SALMOD, a Salinity Management Tool for Irrigated Agriculture

This paper presents an irrigation farm management tool, SALMOD (Salinity And Leaching Model for Optimal irrigation Development), that calculates the profit maximizing crop enterprise composition and irrigation management options for farm specific soil type, drainage status and irrigation system composition subject to various regional control measures and expected irrigation water salinities. After stating the water quality problem, and particularly salinisation in Southern Africa, the input data requirements and the results of SALMOD and their usefulness at farm level, are discussed. The impact of various possible regional or policy regulations are then discussed. SALMOD was developed for irrigators in the lower Vaal and Riet Rivers in South Africa. These farmers have been experiencing rapidly fluctuating salinity levels in their irrigation water, resulting in soil salinisation, yield loss and subsequent financial instability. SALMOD calculates the profit maximizing crop choice and distribution over the farm, matching the crop choice with soil type, drainage status and irrigation system, indicating the optimal leaching vs. yield reduction seasonal management options as well as calculate long term management options such as underground drainage installation, a change in irrigation system or the construction of on farm storage dams. 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. Results show valuable policy information regarding the interactions between artificial drainage subsidisation, return flow restrictions and on-farm storage.