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United States Department of Agriculture

Agricultural Research Service

Title: Scaling Infiltration and Other Soil Water Processes Across Diverse Soil Textural Classes

Authors
item Kozak, Joseph
item Ahuja, Lajpat
item Green, Timothy

Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: September 30, 2005
Publication Date: December 7, 2005
Citation: Kozak, J.A., Ahuja, L.R., Green, T.R. 2005. Scaling infiltration and other soil water processes across diverse soil textural classes. American Geophysical Union 2005 Annual Meeting. SanFrancisco, CA. Dec. 7, 2005.

Interpretive Summary: Our studies showed that the pore-size distribution index (lambda) can scale Brooks-Corey (B-C) formulation of the soil-water retention curves below the air-entry pressure head across dissimilar (Sandy to clayey) soils, and other key B-C hydraulic parameters ( Ksat, air-entry pressure head, and dependant) were also strongly related to lambda. We then examined how these relationships to lambda led to relationships for infiltration across soil textural classes using three different approaches, as well as the subsequent soil water contents during redistribution, evaporation, and transpiration. The Root Zone Water Quality Model was used to generate data for infiltration under four rainfall intensities, redistribution for four initial wetting depths, and evaporation and transpiration under different potential rates in eleven textural class mean soils. Cumulative infiltration could be scaled quite well across textural classes based on knowledge of lamda using the Green-Ampt normalization equations. There were also strong empirical functional relationships between cumulative infiltration at fixed times across soils and the soils' lamda, and between the parameters of the empirical Kostiakov (Lewis) infiltration equation and lamda as well as Ksat. The Kostiakov parameters vs. lamda or Ksat (Ksat was better) provided more compact and explicit relationships across diverse soil classes both for instantaneous ponding and non-instantaneous ponding (e.g., rainfall) infiltration conditions, and could be used to scale and estimate infiltration across these classes. Similar strong relations were found between lamda (and by inference Ksat) and soil water contents across soil types during redistribution, and for evapotranspiration and transpiration. This study is a breakthrough in our understanding of the soil water relationships and scaling among soil textural classes, that could serve as a basis for describing spatial variability of soil water on the landscape for site-specific management and for scaling up results in modeling from plots to fields to watersheds.

Technical Abstract: Our studies showed that the pore-size distribution index (lambda) can scale Brooks-Corey (B-C) formulation of the soil-water retention curves below the air-entry pressure head across dissimilar (Sandy to clayey) soils, and other key B-C hydraulic parameters ( Ksat, air-entry pressure head, and dependant) were also strongly related to lambda. We then examined how these relationships to lambda led to relationships for infiltration across soil textural classes using three different approaches, as well as the subsequent soil water contents during redistribution, evaporation, and transpiration. The Root Zone Water Quality Model was used to generate data for infiltration under four rainfall intensities, redistribution for four initial wetting depths, and evaporation and transpiration under different potential rates in eleven textural class mean soils. Cumulative infiltration could be scaled quite well across textural classes based on knowledge of lamda using the Green-Ampt normalization equations. There were also strong empirical functional relationships between cumulative infiltration at fixed times across soils and the soils' lamda, and between the parameters of the empirical Kostiakov (Lewis) infiltration equation and lamda as well as Ksat. The Kostiakov parameters vs. lamda or Ksat (Ksat was better) provided more compact and explicit relationships across diverse soil classes both for instantaneous ponding and non-instantaneous ponding (e.g., rainfall) infiltration conditions, and could be used to scale and estimate infiltration across these classes. Similar strong relations were found between lamda (and by inference Ksat) and soil water contents across soil types during redistribution, and for evapotranspiration and transpiration. This study is a breakthrough in our understanding of the soil water relationships and scaling among soil textural classes, that could serve as a basis for describing spatial variability of soil water on the landscape for site-specific management and for scaling up results in modeling from plots to fields to watersheds.

Last Modified: 10/21/2014