Effects of Cowpea Leaf Harvesting Initiation Time and Frequency on Tissue Nitrogen Content and Productivity of a Dual-purpose Cowpea–maize Intercrop

Abstract

Cowpea [Vigna unguiculata (L.) Walp.] is an important component of most traditional cropping systems in the semiarid tropics. It provides both leaf vegetable and/or grain. Dual-purpose production of cowpea is most common in subsistence farming systems. Little is, however, known about the effects of cowpea leaf harvesting on tissue nitrogen composition and productivity of most cowpea-based cropping systems. A four-season study was carried out at the National Dry Land Research Center, Katumani, Kenya, to establish the effects of cowpea leaf harvesting initiation time and frequency on 1) tissue nitrogen content of cowpea and maize in a dual-purpose cowpea–maize intercropping systems; and 2) cowpea and maize yield and the overall productivity of a cowpea–maize intercrop measured by land equivalent ratio (LER). Cowpea leaf harvesting was initiated at 2, 3, or 4 weeks after emergence (WAE) and continued at 7- or 14-day intervals until onset of flowering. Cowpea tissue nitrogen content was highest in the control treatment and lowest in cowpea subjected to leaf harvesting from 2 WAE or at 7-day intervals, whereas maize tissue nitrogen content showed the reverse trend. Harvesting cowpea leaves from 3 WAE or at 7-day intervals gave the highest leaf vegetable yield, whereas grain yields were highest when no leaf harvesting was done. Maize yields were significantly improved by harvesting of leaves of the companion cowpea. Harvesting cowpea leaves for use as leaf vegetable increased productivity per unit area of land as measured by LER with the highest productivity achieved when leaf harvesting was initiated at 4 WAE or done at a 14-day interval.