Effects of Enriched Organic Manure on N- fixing Ability of Cowpea (<i>Vigna unguiculata</i> (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