Black C Effects on the Biogeochemical Cycling of Soil Nutrients and Organic C in Amazonian Dark Earths (Terra Preta De Indo)
Biqing Liang, Graduate Student, Department of Crop and Soil Sciences, Cornell University, 9/21/2006,Crop and Soil Sciences Seminar Series, Cornell University. College of Agriculture and Life Sciences.

Abstract:

Black carbon (BC) was found to increase soil cation exchange capacity and to be a key contributor to the high fertility in Amazonian Dark Earth soils, which are unique compared to other commonly found and poor adjacent soils in the humid tropics. Here we study the mechanisms in which BC is involved in soil nutrient retention and organic C cycling. Novel techniques such as synchrotron-based NEXAFS (Near Edge X-ray Adsorption Fine Structure Spectroscopy), NMR (Nuclear Magnetic Resonance Spectroscopy), Microprobe, coupled with density fractionation after long-term incubation with stable isotope labeled material have been used to study the surface chemical properties of BC (especially C functionality), bulk C quality (aromaticity), C, O and cation elemental distribution within soil aggregates, C distribution and long-term dynamics within aggregates. Our research questions are: i) How stable is BC? ii) How does BC surface properties affect soil organic C and nutrient cycling? and iii) How to discriminate the portion of reactive C functional groups by BC oxidation from contribution from adsorption of non-BC materials? It was found that interior regions of BC particles remain highly aromatic even after 7,000 years of exposure in soils. BC can be oxidized on the surface and absorption of labile organic soil C can occur. Both oxidation and absorption of BC lead to creation of reactive C functional groups and further soil nutrient retention in the soils. Studies of depth profiles allowed us to distinguish between the contribution of either oxidation or absorption. The understanding of the basic chemistry of BC and its effects on soil nutrient retention and organic C cycling provides an important knowledge base for sustainable soil fertility management and improving soil fertility with bio-char applications.
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