Consequences of minimum soil tillage on abiotic soil properties and composition of microbial communities in a shallow Cambisol originated from fluvioglacial deposits

A long-term field experiment was run for 12 years to evaluate the impact of minimum tillage (MT) compared to conventional mouldboard ploughing (CT) on soil chemical, physical and microbial properties in a shallow Cambisol formed over fluvioglacial deposits of Drava river in Slovenia. Significant differences between MT and CT were found in vertical distribution of soil organic C (SOC) and nutrients (total N and plant available potassium); under MT, concentrations decreased from the soil surface to the lower layers, as opposed to CT which maintained rather uniform distribution down to the ploughing depth. MT in comparison with CT also increased the proportion of water-stable 2–4-mm-sized aggregates (80.9 and 61.3 %, respectively), water holding capacity (24.8 and 22.2 %, respectively) and plant available water (13.4 and 10.3 %, respectively) in the upper 0–10-cm soil layer. Bulk density, porosity, the proportion of water-stable 1–2-mm-sized aggregates and infiltration rate showed no significant differences between the tillage treatments. SOC content in the upper 0–10-cm soil layer was not significantly different between MT and CT (1.60 ± 0.07 and 1.45 ± 0.05 %, respectively), as well as the overall stock in the investigated soil profile (0–60 cm) remained unaffected (57.4 ± 0.8 and 59.1 ± 2.2 t ha⁻¹, respectively). Microbial biomass, estimated by the total soil DNA, was higher in MT than CT in the 0–10-cm layer. Furthermore, a positive linear dependence of microbial biomass on SOC content was observed. Fingerprinting of bacterial, fungal and archaeal communities indicated that microbial community composition changed by long-term MT, whereas changes in microbial diversity were not detected for any domain. The most pronounced shifts in the composition were found for bacterial communities in the 10–20-cm layer, while the composition of fungal communities slightly changed in the upper 0–10 cm of MT soil. The composition of archaeal communities was not affected by the tillage or by the soil depth. Our results indicate that MT generates modest changes in soil structure and soil water retention properties and could support measures against erosion, drought and nutrient leaching. Considering increased microbial biomass in the topsoil of MT and shifts in microbial diversity, the impacts of MT on soil microbiome are also evident and need to be further investigated to identify the affected functional traits.