This study was designed to evaluate N2-fixation
and N balance of improved cowpea and soybean genotypes in the NGS of Nigeria.
Field experiments were conducted in 2003 and 2004 to assess nodulation,
N2 fixation and N contribution of two cowpea (IT96D-274 and
SAMPEA-2) and soybean (SAMSOY-2 and TGx 1448-2E) on a leached ferruginous
tropical soil (Haplustalf). The legume genotypes and a reference maize
crop (Oba Super 2) were planted in randomized complete block design with
three replications. The N difference method was used in estimating symbiotic
N2 fixation while the N contribution was estimated by the difference
between N fixed and N exported in the grain during harvest. Although nodule
number did not differ significantly among genotypes, the weight was significantly
higher in soybean than cowpea. Significant difference in N2
fixation was only observed between cowpea genotypes and it was attributed
to the differences in maturity period. TGx 1448-2E derived on average
49.8 kg N ha-1 or 37% of plant total N from fixation compared
to IT96D-724 with 15.8 kg N ha-1 or 19%. In both years, N balance
ranged from -30 to 9 kg N ha-1 depending on the genotype. With
the exception of SAMPEA-7 in 2003, all genotypes led to a net negative
contribution to soil N and a positive N balance was only obtained when
the nitrogen harvest index was less than the proportion of Ndfa. The results
show that reasonable maize yield may not be obtained following these grain
legumes without supplementary N added to the soil.
A.A. Yusuf, R.C. Abaidoo, E.N.O. Iwuafor and O.O. Olufajo, 2008. Genotype Effects of Cowpea and Soybean on Nodulation, N2-fixation and N Balance in the Northern Guinea Savanna of Nigeria. Journal of Agronomy, 7: 258-264.