Physiological determinants of cowpea seed yield as affected by phosphorus fertilizer and sowing dates in intercrop with millet

The interaction of cowpea (Vigna unguiculata (L.) Walp.) cultivars with management factors and environments was analyzed in terms of parameters of a simple physiological model. In one set of experiments seven cultivars were sown at three rates of phosphorus (P) fertilizer (0, 8 and 16 kg P ha−1). In another set, five cultivars were sown on two dates relative to sowing of millet (Pennisetum glaucum (L.) R.Br.). All experiments involved factorial combinations of management and cultivar treatments, and were conducted in 1988 and 1989 at two sites in western Niger. Seed yield, shoot dry matter, vegetative (Dv) and reproductive (Dr) durations were determined and crop growth rate (C) and partitioning (p) to seed estimated Application of P increased seed yield by increasing C. As sowing was delayed from 1 to 3 weeks after the millet was sown, there was a reduction in seed yield due to decreases in C, Dv and Dr. Variation in cultivar performance across years was mainly a function of C and partitioning. In both experiments the C of the landrace Sadore Local was greater than that of other cultivars, although the partitioning to seed of this cultivar was unstable due to variable control of insect pest damage It is concluded that the primary causes of G × E interactions were differential canopy development and insect damage effects. Therefore in the development of cowpea cultivars for intercropping with millet, emphasis should focus on light capture capabilities. Improved yields would then seem possible with most cultivars, providing insect damage is controlled