Soil organic matter characteristics, biochemical activity and antioxidant capacity in Mediterranean land use systems

The characteristics of soil quality were measured in adjacent agricultural (horticultural cropping sequence, HC), native grassland (naturally grazed, NG) and forest (indigenous wood of holm-oak, F) soils. The objective of the research was to assess the influence of different land uses on soil organic matter characteristics, biochemical activity and antioxidant capacity in selected fields of the Mediterranean environment in central Italy under a specific climatic regime. Land use induced significant changes in the content and quality of soil organic matter, biochemical activity and antioxidant capacity, with more pronounced differences between soils under HC and F than soils under HC and NG. The HC soil showed the lowest amounts of total organic carbon (TOC), microbial biomass C (MB-C), water-soluble organic C (WSOC), water- and alkali-soluble phenols. The organic matter of HC was characterized by the lowest percentage of MB-C and of light fraction carbon (LF-C). The dehydrogenase activity (DH-ase), metabolic potential (MP), hydrolyzing coefficient (HyC), potentially mineralizable C (C0) and C mineralized (Cm) were clearly lower in HC. The specific respiration activity of biomass (qCO2) was the highest in HC soil (1.3 mg CO2–C mg biomass C 1 ) and lowest in F soil (0.5 mg CO2–C mg biomass C 1 ) and was inversely related with pH, TOC and MB-C contents. The antioxidant capacity of soils (TEAC) was the highest in NG and related to the amount of alkali-soluble phenols. The rate constant of organic matter mineralization (k) appeared to depend on TEAC rather than the relative amounts of the labile C pools. These results seem to explain the role of phenols as controller of the mineralization rate of organic matter.