Metal‐humus complexes in A horizons of Thai and Korean red and yellow soils


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Carbon, Al and Fe (Cpyr, Alpyr and Fepyr) were extracted with 0.1 m Na4P2O7 from 26 A horizon samples of tropical Thai and temperate Korean soils (Ultisols, Alfisols, Oxisols and Inceptisols). The soils, except for one Thai Inceptisol, had similar total C (0.35–3.29%) and Cpyr/total C ratios (0.20–0.41). There were approximately linear relationships between total C or Cpyr and clay content; two groups of soils gave different linear relationships. A curvilinear relationship between Cpyr and (Al + Fe)pyr (milli‐atom kg−1) that can be approximated by an equation: Cpyr= 53 (Alpyr+ Fepyr)1/2– 24 was also found for most Thai and Korean soils. The above relationships indicated that total C and Cpyr would be close to zero at zero clay or zero (Al + Fe)pyr. It was inferred that clay‐humus interaction has a primary importance in the determination of humus content in red and yellow soils in tropical and temperate regions and that the main role of clay is to supply Al and Fe that complex and stabilize humus against microbial degradation.

Original languageEnglish
Pages (from-to)529-537
Number of pages9
JournalJournal of Soil Science
Issue number4
Publication statusPublished - Dec 1988

All Science Journal Classification (ASJC) codes

  • Agricultural and Biological Sciences(all)
  • Environmental Science(all)
  • Earth and Planetary Sciences(all)
  • Soil Science


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