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

164Figure 3: Grain yield of maize as affected by preceding legumes andfallow and inorganic N fertilizer application.the preceding legumes were unable to supply the N requirement ofmaize for optimum yield.Nitrogen fertilizer replacement valueThe graph and linear equation showing the response of maizesucceeding fallow (control) to urea N are shown (Fig. 4). The estimatedNFRV of the soybean, cowpea, and centro were 61, 13 and 39 kg Nha -1 , respectively. The relatively high value obtained for soybeancompared to both centro and cowpea may be attributed to relativelyhigh soil N status after soybean and or other non-N benefi ts of soybeanrotation such as reduced nematodes in the soil (Weber et al. 1995).The NFRV of soybean and centro were both higher than that ofcowpea probably due to higher soil N status with the incorporationof soybean and centro residue compared to incorporation of cowpearesidue (Table 3).The NFRV of soybean obtained in the present study was higherthan the 20 kg N ha -1 obtained by Singh et al. (2001) with residueincorporation in the same ecological zone. This is perhaps due tolower acidity and higher available P status of the soil at the site ofthe study compared to the site used by Singh et al. (2001). At lowpH, available P precipitates as insoluble compounds of P, therebybecoming unavailable (Brady 1999). The NFRV for cowpea obtainedin this study was similar to those reported by Carsky et al. (1999)but lower than 40–80 kg N ha -1 obtained in several earlier studiesconducted in this ecological zone (Dakora et al. 1987; Kaleem 1993;Horst and Hardter 1994; Carsky et al. 2001). Carsky et al. (2001)