When a patch of land is cleared in a tropical rainforest, the vegetation is often burned to enrich the soil with nutrients from the burned plant material. what description applies to this situation?

This method is called Slash-and-burn agriculture.

Explanation:

This is a farming method which consists on cutting and burning the plants in a forest to create a field for agriculture. The cut trees and plants are left to dry, and the they are burned, resulting in a nutrient rich layer of ash which fertilizes the soil, as well as eliminating weeds and pests temporarily. After 3 to 5 years, the soil is depleted of nutrients, causing the farmers to abandon the field and move to a new area. This technique is not sustainable for large human populations.