Evaluation of SWAP for Simulation of Potato and Determination of Adequate Irrigation Depth

Potato is the fifth largest food source in the world, which is widely cultivated in Iran. Due to the sensitivity of this crop to the amount of irrigation water, it is necessary to investigate the effect of different amounts of irrigation on it. For this purpose, SWAP model was used as a powerful tool for potato simulation. At first, to evaluate this model, biennial data (1998-1999) collected from a research station in ChaharTakhteh, Shahrekord were used. These data include five levels of water stress (E0, E1, E2, E3 and E4, respectively, indicating 100, 85, 70, 50 and 30% water supply) and three stress application times (T1, T2, and T3 indicating 50, 100, and 150 days after sowing, respectively). NRMSE values for yield and water use efficiency showed that SWAP model in both calibration and validation were excellent (NRMSE < 0.1). The error of this model for simulating yield in the calibration and validation stages was equal to 1.42 ton.ha-1 (4.6 percent) and 2.36 ton.ha-1 (7.2 percent), respectively. The error value of this model for water consumption efficiency in the mentioned two stages was 0.04 kg.m-3 (4.9%) and 0.33 kg.m-3 (7.7%), respectively. The efficiency of the SWAP for potato simulation during calibration and validation was acceptable. Potato irrigation planning using SWAP showed that to achieve maximum yield, the irrigation water depth in the first growing period is equal to 750 mm and irrigation depths are 900 mm in subsequent periods.