The effect of hysteresis on soil water dynamics during surface trickle irrigation in layered soils

In this study, the development of a numerical model simulating surface drip irrigation from equidistant line sources in stratified soils under various conditions is being presented. The developed numerical model was used to investigate the effects of hysteresis, discharge rate, and soil hydraulic properties on soil water dynamics in stratified soils under surface trickle irrigation. Soil water dynamics were simulated for two sequences of soil layers and for two drip lines discharge rates. Soil water distribution patterns, for all conditions examined, were computed first neglecting hysteresis by using the boundary wetting curve only and second considering hysteresis to evaluate the effect of hysteresis on the obtained results. The numerical results showed that hysteresis has a profound effect on the computed soil water distribution patterns and that the draining process progresses more quickly when hysteresis is neglected than when hysteresis is considered. The inclusion of hysteresis results in reduced water losses under the root zone. Moreover, this reduction seems to be more significant in the case that a fine soil is located below a coarse soil. The results also showed that the irrigation efficiency is higher in the same case; however, irrigation efficiency is generally high in all the examined cases of stratified soils.