Use of Polymer Membranes to Reduce Soil Evaporation and Deep Drainage.

Irrigated agriculture currently produces 40% of the world’s food using 20% of the total cultivated land but uses 70% of all freshwater withdrawals to do so. Meeting the food needs of a growing population will require irrigation to play an even more important role in the future than it has in the past, but with less water. This will require ongoing improvements in irrigation water use efficiency. One way to address this is to increase the percentage of applied irrigation water taken up by the plant relative to that ‘lost’ from the root zone through soil evaporation and/or deep drainage. In this paper we describe surface energy balance and other enhancements incorporated into the HYDRUS2D model that enables assessment of the effectiveness of polymer membrane barriers to water flow in reducing soil evaporation. We discuss in particular the effects of albedo and partial surface coverage of polymer membranes on soil evaporation in drip irrigated systems. Our analysis shows that many small gaps result in greater evaporation loss than a few big gaps with the same total surface area. We conclude by highlighting areas in need of further research.