Ye Wei;Wen QiXiao;Ye W;Wen QX

;Institute of Soil Science, Academia Sinica, Nanjing 210008, China.

characteristics montmorillonite kaolinite humic acids;fulvic acids;land use;humification paddy soils;upland soils;minerals clay minerals;soil organic matter;humus composition china

Chemical characteristics of humic substances in soils with different mineralogical characteristics and under different utilization patterns in Fujian Province, China, together with two pairs of cultivated soils in the North China Plain were studiedby chemical analysis, visible IR spectroscopy and 13C NMR spectrometry. For soils in Fujian the HA:FA ratio and both the aromaticity and the degree of humification of HA were higher in soils with montmorillonite as the predominant clay mineral than in those with kaolinite as the predominant clay mineral, provided these soils were under the same utilization pattern. For pairs of soils with similar mineralogical characteristics the HA:FA ratio was higher and the C:H ratio and the content of carboxyl groupof HA were lower in paddy soils than in upland soils. Among the upland soils and paddy soils studied the HA:FA ratio of soil in Fujian with kaolinite as the predominant clay mineral was the lowest, whilst the soil with montmorillonite as the predominantclay mineral was the highest. The presence of montmorillonite favoured the formation and maturation of humic acid.