Part 1, Section 1: Soil Management
Tillage erosion is a form of erosion that is receiving increased attention. Tillage erosion moves soil from the top of the field downward, exposing subsoil at the crest while burying soil at the bottom. After many years of tillage, topsoil accumulates at the bottom of the slope. If tillage erosion continues, exposed and eroded subsoil from upslope will eventually cover this topsoil at the bottom of the slope. With tillage erosion, no soil has to leave the field, but the effects for productivity and increased yield variability can be very significant. Exposed subsoil has unfavorable properties for crop growth (50 percent yield reduction is not uncommon on clay knobs), but it still takes the same amount of inputs such as seed, fertilizer and herbicides. Because crop growth is poor, the soil is not protected from water erosion, and weeds have a greater chance to become a problem in these areas. Tillage erosion delivers soil from upper slope positions to the lower parts of the slope where water erosion tends to be more important, so tillage erosion tends to reinforce water erosion (Figure 1.1-4).
Unfortunately, many practices that have been promoted to control water erosion do nothing to control tillage erosion. For example, it is suggested that chisel plows cause as much tillage erosion as moldboard plows. Field cultivators can also move substantial amounts of soil. Leaving crop residue at the surface does not control tillage erosion. Narrow contour strips, often promoted on steep slopes to control water erosion, favor tillage erosion because at the top of each strip topsoil is slowly plowed away, exposing subsoil, while soil accumulates at the bottom of each strip. The narrower the strips, the more subsoil can be exposed.
The best solution to control tillage erosion is to eliminate tillage. With the use of continuous no-till systems, tillage erosion can be completely eliminated. If tillage is still part of the crop production system, all unnecessary tillage trips should be eliminated, speed reduced (especially downhill), and tillage tools set to the shallowest depth possible. Down-hill plowing should be avoided. Plowing on the contour causes less tillage erosion, whereas plowing uphill causes the least (although it doesn’t totally eliminate tillage erosion like no-till). It is beneficial to turn soil uphill with contour tillage, but this is practically impossible if slopes exceed 17 percent. Running the tillage tool at constant depth and speed is recommended to limit tillage erosion (so don’t reduce tillage depth or slow down on clay knobs or rock outcroppings). This often means additional horsepower is required to pull the tillage tool, which can result in damage to tillage equipment. The final solution to “solve” tillage erosion is to transport topsoil from depositional areas to hill crests to remediate clay knobs and rock outcroppings.