What is the advantage of two-field and three-field over fallow and slash-and-burn system?

Earlier, the ancient Slavs used the type of agriculture – fallow and slash-and-burn. The fallow assumed that the depleted soil was left on for 10-15 years. During this time, young trees grew on it, and it was completely overgrown with grass. With a slash-and-burn field, they prepared as follows: first, they cut down trees and uprooted the roots, in the second year they burned them, in the third year, they sowed wheat in the soil fertilized with ash. This type of farming gave a good harvest for several years, then the soil was depleted, and it was no longer used.

The slash-and-burn system and the fallow were very laborious, almost all the time people hunted to prepare the land, and as it was unusable, they were looking for other areas for sowing.

Three-field and two-field assumes that the field is used once every two or three years. During the rest, the soil managed to recover and again gave a good harvest.