Comparative Effects of Cowpea and Soybean Genotypes on N 2 - Fixation and N-Balance in Sokoto Dry Sub-Humid Agro-Ecological Zone of Nigeria

Abstract

A field trial was conducted to asses N 2 - fixation and N balance in five cultivars each of soybean (TGX 1945 – 1F, TGX 1951 – 4F, TGX 36 – 54K T, TGX 1951 – 3F and TGX 1935 – 3F) and cowpea (IT88D-867-11, IT89KD-288, IT90K-l372-1-2, I T90K – 82-2 and Bahaushe (local). The legume genotypes and reference millet crop (ZM – 01- 58) w ere planted in a randomized complete block design with three replications. N difference method and th e difference between N 2 - fixed and N exported in grain at harvest were used to estimate N 2 - fixed and N balance respectively. The biomass yi eld (2.9 to 5.23 t ha -1 ) in cowpea cultivars were significantly (P<0.05) h igher than in soybean (0.95 to 1.5 t ha -1 ). Above ground cowpea biomass (vine plus litter ) acc umulated up to 81.03 kg N ha -1 which differed significantly from the 33.13 kg N ha -1 observed in soybean. N 2 - fixed that ranged from 42.27 to 59.07 kg N ha -1 in soybean cultivars was generally higher than tho se of cowpea. All the soybean cultivars recorded significantly (P<0.05) higher grain N than the cowp ea. This explains the high percentage nitrogen harv est index (NHI) (64.33 to 70.22 %) and negative N balan ces (-9.47 to -1.2 kg N ha -1 ) obtained in all the soybean genotypes. On account of the large above gr ound biomass and N content, positive N balances and low percentage N H I, cowpea appeared to perfor m better in contributing to soil N the following year.