The National Soil Erosion Research Laboratory
Contouring entails performing all tillage and planting of crops on or near the same elevation or "contour." It is applicable on relatively short slopes up to about 8 percent steepness with fairly stable soils. By planting across the slope, rather than up and down a hill, the contour ridges slow or stop the downhill flow of water. Water is held in between these contours, thus reducing water erosion and increasing soil moisture. Contouring's impact on annual soil loss rates vary with slope steepness, but typically it's reduced about one half from up - and - down hill farming when the slope is between 4 and 7 percent.