This work was a collaborative effort between Dr. Sharon Papiernik, (a Research Soil Scientist with the USDA-ARS North Central Agricultural Research Laboratory (NCARL) in Brookings, SD), Thomas Schumacher (SDSU, retired), David Lobb (University of Manitoba), and Michael Lindstrom (USDA-ARS in Morris, MN, deceased).
Tillage as a source of erosion
Tillage erosion is the downslope movement of soil by tillage. During tillage, soil is lifted and gravity moves soil downslope. Soil movement by tillage increases with slope steepness. However, net soil transport by tillage is determined by the change in slope. Soil movement by tillage very slowly levels the land surface. Soil is removed from areas where slope is increasing (convex) and deposited in areas where slope is decreasing (concave).
Unlike water erosion, tillage erosion is not strongly affected by slope length. Therefore, in hilly regions that have many changes in slope, tillage erosion can be the dominant erosive force. This applies in the eastern Dakotas, western Minnesota, and throughout the Prairie Pothole Region.
Conditions that influence tillage erosion
Tillage erosion is greatest with frequent, intensive tillage. Soil movement by tillage is affected the tillage operation (implement design; depth, speed, and direction of tillage), topography (curvature, change in slope, steepness), and soil properties (bulk density, soil texture).
Any implement that lifts the soil will cause tillage erosion. Some secondary operations are as erosive as primary tillage operations.
|Tillage implement||Tillage erosion coefficient (kg per m)|
|Light cultivator + air seeder||
|Rotary harrow + grass seeder||
|a From Mollinedo, J., MS Thesis, South Dakota State University (2008)|
|b From Li, S., D. A. Lobb, and M. J. Lindstrom, Soil and Tillage Research (2007) 94:164-182.|
|c From Van Muysen, W. and G. Govers, Soil and Tillage Research (2002) 65:185-191.|
Soil changes resulting from tillage erosion
Tillage erosion degrades soil quality in upper slope positions. The additive effect of years of combined tillage, water, and wind erosion is shallow topsoil in the upper slope (sometimes with exposed subsoil) and deep topsoil accumulation in depressions.
Erosion changes soil organic matter content, soil texture, water holding capacity, nutrient availability, aeration, pH, and other soil properties that affect productivity.
Above: Map of carbonate content in surface soils in a portion of a field in west central Minnesota. In our region, subsoils tend to be high in carbonate. High carbonate content in the upper slope indicates soil removal by erosion to the extent that subsoil is mixed into the surface soil. Carbonate is low in areas of soil accumulation by erosion. Soil removal is highest in the shoulder slope (where the slope breaks). This pattern of soil properties is typical of a landform in which tillage erosion is the dominant erosive force.
Above: Photograph of the portion of the field represented in the map above. Because subsoil is high in carbonates and light in color, the effects of tillage erosion are easily seen in this field.
Productivity changes resulting from tillage erosion
Tillage erosion depletes crop yield in areas of soil loss. In our studies, plant growth and yield was linked to changes in soil properties induced by soil movement by tillage.
We measured yield in an eroded prairie landscape for 4 years (3 years of wheat, 1 year of soybean) and found that grain yields in the most eroded portions of the field were consistently less than half of the yield in non-eroded areas.
Above: Grain yield was lowest in areas affected by soil removal by erosion and highest in areas of soil accumulation. This trend was consistent through 4 years of yield monitoring. Note the similarities between the yield map and the soil map above.
Effects on management
In the eastern Dakotas and western Minnesota, long-term tillage has increased the land area with poor-quality topsoil. Crop yields on eroded land reflect soil properties. Approaches to reduce the effects of soil erosion on productivity are being investigated, including precision agriculture and targeted application of manure and other soil amendments.
The Agricultural Research Service is the chief intramural scientific research agency of the U.S. Department of Agriculture. The NCARL in Brookings, the only ARS facility in South Dakota, is one of the nation’s premier agricultural research laboratories. They develop integrated crop and pest management practices that enhance soil fertility and conservation, improve water availability and quality, increase biodiversity, and reduce insect and weed populations.