期刊
GEODERMA
卷 105, 期 1-2, 页码 81-92出版社
ELSEVIER
DOI: 10.1016/S0016-7061(01)00093-3
关键词
semiquinone free radicals; humification degree; aromatic groups; Brazilian soils
类别
Long-term (5- and 9-year) effects were evaluated of two tillage regimes (conventional tillage: CT; and no-tillage: NT) and two cropping systems (oat/maize: O/M; and oat + vetch/maize + cowpea: 0 + V/M + Q on characteristics of humic acids (HAs) from surface layer (0 to 25 nun) of a subtropical Brazilian Paleudult soil. Generally, soil HA samples from conservation management systems with no soil disturbance (NT) and high crop residue addition (0 + V M + C) showed lowest humification degree, as demonstrated by lowest concentration of semiquinone-type free radicals, determined by electron spin resonance (ESR), and lowest total fluorescence (TF), which is proportional to area under fluorescence spectrum; however, cropping systems had less effect than tillage regimes on two spectroscopic parameters. Since all HA samples presented a maximum fluorescence emission peak around 518 nm, when excited with blue light, we believe that differences in the fluorescence intensity could be attributed to concentration of similar condensed aromatic moiety. This assumption was consistent with strong correlation with stable semiquinone-type free radicals (r = 0.84, P < 0.01), which are believed to be stabilized in humic substances by condensed aromatic structures. The results showed positive effects of conservation management systems on soil humus characteristics, which may therefore be used as alternative parameters in evaluating management system quality. (C) 2002 Elsevier Science B.V. All rights reserved.
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