A Two Domain Mesopore and Matrix Model for Cracking Soils.

The Precision Agriculture Landscape Modeling System (PALMS) is a biophysical model that uses a two-domain, mesopore and matrix, model to simulate water flow in soil.  The model was developed to use knowledge of soil structure, the coefficient of linear extensibility, and soil water content to partition hydraulically active porosity between the mesopore and matrix domains.  The overall goal of this project is to evaluate how effectively the mesopore and matrix model of PALMS can simulate water infiltration and redistribution in soils that develop large cracks with widths much greater than those that are considered mesopores - using the same three parameters to predict the larger cracks.  The degree to which infiltration and redistribution of water in a cracked Vertisol was influenced by intensity of rainfall was evaluated using high and low intensity sprinkler irrigation. Two adjacent 10x10m plots that were separated from each other and their surroundings by a 1.2-m deep hydrologic barrier were irrigated with 7.5 cm of water at high and low intensities. The high intensity irrigation was 7.5 cm/h , a typical rate produced by a heavy thunderstorm, and the low intensity irrigation was between 0.25 and 1 cm/h.  In each plot, neutron access tubes and surface moisture measurements were used to measure water content of the soil profile. It was expected that high intensity irrigation would allow water to be transported to greater depth via the cracking network than the low intensity irrigation. The data collected is being used to determine whether the mesopore and matrix model in PALMS needs to be modified to simulate water movement and storage in soils that develop large cracks.