Properties and Landscape Relationship of Skeletal Soils in Upper Northeast, Thailand

Abstract

A study on properties and landscape relationship of skeletal soils in Upper Northeast, Thailand was conducted on six representative areas of a broad topographic sequence ranging between 250 to 160 meters above mean sea level (MSL).Field check and pedon analysis approach were used to identify soils and their landscape positions. Soil samples were collected from soil genetic horizons of each pedon. Laboratory analysis was carried out using standard techniques in soil analysis emphasizing physical, Chemical and mineralogical properties of the soils. Results of field and laboratory analyses revealed that these skeletal soils generally have poor physio-chemical properties. Their mineralogical composition does neither promote their exchange activity nor their fertility sufficiently, and coarse fragments in most of the soils are lateritic gravels. Generally, these soils have dense gravel zone in their profiles at a shallow depth and some of them also have plinthite or hardened plinthite layer(s) in their subsoil. Root restricting layers in these soils are both layers with abundant gravels and the semi-hardened or hardened plinthite layers. Their profile features vary with their topographic position and characteristics of terrain they occupy. The accumulation of gravels in the soils and the thickness of soils above the plinthite layers indicate seriousness of erosion of the landscape. Their position on landscape ranges from hillslope where skeletal meterials are mostly ferruginous rock fragments down to depression in low erosional terrace region where lateritic gravels dominate the dense gravel zone. The presence of gravels and plinthite layers of various nature in their profiles and their generally poor chemical properties clearly restrict their effective uses for upland field crop cultivation. However, they can be used for tree crop and paddy rice cultivation successfully with proper current soil management practices.