The influence of nitrogen-fixing trees and fertilizer nitrogen levels on the growth, yield and nitrogen uptake of cowpea on a rainfed alfisol

A field experiment was conducted to study the influence of 8- to 9-year-old nitrogen-fixing tree species (Faidherbia albida, Acacia ferruginea, Albizi a lebbeck) and fertilizer nitrogen levels on yield and nitrogen uptake of i ntercropped cowpea (Vigna unguiculata). Grain and dry fodder yields of cowp ea were reduced by 9% to 27% and by 11% to 35% respectively compared with t he sole crop. Application of fertilizer nitrogen produced significantly hig her yields. Nitrogen uptakes by leaves, stems and grain of cowpea were sign ificantly reduced under A. ferruginea and A. lebbeck, but cowpea as sole cr op and under F. albida showed no differences. Nitrogen uptake in different plant parts increased with increase in fertilizer nitrogen level.