Grain yield water use efficiency of cowpea (Vigna unguiculata L. Walp.) in response to planting dates in Botswana

Abstract

Ag Southern Africa is characterized by a high degree of rainfall variability affecting agriculture among other sectors. The timing of the rainfall has shifted as a result of climate change, and variability is expected to be even higher in the future. This threatens grain production, which is dependent on rainfall; strategies such as choice of planting date and crop selection based on water use efficiency could help fanners mitigate some of these impacts. This study investigated the effect of planting dates and genotypic differences on grain yield, water use, and water use efficiency of cowpea. Six cowpea genotypes were planted at four different times (November, December, January, and February). The results indicate that cowpea grown in January used moderate amounts of plant-available water, significantly producing a higher average grain yield of 335.2 kg/ha with a water use efficiency of 3.72 kg/ha. mm-1. BCA001 (blackeye) exhibited the highest grain yield and water use efficiency in all the planting dates, indicating broad adaptation, while landrace BCA019 (speckled grey cowpea), has the potential to be bred for drought tolerance and be released as a variety thanks to its earliness and high water use efficiency.