Determination of phosphorus requirements of Cowpea (Vigna unguiculata) in the acid soils of South-eastern Nigeria using sorption isotherms

Abstract

This study was conducted to determine the phosphorus requirement of cowpea in two locations in southeastern Nigeria (Bende and Umudike) using sorption isotherm. The method used involved equilibrating 3g of soil in 30mls of 0.01m CaCl₂ containing various levels of phosphorus at room temperature for 5 days. From the P sorption curves constructed, the standard P requirement for the two soils were calibrated. The values were very low at 21.5 and 45 µggS^-1 for Bende and Umudike soils respectively. Different phosphorus levels were calibrated from the sorption isotherm curves and used in fertilizing cowpea in potted experiment. The experiment was laid out in split-plot experimental design. The soil type occupied the main plots while the P levels were assigned to the subplots. The results obtained indicated that solution P concentration level of 0.2 µgg^-1, equivalent to 21.5kgha^-1 in Bende and 45kgha^-1 in Umudike gave the best nodulation while grain yield was produced when solution P concentration of 0.4 µgg^-1 equivalent to 65kgha^-1 in Bende and 125 kgha^-1 in Umudike was applied. The grain yield at this level was not significantly different from those at 0.2 µgg^-1 solution concentration of P in both locations. Higher yield were recorded in the soils of Umudike compared to that of Bende.

Keywords: phosphorus, sorption isotherms, Cowpea

Global Journal of Agricultural Sciences Vol. 4(2) 2005: 135-138