How To Measure Soil Carbon

The IPCC special report titled Land Use, Land Use Change and Forestry (Watson et al., 2000) notes that the inability to accurately measure changes in soil carbon at low cost is a major impediment for carbon sequestration projects. It is equally applicable to projects related to the Clean Development Mechanism (CDM) in Article 12 of the Kyoto Protocol. Soil carbon has enormous spatial variability and accurate measurement requires the collection of multiple soil samples at different times, as well as laboratory analyses to obtain estimate of changes in soil carbon. Based on extensive sampling in Africa, Shepherd and Walsh (2002) have developed a promising approach that estimates several soil properties simultaneously using diffuse reflectance spectroscopy in rapid nondestructive ways. The measurement of soil carbon, as well as other soil properties, can be predicted using soil reflectance spectra with accuracy similar to that of duplicate laboratory determinations.

Because this spectral technique allows large numbers of samples to be quickly analyzed, it can be used to thoroughly characterize the soil and its spatial variability within a CDM project. The problem of large spatial variability in soil carbon determinations is addressed by making many measurements, each of which only takes nanoseconds. By returning to the same site at a later date, it is possible to quantify the amounts of soil carbon sequestered or released consistent with CDM verification requirements. This technique can use spectral bands from satellite imagery, thus permitting remote sensing analysis (Shepherd and Walsh, 2002).

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