Simulation of the soybean yield as a function of water sensitivity in rainfed cultivation using the CROPWAT model

Reducing soybean yield is key for decision-making, especially for rainfed crops. Models are tools that can help agriculture obtain this information quickly and practically. Therefore, the objective of this study was to simulate soybean yield as a function of the water sensitivity factor in rainfed cultivation via the CROPWAT model complemented with the Agroecological Zones Model. The experiment was carried out at the Lagoa Dourada farm in the central-southern region of the state of Mato Grosso, Brazil. Agrometeorological data were obtained from the INMET and ANA stations. For the purpose of simulating the maximum yield, the FAO Agroecological Zones Model was used in conjunction with the CROPWAT model to simulate the relative yield drop on the basis of the water sensitivity factor. The agroecological zone model overestimates the maximum yield of soybean in rainfed cultivation. CROPWAT allows the decrease in soybean yield in rainfed cultivation to be simulated on the basis of the water sensitivity factor (K_y). The water requirements of soybean simulated by CROPWAT were higher than the water consumption requirements for practically all harvests, except for the 2015/2016 harvest. The phases of greatest soil water depletion that influence the water sensitivity of soybeans under rainfed conditions during the eight harvests are F₂ and F₃. The reduction of 1.0 units of water in the soil K_y =1 decreases the yield of soybean simulated in CROPWAT by 1.0 units. The models can be used in a complementary way to simulate the maximum yield and the decrease in yield in a satisfactory way.