The correct answer is option 4 - Afforestation. Afforestation refers to the process of planting trees on a large scale. It is done to create new forests or to increase the existing forest cover. However, let`s dissect the other options to understand why they are not the correct answer.
Option 1 - Shelter belts: Shelter belts are rows of trees or shrubs planted to provide protection from wind, reduce soil erosion, and create microclimatic conditions. While they do help in preventing soil erosion, they are specifically designed for wind protection, not on a large scale.
Option 2 - Contour ploughing: Contour ploughing is a farming practice that involves ploughing along the contour lines of the land to prevent soil erosion. It helps to reduce the speed of water flow and retain moisture in the soil. While important for soil conservation, it does not involve large-scale tree plantation.
Option 3 - Strip cropping: Strip cropping is a method where different crops are grown in alternate strips. It helps in reducing soil erosion by breaking the surface water flow. Similar to contour ploughing, it does not involve large-scale tree plantation.
Therefore, the correct answer to the given question is option 4 - Afforestation.