RESPONSE OF COWPEA (VIGNA UNGUICULATA L.) TO SIMULATED LEAF HERBIVORY AND RATE OF APPLICATION OF NPK 15:15:15 IN THE GUINEA SAVANNAH AGROECOLOGY OF GHANA

Abstract

Field studies were conducted at the University for Development Studies during the 2013 and 2014 cropping seasons to determine the combined effects of NPK 15:15:15 and experimental defoliation on growth and yield of cowpea. Seeds of cowpea cultivar ‘Songotra’ were planted and fertilized with 15, 20 or 25 kg/ha of NPK 15:15:15 three weeks after planting (WAP). At 4 WAP, the plants were subjected to 50, 75 or 100% defoliation. The unfertilized (0 kg/ha NPK 15:15:15), or undefoliated plants (0% defoliation) served as control treatments. Treatment combinations were replicated four times in randomized complete block design. Results indicated that plants from the 50% defoliation regime that were fertilized with 20 or 25 kg/ha of the fertilizer had the best performance in terms of growth and total grain yield. Thus in the Guinea Savannah agroecology of Ghana, 50% defoliation of cowpea during cultivation is not detrimental to growth and grain production, provided nutrients equivalent to 20 - 25 kg/ha of NPK 15:15:15 can be applied as fertilizer to the crop 3 WAP.

Keywords: Cowpea, Defoliation, Simulated leaf herbivory, NPK 15:15:15 application, Growth and yield.