12. Soil Envoronment for Rice Cultivation 1
- INDEX -
Classification of Main Tropical Soils
Oxisol
Ultisol
Alfisol
Inceptisol
Entisol
Vertisol
Aridisol
Histosol
Classification of Main Tropical Soils
The distribution of main tropical soils by continent is shown by Table 4. The soil names are based on the order-level classification code of American Soil Taxonomy, of which Andisol is currently being examined to be included in the order. In the following section, we will outline the main soils from the agricultural standpoint of view based on Hisama.
Oxisol
Distributed most widely throughout the old and stable earth surface of the humid tropical zone.
Developed through severe weathering and leaching. Extremely poor in supplies of nitrogen, phosphoric acid, bases, and easily soluble silicic acid. Weak in holding nutrients and water, and low in organic matter accumulation.
Chemical improvements are absolutely needed for agricultural uses.
Ultisol
Developed through a formation process similar to that of Oxisol, but unique in having an illuvial horizon of clay. Poor in bases. Highly acidic and tends to become exceedingly high in exchangeable aluminum; vulnerable to acidic injury and damage by excess aluminum. Has weaker soil structure compared with Oxisol; easily allows crust formation and soil erosion after heavy rainfall.