Abstract:
Study of water distribution in the soil is essential for appropriate design of drip irrigation system. Water distribution in the soil depend on the hydraulic properties of the soil and emitter discharge. Experiments were conducted with the Research Farm of Bastam Agricultural Center, Shahrood, Iran to investigate the water distribution pattern under sandy loam soil. A water and solute transport model Hydrus-2D was calibrated with observed data to simulate the water distribution pattern for different type of soil under varying emitter discharge. HYDRUS-2D is a finite element model, which solves the Richard's equation for variably-saturated water flow and convection-dispersion type equations for heat transport. The model can deal with prescribed head and flux boundaries, controlled by atmospheric conditions, as well as free drainage boundary conditions. The simulations were done for a soil profile of depth Z = 60 cm and radius r= 30 cm, with a trickle emitter placed at the surface. The flux radius was taken equal to the wetted radius considering emitter in centre. Surface area for irrigation without causing pounding was determined from the flux radius and subsequently flux per unit area, resulting from single emitter was estimated. Simulation result revealed that for all the soils water content was more in middle layer. Even after 48 hrs from irrigation adequate water content is available in the active root zone of the onion. This indicates that irrigation interval of 48 hr is appropriate. Amount of percolation below root zone was highest in sandy loam and negligible in silty clay loam soil.
