Grouping of Soil Types to Indicate Erosion Potentialities

AGRICULTURAL workers who use soil or con• * * • servation survey maps as a basis for recommendations for agronomic, forestry or other practices frequently express the opinion that these maps contain too many separations. Soil surveyors have many times discussed the pros and cons of this same question and usually come back to the same answer, and that is, when the use for which the information is designed is limited to one factor, it is possible to eliminate many separations which would otherwise be made. Studies made on soils derived from sandstone and shale in eastern Ohio indicate that certain physical characteristics, particularly depth to the B horizon and the compactness and density of this horizon, are highly important in denoting erosion potentialities. These observations were clearly indicated by studies made in strip cropping areas in Ohio. Briefly, the method used in these studies was based on the determination of the volume of the colluvial fans which accumulated in the meadow strips below cultivated corn strips, and the association of this colluvium with the measurable physiographic and pedological factors which appeared to influence the evident erosion. A more detailed description of the method used in measuring and computing these deposited soil losses from cultivated strips will be presented in another paper. During the fall of 1938, the soil movement from two hundred thousand linear feet of contour cultivated corn strips on various residual and glacial soil types was determined. By selecting samples homogeneous for the measured physiographic factors, it was possible to study the influence of soil type on the effectiveness of strip cropping. When contour strips on a typical Muskingum silt loam were compared with similar strips on Westmoreland silt loam and silty clay loam, no significant difference in the deposited soil loss (measured loss deposited as colluvial fans in the meadow) was found (Table I). The soils of the Muskingum series are derived from parent material of sandstone and shale origin, while the parent material of the Westmoreland complex contains varying amounts of limestone interbedded with the sandstone and shale. However, in southeastern Ohio the limestone is not present in sufficient quantities, in those areas where the Westmoreland complex is usually found, to influence materially the physical properties of the soil or to affect greatly the texture or compactness of the subsoil. On the other hand, there are large areas of residual soils in this section of Ohio which are characterized by moderately heavy to heavy, compact subsoils. These soils are often more deeply weathered, with a better developed solum, than usually encountered in the abbreviated profile associated with soils typical of the Muskingum series. However, it appears that the heavy, compact subsoil has probably been formed by the weathering of alternate and moderately thick layers of sandstone and heavy shale rather than by the processes that usually account for the development of a normal heavy subsoil type. Wellston, Tilsit,