Interrelationships between N₂ fixation and seed yield in cowpea

Typescript (photocopy).Field and greenhouse studies were conducted at College Station, Texas to investigate the interrelationships between biological N2 fixation and seed yield in cowpea [Vigna unguiculata (L.) Walp.]. Seed yield of inoculated and N fertilized (100 kg N/ha) plants was greater than that of the uninoculated and unfertilized control. The seed yield of inoculated plants was equivalent to or greater than that obtained with 100 kg N. In inoculated cowpeas, N fertilization (50 kg N/ha) was found to be beneficial if applied at flowering to high fixing cultivars, 'California Blackeye' and 'Brown Crowder'. Harvest index of the determinate cultivar 'Bush Purple Hull' was relatively higher than the indeterminate cultivars. During the active pod development period, the vegetative tissues accumulated N while supporting the developing pods. The percentage of flowering nodes, pods/peduncle and seed weight appeared to be the most important components influencing seed yield. Breeders should modify plant architecture to obtain more pods/plant and seeds/pod, while retaining the seed size at an economically desirable level. A significant amount of diversity has been observed among cowpea cultivars based on N2 fixation and seed yield components, and the genotypes with the highest diversity have been identified