Pulling Back the Soil Spatial Variability Caused By Long-Term Cultivation.

Long-term intensive tillage has resulted in high spatial variability in soils throughout the Prairie Pothole Region. Crop yields in these eroded landscapes vary with soil properties. A 6-year study was conducted to determine the feasibility of rehabilitating eroded land by moving topsoil from areas of accumulation (lower slope) to areas of topsoil depletion (upper slope). The impacts of intra-landform soil movement on soil properties, crop production, weed populations, and economic returns were determined in a severely eroded landform. Soil was removed from the lower slope and added to the eroded upper slope (15-20 cm depth). These rehabilitated plots were compared with adjacent plots that remained in their eroded (undisturbed) condition. Surface soil organic carbon contents were increased by a factor of 3 in areas of soil addition, with concomitant increases in water infiltration, water availability, and nutrients. Yield in areas of soil addition were 20 to 60% higher than those in eroded plots, providing increased returns of $40 to $230/acre/year (calculated based on local grain prices at the time of harvest). The lower slope is characterized by ~50 cm of accumulated topsoil atop the original A horizon. Soil physical and chemical properties were relatively unchanged by soil removal, but soil fungi and bacteria counts were decreased. In areas of soil removal, yield was reduced by 20-40%; this is at least partially an artifact of the plot layout. Plots are located adjacent to each other, and surface water sheds from undisturbed plots to neighboring rehabilitated plots, causing excessive moisture in areas of soil removal. This multi-year study shows that replacing translocated topsoil can improve soil properties and crop yields in eroded areas, but areas of soil removal must be managed to avoid unacceptable yield reductions.