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Olive cultivation is considered as one of the most significant agricultural activities in Greece, from a financial, social, and ecological point of view. Intensive cultivation practices in combination with the Mediterranean climate, lead to depletion of soil organic matter, erosion, desertification, and degradation of water resources. This paper describes sustainable olive crop management practices that were comparatively applied in 120 olive groves in Greece for 5 years with the participation of three farmers groups. Organic materials recycled in the olive groves during the present study were valuable sources of carbon, nitrogen, phosphorus, and potassium. Carbon content was highest in pruning residue (53.8–54.2%) while all materials studied were considered rich in C ranging between 41.9–46.2% (compost) and 34.9–42.5% (three-phase olive mill waste-OMW). The highest content in nitrogen was detected in compost (2–2.45%) followed by pruning residue (0.93–0.99%) and OMW (0.03–0.1%). Compost was considered a good source of phosphorus (0.3–0.6%) followed by pruning residue (0.08–0.13%) and OMW (0.01–0.3%). Potassium was also considerable in the organic materials recycled ranging 0.5–1.5% in compost followed by pruning residue (0.5–0.7%) and OMW (0.3–1.1%). Adoption of modified pruning also had important contribution toward sustainable management of olive trees. Sustainable pruning resulted in a well-balanced ratio between vegetative growth and fruiting (balanced, every year, in order to eradicate biennial bearing). Significant fluctuation in olive yields was observed in the first years of the project while yields were gradually stabilised by applying sustainable crop management. In parallel, yield increase without additional inputs, lowers the carbon—environmental footprint of the product regarding several environmental impact categories. Results can be integrated in the national agricultural and environmental policy in Mediterranean countries toward the achievement of a circular economy.

In this study, chemical composition and growth responses of chia plants (Salvia hispanica L.) to inoculation with an arbuscular mycorrhiza (AM, Glomus mosseae, Nicol. & Gerd.) fungal inoculum (namely MC10) under the influence of soil pH were investigated. The experiment project included six treatments, i.e., control-non-arbuscular mycorrhiza fungi (NAMF, pH 7.1), control-arbuscular mycorrhiza fungi (AMF, pH 7.1), acid-NAMF (pH 5.1), acid-AMF (pH 5.1), alkaline-NAMF (pH 8.2), and alkaline-AMF (pH 8.2). Stunted growth and leaf chlorosis were noticed mainly in plants grown in soil with acidic pH. An increase in fresh biomass was attained in plants amended with AM fungi in alkaline soil pH. Alkaline sandy soil with low levels of available P stimulated AMF colonization of chia roots, which subsequently enhanced P uptake and translocation in plant tissues. Total proteins, carbohydrates, and total fat content in leaves increased in AMF-inoculated plants in neutral and alkaline soil pH, while only fat content enhanced under acidic soil pH. MC10 inoculum resulted in reduced levels of total phenolics under alkaline conditions, whereas under acidic soil resulted in increased levels compared to the non-inoculated plants. The predominant fatty acids of chia leaves were palmitic (18.3 %), a-linolenic (17.1 %), pentadecenoic (11.0 %), linoleic (7.5 %), oleic (7.5 %), and stearic (6.3 %). Higher concentration of stearic, oleic, linoleic, and a-linolenic acids was observed in the leaves of chia plants grown on control (neutral pH) and alkaline soil in the presence of the MC10 inoculum. Alkaline soil combined with AM inoculation enhanced the nutritional value of chia leaves.