SOIL-WATER DISTRIBUTION UNDER TRICKLE SOURCE

Soil-water distributions in homogeneous soil profiles of Yolo clay loam and Yolo sand irrigated from a circular source of water were measured at several times after initiation of irrigation. The effect of trickle discharge rates and soil type on the locations of the wetting front and soil-water content distributions were determined. Soil-water potential and hydraulic conductivity, as a function of soil-water content, were also measured. A finite element solution of the two-dimensional transient soil-water equation, the theory of time-dependent, linearized infiltration from a circular source the effective hemisphere model, and a generalized solution for axially symmetric flow were compared with the experimental results. In general, the computed vertical advances of the wetting front were closely related to those observed for both soils. All of the solutions provided a better prediction of the wetting front positions for the clay-loam soil than for the sandy soil. The calculated and measured horizontal wetting fronts did not agree for large time, especially for the generalized solution. A more pronounced underprediction of the wetting front positions by the effective hemisphere theory occurred compared to those predicted by the linearized and finite element theories. Soil-water content distributions computed by linearized and numerical solutions, agreed reasonably with measured values in both soils.