Why is it necessary to fertilize cultivated soils

The majority of cultivated soils in Bolivia are low in fertility. In simple terms, the fertility of a soil can be defined as its capacity to produce abundant harvests. Thus, the world fertility implies a series of soil characteristics which include:
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The soil depth, to permit the development of a vigorous root system, as well as its organic matter content and level of nutrients;

A structure which facilitates the circulation of air and water and the capacity to absorb and retain water and nutrients;