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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.

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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.

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A potato field experiment was conducted for 2 consecutive years to determine the effects of nitrogen (N) and potassium (K) fertilization rates on the yield and quality of potato cv. Spunta cultivated on soil low in N and K. A 3 × 4 complete factorial experiment was used with three rates of nitrogen (330, 495, and 660 kg N ha -1 ) and four rates of potassium (112, 225, 450, and 675 kg K 2 O ha -1 ). An additional treatment without fertilization was used as the control. On soils low in N and K, potatoes showed low yield response to K fertilizer. The greatest tuber yields for both years were achieved at 495 kg N ha -1 and 112 kg K 2 O ha -1 (29.81 t ha -1 ) and 225 kg ha -1 (27.13 t ha -1 ), respectively. Differences in mean fresh weight due to treatment application were not significant. Application of 495 kg N ha -1 significantly reduced harvest index (the ratio of tuber dry weight to the total dry weight at harvest) compared to 330 kg N ha -1 , but at 660 kg N ha -1 harvest index achieved the greatest significant value. Potassium fertilization had no significant influence on harvest index. Nitrogen rates positively influenced the number of tubers. The addition of 450 kg K 2 O ha -1 significantly enhanced the number of tubers compared to the lower K rates, and the number was significantly decreased by the application of 675 kg K 2 O ha -1 . Tuber dry-matter concentration was significantly promoted by N fertilization in both cultivation years, but it was negatively affected by K fertilization in the first year of cultivation. There was no change in tuber N with N application, but N application strongly increased nitrate (NO 3 ) concentration, which fluctuated between 360 and 1382 mg kg -1 wet mass. Tuber NO 3 was negatively correlated with tuber yield, indicating that high levels of NO 3 in tubers can adversely affect yield. Tuber response to K fertilization was not in accordance with the rate of applied nutrient.