Soil Organic Carbon (SOC) is a measure of the total amount of organic carbon (C) in soil, independently of its origin or decomposition. Interest in SOC is common among soil scientists and related practitioners because of the importance for principle physical, chemical and biological soil ecological functions and because SOC is a universal indicator of soil quality. Consequently, as variations in SOC levels can have serious implications on many environmental processes such as soil fertility, erosion and greenhouse gas fluxes, the need to estimate SOC changes has become central to several pan-European and global environmental policies.
At a European level, SOC is considered in many policies and strategies of the European Union (EU). The Sixth Environment Action Programme1 required the European Commission to prepare a Thematic Strategies on Soil Protection. The resulting Communication (COM(2006) 2311, adopted by the European Commission on 22/09/2006) sets out the overall objectives through a proposal for a Framework Directive (COM(2006) 232)1 that establishes common principles for protecting soil functions against a range of threats. One of the key goals of the Strategy is to maintain and improve SOC levels. The Directive is supported by an Impact Assessment (SEC (2006) 11651 and SEC(2006) 6201) that contains an analysis of the economic, social and environmental consequences of the different options for soil protection. The assessment reveals that the cost of not taking any additional action to improve the management of SOC stocks (i.e. maintaining the status quo) were significantly higher than the costs of measures to protect soil.
At the international level, all the various Conventions arising from the 1992 United Nations Conference on Environment and Development in Rio (e.g. Climate Change, Biodiversity and to Combat Desertification) have the issue of SOC levels at their core.
The Kyoto Protocol (UNFCCC, 1998), in particular, allows the use of biospheric carbon sinks and sources originating from human-induced activities to meet the Countries’ commitments of greenhouse gas emissions reduction. These activities, listed in Article 3.3 (afforestation, reforestation and deforestation since 1990) and Article 3.4 (forest management, cropland management, grazing land management, re-vegetation) of the Kyoto Protocol, are collectively named “Land Use, Land-Use Change and Forestry” (LULUCF) activities2. The soil is among the mandatory carbon pools to be reported for these activities under the Kyoto Protocol3 and it is certainly one with the highest potential, both in terms of enhancement of C sink and reduced C emission4. The procedures for estimating changes in SOC under the Kyoto Protocol are described by the International Panel on Climate Change report ‘Good Practice Guidance for LULUCF’ (IPCC, 2003). However, as this document mainly addresses general principles – with a focus on the approaches to be applied at the Country scale depending on the level of methodological complexity (“Tier”) -, a more specific protocol for estimating SOC changes even at the plot level (e.g., agricultural field, pasture or forest stand) would be very useful.