Computer Model for Moisture Distribution in Stratified Soils Under a Trickle Source
ABSTRACT THIS research was conducted to: (1) develop a computer simulation model—or use an existing one—to simulate irrigation in stratified soils, (2) study the moisture distribution under a trickle source in a Lakeland sand, and (3) compare results of the computer model with field measurements. Field tests were conducted at various application rates and volumes, a CSMP model was modified for use in stratified soils, and this modified program was used to simulate irrigation in the Lakeland soil. The neutron scattering method was used to measure the moisture distribution to a depth of 150 cm and to a radius of 105 cm from the trickle emitter. For each test, measurements were made before and after irrigation and again after some redistribution period. Also, tensiometers were placed at specified depths at a radius of 45 cm to help locate the wetting front during application and redistribution. Input data for the CSMP simulation model (in-situ tension vs. water content and hydraulic conductivity vs. water content for each soil horizon) were obtained using the instantaneous profile method. Field measurements showed that the shape and size of the wetted zone is more a function of the volume of water applied than of the rate of application. When more than 32 L were applied, the additional water did not greatly increase the horizontal dimension of the wetted zone, but moved vertically through the profile. The CSMP simulation compared favorably with the field measurements in the Lakeland sand.