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Deficit Irrigation Management Decision Tools
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.orgCitation: 5th National Decennial Irrigation Conference Proceedings, 5-8 December 2010, Phoenix Convention Center, Phoenix, Arizona USA IRR10-9685.
Authors: Norman L Klocke, Loyd R Stone
Keywords: Deficit Irrigation, Irrigation Management, Crop Simulation, Water Allocation, Decision Tools
Many irrigators face the prospect that they will not be able to fully irrigate their crops. They are under pressure to develop cropping strategies as pumping capacities dwindle or water supplies become more restricted. These irrigators need to make long term and short term decisions about their deficit irrigation management strategies. Multiple crops in rotation can be an economically viable strategy compared with monoculture when water is limited, but these alternatives need to be evaluated. The Crop Water Allocator (CWA) has been developed for irrigators to allocate limited water among selected crops. CWA calculates net economic returns from all possible combinations of crops, irrigation allocations among crops, and land allocations, proposed by a user’s inputs, and ranks the net returns from maximum to minimum values. Users can also account for net return shifts in response to a range of input variables--rainfall, production costs, commodity prices, irrigation costs, irrigation efficiency, and maximum yields. After crops are selected, the irrigator needs to predict the capabilities of the combination of the irrigation system and the soil to provide water to the crop during the next irrigation season. They need to schedule their water applications to make the best economic use of available water. Major scheduling questions for deficit irrigation include: will pre-season irrigation be beneficial, and when should irrigation be initiated and terminated during the growing season. A computerized decision tool, the Crop Yield Predictor (CYP) has been developed to predict yields from alternative irrigation schedules. The user determines soil water status before or during the cropping season and formulates a potential schedule of irrigation dates and amounts. CYP uses a daily soil water balance coupled with computations of effective evapotranspiration (ETe) to predict crop yields from regional yield-ET relationships. Multiple executions of CYP with alternative irrigation schedules lead to the schedules that give optimum net economic returns from the management scenarios. The CWA and CYP are examples of transferring research based technology to irrigation management decision makers.