A multiple linear regression equation and nomograph were developed which can be used to estimate the erodibility factor, K, of many high clay subsoils. The subsoil erodibility nomograph uses terms involving soil particle size distribution and the amount of amorphous hydrous oxides or iron, aluminum, and silicon in the soil. Multiple regression analysis revealed that amorphous iron, aluminum and silicon hydrous oxides serve as soil stabilizers in subsoils, whereas, organic matter is the major stabilizer in surface soils. Evidence is presented to show that soil erodibility from semi-compacted fill and scalped subsoil surface conditions were essentially identical. It is reported that the scalped condition is the best standard soil surface to base the calculation of the erodibility factor for subsoils.

Report prepared by Purdue Research Foundation, West Lafayette, Indiana. "Project no. 15030 HIX; Program element 1BB042; Roap/Task PEMP 03." Includes bibliographical references (pages 80-81), and appendices.

Conclusions -- Recommendations -- Introduction -- Field experiments -- Laboratory characterization of reference soils for physical, chemical, and mineralogical properties -- Statistical analysis of data obtained in field and laboratory experiments -- A nomograph for estimating the erodibility factor, K, of high clay subsoils. This report presents evidence that the surface soil erodibility prediction nomograph (Wischmeier et al., 1971) which uses terms involving soil particle size, organic matter, structure and permeability, could not be improved upon by consideration of other mineralogical and chemical parameters. However, the surface soil erodibility nomograph did not adequately predict the soil erodibility factor, K, of high clay subsoils studied in the field under simulated rainfall conditions as a part of this project. A multiple linear regression equation and nomograph were developed which can be used to estimate the erodibility factor, K, of many high clay subsoils. The subsoil erodibility nomograph uses terms involving soil particle size distribution and the amount of amorphous hydrous oxides of iron, aluminum, and silicon in the soil. Multiple regression analysis revealed that amorphous iron, aluminum, and silicon hydrous oxides serve as soil stabilizers in subsoils, whereas organic matter is the major stabilizer in surface soils. Evidence is presented to show that soil erodibility from semi-compacted fill and scalped subsoil surface conditions were essentially identical. It is reported that the scalped condition is the best standard soil surface to base the calculation of the erodibility factor for subsoils. It is suggested that a soil-management factor should replace the cropping-management factor in the Universal Soil-Loss Equation when the Equation is used to predict subsoil erosion.