Inappropriate fertilisation results in the pollution of groundwater with nitrates and phosphates, eutrophication in surface water, emission of greenhouse gasses, and unwanted N deposition in natural environments, thereby harming the whole ecosystem. In greenhouses, the cultivation in closed-loop soilless culture systems (CLSs) allows for the collection and recycling of the drainage solution, thus minimising contamination of water resources by nutrient emissions originating from the fertigation effluents. Recycling of the DS represents an ecologically sound technology as it can reduce water consumption by 20–35% and fertiliser use by 40–50% in greenhouse crops, while minimising or even eliminating losses of nutrients, thereby preventing environmental pollution by NO₃⁻ and P. The nutrient supply in CLSs is largely based on the anticipated ratio between the mass of a nutrient absorbed by the crop and the volume of water, expressed as mmol L⁻¹, commonly referenced to as “uptake concentration” (UC). However, although the UCs exhibit stability over time under optimal climatic conditions, some deviations at different locations and different cropping stages can occur, leading to the accumulation or depletion of nutrients in the root zone. Although these may be small in the short term, they can reach harmful levels when summed up over longer periods, resulting in serious nutrient imbalances and crop damage. To prevent large nutrient imbalances in the root zone, the composition of the supplied nutrient solution must be frequently readjusted, taking into consideration the current nutrient status in the root zone of the crop. The standard practice to estimate the current nutrient status in the root zone is to regularly collect samples of drainage solution and determine the nutrient concentrations through chemical analyses. However, as results from a chemical laboratory are available several days after sample selection, there is currently intensive research activity aiming to develop ion-selective electrodes (ISEs) for online measurement of the DS composition in real-time. Furthermore, innovative decision support systems (DSSs) fed with the analytical results transmitted either offline or online can substantially contribute to timely and appropriate readjustments of the nutrient supply using as feedback information the current nutrient status in the root zone. The purpose of the present paper is to review the currently applied technologies for nutrient and water recycling in CLSs, as well as the new trends based on ISEs and novel DSSs. Furthermore, a specialised DSS named NUTRISENSE, which can contribute to more efficient management of nutrient supply and salt accumulation in closed-loop soilless cultivations, is presented.

Salinity, one of the major abiotic stresses in plants, significantly hampers germination, photosynthesis, biomass production, nutrient balance, and yield of staple crops. To mitigate the impact of such stress without compromising yield and quality, sustainable agronomic practices are required. Among these practices, seaweed extracts (SWEs) and microbial biostimulants (PGRBs) have emerged as important categories of plant biostimulants (PBs). This research aimed at elucidating the effects on growth, yield, quality, and nutrient status of two Greek tomato landraces (‘Tomataki’ and ‘Thessaloniki’) following treatments with the Ascophyllum nodosum seaweed extract ‘Algastar’ and the PGPB ‘Nitrostim’ formulation. Plants were subjected to bi-weekly applications of biostimulants and supplied with two nutrient solutions: 0.5 mM (control) and 30 mM NaCl. The results revealed that the different mode(s) of action of the two PBs impacted the tolerance of the different landraces, since ‘Tomataki’ was benefited only from the SWE application while ‘Thessaloniki’ showed significant increase in fruit numbers and average fruit weight with the application of both PBs at 0.5 and 30 mM NaCl in the root zone. In conclusion, the stress induced by salinity can be mitigated by increasing tomato tolerance through the application of PBs, a sustainable tool for productivity enhancement, which aligns well with the strategy of the European Green Deal.

Greenhouse cultivation enables year-round vegetable production and high yields through precise environmental regulation. Yet, the same stable microclimate that promotes crop growth also favors the proliferation of pests and diseases. This review synthesizes current knowledge on how greenhouse climate variables govern pest and disease epidemiology in tomato, cucumber, and sweet pepper. Only greenhouse-based studies were included to ensure direct relevance to protected horticulture. Microclimatic stability determines infection probability, vector behavior, and host susceptibility. Warm, humid conditions promote fungal and bacterial pathogens, whereas dry, high vapor pressure deficit (VPD) environments favor mites and thrips and enhance virus transmission. Species-specific traits further modulate vulnerability. Tomato is dominated by virus–bacterium complexes and foliar/stem fungal diseases, cucumber by phytopathogenic fungi favored by high relative humidity (RH) and soilborne pathogens, and sweet pepper by virus–vector systems and long-cycle fungal infections. Temperature exerts the strongest influence, while RH and VPD jointly regulate surface moisture and vector activity. Light intensity and spectral composition also affect pest orientation and fungal sporulation. Integrating environmental sensing, biological control, and adaptive climate regulation offers a pathway toward preventive, climate-smart Integrated Pest Management (IPM). The review highlights the emerging role of climate-informed decision-support systems (DSSs) and the need for greenhouse-specific datasets to improve pest and disease forecasting.

Drought stress is a critical abiotic constraint on agricultural productivity, particularly affecting crops like pepper (Capsicum annuum L.), which are highly susceptible to water deficits due to their physiological characteristics. The present study investigated the impact of a 40% reduction in irrigation on yield, macronutrient concentrations, and fruit quality across several pepper genotypes. The cultivars evaluated included two landraces, namely ‘JO109’ and ‘JO204’ (Capsicum annuum var. grossum), as well as the California cultivar ‘Yolo Wonder’ and the commercial F1 hybrid ‘Sammy RZ’, which served as controls. The experiment was conducted at the greenhouse facilities of the Laboratory of Vegetable Production, Agricultural University of Athens. Under reduced irrigation, most of the cultivars studied exhibited a decline in yield, which was attributed to a decrease in fruit number in ‘Yolo Wonder’ and a reduction in fruit weight in both ‘JO204’ and ‘Sammy’. In contrast, the landrace ‘JO109’ exhibited consistent yields under both growing conditions, a response likely attributed to elevated K concentration in the leaves and lower Na accumulation in the fruit, indicating enhanced tolerance to water deficit. A decline in leaf K concentration was observed in response to drought stress, while concomitantly increased concentrations of Na, Ca and Mg were recorded. Among fruit macronutrients, only Ca showed a significant decrease under reduced irrigation. Furthermore, fruit firmness (FF), titratable acidity (TA) and total soluble solids content (TSSC) exhibited higher levels under drought stress, particularly in ‘JO109’, while TA remained unaltered. These findings highlight the potential of landraces such as ‘JO109’ to be utilized in breeding programs aimed at enhancing resilience, while maintaining pepper fruit quality under limited water availability.

The recycling of drainage solution (DS) in greenhouses by applying closed-loop soilless cropping systems (CLS) eliminates pollution of aquifers by nitrogen and phosphorus emissions. However, the variable nutrient composition of the DS poses a significant challenge to its recycling in CLS. To addresses this challenge, a strategy was developed, based on daily monitoring of macronutrient concentrations in the DS using ion-selective electrodes (ISE) coupled with a modelling approach applied through a decision support system (DSS). The ISE measurements were input data for the DSS to calculate appropriate rates of different single-fertiliser concentrated solutions for automatic injection into a mixture of DS and raw water. The fertiliser injection rates were transmitted online to a fertigation system equipped with nine different single-fertiliser concentrated solutions and were applied automatically in real time. The objective was to maintain the root-zone nutrient concentrations within an optimal range. To test this technology and to validate the modelling approach applied through this DSS, tomato was grown in a CLS with daily measurement of NO₃^-, K⁺, Ca²⁺, and Na⁺ concentrations in the DS using ISEs. The accuracy of the ISEs was confirmed by comparing their measurements with those from standard laboratory procedures in the same samples. The model approach successfully maintained the target nutrient concentrations in the root zone and increased fruit yield by 7.6 % and the agronomic efficiency of nitrogen by 23 %. The proposed technology is expected to encourage the adoption of CLS by growers thus minimising environmental impacts from greenhouse crops.

Nutrient intake is vital for human health, yet micronutrient deficiencies remain widespread despite sufficient calorie consumption. Biofortification is the process by which the nutrient density of food crops is increased through various strategies without altering key agronomic characteristics. This approach is widely recognised as a cost-effective method for addressing micronutrient malnutrition. When combined with the nutritional properties and inherent resilience of underutilised crops to harsh conditions, biofortification emerges as highly promising and sustainable solution. This study investigates the effects of selenium biofortification by adding different doses of SeO₂ (0, 1, 2, and 4 μM) in the nutrient solution in three underutilised leafy vegetables [Portulaca oleracea L. (purslane), Taraxacum officinale L. (dandelion), and Mesembryanthemum crystallinum L. (iceplant)] grown in an open soilless system. The addition of SeO₂ to the nutrient solution increased yield in all three species, although iceplant exhibited reduced yield at the highest SeO₂ dose. In particular, the total yield of purslane was enhanced by 14–19% when treated with 1, 2, and 4 doses of SeO₂, whilst the dandelion yield increased by 25% under 4 μM SeO₂. Furthermore, the yield of iceplant increased by 14.7–17.8% at 1 and 2 μM SeO₂. SeO₂ application led to a dose-dependent increase in selenium concentration in the shoot tissues while remaining within safe intake limits. More specifically, selenium concentration in purslane, dandelion, and iceplant tissues increased by 92%, 91%, and 89%, respectively, at the highest SeO₂ dose (4 μΜ) compared to untreated plants. Selenium treatment also influenced the nutritional profile of the examined plant species. With regard to the antioxidant activity, the highest recorded value was observed at 1 μM SeO₂ for purslane and iceplant, and at 4 μM SeO₂ for dandelion. These values were enhanced by 20%, 12%, and 27%, respectively, in comparison with 0 μM SeO₂. In conclusion, rootzone SeO₂ supplementation via a nutrient solution can be considered an effective biofortification strategy that enhances growth characteristics and antioxidant properties of the three investigated underutilised leafy vegetables without compromising their nutritional value.