The leaching paradox and return flow management options for sustainable irrigated agriculture

Abstract

Leaching is necessary to maintain an acceptable salt balance in the root-zone of irrigated crops. This however contributes to point and non-point source water pollution externalities if not managed correctly. The use of a linear programming model, SALMOD (Salinity and Leaching Model for Optimal Irrigation Development) is demonstrated to determine the feasibility of leaching. artificial drainage, and on-farm storage/evaporation ponds to manage degraded return flows entering the water source and groundwater. Results show optimal cropping compositions and management practices to maximise farm returns subject to water quality conditions and return flow constraints. The economic effects of constraining return-flows and of water pricing policy on the volume of return flows are also determined. Results show valuable policy information regarding the interactions between artificial drainage subsidisation, return flow restrictions and on-farm storage.