Option 1: Mulching is a method of covering the soil with a layer of organic or inorganic materials to conserve moisture and suppress weed growth. It does not involve building barriers or collecting water.

Option 2: Contour barriers are barriers constructed along the contour lines of a slope. They help to slow down the flow of water and prevent erosion by trapping sediment. Trenches are also made in front of the barriers to collect water, reducing runoff and allowing it to infiltrate into the soil.

Option 3: Rock dams are structures made of rocks and stones that are used to control the flow of water. However, they are not specifically related to soil conservation or contour barriers.

Option 4: Terrace farming involves constructing flat platforms on sloping terrain to create a series of steps or terraces. While terrace farming helps with soil conservation by reducing soil erosion, it does not involve the construction of barriers or water collection trenches.

The correct answer is option 2, contour barriers, as it accurately describes the method of using barriers and trenches to collect water and prevent erosion along the contour lines of a slope.