Effects of organic manure and cowpea (Vigna unguiculata (l.) Walp) varieties on the chemical properties of the soil and root nodulation

An experiment was conducted in the Teaching and Research Farm of the Faculty of Agriculture and Veterinary Medicine, Imo State University, Owerri southeastern Nigeria to investigate effects of organic manure (poultry and cow dung) on 5 cowpea varieties (IT93K-452-1, IT89KD-288, Vital 7, IT848-2246-4 and Ife brown) on the soil chemical properties and nodulation of roots of the cowpeas. The experiment was arranged in a randomized complete block design of a split plot fashion in three replications with the varieties of cowpea on the main plots while the organic manures and a control (no-treatment) plot constituted the subplots. The organic manure was incorporated into the soil by pulverizing the manure with the tilled soil and cowpea seed sown two weeks post incorporation at a planting distance of 50 cm x 50 cm. Four plants were randomly selected at flowering stage and the number of nodules on the plant counted and recorded; the dry weights of the nodules were determined and yield was also estimated. Results revealed that organic manure significantly influenced the nodulation of the cowpea varieties as poultry manure gave the highest number of nodules (15.9) which was significantly different from the values (12.2 and 10.3) observes from cow dung-treated plots and untreated plots respectively. Also the organic manures significantly influenced the chemical properties of the soil as poultry manure improved the Nitrogen (0.320), Phosphorus (6.8) and Potassium (0.04) levels of the soil. The yield of cowpea was also improved with the application of poultry manure with a mean yield of 744.7kg/ha, which was significantly different from values (571.9kg/ha and 505.0kg/ha) observed for untreated plots and cow dung treated plots respectively. There was significant difference in the number of nodules among the cowpea varieties. Vita 7 variety recorded the highest mean number of nodules (15.4), which was significantly different from the other varieties. It is recommended that Vita 7 varieties should be used for cowpea cultivation in the Southeastern Nigeria, especially when poultry manure is the main source of fertilizer. Keywords: Effect, chemical, properties, nodulation, cowpea varieties, yield, soil, organic manur