Assessment of the Effect of Crop Rotation on Soil Health and Maize Yield in Oyo State

This study assesses the effect of different crop rotation sequences on soil health indicators and maize grain yield in Oyo State, South West Nigeria. Continuous monoculture of maize is a widespread but agronomically unsustainable practice in many Oyo State farming communities, associated with progressive soil nutrient depletion, build-up of soil-borne pathogens, and declining yield trends. Crop rotation with legumes and other crop families offers biological and economic benefits without the capital requirements of external inputs. This study establishes a long-term field experiment at the Institute of Agricultural Research and Training Ibadan, comparing four rotation sequences over four years: continuous maize monoculture, maize-cowpea rotation, maize-soybean rotation, and maize-melon rotation, all managed without external fertiliser addition. Soil organic matter, total nitrogen, microbial biomass carbon, bulk density, and maize grain yield are measured annually. Findings reveal that by year three, maize yields in continuous monoculture decline by 38 percent from baseline, while maize-soybean rotation maintains yields within 6 percent of baseline. Soil nitrogen under soybean rotation is 24 percent higher than monoculture by year four, reflecting legume nitrogen fixation contributions. Soil microbial activity is consistently highest in legume rotation plots. The study concludes that cereal-legume rotation is a highly effective soil health maintenance strategy in Oyo State conditions. It recommends maize-soybean two-year rotation as the standard extension recommendation for Oyo State farmers.

Keywords: crop rotation, soil health, maize yield, Oyo State, legume rotation.