Carbon Speciation and isotopic characterization of agricultural terrains from distinct pedoclimatic settings of the Emilia Romagna Region (Northern Italy)

The presented study is in the framework of the project SaveSOC2, promoted by the Emilia-Romagna region in order to understand and mitigate the Soil Organic Matter (SOM) deterioration processes. EA-IRMS analyses have been carried out at the University of Ferrara following the method recently defined by Natali et al. (2018), properly designed to characterize from the elemental and isotopic point of view the distinct inorganic (TIC) and organic (TOC) soil carbon pools. Results have been cross-checked those obtained by calcimetric and thermogravimetric analyses performed at the University of Bologna, showing a very good agreement both for TIC and TOC. Total carbon (TC, and nitrogen TN), TIC and TOC are primarily related to the parent material and to the depositional facies, and are therefore correlated with textural and mineralogical features. The differences among the relative amount (wt%) of TIC and TOC, and the associated isotopic compositions (δ13CTIC and δ13CTOC in ‰, respect to the V-PDB standard) in topsoils (20-30 cm depth) and subsoils (90-110 cm depth) have been evaluated to delineate the soil carbon pools evolution along the soil profile. It is generally observed a progressive TOC depletion and δ13CTOC enrichment with depth, which indicates microbial reworking and mineralization processes. The reverse is observed only in peaty and clayey soils, where organic carbon increase with depth and the associated δ13CTOC value systematically decrease, indicating that microbial activity has been inhibited, possibly as a result of waterlogging and/or reducing conditions. In this case, the surface depletion of SOM is possibly related to loss of organic compounds by oxidative processes that are favored by intensive agricultural activities. The recorded levels of organic carbon will be compared with historical data available for some of the investigated areas since 1938, in order to evaluate organic losses in the last eighty years, and the associated potential GHG contribution to the atmosphere. The results of the project SaveSOC2 will be transferred to the actively involved local farmers, since the final goal of the project is the definition of “best practices” reconciling farm productivity and environmental sustainability.