Contour plowing/ploughing conserves soil by following the lay of the land and creating ridges that form a water break to prevent soil erosion. Furrows that do not follow the lay of the land cause rapid runoff during rainfall by forming a convenient channel for the water to flow downhill.
Contour plowing/ploughing was heavily promoted by the U.S. government during the 1930s. In 1935, the Soil Conservation Service was founded in response to the threat of desertification and soil erosion caused by the Dust Bowl. State governments and the Soil Conservation Service worked together to create agriculture programs in universities. These programs helped to educate farmers about soil conservation methods like contour plowing and by 1938, soil loss had been reduced by 65 percent.
In addition to preserving the soil and preventing erosion, contour plowing/ploughing helps cut down fertilizer loss, as well as increasing crop yields by up to 50 percent. Contour farming works best when employed alongside other soil conservation methods like strip-cropping and terrace farming. Strip-cropping is the practice of planting crops in strips and sowing plants like alfalfa in between the strips. The dense root structure of alfalfa helps to keep the soil in place during heavy rainfall. Terracing refers to planting and plowing on multiple tiers of land that resemble graduated steps.