Characterization of dissolved organic matter derived from rice straw at different stages of decay

• Published in: Journal of soils and sediments 2010-07, Vol.10 (5), p.915-922
• Main Authors: Chen, Hua-Lin, Zhou, Jiang-Min, Xiao, Bao-Hua
• Format: Article
• Language: English
• Subjects: Carbohydrates; Centrifugation; Chemical composition; Decay; Dissolved organic carbon; Dissolved organic matter; Distilled water; Earth and Environmental Science; Environment; Environmental Physics; Farm management; Fourier transforms; Ismess 2009 • Research Article; Matter & antimatter; Microorganisms; NMR; Nuclear magnetic resonance; Organic chemistry; Reactors; Rice; Rice straw; Soil Science & Conservation; Spectroscopy
• ISSN: 1439-0108; 1614-7480
• DOI: 10.1007/s11368-010-0210-x

Purpose Returning of rice straw into paddy field, which not only can increase the organic carbon content of soil but also can introduce dissolved organic matter (DOM) into soil, is a popular farm management strategy. However, chemical and structural heterogeneities of DOM derived from rice straw are not well characterized. The aim of this paper was to study the chemical and structural characteristics of DOM derived from rice straw at the different stages of decay. Materials and methods A total of ten different DOM samples were obtained from aerobic biodegrading rice straw for ten different incubation times. Glass bottles contained a certain amount of rice straw, quartz sand, inoculum, and distilled water were placed on an incubator. At each time of interval, five replicate reactors were taken from the incubator and each was filled with 60 ml distilled water and shaken. After centrifugation, the supernatant was withdrawn from each replicate reactor and filtered through a 0.45-μm membrane filter. The filtrates were analyzed for chemical and structural characteristics of the DOMs using elemental analyzer, Fourier transform infrared (FTIR) spectroscopy, and 1 H, 13 C-nuclear magnetic resonance spectroscopy. Results and discussion The results showed that the contents of dissolved organic carbon decreased dramatically in the early stage (from day 0 to day 3), then increased nearly linearly till day 63, and finally leveled off at about 22–24 mg g −1 straw (from day 63 to day 180). The FTIR spectroscopy data indicated that the functional groups of the DOM samples were characterized by carboxyl, aliphatic, and aromatic groups. The elemental composition showed that the H/C atomic ratios decreased as a function of decay time, indicating aromaticity of DOM increased with decay time. The 1 H, 13 C-NMR spectra showed that the contents of carbohydrates decreased while the contents of aromatic groups increased as straw decay proceeded, suggesting carbohydrates were consumed faster than aromatic groups by microorganisms. Conclusions Our results indicate that the DOM derived from rice straw are highly heterogeneous in terms of their structural and functional groups, and aromatic groups remain longer than other groups do, suggesting that the aromatic groups represent the stable portion of DOM.