Agricultural Irrigation Management in Semi-arid Areas
Marin Municipal Water District
The aim of soil salinity control is to prevent soil degradation by salinization and reclaim already salty soils. The primary man-made cause of salinization is poor agricultural irrigation practice and water conservation. River water or groundwater used in irrigation contains dissolved salts, which remain behind in the soil after the water has been utilized due to crop evapo-transpiration. The primary method of controlling soil salinization is to waste up to 20 percent of the irrigation water to leach salt from the soil. This leachate has to be drained and discharged through an appropriate drainage system or it percolates to the ground water. The salt concentration of the drainage water is up to 10 times that of the irrigation water. If this practice is utilized, salt export matches salt import and it will not accumulate. Obviously, irrigation conservation practices such as drip irrigation only accelerate this problem. However, the sink for this evaporite suffers the consequences of either salt buildup or substantial salinity increase in the receiving water body. Based on the FAO/UNESCO Soil Map of the World, the magnitude of poor salinity control is demonstrated by a real impact on the World's soils that already exhibit salinization as follows: Region Salinized Area (10^6 ha)Australia 85Africa 70Latin America 60Middle East 50Europe 20Far East 20North America 15. To address a problem of this magnitude, the preparation of salt and water balances for distinguishable sub-areas under irrigation and the use of agro-hydro-salinity models is critical to minimizing the impacts of and extent/severity of salinization. This paper discusses the soil/water chemistry of irrigation and the use of agro-hydro-salinity models in the management of modern irrigation practice, especially when combined with food plant processing wash water disposal. Practical guidance will be provided based on the experience of the author at over 100 types of agriculture and food processing facilities located through the world.