Factor for Estimating Nitrogen Contribution of Cowpea as a Cover Crop

The nitrogen contribution of cowpea [Vigna unguiculata (L.) Walp.] above-ground biomass was estimated using the per cent nitrogen and per cent dry matter of 24 cowpea entries. Cowpea growth stage was assigned a maturity index, and an ʹN factorʹ was calculated. Results for this species-specific ʹN factorʹ ranged from 12.5 at the vegetative stage to 13.5 at the reproductive stage. Using the ʹrule of 16ʹ as developed for sampling the fresh biomass of other legume cover crops, the amount of nitrogen contributed by cowpeas can be estimated by using an average ʹN factorʹ of 13.