Submitted to: Elsevier
Publication Type: Book / Chapter
Publication Acceptance Date: May 27, 2004
Publication Date: December 15, 2004
Citation: Rawls, W.J., Nemes, A., Pachepsky, Y. 2004. Effect of soil organic carbon on soil hydraulic properties. Elsevier Development in Soil Science. Amsterdam, The Netherlands: Elsevier. 30(6):95-111. Technical Abstract: The soil hydraulic properties that are most affected by organic carbon are porosity, water retention and saturated hydraulic conductivity. The effects of organic carbon are not straight forward consequently reports about the relationship between soil water retention and organic carbon content and saturated hydraulic conductivity are contradictory. The literature is reviewed. Regression trees and Group Method of Data Handling revealed a complex joint effect of texture, horizon, taxonomic order and organic carbon on water retention at -33 kPa and '1500 kPa. Adding information on taxonomic order and on taxonomic order and organic carbon content to the textural class brought 10% and 20% improvement in water retention estimation, respectively, as compared with estimation from the textural class alone. Using total clay, sand and silt along with organic carbon content and taxonomic order resulted in 25% improvement in accuracy over only using textural classes. Similar, but lower trends in accuracy were found for water retention at -1500 kPa and the slope of the water retention curve. At low organic carbon contents, the sensitivity of the water retention to changes in organic carbon content was highest in sandy soils. Increase in organic carbon content led to increase of water retention in sandy soils, and to a decrease in fine-textured soils. At high organic carbon content, all soils showed an increase in water retention. The largest increase was in sandy and silty soils. The organic carbon effect on saturated hydraulic conductivity was shown to be directly related to the organic carbon effect on water retention as given in the Kozeny-Carman equation describing the saturated hydraulic conductivity.