What should be done to maintain soil fertility?

Soil fertility often falls due to its depletion, since the same type of cultivated plants suck out useful elements. For this reason, people in different parts of the world have come up with methods to enrich it since antiquity. In European countries, it was customary to give the land a rest every three years. That is, there is nothing not to plant on it. They also use different fertilizers, both natural and chemical. From natural, which have been used for a long time, animal droppings, burnt vegetation, and so on.