Fluctuation in rainfall in Ogun-Osun River Basin, Nigeria in the recent times is a challenge to crop production. Therefore, agronomic practices need to be designed to improve water productivity under rainfed conditions. Improving water productivity requires vapour shift or transfer whereby soil physical conditions, soil fertility, crop varieties and agronomy are applied in tandem and managed to shift the evaporation into useful transpiration by plants. Water conservation practices: Tied ridge, Mulch, Soil bund, Tied ridge plus Soil bund, Tied ridge plus Mulch, Mulch plus Soil bund and Direct sowing were used in cultivating Soybeans for two rainy seasons in Ile-Ife, Nigeria. Full and deficit irrigation application during reproductive stages were used with in-line drip irrigation for two seasons.

Seasonal rainfall influenced the water storage in the soil. Transpiration, seed yield and water productivity were related to Total Intercepted Photosynthetically Active Radiation. Yield and economic productivity increased under water conservation practices. Productivity decreased most when irrigation was skipped during seed filling and the production costs under drip system are high. Rainfed cultivation of soybeans when rainfall and solar radiation are optimum, is the best option.

The AquaCrop model was calibrated and validated to predict canopy cover, aerial dry biomass, seed yield, soil water content, crop water use, and water productivity under full and deficit irrigation conditions. The model performed the best in simulating aerial dry biomass under full irrigation. The simulated and measured data compare adequately and the performance of the model was satisfactory.