Optimization of irrigation scheduling under Kapuwaththa irrigation tank in Hambantota district, Sri Lanka

Abstract

Land use and irrigation management become vital for sustainable agriculture in the context of climate change. The model CROPWAT 8.0 was used in this study for the determination of crop water requirement and irrigation scheduling with the objectives to optimize irrigation scheduling under the Kapuwaththa irrigation tank and to recommend better water management options. Three years (2018-2020) of weather data, soil data and crop data from relevant sources were used as input in the model. The CROPWAT automatically calculated the daily soil moisture balance until the end of the growing season, the totals of effective rainfall and irrigations applied. Based on the modelling application, the respective water requirements per season were 691 mm and 830 mm for Maha and Yala seasons, respectively, whereas the actual amounts applied were 725 mm and 967 mm. The study indicates that the farmers over irrigated the fields by 5.0% and 16.5% in Maha and Yala respectively, when the irrigation efficiency of the scheme is 40%. If the actual application efficiency of the scheme is more, the over irrigation will be more than the amounts given by the model. CROPWAT model can be used as a good tool to schedule the irrigation for paddy under a village tank. The model could be used in optimizing the use of rainfall and saving water, but the effective rainfall calculation method needs to be applied with caution from place to place, and the coefficients of the dependable rainfall method needs to adjusted accordingly to get accurate results.