How much can regional agri-environmental measures contribute to SOC stocking in the soils of Sicily?

Soils have a great potential in stocking soil organic carbon SOC, but how much can human activities, and particularly agricultural ones, contribute to increase (or decrease) the SOC content? Which kind of agricultural practices are the most effective? From the soil database of Sicily we have selected 52 profiles, whose first 40 cm from the soil surface were analyzed for the SOC, of which 15 analyzed also for nitrogen N content, localized in the clayey hills and limestone marine terraces of the western Sicily, cultivated with grain crops and orchards (mainly olive groves and vineyards), surveyed and analyzed in a period from 1995 to 2008. By interviews to the farmers owners of those parcels, we collected informations about the agricultural practices (tillage, fertilization, rotations, associations and soil protection measures) adopted in the period of the survey, for each of the 52 fields. The adoption of any of the agri-environmental measures promoted by the Region of Sicily was also verified. In the same study area we collected, in 2013 and 2014, samples of the first 40 cm from the soil surface, of 22 parcels cultivated with grain crops, and performed the interviews to the farmers to check the agricultural practices adopted. The samples where analyzed for SOC and N, and also for the humic and fulvic SOC fractions. An analysis of variance was performed. The results demonstrated that reduced tillage practices were the most effective in stocking SOC in soils, especially if associated with other biological farming practices promoted by the regional agri-environmental measures. In fact the SOC and C/N ratio were significantly higher with reduced tillage, associated with biological farming. Instead the SOC, and its humic and fulvic fractions, did not result significantly different comparing biological versus chemical fertilization practices alone. The N content was significantly higher with chemical fertilization.