Effects of Enriched Organic Manure on N- fixing Ability of Cowpea (Vigna unguiculata (L) Walp) Grown in Maize Mixture

Abstract

Field experiments were carried out during the 2008 and 2009 cropping seasons to evaluate the effects of enriched organic manure on both nodule count and N-fixing ability of two varieties of cowpea (ITAS EARLY and IAR 1060). The treatments were: poultry manure (0 , 3 ,and 6 t ha^-1); NPK 20-10-10 fertilizer (0 , 30, and 60 kg N ha^-1). Treatments were combined factorially to give nine treatment combinations. The experiments were laid-out in a randomized complete block design (RCBD) with three replications. Each experiment plot measured 3 m x 4 m with an alley of 1 m between blocks and 0.5 m between plots. Four seeds were planted per hole at 25 cm plant-to-plant distance in a maize mixture and later thinned to two plants per stand at two weeks after planting (2 WAP).,This gave a total population of about 80, 000 plants per hectare. The nodule count and N-fixed were determined at 3, 6, and 12 weeks after planting (WAP). The results showed that the combined NPK 20-10-10 with poultry manure contributed to the differences (P<0.05) in number of count obtained per plant of cowpea as well as the amount of N-fixed in the experiment. The higher rates of NPK 20-10-10 fertilizer, number tend to reduce the number of nodules as well as the amount of N-fixed. The highest nodules (86.6 and 102.2) and N-fixed (42.05 and 59.50 kg ha^-1) for 2008 and 2009, respectively were from the combination of 6 t ha^-1 of poultry manure and no NPK 20-10-10 fertilizer application on cowpea variety, ITAS EARLY. This suggested that cowpea variety (ITAS EARLY) tolerated high nutrient in N-fixation and as such a better choice as a leguminous component than IAR 1060 in a cropping system.

Keywords: Enriched organic manure, N-fixation, nodules count, cowpea varieties