Abstract
Cowpea cv. 'K 2809' grown in a plastic house, was given, alone or in combination, a single dressing of N at a rate of 10·5 kg/ha and/or with a nutrient solution containing 25 p.p.m. N; appropriate treatments were labelled with 15N. Control plants received no applied N. All plants were inoculated with Rhizobium strain CB 756. Only 20 per cent of the starter was taken up and it had little effect on growth or yield. Its distribution throughout the plant is described. About half was found in the seeds, but very little was incorporated into nodules. Plant receiving 25 p.p.m. nutrient throughout were one-third larger than those relying only on nodular N. At this low level of applied seed yields were proportional to plant size. The source of 88 per cent of the nitrogen in the seed was symbiotic N and an estimated 40 to 50 per cent of stored nitrogen moved from structural parts to the seeds during their development. Some comparisons of mobilizable N are made with equivalent treatment in previous experiments in the series. The difficulties of satisfying the need of a wellfruiting plant for nitrogen for the developing seed are discussed.
