Sandy Soils with Hard Pans
These include sandy soils in which active amorphous material (organic matter and aluminum with or without iron) has been precipitated in the subhorizon. This is designated as the spodic horizon. Under c matter content. This in turn overlies a white or light gray, strongly leached, A2 horizon gradin natural vegetation; they usually develop a thick dark surface horizon that is relatively high in organiginto a dark brown or dark reddish brown illuvial horizon or spodic horizon which commonly occurs within 1 m from the soil surface. The thickness of the spodic horizon is variable but generally ranges from 20 to 50 cm. The underlying material consists mainly of brown sand or grayish brown sand with mottles in places. It should be noted that the degree of cementation in the spodic horizon may vary from weakly to strongly cemented. But on average, they are strongly cemented.
The major constraints for agronomic production of these soils are acute nutrient deficiency, severe moisture stress, and being subject to ponding during the peak of the rainy season. Therefore, currently, these soils have low agricultural potential. However, patches have been opened for the cultivation of certain crops such as pineapple, vegetables, cashew nut, and coconut. Of these, pineapple and cashew nut yields are satisfactory, provided that organic residue and fertilizers have been applied. Coconuts grown on these soils, in general, are very poor and show distinct symptoms of nutrient deficiency. Pasture development on these soils can be one of the better uses. However, it needs practical fertilization for fertility amendments. Fast growing trees like Acacia spp., Casuarina and Eucalyptus with improved grasses (intercropped) are also recommended for agroforestry. In southern Thailand, a native hardwood named ‘Fragrea fragans’ (ตำเสา in Thai) can be an attractive source of income for farmers.