In most of Southeast Asia, the soil is poor. What causes the soil in the same areas to be ricker and more productive? With mostly poor soil why does plant growth remain strong throughout most Southeast Asia?

Most of the soil used for agriculture in Southeast Asia is a soil that was once part of a dense tropical forest. This soils are very rich in nutrients, but they weather very fast as well when the forest is cleaned out and they are on an open space, so they are fertile for just few years. In the same area we also have soils that are rich and fertile all the time, these soils are along the banks of the bigger rivers. This rivers flood their surrounding areas every year so enrich the soil, thus making it a fertile alluvial soil. Plant growth still remains strong because there are enough alluvial soils, but most importantly most of the plants that are grown here do not require rich soils to grow and prosper.