Assessing 4 per 1000 soil organic carbon storage rates under Mediterranean climate: a comprehensive data analysis

Soil Organic Carbon (SOC) is considered a proxy of soil health, contributing to food production, mitigation, and adaptation to climate change and other ecosystem services. Implementing Recommended Management Practices (RMPs) may increase SOC stocks, contributing to achieve the United Nations Framework Convention on Climate Change 21(st) Conference of the Parties agreements reached in Paris, France. In this framework, the 4 per 1000 initiative invites partners implementing practical actions to reach a SOC stock annual growth of 4 parts per thousand. For the first time, we assessed the achievement of 4 parts per thousand objective in Mediterranean agricultural soils, aiming at (i) analyzing a representative data collection assessing edaphoclimatic variables and SOC stocks from field experiments under different managements in arable and woody crops, (ii) providing evidence on SOC storage potential, (iii) identifying the biophysical and management variables associated with SOC storage, and (iv) recommending a set of mitigation strategies for global change. Average storage rates amounted to 15 and 80Mg Cha(-1)year(-1)x1000 in arable and woody crops, respectively. Results show that application of organic amendments led to significantly higher SOC storage rates than conventional management, with average values about 1.5 times higher in woody than in arable crops (93 vs. 63Mg Cha(-1)year(-1)x1000). Results were influenced by the initial SOC content, experiment duration, soil texture, and climate regime. The relatively lower levels of SOC in Mediterranean soils, and the high surface covered by woody crops, may reflect the high potential of these regions to achieving significant increases in SOC storage at the global scale.