116. Two major concerns regarding land-based C sequestration are the issues of: (i) measuring C pool and flux over the landscape and regional scales, and (ii) permanence. It is argued that data on soil C based on point-scale measurements are expensive and highly variable, and that sequestration may not last forever because the C may either be re-emitted or require additional inputs to maintain the practices that keep it sequestered. These are relevant concerns which must be addressed objectively. Several innovative techniques have been developed to assess soil C through field (in situ) measurements by using laser-induced breakdown spectroscopy (LIBS) (Ebinger et al., 2006), rapid analyses of soil samples by spectroscopic methods (Reeves et al., 2002), and by non-invasive and tractor-mounted techniques used over a landscape based on inelastic neutron scattering (INS) principles (Wielopolski et al. 2000). Increasing attention is also being paid to near-infrared reflectance (NIR) spectroscopy for the rapid and cost-effective determination of soil C and N concentrations (Shephard and Walsh, 2002; Brunet et al., 2008). West et al. (2007) described a C accounting framework that can estimate C dynamics and net emissions associated with changes in land management on a regional scale (i.e., Midwest U.S.A). This technique integrates field measurements, inventory data and remote sensing products to estimate changes in soil C and estimates where these changes are likely to occur at a sub-county resolution. Credible techniques based on ∂13C analyses are also available to determine SOC stability (permanence), turnover and source of C (Clay et al., 2007). There are also thermi-gravimetry methods to distinguish between fossil C (coal-derived C) and recent organic C (Maharaj et al., 2007).
