Chemistry and clay mineralogy of Thai Natraqualfs

摘要

Thai Natraqualfs including saline-sodic and sodic soils from eight sites on alluvium or wash over residuum derived from clastic sedimentary rock under a tropical savanna climate were investigated. They have a large variation in EC values ranging from0.3 - 60.5 dS/m with variable ESP values ranging from 0.1-31.5% and SAR values ≤ 13. Kaolinite is the dominant mineral in the clay fraction with small amounts of smectite and a trace of illite. Transmission electron microscope (TEM) micrographs of kaolinite show a variety of crystal morphologies including euhedral, subhedral and anhedral platy crystals. Anhedral crystals are abundant in saline-sodic soils and a high proportion of euhedral crystals occur in sodic soils. The median size of kaolinite crystal ranges from 43-69 nm. Morphology and size of kaolinite crystals for these Natraqualfs are statistically related to electrical conductivity and soil pH. Decreasing kaolinite crystal size is associated with increasing soil salinity and exchangeable Na.