Abstract
A geochemistry study was carried out on 248 samples from 28 pedons of salt-affected soils (Natraqualfs) formed on alluvial and wash deposits over salt-bearing rocks in five transects in the Khorat basin, Northeast Thailand, under tropical savanna climate to determine if salinization had affected the chemical properties of the soils. This project had the objective of providing the more detailed information needed to improve agricultural practices in the area. The soils were saline sodic, sodic, and acid saline sodic with halite in salt crusts and calcite in the lower part of some soil profiles. Smectite was a minor constituent of these kaolinitic soils and was more abundant in saline soils where it may have crystallized from soil solution or derived from underlying saline rocks. The chemical composition of the soils was highly diverse caused mostly by variation in texture of parent materials rather than the effects of salinity. Plots of geochemical factor scores and textural properties versus depth showed clear evidence of depositional layering in many profiles. Five main chemical affinity groups may be recognized; Group 1 consisted of elements associated with clay minerals and oxides: Al, Ga, Cs, Sr, Fe, U, Pb, Rb, V, Be, and Zn; Group 2 consisted of sand, Si, Mo, and Cr; Group 3 consisted of pH in water and pH in KCl; group 4 reflected biological activity and consisted of S, organic carbon, and N; and group 5, composed of electrical conductivity, Na, Cl, Br, and I, represented the only distinct effect of salinity on soil composition. The higher percentages that could be explained by the two factors of the low electrical conductivity and low exchangeable sodium percentage samples indicated well the difference between the salt-affected soils and the adjacent nonsalt-affected soils in the total set of samples. They also indicated that the geochemical diversity existing in these soils could at least partially be attributed to the effect of salt in the natural soil system.
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