What is contour farming and how does this help control soil erosion?

Contour farming is the practice of plowing the land following the topography of the land surface. The practice is used in hilly or even mountainous terrain. By plowing following the topography, the land is much more resistant to erosion by creating barriers to the free flow of water down the slope of the hill. This helps keep the topsoil in place, enabling crops to become established and grow.