For any sustainable system of agriculture, soil fertility must be the basis. To understand the role of soil fertility in sustainable agriculture, one must look at the wheel of life. In nature, everything is related to one another. If one simply siims at producing the highest yield, it may be possible somehow for a short time, but in the long run, it will be counter-productive. We have seen this in our Green Revolution period, wherein the wheel of life was not followed. The growth and decay is the wheel of life, where one functions as the counterpart of the other.

In organic farming, more attention is given to building the humus in soil rather than working out the nutrient requirement of individual crops and therefore, this chapter deals not just with the package of nutrient requirement of different crops but also discusses the process of building the soil for better nourishment of crops.

The well-decomposed organic material in soil is called humus. Humus is the end product of the decomposition of organic matter. It is not a food for organisms. It holds some essential nutrients and releases them slowly to plants. It is also capable of holding harmful chemicals and prevents them from causing damage to the plant. Humus helps to retain water in light sandy soil and lessens the compaction problem in heavy soil.