Soils of which territories of Southeast Asia are especially fertile? Why?

In Southeast Asia, red earth and lateritic soils predominate, mostly heavily podzolized; tea, coffee and many other plantation crops have been successfully bred on such soils. Very fertile volcanic soils have formed on the slopes and around volcanoes. Alluvial soils in the valleys of large rivers in their middle and lower reaches are also very fertile; these are the main areas of rice cultivation and centers of maximum concentration of the population.