By David Kringen
At the end of May, I had the opportunity to spend an afternoon touring the loess hills area of Minnehaha County with Anthony Bly, SDSU Extension Soils Field Specialist; Al Miron, SD Corn and SD Soil Health Coalition Board Member; and Jim Ristau, SD Corn Sustainability Director. Loess is defined as material transported and deposited by wind and consists primarily of silt-sized particles. While the entire county has been glaciated, roughly two-thirds of the glacial till on the Eastern side is covered in loess (USDA 2004). Loess tends to develop into deep, rich, well-drained soils and can be some of the most agriculturally productive soil available. General soil map units on the hillsides typically include the Moody-Nora and Nora-Crofton associations (Figure 2). While the soils in these associations are well-suited for crop production in areas where slopes are less than 15%, controlling erosion by wind and water, and conserving moisture are the most important management considerations (USDA 2004).
Figure 2. Typical pattern of soils and parent material in the loess region of Minnehaha County (USDA 2004).
Management Concerns
Based on the management concerns alone, one would assume that no-till farming would be the norm in the region, when in fact the opposite is true and no-till is the exception. The vast majority of crop ground in the loess is tilled with little residue remaining on the surface. We saw several examples where the A horizon (topsoil) had completely eroded from the hill’s summits and shoulders into the lower elevations and filled the drainage ways. There are even instances where the subsoil (B horizon) is now eroding and covering the previously eroded topsoil (Figure 3). These are not sustainable practices and could mean considerable loss of production within a generation if continued.
Figure 3. Soil probe sample taken within a drainage in the loess region of Minnehaha County. Subsoil erosion (B horizon) covering up topsoil (A horizon).
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