Submitted to: International Soil Science Society Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: October 1, 2001
Publication Date: October 23, 2001
Citation: RAWLS, W.J., PACHEPSKY, Y., SOBECKI, T., BLOODWORTH, H. INFERRING SOIL HYDRAULIC PROPERTIES FROM SOIL ORGANIC CARBON. CD-ROM. AGRONOMY ABSTRACTS. ASA-SSA-SSA. Technical Abstract: Reports about the relationship between soil water retention and organic carbon content are contradictory. We hypothesized that this relationship is affected by a) proportions of textural components, b) amount of organic carbon, and c) quality of organic matter. To test the hypothesis, we used National Soil Characterization data base and the data base from pilot studies on soil quality as affected by long-term management. Correlations between water retention at -33 kPa and organic carbon were weak within textural classes and with taxonomic orders. Regression trees and Group Method of Data Handling revealed a complex joint effect of texture and taxonomic order on water retention at 33 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. 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 matter content was highest in sandy soils. Increase in organic matter content lead to increase of water retention in sandy soils, and to a decrease in fine-textured soils. At high organic carbon values, all soils showed an increase in water retention. The largest increase was in sandy and silty soils. Results are expressed as equations that can be used to evaluate effect of the carbon sequestration on soil hydraulic properties.