Slowing and protecting the surface from water flow is how you prevent soil from washing away. Contour plowing follows the natural outlines of the land, which means runoff moves along the slope rather than straight down. That reduces the speed and erosive energy of the water. Terracing turns a slope into a series of level steps, each acting like a small catchment that traps water and keeps soil in place. Together, these practices dramatically cut soil detachment and promote infiltration, so the soil stays where it belongs even on steeper ground. The other options don’t achieve that protection. Monoculture planting and heavy tillage disrupt soil structure and expose bare soil, increasing erosion. Clear-cutting forest removes the protective canopy and litter that shield soil from raindrop impact, leading to more runoff and erosion. Free drainage solves a water-logging issue but doesn’t address soil surface protection or runoff energy, so it can leave erosion unchecked. So, contour plowing and terracing are the most effective for reducing soil erosion because they directly lessen water speed on the surface and keep soil from being carried away.