Effects of crop rotation and nitrogen fertilization on soil chemical properties and microbial properties in southwestern Nigeria. Soil Fertility and Plant Nutrition
- H. Eria
Although, in Southwestern Nigeria, many aspects of Agronomy of cowpea have been accorded research attention with a view to raising its present yield on farmers’ farms, However, there is still dearth of published scientific data and information on soil nutrient status and weed biomass as affected by cowpea – based intercropping systems. To this end, a two – year field experiment was conducted in 2010 and 2011 cropping seasons at the Teaching and Research Farm of the Ekiti State University, Ado – Ekiti, Ekiti State, Nigeria, to evaluate the effects of different cowpea – based crop mixtures on soil nutrient status, weed biomass, yield and yield components of cowpea (Vigna unguiculata). The experiment was laid out in a randomized complete block design with three replicates. The different cowpea – based crop mixtures included: sole cropped cowpea (SCC), which served as the control; cowpea / maize (CM); cowpea / cocoyam (CC) and cowpea / okra / melon (COM). The results obtained indicated existence of significant (P = 0.05) differences among the different cowpea – based crop mixtures as regards their effects on weed biomass, yield and yield components of cowpea. Relative to the initial nutrient status of the soil, prior to 2010 cropping season, the percentage decreases in soil organic carbon (SOC), adduced to cowpea – based mixtures, after 2010 cropping season were 9, 18, 27 and 23 for the respective SCC, CM, CC and COM. Conversely, at the end of 2011 cropping season, increases of 5, 14, 21 and 27% in SOC were recorded for SCC, CM, CC and COM, respectively. At the end of 2010 cropping season, cowpea – based mixtures resulted in decreases of 8, 31, 23 and 18% in total N for the respective SCC, CM, CC and COM. On the contrary, at the end of 2011 cropping season, cowpea – based mixtures resulted in increases of 10, 18, 3 and 26% in total N for SCC, CM, CC and COM, respectively. Available P decreased at the end of 2010 cropping season by 7, 21, 16 and 26% for the respective SCC, CM, CC and COM. In contrast, available P increased at the end of 2011 cropping season by 9, 21, 16 and 28% for SCC, CM, CC and COM, respectively. The mean values of cowpea seed yield data over the two years of experimentation indicated that, cowpea based intercropping significantly decreased cowpea seed yield from 4.3 t ha -1 for SCC to 3.77, 3.32 and 3.98 t ha -1 for CM, CC and COM, respectively.