Because of this increased concentration, regrowth of plants is minimal, leading to increased erosion, which leads to a decrease in the fertile topsoil, leading to even less regrowth.
Afterwards during the season of subsidence, the water would subside, or recede, revealing a new layer of fertile black silt and allowing for the planting of various crops.
The part of the immigrant who moves out still stays in colonizing area newly after turmoil area restores advantageous circumstances, and from diffusing toward poor Da field fertile.
Advanced biofuels from cellulosic material - plant waste and wood - are better, because they don't compete directly with food, but they still need reasonably fertile land in which to grow.
For centuries, the annual floods of the Nile, Tigris, and Euphrates, for example, have brought fertile silts and water to the inhabitants of their lower valleys.