Application of the principle of calculated risk to scheduling of supplemental irrigation, II. Use on flue-cured tobacco

Abstract

A simulation model was constructed to test the application of an irrigation-scheduling decision model which incorporated the basic concepts of calculated risk. Inputs for the model included: (1) the official probability precipitation forecasts for the periods “today”, “tonight” and “tomorrow”; (2) initial soil moisture content; (3) daily precipitation; (4) daily mean temperatures; (5) daily potential evapotranspiration and daylength values; (6) functions relating existing soil moisture content and stage of growth to the corresponding damage done to the crop; and (7) cost of irrigation. The loss functions were developed specifically for flue-cured tobacco. Two methods were used for calculating the cost of the irrigation. The decision criterion was applied by means of the simulation model to data from three growing seasons. The results were compared to the results as arrived at by irrigating at a 50% available moisture depletion level. It was found that the new criterion (using either method for calculating the cost of irrigation) yielded less total cost plus loss and achieved a better utilization of the available water than did the 50% criterion. While the state of the art does not allow extremely well-based development of the input variables and parameters, available data have shown the concepts of the model to yield adequate results. Much future development of the approach remains, however.