Research Article

PHOSPHORUS AND NITROGEN FERTILIZATION OF SOYBEAN IN THE NIGERIAN SAVANNA

ALPHA Y. KAMARA^a1 c1, FRIDAY EKELEME^a2, LUCKY O. OMOIGUI^a3 and HAKEEM A. AJEIGBE^a4

^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

SUMMARY

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)

Correspondence:

^c1 Corresponding author. C/o L.W. Lambourn & Co., Carolyn House, 26 Dingwall Road, Croydon CR93 EE, UK. E-mail a.kamara@cgiar.org