Drought Adaptation of Cowpea. I. Influence of Drought on Seed Yield1

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Abstract
Field studies were conducted to determine cowpea [Vigna unguiculata (L.) Walp.] response to different intensities of drought at different stages of growth to guide programs for the development of improved cultivars and improved management practices for semi‐arid zones.Two cowpea cultivars were subjected to different levels of irrigation using a line‐source sprinkler system in the field on a coarse‐loamy, mixed, thermic Haplic Durixeralf soil during 2 years with contrasting weather patterns. Well‐watered plants were irrigated weekly. In other treatments, water was not supplied during either the vegetative, flowering, or pod filling stages.Dry seed yields of well‐watered treatments were negatively correlated with degree days above 35 C during flowering.Yields of both cultivars were not reduced by drought during the vegetative stage, compared with the weekly irrigated treatment, providing subsequent environmental conditions were conducive to rapid recovery of growth and efficient pod set. Drought during the flowering stage substantially reduced yields, but partial yield recovery was observed where drought caused all flowers to abscise and the subsequent environment, after irrigation was resumed, permitted a new flush of flowers to produce pods. Drought during pod filling substantially reduced yields of both cultivars in both years.Variations in yield due to environmental stresses were mainly due to variations in number of pods/m2 except for drought during pod filling which resulted in both low pod density and small seed. Yield with abundant water or drought during pod filling appeared to be partially source limited, whereas intermediate levels of drought at other stages may have resulted in sink limitations on yield because these treatments produced the heaviest seed.

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