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.
