cultivation is an agricultural system in which plots of land are
cultivated temporarily, then abandoned and allowed to revert to their
natural vegetation while the cultivator moves on to another plot.
When you cultivate a crop the plants take some nutrients out of the
soil, and put some into the soil. Shifting cultivation helps to keep a
good amount of diverse nutrients in the soil.
One crop might take all of the nitrates out of the soil so after a year
or two you have no nitrates in that area and the plant will not grow
well. This is when you would either leave that area alone for a few
years or plant a crop that puts nitrates back into the soil. Crop
rotation is key in large-scale, long term operations.