Background and Aim: Water and fertilizer stress have a negative effect on many physical and chemical processes related to the efficiency of water productivity in soybean, thus leading to a decrease in the yield and quality of the plant. Predicting yield response for evaluating irrigation and fertilizer management strategies is of particular importance for making decisions. One of the decision support models in soybean is the CSM-CROPGRO-Soybean model, which is included in the DSSAT software package. The researches in the farm to determine the optimal solutions are done in agriculture and this item, in addition to the cost, is also time consuming, so the aim of this research is to use the DSSAT simulation model to evaluate the yield and water productivity in soybean plant under the conditions of water stress and nitrogen fertilizer were in Hormozgan province.
Method: The current research was idone in the form of split plots in the form of a randomized complete block design in 3 replications, in Hormozgan province and in Haji Abad city in the years 2021 and 2022. The main factor includes no irrigation and supply of 40, 60, 80, 100 and 120% of water requirement and the sub-factor of nitrogen fertilizer amounts included consumption of zero, 50, 100, 150 and 200 kg/hectare. The data and information needed to implement the model include location, meteorological information, soil information and agricultural operations, and the estimation in the model was done using a combination of graphic and statistical methods. Comparison of values and distribution of simulated and measured data was presented with 1:1 graph and line.
Results: The amounts of water use in the treatments of 40, 60, 80, 100 and 120 percent of water requirement in 1400 were 265, 354, 444, 533 and 623 mm, respectively and in 1401 were 259, 347, 435, 541 and 632 mm, respectively. The root mean square of the relative error (RMSEn) based on the years 1400 and 1401 showed that the yield of seeds, pods and biomass and the water productivity based on the yield of seeds, pods and biomass in the first year were 0.162, 0.161, 0.099, 0.304, 0.454 and 0.223%, and in the second year it was 0.195, 0.172, 0.106, 0.349, 0.485 and 0.247%, respectively. Wilmot agreement index (d) in the year 1400 for seed yield, pod and biomass respectively 0.902, 0.891 and 0.939% and for water productivity based on seed yield, pod and biomass respectively 0.828, 0.810 and 0.970 percent. In 1401 were for seed yield, pod and biomass 0.872, 0.885 and 0.936 percent respectively and for water productivity based on seed yield, pod and biomass respectively 0.889, 0.766 0 and 0.961 percent. The closeness of this index to the number one, it indicates the reliability of the simulated values.
Conclusion: In general, based on the statistical results, the simulation of seed, pod and biomass yields under the effect of different irrigation requirements and different levels of nitrogen fertilizer was acceptable and it seems that the use of the model as a useful tool to support scientific research and improving decisions in water use management in soybeans in the study area are recommended.
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