Simulation of heterogeneous soil salinity under unsteady condition from a line source

Limitation of water resources has led to unusual waters applications and the use of high-efficiency irrigation systems such as drip irrigation in some areas. The mismanagement of water resources has caused increases the accumulation of salts in the soil. Due to the executive limitations of field experiments such as high cost and timeconsuming, using of simulator models for studying different management scenarios is recommended. Purpose of this research is evaluation of the salt transport in heterogeneous heavy soil and unsteady conditions with estimating hydraulic and solute transport parameters using inverse solution with the HYDRUS-2D model.
Drip irrigation system was applied as a line source and was done with water salinity of 1.279, 2.5 and 5 dS/m. Soil profiles were drilled to 40cm depth and networking with dimensions of 10 × 10 cm was performed. 48 hours after irrigation. In order to check the status of solute, sampling from beneath the tape and horizontal distance of 20 cm from the tape was used to determine the salinity of the soil saturation extract. ECe observed values of field experiments were compared with ECe simulated values using statistical indices i.e. nRMSE and CRM.
Simulated soil salinity values were slightly lower than the observed values. Also it was observed that the maximum amount of salinity was in the surface layer of soil, this could indicate the need for salt leaching in cases such as the early stages of plant growth which is more sensitive to salinity. According to HYDRUS model estimations, ranges of longitude dispersion coefficient (DL) and transverse dispersion coefficient (DT) were between 24.57-39.56 (cm) and 0.1298-5.2680 (cm), respectively; These differences in coefficients of different may be due to the soil heterogeneity and the high spatial variability in soil transformation parameters. Ranges of nRMSE for beneath the tape and the horizontal distance were between 2.79-18.49% and 3.084-20%, respectively. Simulations placed in good to excellent category. Ranges of CRM for beneath the tape were between -0.049 and 0.097 and the horizontal distance were between -0.065 and 0.081.
Despite heavy soil texture and soil heterogeneity in the study area andaccording to statistical indices i.e. nRMSE and CRM, HYDRUS-2D model could estimate satisfactorily the hydraulic and the solute transport parameters using inverse solution and simulated salinity with good quality; Thus, this model can be used as a suitable tool for the design and management of drip irrigation with saline and brackish water.