Chemical Alterations of Tropical Peat Soils Determined by Waksman's Proximate Analysis and Properties of Humic Acids

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The objective of this study is to analyze the chemical characteristics of tropical peat soils under natural swamp forest and their changes after reclamation. Peat soils were sampled from coastal swamps in southern Thailand and southern Peninsular Malaysia. These soils were at various stages of reclamation. The contents of water-soluble constituents in plant materials such as polysaccharides, tannins, and hemicellulose decreased with the soil depth due to leaching from subsoils below the water table. In the surface soil, readily decomposable organic constituents, namely polysaccharides, tannins, hemicellulose, and cellulose were decomposed and converted into humic acids during the first 5 y of reclamation. The humification degree of the newly formed humic acids increased in the succeeding 10 y of reclamation. Multiple regression of the pyrophosphate index, which reflects the decomposition stages of peat soils, and some other variables for their relevant characters were computed. Decreasing amounts of cellulose and lignin and increasing amounts of humic acids were found to be suitable variables for expressing the humification processes (r^2= 0.82). As a result of an NMR study, humic acids of tropical peat were considered to have long aliphatic chains, because they are likely to be partially derived from aquatic algae.
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