Dimitrios Savvas’s research while affiliated with Agricultural University of Athens and other places

This study investigates the effects of nitrogen fertilization, irrigation, and biostimulant application on the growth and nutrient composition of Cichorium spinosum L. The experimental design included two nitrogen rates (NR100 and NR30, 100% and 30% of plant requirements), two irrigation levels (WA100 and WA50, 100% and 50% of water availability,), and foliar application of a nitrogen-rich biostimulant (BS and NoBS, biostimulated or not biostimulated). In comparison to NR100, NR30 reduced agronomical parameters leaf number, leaf area, leaf fresh, and dry weight by 13.53%, 24.93%, 20.76%, and 15.00%, respectively, whereas dry matter content was increased by 7.64%. WA50 also resulted in reduction in the agronomical characteristics by 8.62%, 7.19%, 5.53%, and 5.26, respectively, whereas the dry matter content was not affected. BS positively affected the agronomical characteristics by 7.49%, 8.01%, 7.18%, and 5.56, respectively, whereas the dry matter content was not affected. The effects of nitrogen rates and water availability suggest the more pronounced impact of nitrogen compared to water stress on the agronomical characteristics. Biostimulant application partially mitigated the effects of NR30 but was ineffective against WA50. The nutrient content of the leaves was also affected. NR30 reduced leaf nitrate, calcium, and zinc content, but increased iron, manganese, and copper concentrations. WA50 altered magnesium and zinc levels: it increased the former and decreased the latter. The interaction between nitrogen and water stress notably affected the plants’ calcium content, which was higher under the NR100 x WA50 treatment. These findings provide significant insights into the perlite-based cultivation of C. spinosum L., and its resilience against drought stress. Moreover, the beneficial effects of sufficient nitrogen rates on leaf fresh weight of Cichorium spinosum L. outline the importance for improving nutrient solution management schemes. Biostimulant application demonstrated promising results and could, after further research, become a viable solution for maintaining optimal yields under nitrogen stress.

The objective of this study was to examine the integration of a wild leafy vegetable, Cichorium spinosum L., in vertical farms. This research comprises two experiments focusing on different “white” light products and nutrient solutions. During both experiments, the temperature varied between 25 and 28 °C, relative humidity ranged from 50 to 70 %, carbon dioxide was at 450 ppm, and light intensity was set at 300 μmol m⁻² s⁻¹ respectively. In the lighting experiment, the three spectra used had the commercial names Neutral, Full and a SunLike™, and their spectral composition (blue:green:red:far-red) were 14:32:43:10, 16:36:40:8, and 21:34:36:7 respectively. The photoperiod was set to 12 h and the plant density was 50 plants m⁻². Results showed no significant impact on agronomical parameters and leaf anatomy. The stomatal length and width decreased as the red:blue ratio of the light sources decreased, being greater in the Neutral treatment (red:blue ratio of 3.1) compared to the Full and SunLike™ (red:blue ratios of 2.5 and 1.7 respectively). Based on these results the preferable “white light” product was the one with the highest efficiency and lowest market price at the time of the experiment. In the nutrient solution experiment, the agronomical and nutritional attributes of stamnagathi plants supplied with a control nutrient solution, “N10-Fe15” were compared to plants cultivated under limited nitrogen, “N4-Fe15” and elevated iron, “N10-Fe48”, EC was 1.5 ds m⁻¹, and pH was 5.6–6.5. The experiment simulated commercial practices by increasing the photoperiod to 15 h and plant density to 100 plants per square meter. The results did not demonstrate significant effect of the nutrient solution differences on the agronomical characteristics except from a decrease in total Kjeldahl nitrogen under limited nitrogen conditions. Notably, leaf tissue phosphorus content increased under elevated iron conditions. The nitrate content remained within safe for consumption thresholds for all treatments. Based on these results, stamnagathi can be integrated in vertical farms under limited nitrogen conditions. Stamnagathi's resilience to elevated iron in the nutrient solution demonstrated its potential for future biofortification experiments.

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.

The aim of this research is to introduce innovative cultivation practices that result in reduced nitrate levels in baby leaf lettuce grown under vertical farming conditions while maintaining high productivity. For this reason, three experiments were conducted. The first experiment focused on the impact of two “white” light spectra with a blue:green:red:far-red ratio of 14:32:43:10 (BlowRhigh) and 21:34:36:7 (BhighRlow). The second experiment assessed the effects of two nitrogen supply conditions: sufficient total nitrogen (N15) and limited total nitrogen (N5), and foliar biostimulant application. In the third experiment, the impact of replacing the nutrient solution in the N15 treatment with tap water for an additional 24 h (TW24) on leaf nitrate content was examined. Results from the lighting experiment revealed no significant effects on agronomical parameters or nitrate content between the two light spectra. Reducing nitrogen content in the nutrient solution reduced leaf nitrate content but negatively influenced agronomical characteristics. Biostimulant application and replacing the nutrient solution with water reduced leaf nitrate content compared to the control and positively affected growth. The most favorable outcomes were observed in plants supplied with sufficient nitrogen and foliar biostimulant but also cultivated for an additional 24 h with tap water (Sp-N15-TW24).

The use of biostimulants consisting of plant growth-promoting rhizobacteria (PGPR) has been rapidly expanding in horticulture in recent years. In the current study, a novel mix of six Bacillus sp. strains (B. subtilis, B. pumilus, B. megaterium, B. amyloliquefaciens, B. velezensis, B. licheniformis) was tested as a PGPR biostimulant in two experiments with zucchini squash (Cucurbita pepo L.). The first experiment took place in greenhouse soil in winter, while the second experiment was conducted in an open field during summer. In both experiments, seeds of the local landrace “Kompokolokytho” and the commercial hybrid “ARO-800” were either inoculated or non-inoculated with the PGPR biostimulant. The application of the six Bacillus sp. strains increased both the vegetative growth and the yield of zucchini squash, and these effects were associated with significantly higher shoot phosphorus levels in both experiments and both genotypes. Furthermore, at the end of the cultivation, the colony-forming units of Bacillus sp. were appreciably higher in plants originating from inoculated compared to non-inoculated seeds, indicating that the tested mix of Bacillus sp. can be successfully applied through seed inoculation. “ARO-800” produced more vegetative and fruit biomass than “Κompokolokytho” under greenhouse cropping conditions, while in the open field crop, both genotypes performed equally. Presumably, this response occurred because “ARO-800” did not express its full yield potential in the open field due to stress imposed by the high summer temperatures, while the local landrace, which is traditionally grown in open fields, may be more resilient to stress conditions frequently encountered in open fields.

Cabbage is an annual vegetable crop species cultivated throughout the year. The development of high-yielding cabbage hybrids and the optimization of several agronomic management practices such as fertilization and crop rotation have resulted in increased soil fertility, crop yield and product quality. This study aimed to investigate the effects of the farming system (organic and conventional) and the applied rotation scheme on soil nutrient content, head yield and the nutrient content of cabbage. The preceding crops included either pea (P), faba bean (F) or cabbage (C), and thus, the rotation schemes were P-C, F-C and C-C. Sheep manure was applied in the organic farming system, and the inorganic fertilizer 11-15-15 (N-P2O5-K2O) was applied to the conventionally cultivated plants. The results reveal an interaction between the farming system and the preceding crop for the head yield, with the lowest values (57.00 t ha−1 and 53.87 t ha−1 in 2015/2016 and 2016/2017, respectively) recorded in plots where cabbage was cultivated as a preceding crop under the organic farming system. The N, P and K contents in head tissues were affected only by the farming system, with the greatest values recorded in the conventional farming system. Both factors affected the nutrient content in the soil. Specifically, the highest values of NO3− and total N content in the soil were recorded in the P-C and F-C rotations, and the K content was higher in the continuous cabbage cropping system (C-C). Moreover, the NO3−, P and K contents in the soils were higher in the conventional farming system compared to the organic system. To conclude, combining inorganic fertilization in a crop rotation scheme with legume species such as pea and faba bean as preceding crops for cabbage can result in increased soil fertility and head yield.

In this study, we implement a linear programming farm model to explore the impact of climate change-induced multiple stress on the financial viability of greenhouse tomato growers. The main results are that new technologies and innovations can compensate growers for any profit loss associated with climate change. However, if the cost of adaptation is high enough, then its financial benefits are constrained by how efficient these innovations are in terms of productivity. We did not observe significant differences in input use between ‘innovative’ and ‘conventional’ production, and the yield under the adoption of new technologies was higher compared to ‘conventional’ production.