a1 International Institute of Tropical Agriculture (IITA), Ibadan, Oyo State, Nigeria
a2 College of Crop and Soil Sciences, Michael Okpara University of Agriculture, Umudike, P.M.B 7267, Umuaia, Abia State, Nigeria
a3 Department of Plant Breeding and Seed Science, College of Agronomy, University of Agriculture, Makurdi, PMB 2373, Benue-Nigeria
a4 International Crop Research Institute for the Semi-Arid Tropics (ICRISAT), Kano, Nigeria
Soybean (Glycine max) is a major cash crop in the savannas of Nigeria although productivity is typically constrained by poor soil fertility. The objective of this research was to determine the interactive effect of N and P on soybean productivity in the northern Guinea and Sudan savannas of northeast Nigeria. Experiments were conducted using locally adapted early and late maturing cultivars. Two rates of N and three rates of P fertilizer were also compared at both sites over two years. At both sites, pods plant−1 and seed yield were higher in 2006 than in 2007, possibly due to better rainfall distribution in 2006. Nitrogen fertilizer had no significant effect on seed yield or pods plant−1. Application of P fertilizer increased pods plant−1 by 40–66%. Averaged across site and year, seed yield with no P was 1057.2 kg ha−1 while yield with 20 and 40 kg ha−1 P were 1941.0 kg ha−1 and 2371.5 kg ha−1, respectively. No significant interaction effect between N and P fertilizer on seed yield and pods plant−1 was observed. The late maturing cultivar yielded less than the earlier maturity group cultivar in 2007 likely due to moisture stress. For optimum seed yield 40 kg of P fertilizer ha−1 is recommended for soybean production in both locations. Our results suggest that N fertilizer is not critical for soybean production in this area.
(Accepted May 25 2011)
(Online publication August 01 2011)