m t; s b; a s; a n
Abstract
Determation of moisture distribution pattern is time-consuming and a costly field tests. Simulation models are a suitable alternative in answer to issues of water movement and distribution. In this research, soil moisture under drip irrigation was simulated with SWAP model and the model efficiency was ...
Read More
Determation of moisture distribution pattern is time-consuming and a costly field tests. Simulation models are a suitable alternative in answer to issues of water movement and distribution. In this research, soil moisture under drip irrigation was simulated with SWAP model and the model efficiency was evaluated by comparing the simulated results with field results. SWAP model was evaluated based on the information gathered from a research field of Water Sciences Faculty, Shahid Chamran University of Ahvaz under corn cultivation and equipped with drip irrigation system. The hydraulic parameters were obtained from RETC model in the growing season of 2012-13. Required data were collected by field experiments. The experiments consisted of two treatments of salinity including treatments T1 (Karun River water with salinity of 3dS/m) and treatments T2 with salinity of 3.5 dS/m. Planting was done by hand in plots including four rows of 3 m with row spacing of 75 cm and with a plant density of 80,000 plants/ha. Irrigation system was drip tape with emitter holes spacing of 20 cm and discharge of 2.2 lit/h at a pressure 0.6 bar. Comparison of the measured soil moisture with simulated soil moisture to a depth of 90 cm depth was performed on the ridge and 10 and 20 cm from emitter by drawing graphs and calculation of Maximum Error (ME), Normalized Root Mean Square Error (NRMSE) and Coefficient of Residual Mass (CRM). Computed values of ME, NRMSE and CRM in different locations were as follows: 10 cm from emitter: 0.02, 14.41 and -0.0016 cm3 cm-3; 20 cm from emitter: 0.07, 15.49 and -0.036 cm3 cm-3, and on the ridge: 2.1, 12.52 and -0.036 cm3 cm-3. SWAP model accuracy in estimating changes in moisture away from the emitter decreased with increasing distance from the emitter. This may be due to low precision of the model under high salinities. Generally, the results obtained from stimulating by SWAP showed that this model could stimulate moisture distribution in soil under drip irrigation with salty water. This model can be used as a useful tool for evaluation of moisture distribution around the a dripper.