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.

Nutrient availability after fertilising agricultural soils is affected by many factors, including soil moisture conditions and physicochemical properties. Herein, the availability of potassium in soil enriched with biochar is studied, considering either saturated or unsaturated moisture conditions and questioning key ion exchange approaches, such as equilibrium exchange (E.E.) and kinetic exchange (K.E.). Potassium release is simulated from a soil–biochar mixture of 0, 0.5, 1 and 2% by coupling HYDRUS-1D and PHREEQC models. The water flow, mass transport and geochemical processes are simulated for a cultivation period that imitates agronomic and environmental conditions of a common agricultural field in Northern Greece. Potassium is released gradually during the irrigation period in the case of unsaturated flow conditions as opposed to its complete release over a few days in the case of saturated flow conditions in the soil. Regarding ion-exchange processes, the soluble amount of potassium is more readily available for transport in soil solution when using the E.E. approach compared to the K.E. approach that assumes a kinetically controlled release due to interactions occurring at the solid–solution interface. The increased proportion of biochar in soil results in a doubling of available potassium. Among the four modelling schemes, although the total mass of potassium released into soil solution is similar, there is a significant variation in release time, indicating that simplified saturated conditions may lead to unrealistic estimates of nutrient availability. Further experimental work will be valuable to decrease the uncertainty of model parameter estimation in the K.E. approach.

The conservation of natural resources is indispensable for supporting sustainable development. Water–Energy–Food–Ecosystem (WEFE) nexus management is widely acknowledged as the utmost priority of our time. Considering the specificities of the different nexus sectors, conflicting views of sustainability may arise from different stakeholders. This paper presents and analyses an effective stakeholders’ participation strategy aiming at identifying WEFE challenges in the Pinios River Basin (PRB), the most agriculturally productive and natural resource-stressed basin of Greece. The presented methodology was developed in the context of a Learning and Action Alliance (LAA) scheme adopted by the H2020 REXUS project, intended to support resilient nexus system management with the engagement of stakeholders. The proposed comprehensive methodology comprises multiple phases, including “framing”, “mapping”, “involvement”, “co-production”, and “sharing” phases. The involvement phase is the most interactive one, including the organisation and outputs of efficient crowdsourcing theme sessions organised in the framework of the first REXUS PRB stakeholders’ workshop. This paper illustrates and analyses stakeholders’ perceptions regarding nexus status in the PRB and reveals the most critical challenges in the pilot basin, along with their interdependencies and correlations. The determination of nexus challenges insights by stakeholders could significantly contribute to redefining policies so that they align with sustainable development aims. This methodology is proposed to form the baseline strategy in stakeholders’ engagement for future nexus management studies.

Gaining a comprehensive understanding of how weed communities respond to both environmental and human-induced factors is of paramount importance in developing effective and ecologically sound weed control strategies. The objectives of the current research were to (1) assess the effect of the main weed management practices used in Greek olive groves on weed species’ diversity; (2) explore the filtering effect of management, site, and soil variables in determining weed species’ composition; and (3) shed light on the association between weed species’ composition and the diversity of the understory vegetation of olive groves. To accomplish these objectives, winter weed species’ coverage was assessed in 116 olive groves, both conventional and organic, distributed across three provinces in southern Greece. The investigation encompassed 29 explanatory variables, categorized into three groups: soil (22), management practices (6), and site conditions (1). It was confirmed that glyphosate use may lower biodiversity and species richness; however, this trend was not universal. In fact, the negative influence of the presence of Oxalis pes-caprae L. on species richness and diversity far outweighed the effect of spraying glyphosate. Redundancy analysis (RDA) revealed that among the 29 variables used to describe the ecological niche, eight (i.e., Mn, Mg, chemical spraying, mowing, rotary tiller, grazing, irrigation, and elevation) were significant and explained 21.5% of the total variation in weed species’ data. Interestingly, the soil Mn concentration was identified as the most influential one, highlighting the importance of soil micronutrients in determining weed species’ composition. The variation partitioning procedure demonstrated that the effect of the management variables on weed species’ composition accounted for 2.2 times the variance of soil variables and 4.5 times the variance of elevation. The present findings might help to enhance optimal management in olive groves that can sustain the biodiversity of flora and, in turn, provide various ecosystem services to agro-ecosystems.

The accelerated climate crisis has exacerbated the existing water and soil management challenges in the Mediterranean region, which are usually attributed to the combination of both irrational irrigation and unsustainable farming practices. The current conditions and future projections indicate that water-related risks are expected to intensify during the coming decades. Moreover, farmers often do not possess high environmental awareness; they adopt non-sustainable farming practices such as the extensive use of herbicides instead of mowing/mulching for the weeds, thus affecting soil hydraulic characteristics and fertility. To investigate the effects of different weed-management practices on soil organic carbon and thus on soil water holding capacity and infiltrability, an extensive soil-sampling campaign was performed in the semi-arid Mediterranean agricultural pilot basin of Agia—Greece. The pilot is located in the Pinios river basin, which constitutes the most highly productive agricultural plain in the country. The Agia basin was selected since it presents the uneven spatiotemporal distribution of groundwater resources and the wide application of herbicides, while an urgent need exists to sustain and improve agricultural production, with the main crops being apples and cherries. Moreover, the Agia basin constitutes a highly instrumented area where the Pinios Hydrologic Observatory belonging to the International Long Term Ecological Research network has been developed, and thus additional field measurements could contribute to the overall data-collection framework. Soil sampling was conducted in apple orchards in April 2022, just before the beginning of the growing season. Ninety six soil samples in total were collected from eight different fields; half of them applied systematic herbicides treatment, and others mulching. For the upper soil profile (0–10 cm depth), the results indicate that soil organic carbon in the fields applying mowing was found to be higher by more than 30% compared to the fields applying herbicides. The corresponding difference for soil depth of 10–30 cm was 7%, thus demonstrating the effectiveness of mulching in increasing soil organic carbon. The results of the current study could be upscaled at a larger scale in the context of adapting agricultural water-stressed regions to climate change, whilst contributing significantly to the production cost and the preservation of the ecosystemic values of the regional nexus.