The Relation of Sheet Erosion to the Structure of Duffield Silt Loam
1939
Zwerman, Paul J.
SummaryDuffield silt loam was studied in four locations, representative of no apparent erosion, slight erosion, moderate erosion, and severe erosion. Field studies of soil structure were made with the infiltration technique of Musgrave. Detailed morphological notes were taken of the complete soil profile of each erosion area. Profile samples were taken for laboratory analysis. In the laboratory the following physical proper ties were studied by horizons: porosity, aggregate composition, mechanical composition, and organic matter content. Infiltration rates, which are indicative of field structure, were in the following order of increasing erosion: 9.9, 5.5, 10.6, and 3.3 surface inches during a 7.5 hour period. The variation in rates of infiltration were explained on the basis of effective soil porosity which was, in turn, governed by the number and size of soil aggregates and their relation to confined air and non-capillary soil porosity. These physical characteristics controlling water movement, were accounted for by the difference in mechanical composition and content of organic matter. It was concluded that, as sheet erosion progressed on Duffield silt loam, soil structure did deteriorate. That is, badly eroded areas have a less favorable structure for movement of water and air. The rôle played by confined air in the process of water movement needs additional study. Even in a “uniform” carefully selected area, field variations in the physical characteristics of a single soil type are so great that the results of infiltration measurement can be interpreted only when considered in light of the physical characteristics of the various soil horizons determined in the laboratory.
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