Spectroscopic Evidence for Carbon Stability in Organic Residual-Amended Soils.

Application of organic residuals (e.g. biosolids, composts) to soil may provide an effective method for sequestering carbon (C), but the long term stability of such C is not well known. We investigated a series of field sites across Virginia in 2011 to determine the amounts of C remaining in soils years following amending with biosolids and composts during 1984-2011. Total organic C (TOC) of soils is determined by dry combustion method to reveal C accumulation rate. Pre-treated C fractions are obtained by physical separation methods in order to extract organic C. The development of C-distribution on functional groups in soil C fractions is investigated via solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy with direct-polarization (DP) and magic angle spinning (MAS) and near-edge X-ray absorption spectroscopy (NEXAFS) technique. The results showed that C stocks from the organic residual treatments were significantly higher than the control at a depth of 0-15 cm and increased with organic residuals application rate. The investigation from NMR and synchrotron beam reveals the chemistry of organic amendments that promote soil C stability and lays a foundation for studies on carbon sequestration potential in organic residuals-amended soils. This research provides quantitative and qualitative information about soil C dynamics in soils receiving organic residuals during long term periods.