An evaluation of the influence of available soil water storage capacity on growing season length and yield of tropical pastures using simple water balance models

Abstract The results of a comparative study of the soil water balance, plant water relations and dry matter production of pastures on three soils with available water storage capacities of 75, 150, and 180 mm are reported. Differences among sites in growing season length varied from nil to 27% in the four years of study. To enable sampling of a much larger number of years, the methods of systems analysis and simulation are used. The experimental data is used to test or to formulate simple models which are in turn used to simulate the growing season length and dry matter production in 60 years for which rainfall records are available. The results of the simulation study portray the extreme variation in production among years in this seasonally-dry tropical climate. While the advantage conferred by a soil storing 180 mm available water as opposed to 75 mm would be expected to be nil 1 in 8 years, the average increase in pasture yield expected in 70% of years would be 34%.