Cowpea Response to Row Width, Density, and Irrigation 1

Abstract The interrelationships among row width, plant density, and irrigation are not well understood for cowpea [ Vigna unguiculata (L.) Walp.], as shown by previous conflicting results describing the sensitivity of cowpea to drought. Two experiments, a three factor central composite, second order design in incomplete blocks, and a two factor split plot randomized block design, were used to quantify the yield responses of ‘California No. 5’ cowpea established at five row widths (25 to 125 cm), five plant densities (4 to 34 plants m −2 ), and five (0 to 200 cm) and two levels of irrigation at planting. Cowpea was grown on sandy clay loam soils (fine, mixed thermic families of Aridic and Torrertic Paleustolls) on the research farm in Lubbock and the Slab farm in Hereford, Tex. Seed yield was very dependent on irrigation, increasing linearly from 635 kg ha −1 to 2043 kg ha −1 at the Lubbock site without evidence of diminishing returns. At the second site more water was available from rainfall and irrigation and yields were greater (2837 kg ha −1 ). Highest yields were obtained with the combination of wide rows and high plant density while lowest yields resulted with high plant density in narrow rows. Of the components of seed yield, pod number per plant and seed number per pod were important regulators of seed yield, while seed size remained reasonably constant. Seed yield and harvest index results suggested that, in narrow rows, the more uniformly spaced plants explored the complete soil volume earlier, extracting more of the available soil water during vegetative growth, and leaving less available for reproductive growth than in wide rows. This restriction on reproductive development in narrow rows was accentuated most when plant densities were highest. Our study shows the need to examine plant interactions before management recommendations can be firmly established.