Simulating Effects of Drainage Design Parameters on Optimum Crop Yield Using Drainmod

Agricultural water management system aims to provide crop water requirements to sustain optimum yield. Some of the factors influencing optimum crop yield are drainage design parameters in water-logged soils. Hence, the impact of drainage design parameters on optimum crop yield was examined. Field experimentation was for 12-weeks which includes land preparation, planting to maturity of Corchorus olitorius (‘Ewedu’) on a poorly-drained sandy-loam topsoil of National Horticultural Research Institute Ibadan ‘fadama’ field. Hourly rainfall and daily minimum and maximum temperature data for 32 years (1963–1994) for Ibadan was obtained from Nigerian Meteorological Station as DRAINMOD input data. Aluminum drainage pipes at 110 cm drain spacing, 60 cm drain depth and effective radius of 5.08 cm was installed. Depth from drain to restrictive layer was 204.3 cm while drainage coefficient was 1.3 cm/day. Drainage system parameters, such as drain spacing, drain depth, effective drain-pipe radius were varied and effects on crop yield observed. Field evaluation was conducted at 60 cm and 110 cm drain depth and spacing respectively, and relative crop yield of 35.60% was observed. Predicted results showed that peak values of simulated relative yield of 36.39% was attained at 40 cm, 45 cm, and 55 cm drain depth, corresponding to 120 cm, 115 cm and 105 cm spacing respectively when drain depth was varied with drain spacing at constant drain-pipe effective radius. It was concluded that if land availability is limiting and there is availability of cheap labour typical of developing countries, drain depth of 55 cm, and drain spacing of 105 cm and drainage pipe effective radius of 2.54 cm (i.e. 1-inch pipe) corresponds with the optimum yield of Corchorus olitorius. However, shorter drain spacing requires more drainage pipes and land reformation; hence increase in production cost.KEYWORDS: Water management, Drainage design, ‘Fadama’ soils, Relative yield, DRAINMOD