answer:Very complicated topic and you need to narrow it to a time period and a people. The parts in Exodus which direct farmers to let land lie fallow every 7th year seem to indicate basically a welfare program for widows, orphans and criminals, who could sneak on to your land and feed themselves. In my studies, American Indigenous people would farm land until they reached a point of diminishing returns, then abandon farmland and burn new areas of forest for farmlands in a semi-nomadic existence. Nitrogen can be burned from the soil due to agriculture, but different crops can fix nitrogen from the air. My understanding is modern fallow practices are based on the use of domesticated clover to fix nitrogen into the soil in off periods, which is a far better method than the use of pea and bean crops previously. Of course, modern fertilizers make the whole thing moot.