Properties of red Oxisols on calcareous sedimentary rocks in Thailand

S. Tawornpruek, I. Kheoruenromne, A. Suddhiprakarn, Robert Gilkes

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    An analysis of properties of red Oxisols on calcareous sedimentary rocks under different climatic regimes in Thailand was carried out to ascertain their similarities and differences. These soils are Kandiustox in Northeast Plateau and Kandiudox in Peninsular Thailand and have characteristics typical of highly weathered soils. They are very deep (> 2 in depth), are generally acidic (pH 5-6), clayey, have low cation exchange capacity and negative Delta pH values. Their profile development illustrates some differences being Ap(A)-Bt-Bto for Kandiustox and Ap-Bto or Ap-Bto-Bo for the Kandiudox which can be due to differences in leaching conditions under different moisture regimes and a more favourable natural condition for iron oxide accumulation in the Kandiudox. These soils generally have low bulk densities (0.77-1.36 Mg m(-3)) and low available water for plants (5.0-9.3 wt.%). The fabric of the soils indicates that there are more well rounded micropeds in Kandiudox than in Kandiustox and the sizes of microaggregates in these soils are somewhat different ranging from 10 to 1000 mu m in Kandiustox and 50-1400 mu m in Kandiudox. The iron oxide concentration in microaggregates is more variable in the Kandiudox possibly indicating a more complex pedogenesis in these soils as compared to the Kandiustox. Kaolin, quartz and hematite are the dominant minerals in all these Oxisols. gibbsite and goethite are major minerals only in the Kandiudox and boehmite occurred in only one Kandiudox in tropical rainforest environment. Differences in mineralogy also indicate the influence of parent material composition. Soil properties that relate to soil fertility status particularly organic matter concentration (2.1-34.5 g kg(-1)), available phosphorus (0.-347.5 mg kg(-1)) and available potassium (5-233 mg kg(-1)) are poor and similar for the Kandiustox and Kandiudox profiles. Both groups of Oxisols have low values of cation exchange capacity which is in consistent with the dominance of low activity clays (kaolin, sesquioxides) with the Kandiudox profiles having lower mean CEC (6.7-10.2 cmol kg(-1)) than the Kandiustox (11.5-16.3 cmol kg(-1)) profiles. (c) 2006 Elsevier B.V. All rights reserved.
    Original languageEnglish
    Pages (from-to)477-493
    Issue number3/4
    Publication statusPublished - 2006


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