Impact of Mild Water Stress During the Flowering Stage on Leaf Functional Traits and Yield of Selected Cowpea Varieties Grown in The Low Country Dry Zone of Sri Lanka

Abstract

Cowpea [Vigna unguiculata (L.) Walp.] is an important legume growing in tropical regions. Cowpea is grown in the Dry Zone of Sri Lanka as an inter-season crop. Rising temperatures and unpredictable precipitation patterns are major factors contributing to soil moisture stress in tropical agriculture. Despite the short life cycle, it is highly likely that cowpea experiences mild soil moisture stress (around 70% of field capacity) conditions at flowering stage due to enhanced evapotranspiration in response to increasing air temperature. In this study, five cowpea varieties were subjected to two soil moisture conditions; field capacity and mild water stress, at the onset of flowering under a split-plot design for two consecutive inter-seasons with the objectives to determine the leaf gas exchange and hydraulic traits of cowpea exposed to soil moisture stress and the underlying relationships between yield reduction and leaf gas exchange, hydraulic, and agronomic traits. The yield reduction (p<0.05) in the five varieties tested was associated with a reduction in leaf net assimilation rate, number of pods/plant, and number of seeds/pod. Variety-dependent reductions in leaf functional traits in many varieties leading to a reduction in yield parameters (p<0.05) were obvious under mild water stress conditions. Despite the water stress variety, Waruni performed well in both moisture conditions. As conclusion, cowpea varieties for inter-season cultivation should be selected based on ability to maintain yield under mild water stress conditions. A special emphasis should be placed on commencing cultivation as soon as the main crop is harvested to better utilize the residual moisture.