Demand-Driven Technologies for Sustainable Maize ... - IITA

220in soybean than in maize grain during the soybean crop cycle, mayresult from the positive, interactive role of P and N resulting from Nunaccounted in the N balance estimates, the additional N given tomaize at planting, residual P from previously applied RP and TSP,differential VAM colonization within P treatments, and changes in soilphysical properties (Horst and Härdter 1994; Obi 1999) and the otherrotation effects. The trends observed in the study, however, suggestthat the potential exists for the identifi cation of soybean genotypes withthe capacity to contribute to N and P nutrition of maize in rotation,but this effort must be directed at developing soybean genotypes withenhanced P uptake from less bioavailable P fractions, maximizing%Ndfa under low P conditions, and reducing N and P harvest indicesby maximizing total N and P in stover rather than in grain.ConclusionThe response of soybean genotypes to P application was moderateand seemed to have been infl uenced by other biophysical factors.The N balances estimated for the soybean genotypes were generallynegative due to the large N exports in the grain but cannot be used todirectly account for observed variations in N nutrition and grain yieldsof maize that followed in rotation. P availability to maize resulting fromprevious P application of the soybean genotypes was relatively low andcould not sustain high maize yield at certain sites. The results have alsoshown that increases in biomass, and total N and P in maize in rotationwith soybean could be infl uenced by specifi c interactions among soilN, P, and crop genotype during the two rotation cycles.AcknowledgementThe research work was supported for its fi eld and greenhouseexperiments by the Australian Centre for International AgriculturalResearch (ACIAR) through contract grant no SMCN2/1999/004.ReferencesAbaidoo R.C., Dashiell K.E., Sanginga N., Keyser H.H., Singleton P.W. (1999).Time-course of dinitrogen fi xation of promiscuous soybean cultivarsmeasured by the isotope dilution method. Biol Fert Soils 30: 187–192.AbdelGadir A.H. (1998). The role of mycorrhizae in soybean growth in P-defi cient soil in the humid tropics. PhD. thesis. Cornell University. 255 pp.Alvey S., Bagayoko M., Newmann G., Buerkert A. (2000). Cereal/legumerotation in two West African soils under controlled conditions. Plant Soil23:45–54.Bagayoko M. Buerkert A., Lung G., Batiano A., Römheld V. (2000a). Cereal/legume rotation in two Sudano-Sahelian West African: soil mineralnitrogen, mycorrhizae and nematodes. Plant Soil 218:103–116.