Sizing on-farm reservoirs for crop-fish integration in rainfed farming systems in Eastern India

For natural resource management and sustainable development of rainfed farming systems, the optimum size of the rainwater storage and recycling processes is essential for mitigating the uncertainty of rainfall. In the present study, a model is developed to predict the optimum size of the on-farm reservoir so as to provide supplemental irrigation to rice in monsoon season, pre-sowing irrigation to mustard in winter and to support fish cultivation in rainfed farming systems in Eastern India. The model is based on water balance approach for both the crop field and the reservoir, where hydro-meteorological parameters and the irrigation management practices are input to the model. The model predicts the reservoir sizes in terms of the percentage of the farm area under unlined and plastic lined conditions for two side slopes (horizontal:vertical) of 1.5:1 and 1:1 and two reservoir depths of 2 m and 2.5 m. The study reveals that for a 1.5:1 side slope, a return period of 5 yrs requires 21.4% and 17.5% of the farm area for the unlined and 17.3% and 13.2% of the farm area for the lined reservoirs for depths of 2 m and 2.5 m, respectively. However, the same return period requires 18.9% and 14.9% of the farm area for the unlined and 14.7% and 10.7% of the farm area for the lined reservoirs at 1:1 side slope with a depth of 2 m and 2.5 m, respectively. Based on the simulated sizes, 1 yr of field experiments are undertaken for the plastic lined and unlined reservoirs with rice–mustard cropping system along with fish cultivation in the reservoirs. Economic analysis of the study reveals the benefit–cost ratio of 1.28 and 1.75, internal rate of return of 18.1% and 29.2% and capital recovery periods of 8 and 5 yrs for the unlined and lined reservoir, respectively.