Saturday, 15 July 2006

Long-Term Oxidation of Biomass-Derived Black Carbon and Effects on Soil Fertility and Organic C Cycling.

Biqing Liang1, Johannes Lehmann1, James Kinyangi1, Dawit Solomon1, Janice Thies1, and Flavio Luiz„o2. (1) Cornell Univ, Bradfield Hall, Ithaca, NY 14853, (2) Instituto Nacional de Pesquisa da Amazonia INPA, Manaus, Brazil

Black C is found enriched in Anthrosols (Terra Preta de Indo), which are adjacent to highly depleted tropical soils. It was hypothesized that BC can significantly contribute to positive charged cations and soil fertility retention and lead to slower cycling of soil organic C. Highly aromatic black C particles were studied by Synchrotron-based FT-IR (Fourier Transform-Infrared spectroscopy in transmission) techniques for surface chemical functional groups after ultra-thinly sectioned. Predominant C=C aromatic-C (1595 cm-1) was observed, conjugated with C=O stretching of mainly carboxyl-C and ketons, ester and quinones (1710-1690, 1630 cm-1). Weak CH3, CH2 (2922-2856 cm-1) peaks showed up with moderate amount of CH2 bending and CH deformation of aliphatic-C (1433, 1393 cm-1). The overall level of oxidation of particulate black C particles were lower compared to Non-black C, which showed up huge peaks at 1115 and 1037 cm-1 indicating OH of carboxyl-C and C-O stretching of polysaccharides. Microprobe coupled with EDS was used to measure the C, O, Cl, and K content on black C thin sections. The outside of black C were found to have higher O to C ratio, which indicated a higher level of oxidation than the inside of the particle. The more abundance of anion Cl and cation K implied the possible strength of Black C to absorb nutrients in the soil, as well as Non-black C materials. Long term incubation experiment verified that the organic C cycled slower in Anthrosols with high black C content than adjacent soils with low black C content by showing significant less soil respiration. We concluded that black C plays an important role in soil nutrients and organic C cycling in Anthrosols.

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