Effect of nitrogen and phosphorus fertilization on maize/rice intercropping system at Samaru, northern Nigeria

The generally low fertility status of the savanna soils requires the application of fertilizers to supply adequate amounts of nutrients needed by cereal crops to raise yields.The effect of nitrogen (N) and phosphorus (P) on grainyield, soil nitrogen and uptake of Nand P by maize (Zeamays L.) and rice (Oryza sativa L.) in a mixed cropping system was studied in a field experiment at the Samaru Farm of the Institute for Agricultural Research in 1990 and J 992. Factorial combinations of four levels of N (0, 60, 120 and 180 kg N ha'l) and three levels of P (0, 13.2 and 26.4 kg P ha'l) were laid in a randomized complete block design with four replications. The number of tillers per rice plant increased significantly with increasing levelsof N up to 180 kg N ha'l while cobs/m' of maize increasedonly up to 60 kg N ha,l, but the response of leaf areaindex (LAI) to increasing levels of N was not consistent.The significant increase in these variables as affected byP was only from °to 13.2 kg ha'l However, the applicationof 13.2 kg P ha'l at each level of N significantly (P 0.05) increased maize and rice yields, with the highestgrain yields of both crops recorded when 120 kg N ha,land 13.2 kg P ha'l were applied. Crude protein increasedin maize and rice leaves with increasing levels of N up to120 kg N ha'l, but the effects of P on the variable was notconsistent. Percent P in crop leaves was unaffected bythe application of increasing levels of Nand P, and nointeraction effect was observed between the levels of Nand P. Soil analysis after harvest showed that increasinglevels of Nand P increased the residual Nand P in thesoil. For sufficient supply of Nand P to raise maize andrice yields, and to have reasonable residual amounts of these elements in the savanna soils at Samaru, the application of 120 kg N ha,l and 13.2 kg P ha·1 seem adequate.