Use of the FAO CROPWAT model in deficit irrigation studies

Dwindling water resources and increasing food requirements require greater efficiency in water use, both in rainfed and in irrigated agriculture. Regulated deficit irrigation provides a means of reducing water consumption while minimizing adverse effects on yield. Models can play a useful role in developing practical recommendations for optimizing crop production under conditions of scarce water supply. To assess the applicability of the FAO CROPWAT model for deficit irrigation scheduling, a study utilized data provided in studies from a joint FAO/IAEA coordinated research project (CRP) on 'The use of nuclear and related techniques in assessment of irrigation schedules of field crops to increase effective use of water in irrigation projects,' carried out in Turkey, Morocco and Pakistan on cotton, sugar beet, and potato, respectively. The study revealed that the CROPWAT model can adequately predict the effects of water stress, but requires calibration of the main crop parameters. Procedures were developed to calibrate the various crop parameters based on research findings from the treatments. The study demonstrated that the model could be useful in improving the design of experimental methods in research studies and in identifying inconsistencies in procedures and results. Furthermore, the model permitted a more systematic analysis of results, a more uniform presentation of data, and a greater compatibility of results. Moreover, this paper concludes that models are a powerful tool for extending findings and conclusions to conditions not tested in the field, and that useful predictions on deficit irrigation scheduling are possible under various conditions of water supply, soil, and of crop management. (author)