Assessment of HYDRUD-1D model in simulation of soil moisture and nitrogen in onion farm under drip irrigation

Water management and fertilizer nitrogen in agricultural products should be improved due to lack of resources, environmental problems and health. Modeling in recent years has had an important role in improving irrigation, fertilizer operations in new irrigation systems. The aim of this study was to evaluate the capability of Hydrus-1D model to simulate the effect of different combinations of water and nitrogen regimes in a drip irrigation system for the dung. This study was done in a drip irrigation fertilizer system and under field conditions for onion cultivation. Moisture levels and nitrogen concentration were obtained in field with 48 hr irrigation and fertilizer nitrogen injection with the concentration of 0.116 hr. Applying boundary conditions and initial in Hydrus-1D model, moisture and nitrogen were estimated at four depths 0-15, 15-30, 30-45 and 45-60 cm. In this study, changes of moisture content and nitrogen concentration during different growth months by Hydrus-1D model were evaluated. Results indicate higher moisture content of the three at 30, 60 and 90 days after transplanting bulbs in the ground layer 15-0 cm and 10 cm at the location of emitters. The humidity was higher in the first layer of soil at 10 cm eye drops due to the settlement of the soil. Measurement and modeling of nitrogen showed increasing nitrogen content at 30 and 9 days after transplanting in 15-0 cm layer of soil at the site of emitters than two months after transplanting. Reducing nitrogen at 10 cm droppers and 60 days after transplanting could be due to plant bulbs at 10 cm from droppers, increasing vegetation cover and food for the plant. Compared to moisture simulations at depth of 60 cm and 10 cm at place droppers showed that root mean square error were 0.0067 and 0.0062, mean absolute error were 0.0044 and 0.0047 and the coefficient of determination were 0.9 and 0.99, respectively. Similarly, compared to nitrogen simulated with observed in place dropper and 10 cm showed the root mean square error were 0.015 and 0.011, the mean absolute error were 0.014 and 0.009 and the coefficient of determination were 0.92 and 0.99, respectively. Calculating error statistics indicate low error and high coefficient of determination in application of Hydrus-1D model and accuracy of this model in the simulation of moisture and nitrogen distributed in the root zone.