Abstract
Scarcity of water has urged farmers, managers and engineers in the field of water resources engineering to explore the parameters of drip irrigation for its high performance and optimal working. Wetting pattern of soil under drip emitter is one of the most important parameters affecting the efficiency of the drip irrigation system. In this paper standard sand box model experiments were executed to identify the wetting pattern of various soils under different emitter discharges. The tests were performed on four types of soil including sandy loam, loam, clayey loam and clay. Equal volume of water was supplied in each experiment. The wetted diameter and depth of soil for a single emitter were monitored with the help of sand box model. The wetted radius on surface of soil and at some depth where it was maximum were measured in every experiment. Similarly, the maximum wetted depth and the depth of maximum wetted diameter were recorded. The volume of wetted soil was estimated using the measured data. The soil samples were collected and tested in the laboratory. The percentage of moisture in soil samples was recorded by gravimetric method in laboratory. Finally, the optimal emitter discharge and conditions for an efficient drip-irrigation system were obtained. The emitter discharge of 4 l/h was found to be the optimal for sandy-loam whereas 3 l/h produced optimal results for the other three types of soil. Empirical equations were developed to determine the maximum wetted radius and depth on the basis of different parameters including emitter discharge, irrigation time, soil bulk density, hydraulic conductivity, initial and final soil-moisture-contents and percentage of sand, silt and clay in soil formation. Subsequently additional data was obtained (for sandy loam and clayey loam) by varying emitter discharge over a broader range (1.0 to 30.0l/h) to improve the effectiveness of equations. Values of the empirical parameters of the equations were determined using "Generalized Reduced Gradient Non-Linear Optimization Technique". The empirical equations with these parameters performed well and produced reasonable accuracy (Nash and Sutcliffe coefficient up to 99%). The equations can be useful to predict data for design of an efficient drip irrigation system in absence of resources to perform experiments.