SCALING OF INFILTRATION AND REDISTRIBUTION OF WATER ACROSS SOIL TEXTURAL CLASSES

Authors: Kozak, Joseph; Ahuja, Lajpat

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2004
Publication Date: 6/1/2005
Citation: Kozak, J.A., Ahuja, L.R. 2005. Scaling of infiltration and redistribution of water across soil textural classes. Soil Science Society of America Journal. 69:816-827.

Interpretive Summary: Scaling of Infiltration and Redistribution of Water across Soil Textural Classes The amount of water entering the soil (infiltration) upon a rain event and the subsequent movement of that water within the soil (redistribution) were examined with respect to eleven soil type, i.e. clay to sand. It was found that there is a strong relationship between infiltration and soil type drainage index (l) and redistribution and l. Because of this strong relationship, a mathematical model was developed that could estimate infiltration and redistribution based on soil type, rain intensity, and rain duration. This study will help in understanding how the amount of soil water changes across a unit area upon a rainfall event in order to develop agricultural site management. For example after a rainfall, the amount of water entering and moving through the system can be estimated. This will give insight into whether enough water was supplied to the system or if irrigation needs to be applied to the field for optimal crop growth. This model will also help in crudely estimating the infiltration and redistribution of a large watershed based on actual measurements of infiltration and redistribution of a small unit area, thereby limiting the number of field measurements.

Technical Abstract: Results with a one-parameter model showed that the pore-size distribution index (l) described in the Brooks and Corey formulation of soil hydraulic properties can scale the soil-water retention curve below the air-entry pressure head (yb) values across dissimilar soils. Further, it is shown that yb and saturated hydraulic conductivity (Ksat) are also strongly related to l, and thus all hydraulic parameters may be estimated from l. We then examined how these relationships to l lead to relationships for infiltration and soil water contents during redistribution across soil textural classes. The Root Zone Water Quality Model simulated infiltration and redistribution in eleven textural class mean soils for four rainfall intensities and two initial conditions. All infiltration results across textural classes were scaled quite well by using the l-derived normalization variables based on the dimensional analysis of the Green-Ampt model. Both infiltration and redistribution were also strong explicit functions of l. These explicit functions can be used as nomographs for interpolating values for different soils. Additionally, we show that they may be used to approximately scale infiltration and soil water contents across soil types and estimate these variables for unknown soils where data for one dominant reference soil type is known. This study enhances our understanding of the soil water relationships among soil textural classes and is a step towards meeting needs for (1) quantifying spatial variability of soil water for site-specific management and (2) for scaling up results in modeling from plots to fields to watersheds.