IT IS NOT ALWAYS SAFE TO SAVE WATER EFFECTS OF WATER-SAVING IRRIGATION METHODS ON SOIL SALINITY CONTROL IN SEMI-ARID REGIONS

摘要

The progressive scarcity of water for irrigation in many (semi-)arid and sub-humid regions has urged individual irrigators and water management organizations to minimize irrigation water supplies and recycle drainage water. Measures have been taken at field level and at river basin or irrigation command area level to increase overall irrigation efficiencies and reallocate “saved” water.The authors argue that such policies in already water-short regions may not always result in sustainable benefits for agriculture, fishery and ecological values, notably in the lower parts of irrigation command areas and drainage catchments. Due to serious shortages of fresh irrigation water that occur in the tail ends of some irrigation systems, these areas depend for their survival on the flows of mixed tail and (sub-)surface water draining from better watered areas. Moreover, savings at field level may be insignificant at basin level. Increasing water application efficiency in water-short regions can cause a significant decrease in leaching and irrigation surface runoff. Depending on the water quality this will eventually result in increased soil salinity levels and decreased crop yields, which will be difficult to redress.