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Why were fields left fallow in slash-and-burn agriculture?

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Map of Mesoamerica showing the geographic distribution of various Indigenous peoples, with regions labeled for groups such as the Maya, Nahua, Zapotec, Mixtec, Otomi, Mazahua, Huastec, Tarasco, and others across present-day Mexico and parts of Central America. Boundaries indicate the approximate areas inhabited by each group. — Mesoamerican Indian Distribution of Meso-American Indians.

In slash-and-burn agriculture, fields are left fallow to allow the land to recover its natural fertility and vegetation after a period of cultivation.12

Farmers typically abandon a plot for several reasons:
* Soil Exhaustion: Over time, the nutrients in the soil are depleted, leading to a decline in fertility.12
* Weed Encroachment: Fields often become overrun by weeds, making continued cultivation difficult.12

By leaving the land fallow, the area is allowed to revert to a secondary forest or bush. This traditional practice is a sustainable adaptation to tropical environments, as it enables the soil to regenerate naturally without the need for synthetic fertilizers. After a period of recovery—often around a decade—the site can be cleared and used again.12