Comparative Effects of Cowpea and Soybean Genotypes on N2 - Fixation and N-Balance in Sokoto Dry Sub-Humid Agro-Ecological Zone of Nigeria.

  • A Muhammad
  • AU Dikko
  • M Audu
  • A Singh
Keywords: Legume genotype, N2 fixation, N balance and Nitrogen Harvest Index (NHI)

Abstract

A field trial was conducted to asses N2 - fixation and N balance in five cultivars each of soybean (TGX 1945 – 1F, TGX 1951 – 4F, TGX 36 – 54KT, TGX 1951 – 3F and TGX 1935 – 3F) and cowpea (IT88D-867-11, IT89KD-288, IT90K-l372-1-2, IT90K – 82-2 and Bahaushe (local). The legume genotypes and reference millet crop (ZM – 01- 58) were planted in a randomized complete block design with three replications. N difference method and the difference between N2 - fixed and N exported in grain at harvest were used to estimate N2 - fixed and N balance respectively. The biomass yield (2.9 to 5.23 t ha-1) in cowpea cultivars were significantly (P<0.05) higher than in soybean (0.95 to 1.5 t ha-1). Above ground cowpea biomass (vine plus litter ) accumulated up to 81.03 kg N ha-1 which differed significantly from the 33.13 kg N ha-1 observed in soybean. N2 - fixed that ranged from 42.27 to 59.07 kg N ha-1 in soybean cultivars was generally higher than those of cowpea. All the soybean cultivars recorded significantly (P<0.05) higher grain N than the cowpea. This explains the high percentage nitrogen harvest index (NHI) (64.33 to 70.22 %) and negative N balances (-9.47 to -1.2 kg N ha-1) obtained in all the soybean genotypes. On account of the large above ground biomass and N content, positive N balances and low percentage N H I, cowpea appeared to perform better in contributing to soil N the following year.
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