Many of these alluvial sediments have undergone little soil formation. Soil texture varies from medium to fine. It is usually more coarse on natural levees and finer in depressions and back swamps. Although many soils are fertile, problem soils such as acid sulfate and saline soils occur, particularly near coasts. The cropping systems vary depending upon the time, depth, and duration of flooding.
Rice is the only food crop that can be grown during the rainy season.
Most rice varieties can survive complete submergence for only 3 or 4 days, but submergence-tolerant varieties can survive for about 12 days. They are grown during the wet season in rainfed lowland and deepwater areas where flash floods occur. Deepwater and floating rice are sown or transplanted before the floodwaters rise and flower about the time of maximum water depth. Floating rices are those which elongate very rapidly under submergence, sometimes up to 20 cm per day. They are adapted to rapidly rising water and very deeply flooded areas.