Characteristics of skeletal soils on a Toposequence in Sakon Nakhon Basin
1993
Boonma Dee-Saeng
These soils have loamy sand to clay texture and they contain coarse fragments larger than two millimeters throughout their profiles. The amount of coarse fragments in the soils is more than 35 percent by volume in their family control sections. Therefore they are considered shallow soils. Their bulk density is directly related to the amount of coarse fragments present. The thickness of soil layer above the layer of dense coarse fragments tends to increase with the decrease of elevation while the thickness of layers with dense coarse fragments decreases where the elevation decreases. These soils are strongly to mediumly acidic. They have low inherent fertility, very low to low organic matter content and available phosphorus whereas their available potassium values vary from very low to very low to very high. Their cation exchange capacity and base saturation range from low to high. Mineralogically, kaolinite, illite, smectite, vermiculite, chlorite, goethite, gibbsite and quartz are found in their clay fraction but only kaolinite can be considered dominant clay species. Quartz dominates their silt fraction. Other minerals in their silt fraction are goethite, hematite and gibbsite, in a very small amount. These soils can be classified in to five Alfisols and one Ultisols. Based on their fertility and suitability the soils on generally steep slope are poorly suited for economic crops but can be very well suited for forest use to promote nutrient cycling and to reduce erosion problem. Other soils on the uplands are suited for pasture, upland crops and para rubber plantation. Forest plantation of Acacia aurita, Eucalyptus camaldulensis, Casuarin eqisetifolia, Pterocarpus macrocarpus, Tectona grandis should be recommended in these area. However, in lowlands these soils are suited for paddy rice.
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