Moisture distribution in soil irrigated with a line source subsurface trickle irrigation system

Soil moisture distribution resulting from a line source subsurface trickle irrigation system was studied on bare and cropped layered soils. The soil type was an Uchee loamy sand. The Continuous System Modeling Program (CSMP) Model was used to simulate the soil moisture distribution resulting from the linesource. The model was modified and developed in FORTRAN programming language. The modification included the effects of layered soil, source position, number of sources, soil evaporation and plant transpiration. The model was also used to simulate daily and one-in-several-days irrigations.

Field and laboratory experiments were conducted to determine the soil moisture retention curve, the hydraulic conductivity, and soil moisture distribution from the line source. This data was used for model verification with the lateral lines buried 13 inches below the soil surface and spaced 36 and 72 inches apart. Simulated and measured soil moisture distributions were in good agreement. Simulated moisture distribution indicated that the wetting front expansion is more a function of irrigation volume than irrigation rate. However, the irrigation rate does affect the soil moisture distribution. A higher rate will result in a larger quantity of horizontal water movement. The simulation also indicated that a one-in-ten days irrigation causes more horizontal movement than a daily irrigation.