Influence of land use on soil quality and stratification ratios under agro-silvo-pastoral Mediterranean management systems

•SOC and TN concentrations and stocks were evaluated.•The stratification ratios of SOC and TN in different land uses were studied.•Land uses at low cropping intensity have higher stratification ratios.•Microbial biomass and microbial quotient were in agreement with stratification ratios.•Optimum values of C:N were found in land uses at low cropping intensity. A case study from north-eastern Sardinia (Italy) in semiarid conditions is presented. Agriculture is mainly extensive and markedly agro-silvo-pastoral, and is typical of similar areas of the Mediterranean basin. The following land uses at different levels of crop intensification were considered: tilled vineyard (TV), no-tilled grassed vineyard (GV), hay crop and pasture with sparse cork oaks (HC and PA), semi-natural systems (SN, former vineyards set-aside about 30 years ago), cork oak forest (Quercus suber L.) established in the past century (CO). Some soil quality parameters were considered: soil organic carbon (SOC) and total N (TN) concentrations, stocks and their stratification ratios with depth (SRs), microbial biomass carbon (MBC) and its quotient to SOC (qmic), and C:N ratios. Both in terms of concentrations and stocks, SOC and TN were generally higher in HC, PA, CO and SN: in these land uses SOC in the topsoil were in the range 17.0–24.3gkg−1 and 48.9–65.4tha−1; TN values were 1.07–2.08gkg−1 and 3.1–6.0tha−1. SOC and TN SRs under the CO land use were higher than 4, quite above the proposed threshold (≫2), >2 in GV, and ≥2.0 in PA. MBC in mgkg−1 and qmic in μgg−1 were higher under CO (194 and 0.89) and GV (156 and 0.97). C:N ratios had optimum or nearly optimum (9–12) values in CO, PA and the GV, in agreement with the SRs, MBC and qmic. A positive and significant correlation was found between SOC and TN concentrations in all the land uses.