Water and soil quality in Mediterranean orchards managed with sustainable or conventional systems

Climate change, in terms of increased temperature and extreme precipitation regimes, will have agricultural consequences due to the interrelations between climate, land and water use, soil degradation and landscape changes. Conservation agriculture offers new chances to mitigate the effects of climate change. In sustainable agro-forestry systems, management practices are able to increase carbon (C) inputs into the soil and possibly reduce GHGs emissions due to some revised field operations (e.g., irrigation techniques, use of recycled water, pest and disease management, fertilization, soil and plant farming systems). Carbon enrichment increases biological activities by improving soil structure, as well as the soil moisture and nutrient contents, that are beneficial to plant growth and production. This study reports results on the effects of changed soil management practices of Mediterranean orchards from conventional management (Cmng: soil tillage, mineral fertilizers, burning of pruning residues) to sustainable management (Smng: no-tillage, pruning residues, cover crop retention, and compost application) on water quality and management, plant microbiota and physiological status, soil microbiota and organic carbon (SOC). Results show that an 18-year period of Smng (including C inputs at a mean rate of 8-9 t C ha-1 year-1) caused increases in SOC concentration (from 1.0-1.3% w/w up to 1.7-2.0% in the topsoil), soil water retention (up to 40% more) and soil permeability (from 13 to 160 mm H2O day-1), so allowing farmers to save irrigation water and improve soil structure. The adoption of a correct irrigation management had a key role in the potential role of orchards in C sequestration (soils become from C sources to C sinks) and in the consequent greenhouse effect mitigation. Indeed, compared to dry areas, wetted soils generally had a higher microbial respiration and SOC mineralization, and a faster bacterial C and N turnover. Finally, the Smng brought beneficial effects on plant yield, that was improved by 30-50%, compared to Cmng. The endogenous C additions had significantly effects on the reserves of soil water and nutrients (N, P, K, Ca, Mg) and on CO2 soil emission. Promoting cost-effective sustainable land use strategies can avoid SOC decline, soil erosion and soil degradation, with consequent benefits in terms of reduced irrigation volumes and higher water quality. This is essential for sustaining and improving plant yield and quality.