Differential Responses of Cowpea (Vigna Unguiculata) Lines to Phosphorus Fertiliser in a Low Phosphorus Soil in the.Southern Guinea Savanna of Nigeria

Abstract

Fifteen cowpea (Vigna unguiculata) lines selected from a pot experiment for tolerance to low P were further evaluated for two years under field conditions for their response to low (0 kg P ha-1), intermediate (20 kg P ha-1 ) and high (40 kg P ha-1) P fertilizer rates. The experiments were conducted within the Southern Guinea savanna ecological zone of Nigeria. The cowpea lines exhibited differential responses to phosphorus. The average range of N2-fixed by the cowpea lines was 26-75% at low P, 32-74% at intermediate P and 30-70% at high P. Arbuscular mycorrhizal infection of cowpea roots were 11-28%, 12-22% and 1I -22% at low, medium and high P rates, respectively. Based on their dry matter and grain yields with or without P application, the cowpea lines were classified into four groups. Group I (Non-responders) had low yield with or without P application. Group 11 (Tolerant) produced high yield without P and low yield with P application. Group III (Sensitive) showed low yield without P and high yield with P application. Group IV (Responders) had high yield with or without P application. High dry matter production at low P was exhibited by six lines, while seven lines produced high grain yields. Cowpea line 1T90K-284-2 consistently out-performed other lines at low P, thus showing good prospects for, both grain and fodder production in low P soils.