Effect of Water Potentials on Growth and Yield of Cowpea (Vigna Unguiculata [L] Walp)

A field experiment was conducted for two consecutive seasons during 2003/2004 and 2004/2005 in the Demonstration Farm of the Faculty of Agriculture, University of Khartoum at Shambat to study the effect of different water stress levels on growth and yield of cowpea (Vigna unguiculata L. [Walp]) cultivars. Two cowpea cultivars were used in this study, namely: Ein el Ghazal (Line 1-12-3) and Dahab el Goz (IT84s-2163). Six water stress levels (-2.5, -5.0, -7.5, -10.0, -12.5, and -15.0 bars) as estimated by predawn leaf water potential using pressure chamber was applied. The results showed that water stress treatments significantly reduced the number of leaves per plant, leaf area index, leaf area ratio, shoot\root ratio and biomass production. Similarly, seed yield was significantly reduced by water stress treatments, particularly at lower soil water potentials (-12.5 and -15.0 bar). The reduction in yield was associated with substantial reductions in yield components. Significant differences were observed between the two cultivars in the different characters studied. In this respect, Dahab el Goz (V2) exhibits vigorous growth (greater number of leaves per plant, leaf area index, leaf area ratio and deep root system) and seed yield compared to Ein el Ghazal (V1). The critical water stress levels as estimated by soil water potentials for cowpea growth and yield were found to be lower than -10.0 bars.