Evaluation of water management effects on potato yield and water productivity in northeast Iran using the SWAP model

The agro-hydrological SWAP model was employed for simulation of evapotranspiration, yield, and water productivity of potato under six irrigation scenarios (100, 90, 80, 70, 60, and 50% potato water requirement (WR)) in Fariman, Ghoochan, and Golmakan in the northeast Iran. The results showed that the SWAP model well-simulated potato yield and water productivity. The model slightly overestimates the potato yield and underestimates the water productivity. The results revealed that irrigation scheduling is an important factor effecting on evapotranspiration, yield, and water productivity of potatoes. By decreasing irrigation water to 50% WR, potato evapotranspiration and yield decreased in all three study areas. However, potato water productivity increased in Fariman and Golmakan and decreased in Ghoochan, as irrigation volume decreased to 50% WR. In Fariman and Golmakan, irrigation at the rate of 80% WR led to the best irrigation management to have maximum water productivity (2.96 and 2.48 kg m−3, respectively) and acceptable potato yield (21,376.2 and 10,998.7 kg ha−1). In Ghoochan, by adopting the irrigation scenario at the level of 90% WR, the potato yield decreased by approximately 7.6% compared to the full irrigation conditions. However, the highest amount of water productivity (2.27 kg m−3) was achieved.