Using NIAZAB System to Determine Soybean Water Use Based on the Inverse Solution of the Production Functions under Different Irrigation Conditions

Soil and Water Research Institute (SWRI) has presented NIAZAB system to estimate and determine crops water requirement, water consumption, and irrigation planning at the scale of region, district, and plains in Iran. The current research was conducted in order to use NIAZAB system (including Tafteh, Pasquale and Reas methods) in determining the amount of water used for soybean cv. Williams, based on the inverse solution of the production function. The experimental treatments in this research included no fertilizer and application of of 150 kg N ha-1 and different irrigation treatments including 100%, 80%, 60%, and 40% of water requirement. Experimental design was split plot in the form of randomized complete blocks with three replications, and was conducted in Hajiabad Region, Hormozgan Province, in 2020 and 2021. The values estimated by the system and measured showed that, in the first year, the average relative error (ARE) in eatimation of evapotranspirationin by Tafteh, Pasquale and Reas methods were 7.49%, -0.05%, and 9.14%, respectively. In the second year, these values were 6.47%, -1.29%, and 9.06%, respectively. The ARE in the physical water productivity in the mentioned methods was -8.23%, -0.73%, and -10.08% in the first year, and -7.10%, 0.58%, and -10.07% in the second year, respectively. In Tafteh, Pasquale, and Reas methods, the root mean square error (RMSE) were 43, 35, and 49 mm, respectively, and the normalized root mean square error (RMSEn) were 0.093%, 0.076%, and 0.105%, respectively. Considering the results, NIAZAB system estimated the amount of irrigation water and evapotranspiration with acceptable approximation and it can be used for estimation of water consumption in the studied area.