Using present and past climosequences to estimate soil organic carbon and related physical quality indicators under future climatic conditions

This research aimed at testing the use of present and past climosequences to estimate soil organic carbon (SOC) and related physical quality indicators under future climatic conditions. The influence of climate on soil features was studied for four combinations of typical Mediterranean soil types and cropping systems, placed along climosequences of the past (P1: 1961-1990), present (P2: 1981-2010) and future (P3: 2021-2050). The four test areas were located in Italy, each one characterized by the same soil typology and cropping system, placed on similar morphological position and parent material, wide enough to cross climatic boundaries. Legacy soil profiles that were sampled in the P1 time-period were re-sampled in 2010-2011, to check for possible variations in soil characteristics. Besides SOC content and stock (C-stock), we examined some physical quality indicators for which the existence of relations with SOC is well-known, namely soil compaction and soil crusting susceptibility, soil erodibility, and soil loss by water erosion.Among several climatic indexes, the de Martonne index (IDM) resulted the most correlated with SOC. The IDM vs. SOC relationship was significant and not different in both P1 and P2 climosequences, highlighting the temporal stability of the relation between climate and SOC content. In the Vertisols of Sicily, cultivated under cereals, the P3 climosequence predicted a SOC reduction of more than 11%. This will lead to an increase of soil erodibility, susceptibility to compaction, and surface crust formation. On the contrary, in the Luvisols under forage crops of the Po Plain, a substantial C-stock increase (28.8%) is expected, with a consequent improvement in soil physical indicators. For the Luvisols under meadows of Sardinia, an increase in erosion of 13.5% is expected, because of increased precipitation volume (7.4%) and aggressiveness. In the Andosols under olive trees of Campania there is a predicted reduction in the C-stock (-6.3%) and an associated increase in soil loss (4.6%), while no marked variation is expected for the other soil physical indicators.We can conclude that climosequences are a useful tool to predict the future dynamics of some soil physical characteristics affected by climate change. C-stock and soil loss by water erosion are expected to change significantly under future climatic conditions, while minor changes are observed for erodibility, compaction and crusting susceptibility, even when SOC variations are significant. In the climosequences, the considered soil physical quality indicators resulted proportionally more affected by the cropping system than by the climate and, within the same cropping system, more variable according to the climate than the time. This outcome confirms the fundamental role of soil physics in controlling the resilience of the soil system to climate change.