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Marginal land and problem soil of Thailand


Sandy Soils
               Physiographically, these soils are developed on the beach ridges, slope wash or aeolian sand. The native vegetation grown on beach ridges mainly comprises Casuarina equisetifolia and other low shrubs or grasses where at the peneplain or slope wash, dipterocarps are developed. These soils have little or no prominent horizon other than an A or Ap and C horizon. They are normally sandy throughout the soil profile. The color is variable depending upon ferruginous coatings of quartz residue. They may be brownish, reddish, grayish or whitish in various places. However, beach sand or dune sand, in general, is ‘browner’ than sands on the older landscape. Due to the very high sand content in the profile, they are very low in CEC, organic matter content, basic cations, and available P and K. Thus, they are very low in nutrient status. They also have a low water holding capacity, available moisture content, and a rapid permeability. The groundwater table, if present, is generally below 2 m from the soil surface for most of the year.
               Although these soils have low agricultural potential they have been cultivated for some economic crops. On the coastline where the water table is not too deep, they have been used exclusively for coconut production. In other areas of sandy soils, upland crops such as cassava, pineapple and beans are grown. For better usage, forage crops including improved grass varieties like signal grass together with legumes should be intercropped between coconut rows on the coastal sandy soils. For sandy soils in areas with less rainfall, improved pasture should be developed. Commercial fast growing trees are also suggested.