Nitrogen Nutrition of Cowpea (<i>Vigna unguiculata</i>). I. Effects of Applied Nitrogen and Symbiotic Nitrogen Fixation on Growth and Seed Yield

Abstract

SUMMARY Effectively nodulated cowpea plants, grown in pots without applied nitrogen, were vegetatively equal to non-nodulated plants supplied with 60 ppm N throughout growth (88 days) and produced significantly greater seed yields. Supplying non-nodulated plants with 120 or 240 ppm N improved seed yields (but not significantly) compared with plants completely dependent on symbiotic fixation. Nodulation promoted branching, and improved pod set and/or retention compared with plants relying on applied N.