HUMIFICATION DEGREE OF SOIL HUMIC ACIDS DETERMINED BY FLUORESCENCE SPECTROSCOPY
作者:
Débora M. Milori,
Ladislau Martin-Neto,
Cimélio Bayer,
João Mielniczuk,
Vanderlei Bagnato,
期刊:
Soil Science
(OVID Available online 2002)
卷期:
Volume 167,
issue 11
页码: 739-749
ISSN:0038-075X
年代: 2002
出版商: OVID
关键词: Soil humic acids;humification degree;electron spin resonance;semiquinone free radical;fluorescence spectroscopy;soil tillage;soil organic matter stability
数据来源: OVID
摘要:
The humification process increases semiquinone-type free radical concentrations (SFRC) in humus. Their quantification by electron spin resonance spectroscopy (ESR) has been a good indicator of the degree of humification of soil organic matter. As an alternative to relatively complex and expensive ESR spectroscopy, fluorescence spectroscopy was used in this study to evaluate the humification degree of 18 humic acids (HA) extracted from four Brazilian soils under different land use, tillage, or cropping systems. Two fluorescence humification indexes of HA were calculated based on work done byZsolnay et al. and Kalbitz et al. in 1999, and a third new fluorescence index was proposed. Our proposal is to use the blue wavelength (465 nm) as the HA fluorescence excitation source. As this wavelength is more resonant with the humificated groups present in soil HA samples, our hypothesis is that the resultant fluorescence will provide information about these structures and, therefore, on the degree of humification of the HA. The SFRC varied from 1.90 × 1017to 14.75 × 1017spins/g HA, characterizing a wide range of the degree of humification of soil HA. The lowest SFRC occurred in native forests (1.90 × 1017to 7.50 × 1017spins/g HA) and pasture soils (2.30 × 1017to 4.64 × 1017spins/g HA). In cultivated sites, soil HAs from no-tillage soil were less humified (2.41 × 1017to 13.30 × 1017spins/g HA) than those in conventionally tilled soil (5.68 to 14.75 × 1017spins/g HA). The three fluorescence indexes show the same tendency as SFRC. Our fluorescence method was closely related to procedures found in the works of Zsolnay et al. and Kalbitz et al. (R∼0.9, P < 0.0001) and with SFRC (R∼0.85, P < 0.02), showing their potential as a simple and sensitive technique for evaluating the effect of land use and soil management systems on the humification degree of soil humic acids.
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