The correct answer is: d) All of the above.
Crop rotation is the practice of growing different types of crops in the same field in a planned sequence. This helps to improve soil fertility by preventing the build-up of pests and diseases, and by replenishing nutrients that are used up by the crops.
Mulching is the practice of covering the soil with a layer of organic material, such as straw, leaves, or compost. This helps to improve soil fertility by preventing erosion, retaining moisture, and suppressing weeds.
Green manuring is the practice of growing a crop of plants specifically to be turned into the soil as a green manure. This helps to improve soil fertility by adding organic matter, nutrients, and beneficial microorganisms to the soil.
All of these traditional practices help to improve soil fertility in Punjab.