Residual Effects of Organic Manure and Inorganic Fertilizer on Maize Grain Weight and Some Soil Properties in Asaba Area of Delta State

This study was carried out in the Teaching and Research Farm of Delta State University, Asaba Campus from March 2008 to December 2009 to evaluate the effects of previously applied amendments on maize grain weight and some soil properties. The experiment was carried out in a Randomized Complete Block Design (RCBD) replicated three times in a factorial layout. Four different rates of poultry dropping, cattle dung and NPK 20:10:10 fertilizers were applied to maize varieties sown at 75cm x 15cm and the residual effects of the amendments on some soil properties were investigated. The results indicated that hybrid maize variety 9022-13 was superior with grain weight of 1.24 tha and that plants sown on plots where 450kg haof NPK 20:10:10 had the highest grain weight (1.56tha). Bulk density of plots treated with poultry manure was highest (1.35 Mg/m), followed by plots treated with cattle dung (1.34 Mg/m). Plots treated with inorganic fertilizer had the lowest bulk density (1.32 Mg/m). Also, plots treated with 30tha of organic manure had the highest bulk density (1.37 Mg/m), while the control plots had the lowest (1.30 Mg/m). The exchangeable cations (Ca, Mg, K, and Na) increased with higher rates of manure/inorganic fertilizer (P<0.05). The interaction results showed that pH, organic C,N, C/N and all exchangeable cations were increased by the rates of application of organic manure/inorganic fertilizer and they were significantly (P<0.05) different from each other. Based on this study, it is recommended that (i) Farmers who prefer mineral fertilizer should apply 450 kgh of NPK 20:10:10 to promote the release of exchangeable cations that increase maize yield (ii) Farmers who practice organic agriculture in Asaba agro-ecological zone should apply 30tha of poultry manure to enhance maize yield.