Estimation of soil drainage losses following irrigation

Abstract

Soil moisture data, collected in the course of a field trial with flood irrigated perennial pasture on a red-brown earth, are used to present a water balance from which soil drainage losses can be estimated. Both water intake, and water storage in the root zone one or two days after irrigation, were related to the pre-irrigation water storage (S,). Substitution of the calculated regression relationships in the water balance equation led to an expression for water losses in terms of S, and evapotranspiration. As the latter is of the same order as tank evaporation (E) for several days after irrigation, it was possible to express soil drainage losses in terms of S, and E. The results indicate that it is difficult to prevent water loss by deep percolation, if irrigating this soil for optimum pasture production.