Gully growth can be directly related to the increased peak runoff rates of conventionally tilled fields. Residue protects soil from the forces of wind and water that cause soil erosion. Wind erosion will not begin if the soil surface is protected from wind. Once soil begins to blow, particles of sand bounce along the soil surface detaching more particles on each impact. While wind erosion is very visible, it accounts for only a small percentage of total erosion in Iowa.
Water erosion causes the majority of production loss and off-site damage in Iowa.
When conservation tillage practices are adopted, soil erosion is reduced by protecting the soil surface from rain drop energy that detaches soil particles from the soil surface. Residue left on the surface also creates small dams that store water so it can be absorbed by the soil at a later time. These small dams slow runoff and thus reduce the amount of soil the runoff carries. The effects of water erosion are reduced yields from the land and pollution of water with sediments. Conservation tillage can reduce the impacts of both by keeping the soil on the land and out of the water.