Salt Balance, Irrigation Efficiency and Drainage Design

A simplified procedure is presented to predict how much irrigation water is necessary, in addition to that for evapotranspiration, to maintain salt balance in the root zone. Key factor in the procedure is the leaching efficiency, which appears to range from 0.2 for fine-textured soils to 0.6 for coarse-textured soils. Also taken into account are the salt tolerance of the crop, the salt concentration of the irrigation water, and the evapotranspiration. The procedure accurately predicted the known leaching requirements for salt balance of three irrigated regions. In defining irrigation efficiency, distinction is made between an efficiency of water utilization and an efficiency of water application. In conclusion, it is shown how the drainage flow from the root zone decreases with time after an irrigation and how the water table response of a system of parallel drains to this flow can be computed for the design of a drainage system to avoid high water tables.