IRRIGATION WATER MANAGEMENT AND SOIL-WATER HYSTERESIS-A COMPUTER MODELING STUDY WITH STOCHASTIC SOIL HYDRAULIC PROPERTIES

ABSTRACT The numerical water flow model SWATRE was adapted to investigate the influence of hysteresis of spatially variable soil hydraulic properties on groundwater level, drainage flow, surface soil water pressure head, and plant transpiration and to analyze the importance of this hysteretic behavior in the context of irrigation water management. Computer simulations applying the main drying and wetting curve of the water retention functions were compared with simulations that used the appropriate scanning curves. We used Monte-Carlo analysis for simulation of irrigation during a growing season and analyzed the results for both a furrow and a trickle irrigation scenario. Although the differences were small, the use of hysteresis rather than utilizing the main drying curve yielded significant differences in drainage and surface soil water pressure head during most of the growing season. Differences in soil water regime between the hysteresis and main drying curve case were greater for the trickle than for the furrow system, due to longer periods of wetting for the trickle irrigation scenario. However, the results of this study also showed that soil spatial variability has a greater influence on simulation results than hysteresis. KEYWORDS. Irrigation management. Hysteresis, Drainage, Modeling.