Not all farmlands are created equal — some are flat, some are on a moderate slope, and some are hilly. On hilly agricultural landscapes, soil erosion can be a significant problem because soil properties and crop yields can vary throughout the field and often reflect the pattern of soil movement, resulting from the combined erosive effects of tillage and water.
“Soil erosion is estimated to result in losses of about $44 billion each year in the United States alone, with similar losses throughout the world,” said Sharon Schneider, Research Leader at the Integrated Cropping Systems Research Unit in Brookings, SD. “A large portion of that cost is due to decreased soil productivity.”
Over time, and exasperated by extreme climate conditions, nutrient-rich topsoil will naturally move downward on a farm. Consequently, elevated slopes on a hill may be depleted of soil organic matter, plant-essential nutrients, and available water. These areas are typically low-yielding, especially in dry years. Conversely, lower elevated slopes tend to have deep topsoil accumulation, with soils high in organic matter and nutrients, making them high-yielding in dry years but low-yielding in years with excess moisture. When it comes to yields, growers want consistency, but this can be a challenge on a farm with varying elevation levels.
“We need to restore the productivity of eroded land without undermining the productivity of ‘good’ soils,” said Schneider. “One intuitive method to achieve this is to reverse the soil erosion process by moving soil from where it accumulates to areas where it was lost.”
Schneider and her research team wanted to see if they could improve the productivity of eroded land by replacing translocated topsoil. Researchers moved 6-8 inches of deposited topsoil from the lower slopes to the upper slopes, where soil erosion has reduced the amount of topsoil present. Soil was moved in three plots, and three other plots remained in their eroded condition for comparison.
On the upper slope, researchers found that surface soils in areas of soil addition had 2-3 times higher organic carbon and higher nutrients, water content and other properties compared with areas with no soil added. As a result, corn yields were 21-53 percent higher and soybean yields were 12-59 percent higher in areas of soil addition, with the largest yield increases observed in the most eroded landscape positions.
“These yield increases were achieved with no increase in the number of plants and no additional inputs,” Schneider said. “Adding soil also increased soil organic carbon and increased plant-essential nutrients, water infiltration, and other soil properties that affect productivity. Adding topsoil restored the productivity of the upper slope so that crop yields were consistent from the top to the bottom of the slope.”
On the lower slope, which had a deep accumulation of topsoil, removing 15-20 cm of soil did not result in a large change in most soil properties. However, corn and soybean yields were lower where soil was removed. The largest yield reduction was in the lowest landscape position, which was affected by excessive moisture in wet years.
“In our studies, we can say that areas of soil removal had high water content and low microbial populations compared to areas with no soil removed,” Schneider said. “In wet years, crop yields were decreased in areas of soil removal. The differences might partially be an artifact of the experimental design, where plots were situated side-by-side so water moved to the small-scale depressions we created when we removed soil.”
In light of this research, Schneider recommended that growers consider soil-landscape rehabilitation for their most highly eroded acres.
“This is a really targeted approach,” Schneider added. “Lots of factors will be at play, including their capabilities to move soil, and the distance between the source of soil and where they want to place it. Landowners could potentially reduce costs by coupling this with other soil-moving operations like cleaning out drainage ways, which would have no negative implications on crop yields in areas of soil removal.”
For more information on this study, check out the published articles below:
Crop Responses to Topsoil Replacement Within Eroded Landscapes
Key Soil Properties and Their Relationship With Crop Yields as Affected by Soil-Landscape Rehabilitation
Soil Properties and Productivity as Affected by Topsoil Movement Within an Eroded Landform
Soil-Landscape Rehabilitation with Dr. Sharon Schneider