Which of the following is not a way of maintaining soil fertility?

Monocropping is not a way of maintaining soil fertility. Monocropping is a practice of growing only one type of crop on a piece of land repeatedly without rotating it with other crops. This practice can lead to soil degradation and nutrient depletion as the same nutrients are continuously extracted from the soil, and the land is susceptible to soil erosion and pests. On the other hand, cover cropping, manuring, mulching, and mixed farming are all effective ways of maintaining soil fertility. Cover cropping involves planting crops that cover the soil surface, which can help to improve soil structure and fertility, reduce soil erosion, and add organic matter to the soil. Manuring involves adding animal or plant waste to the soil, which can provide nutrients and improve soil structure. Mulching involves adding a layer of organic material to the soil surface, which helps to retain moisture, suppress weed growth, and improve soil fertility. Mixed farming involves growing different crops and/or raising animals on the same piece of land, which can help to maintain soil fertility by reducing soil erosion, diversifying nutrient inputs, and improving soil structure. In summary, while monocropping can lead to soil degradation and nutrient depletion, cover cropping, manuring, mulching, and mixed farming are all effective ways of maintaining soil fertility.