JWSS - Journal of Water and Soil Science

Changes in soil infiltration cause changes in irrigation efficiencies; therefore, estimating it in calculating irrigation efficiencies provides a more accurate estimate of irrigation performance indicators. In a study conducted on ARC2-7 farm in Amirkabir agro-industry in the 2010-2011 crop year, during four irrigations; two furrows were selected in terms of uniform infiltration and variable infiltration with a length of 140 and a width of 1.83 m. In the furrow assuming uniform infiltration two flume type II, at the beginning and end of it, were installed and the cumulative infiltration was determined by the volume balance method. The furrow with variable conditions was divided into four sections by installing five flumes. By examining the spatial variations of the mean cumulative infiltration, its value decreased from the first to the fourth section for the first irrigation by 15% and for the subsequent irrigations by 13%. Temporal changes of cumulative infiltration decreased by 27 and 30% for the first and second sections and by 26% for the third and fourth sections. An 11% increase in the average weight of the aggregate diameter and a 7% decrease in bulk density indicate physical changes in the soil. Surface runoff losses increased from 8 to 18.77% in the furrow assuming uniform infiltration and from 10.91 to 19.77% in the furrow with variable infiltration, and application efficiency decreased by 6%.

In the present study, a model was developed using a system dynamics approach to simulate and optimize the profitability of crops of the Jofeyr (Isargaran) Irrigation and Drainage Network located in Khuzestan Province. To validate the results, the statistical indicators of root mean square error (RMSE), standard error (SE), mean biased error (MBE), and determination coefficient (R²) were used. To validate the simulation results of the benefit-cost ratio, the values of these indicators were obtained 0.25, 0.19, 0.005, and 0.96, respectively. Then, to determine the optimal cultivated area of the network and increase the profitability, the cropping pattern was determined both non-stepwise and stepwise in 2013 to 2017 cropping years. In the non-stepwise, the cultivated area of each crop changed from zero to 2 times of current situation. In stepwise, due to social and cultural conditions of inhabitants, this change was slow and 10% of the current situation every year. The analysis of the results showed the success of the model in optimizing and achieving the desired goals and the total benefit-cost ratio increased in all years both non-stepwise and stepwise. For example, in 2017 compared to 2016, production costs decreased by 7.1 percent and sales prices increased by 5.8 percent, and increased the benefit-cost in 2017 compared to the previous year. The results showed that the present model has good accuracy in simulating and optimizing the irrigation network, its cropping pattern, and defining other scenarios.