Estimating carbon credits variations supplied from agricultural and forest soils of Italy between 1979 and 2008.

Soils contain approximately three times the world amount of organic carbon in vegetation and approximately the double of that present in the atmosphere. However, soil organic carbon (SOC) has been found lowering in many areas, while atmospheric CO2 was on increase. It is well known that there is a marked inter-dependence between SOC and climate, nevertheless, recent researches have demonstrated that changes of land use and management can cause gains or losses of SOC greater than climatic changes. Italy, which has joined the Kyoto Protocol, has decided to consider only forest management within the additional activities contemplated for the count of carbon credits, and to launch a monitoring campaign of SOC only in forests. The scope of this research work was to demonstrate that it is possible to estimate carbon credits variations supplied from both agricultural and forest soils of Italy during last the 3 decades (from 1979 to 2008), taking into account changes due to climate change. The soil database of Italy was the main source of information. SOC content was expressed as percentage by weight (dag kg-1) analysed by the Walkley-Black procedure and converted to ISO standard. The CRA - CMA (Research Unit for Climatology and Meteorology Applied to Agriculture) database was the source of information for climatic data. We considered the mean annual temperature and mean value of total annual precipitations of the two periods 1961-1990 and 1991-2006, and we mapped them by regression kriging with elevation and latitude as predictors. The soil organic carbon stock (CS) was calculated referring to the first 50 cm, obtaining a single value for every observation. A series of geographic attributes were used in order to spatialize site information. A linear multiple regression was used to interpolate the values, using the variable CS as target and the geographic attributes as predictive variables. The model also considered the interaction between decade, land use, and climate, to take into account the effect of climatic variables on the SOC content in the different land uses. The SOC variations due to climate change were then subtracted from the total, for the calculation of carbon credits that may be attributed to agricultural and forest management. Carbon credits were calculated following the Emission Trading System (EU-ETS, EU Directive 2003/87/EC), and the exchange rate given by the Carbon Dioxide Emission Allowances Electronic Trading System (SENDECO2) at September 2010.Our results indicate that CS highly correlates with the main groups of land use (forests, pastures, crop lands), as well as with soil humidity and temperature regimes, lithologies, and morphological classes. CS diminished remarkably in the second decade, while slightly recovered between the second and third decade. Climate change influence on SOC content was limited, as a whole, but relatively more pronounced in meadows. The Italian CS passed from 3,32 Pg in 1979- 1988, to 2,74 Pg in 1989-1998, and 2,93 Pg in 1999-2008. The equivalent lost of carbon credits occurred from the first to the second decade totalled some 24,260 M€, while in the following decade carbon credits recovered about 6,921 M€, mainly because of the SOC increase obtained in the arable lands. This study demonstrates the possibility to consider carbon credits from agricultural soils, in addition to forest. Therefore, Italy should extend also to agricultural soils (crop lands and meadows) the current monitoring of SOC for the time of engagement of the Kyoto Protocol.