Grin yield (kg h -1 ) c c d M 0 P 0 M 0 P 1 M 1 P 0 M 1 P 1 1st 2nd C 2nd R 3rd C 3rd R 4th C 4th R 5th C 5th R Riny 2003 Dry 2003 Riny 2004 Dry 2004 Seson C = continuous mize, R = mize-green grm rottion, M0P0 = no mnure, no minerl P; M0P1 = no mnure, 15 kg P h 1 ;M1P0=2th 1 mnure, no minerl P; M1P1 = 2 t h 1 mnure, 15 kg P h 1. The lsd0.05 vlues re 450, 568, 743, 477 nd 106, respectively. Columns within sesons mrked with different letters re significntly different t P < 0.05 Figure 5: Effect of phosphorus (P) ppliction (kg h 1 ) nd legume residue mngement (removl versus incorportion) on grin yield of mize in the 5 th seson t Yezin, Mynmr (2004 dry seson). Grin yield (kg h -1 ) kg P, incorported 0 kg P, removed 15 kg P, incorported 15 kg P, removed continuous mize t 2 t Mnure The lsd0.05 vlue ws 42. Columns within sesons mrked with different letters re significntly different t P <

10 Figure 6: Effects of cropping system nd mnure ppliction on mycorrhizl infection of mize in the 2004 riny nd dry seson t Yezin, Mynmr (2004) t Mnure 2 t Mnure Mycorrhiz Infection % M - M M - G M - M M G (R) M G (I) 2004 Riny 2004 Dry M-M = continuous mize, M-G = mize-green grm rottion; R = legume strw removed; I = legume strw incorported. The lsd0.05 vlues 22.6 nd 31.0, in seson 4 nd 5, respectively. Columns within sesons mrked with different letters re significntly different t P < Figure 7: Effect of cropping system nd mnure ppliction on plnt-prsitic nemtodes in soils of mize cropping systems experiment in the 4 th nd 5 th seson t Yezin, Mynmr (2004). 400 Nemtodes per 100 g soil t Mnure 2 t Mnure 0 Continuous Rottion Continuous Rottion 2004 Riny 2004 Dry The dt re ck trnsformend fter log-trnsformtion for sttisticl nlysis; lsd0.05 vlues of trnsformed vlues re 0.26 nd 0.64, respectively. Columns within seson mrked with different letters re significntly different t P <

11 4 Discussion 4.1 Green grm Over the five cropping sesons green grm TDM nd grin yield steeply declined which likely reflected effects of N deficiency for s evidenced y the decline of N concentrtions over time. During the first sesons V-3726 consistently showed highest TDM nd grin yield which ws lso reflected in its high LAI nd numer of pods per plnt. Although not significnt except for the 1 st seson, P ppliction tended to increse RLD in ll sesons, which likely reflected P effects on shoot growth. Ahmd et l. (2001) reported totl N concentrtion in green grm rnging from 26 to 36 mg g 1,wheres Lwn nd Ahn (1985) showed N concentrtions of 6 16 mg g 1 nd P concentrtions of2 2.9gkg Mize The results clerly showed tht regrdless of the tretment mize growth ws strongly limited y N supply which lso led to the drmtic decline in yields over time nd the decline in shoot N concentrtions to 68% of the vlue mesured in the second seson. Similr results were found y Cheruiyot et l. (2001) who reported tht growing continuous mize resulted in strong growth decline following limited soil N. The dt did not show ny llevition of this yield decline or significnt difference in shoot N concentrtion in plots with green grm rottion. Further studies using cetylene reduction ssys or 15 N nlysis would hve een needed to determine the level of N 2 -fixtion y green grm in this study. The sence of difference in the N-sttus of mize grown in the two cropping systems indictes tht under the conditions of this experiment N 2 -fixtion of green grm my hve een severely hmpered despite the strong presence of reddish nodules on roots. At this level of N supply soil P ws pprently not limiting despite its low vilility (6.8 mg Bry-1 P kg 1 in the initil soil). Only this would explin the smll response of mize growth to regulr P pplictions in orgnic form (mnure) nd s minerl fertilizer. Lcking rottion effects on mize growth in the 2 nd seson re likely due to the erroneous fllow phse following the first cropping seson in The increse in RLD with P ppliction is in greement with erlier findings on P-poor sndy soils from West Afric which showed incresed root iomss, root to shoot rtio nd lterl root length fter P ddition (Mrschner et l., 2004). Higher TDM yield of mize due to mnure were oserved in seson 2, which my lso e linked to the oserved increse in ph from 5.6 to 6.8 fter five sesons in plots with nd without mnure ppliction. Similr mnure-induced ph increses were oserved previously y Hrris (2002) nd Chettri et l. (2003). Wddington nd Krigwindi (2001) reported tht on on-frm grin yields from continuous mize (one seson per yer) without fertilizer rnged from t h 1 over five yers. In contrst, in the 5 th seson of this experiment mize grin yield ws < 0.5 t h 1. McDongh nd Hillyer (2003) lso reported tht for moderte millet grin yield (1000 kg h 1 ) in Afric, kg N h 1 nd kg P h 1 minerl 133

12 fertilizer were essentil. Kwih et l. (2003) oserved tht ppliction of 5 t dry mtter h 1 of Tithoni nd Croton ws similr to the effects of 120 kg N h 1 nd 50 kg P h 1 of inorgnic fertilizers in enhncing on mize grin yield. In this experiment only kg N ws dded nnully through the ppliction of mnure. This ws too low to sustin mize yields t verge N removls of 70, 74, 43, 32, 4 kg h 1 per seson. Giller nd Cdisch (1995) reported tht the removl of legume stover t hrvest frequently leds to net removl of N from the soil. Therefore the recycling of residues to the soil is essentil for the N-lnce in grin legumes. Nevertheless, food legumes such s cowpe, green grm nd pigeon pe were found to increse yields of susequent cerel crops in semi-rid Indi y n equivlent of kg N h 1 (Kumr Ro et l., 1988). Similr results were found y Rego nd Ro (2000) in sorghum pigeon pe intercropping on Vertisol in Indi (2000). For mize Herrmnn nd Tue (2005) reported criticl shoot N concentrtion of 10.5 g N kg 1 TDM. Chettri et l. (2003) reported tht the ppliction of 7 t h 1 mnure to rice nd whet crops over eight yers hd no eneficil effect on yields. But Hrris (2002) showed mnure-induced yield increses due to the improvement of N, P, K nd micronutrients nd of soil physicl properties. In contrst to the ltter results, mnure effects on crop yield were very smll in this experiment. This might hve een due to the ppliction rte of only 2 t h 1. The slightly (from to mg N g 1 ; from 3.24 to 3.73 mg P g 1 )incresed N nd P concentrtion of rottion mize compred to continuous mize might hve een due to smll (though sttisticl not significnt) increse in mycorrhizl infection. Without mnure, however, mycorrhizl infection rtes were not ffected y cropping system. For nemtodes, smll, though significnt decrese in numers ws oserved with green grm rottion in the riny seson of 2004, ut differences were insignificnt in the following dry seson. The compred to the results of Bgyoko et l. (2000) missing consistent rottion-induced decline in nemtodes my e due to the fct tht in ll tretments overll infesttion levels were smll nd unlikely to cuse much hrm to plnt roots. 5 Conclusions In the sence of minerl N fertilizers nd with only moderte mounts of pplied cttle mnure the green grm rottion filed to increse mize yields compred to the monoculture mize system. The results indicte tht under the conditions of this fiveseson experiment, N 2 -fixtion of green grm might hve een severely hmpered nd thecrop seffectsonthen lnce negtive when seeds nd stlks were removed. The sence of significnt effects of green grm on mycorrhizl infection nd nemtodes in susequent mize my further explin lcking legume-rottion effects on this crop. The results strongly suggest tht prt from 2 t h 1 mnure, ppliction of minerl N fertilizer is needed to mintin growth nd grin yield of mize irrespective of the rottion with different green grm cultivrs. 134

13 Acknowledgements The uthors re grteful to the Germn Acdemic Exchnge Service (DAAD) for scholrship to the first uthor nd to the technicl ssistnce of Cludi Thieme, Ev Wiegrd nd Burkhrd Heiligtg. References Ahmd, T., Hfeez, F. Y., Mhmood, T. nd Mlik, K. A.; Residul effect of nitrogen fixed y mungen nd lckgrm on susequent rice nd whet crops; Austrlin Journl Experimentl Agriculture; 41: ; Bgyoko, M., Alvey, S., Neumnn, G. nd Buerkert, A.; Root-induced increses in soil ph nd nutrient vilility to field-grown cerels nd legumes on cid sndy soils of Sudno-Shelin West Afric; Plnt nd Soil; 225: ; Bgyoko, M., Buerkert, A., Lung, G., Btiono, A. nd Römheld, V.; Cerel/legume rottion effects on cerel growth in Sudno-Shelin West Afric: Soil minerl nitrogen, mycorrhize nd nemtodes; Plnt nd Soil; 218: ; Bgyoko, M., George, E., Römheld, V. nd Buerkert, A.; Effects of mycorrhize nd phosphorus on growth nd nutrient uptke of millet, cowpe nd sorghum on West Africn soil; Journl of Agricultul Science; 135: ; 2000c. Btiono, A., Christinson,B.C., Bethgen, W. E. nd Mokwunye, A. U.; A frm-level evlution of nitrogen nd phosphorus fertilizer use nd plnting density for perl millet production in Niger; Fertilizer Reserch; 31: ; Buerkert, A., Bgyoko, M., Alvey, S. nd Btiono, A.; Cuses of legumerottion effects in incresing cerel yields cross the Sudnin, Shelin nd Guinen zone of West Afric; in: Plnt nutrition, food security nd sustinility of groecosystems through sic nd pplied reserch. Developments in Plnt nd Soil Science, edited y Horst, W.; ; Kluwer Acdemic Pulishers, Dordrecht, The Netherlnds; Buerkert, A., Btiono, A. nd Piepho, H.-P.; Efficient phosphorus ppliction strtegies for incresed crop production in su-shrn West Afric; Field Crops Reserch; 72:1 15; Cheruiyot, E. K., Mumer, L. M., Nkhone, L. N. nd Mwong, S. M.; Rottionl effects of grin legumes on mize performnce in the rift vlley highlnds of Keny; Africn Crop Science Journl; 9: ; Chettri, G. B., Ghimiry, M. nd Floyd, C. N.; Effects of frmyrd mnure, fertilizers nd green mnuring in rice-whet systems in Bhutn: results from longterm experiment; Experimentl Agriculture; 39: ; FAO; Selected Indictors of Food nd Agriculture Development in Asi-Pcific Regions; RAP Puliction 2004/20. FAO-RAPA, Bngkok; Fris, D. G.; Mnging AGLN crops in rice-sed cropping systems: Summry proceedings of the Mynmr - AGLN/ICRISAT workshop nd monitoring tour; ICRISAT, Indi; Friesen, D. K., Ro, I. M., Thoms, R. J., Oerson, A. nd Snz, J. I.; Phosphorus cquision nd cycling in crop nd psture systems in low fertility tropicl soils; Plnt nd Soil; 196: ;

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