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

165Figure 4: Maize grain yield after fallow as a function of urea - N rate.have suggested that the relatively high value they obtained may bedue to the planting of the maize immediately after cowpea harvestwithin the same rainy season, which made the N from the cowpeato be effi ciently utilized by the subsequent maize crop. The relativelylower value obtained in this study compared to that of Dakora et al.(1987) and Horst and Hardter (1994) may be attributed to the use offallow instead of a crop as control. The use of fallow probably gave alower estimate of NFRV because of nutrient accumulation in the fallowplots. Dakora et al. (1987) and Horst and Hardter (1994) both usedmaize as the control while Kaleem (1993) used yam as the control.The growth of two crops of legume in one season, as done by Horstand Hardter (1994), may also give higher estimates of NFRV.The estimated NFRV of centro after one year of cultivation wassimilar to values obtained by Tarawali (1991) after 2- to 4-year fodderbanks and values quoted by Carsky and Iwuafor (1999) after twoyears of cultivation for some other herbaceous legumes. The similarityof NFRV, despite differences in years that the experiments wereconducted, suggests that farmers should be encouraged to incorporatethe aboveground residues into the soil rather than allow them to beblown away by the wind or eaten by livestock during the long dryseason (Carsky and Iwuafor 1999). Incorporation of the residue withseeds will ensure that higher N is returned to the soil for the use ofthe subsequent crop.