Underutilized leafy greens are considered as functional plant species primarily due to their resilience to abiotic stress factors, low nutrient requirements, and high nutritional value. Over the past 30 years, many experiments have been conducted to identify nutrient-efficient species, cultivars, landraces, and ecotypes, but few have successfully entered mainstream agriculture. The integration of these species into advanced horticultural systems, such as hydroponics, has the potential to further strengthen their impact on sustainable agriculture by minimizing use of resources, enabling year-round cultivation, and improving the nutritional profile of the harvested produce. As leafy vegetables, a primary food safety concern is the accumulation of nitrates in the leaves. In hydroponics, this issue is usually addressed by balancing the NH₄-N/total-N ratio (N_r) in the nutrient solution. Provided that the plant responses to high ammonia supply are species-dependent, three wild leafy greens, iceplant, corn salad, and common purslane, were grown in a soilless culture, with perlite as the substrate, under low (0.04) and high (0.12) N_r on a molar basis. Additionally, the potential of protein hydrolysates (PH) and seaweed extracts (SW) to alleviate plant tolerance to excess ammonia supply was also investigated. In terms of yield, high N_r led to significant yield restrictions in iceplant that reached 28%, while on corn salad, it had a positive impact, with yield increasing by 18%. Both biostimulant applications enhanced iceplant productivity only under optimal N_r conditions (0.04). Apart from yield responses, biofertilizers had no substantial impact on the plant nutrient profile. In contrast, high N_r suppressed nitrate accumulation in fresh leaves, while enhancing micronutrient uptake in all three plant species. In conclusion, this study highlights the pivotal role of biostimulants as plant stress protectors and growth regulators and identifies the optimal N_r ratio for maximizing the yield and quality performance of corn salad, iceplant, and common purslane in soilless cultivation systems.

Barley (Hordeum vulgare L.) is a key cereal crop for malting and brewing, where grain plumpness and optimal grain protein concentration (GPC) are essential quality traits. This study investigated the combined effects of nitrogen fertilization strategies and a seaweed-based biostimulant (Ascophyllum nodosum extract) on malting barley production across four environments in Thessaly, Greece, over two growing seasons. Treatments included urea (U), urea with biostimulant (U + B), urea with urease inhibitor (UI), urea with urease inhibitor and biostimulant (UI + B), and a control (no fertilization). Applications were tested on genotype G20 at mid-development (Z30–33) and genotype G45 at an earlier stage (Z24–30). UI + B treatment consistently enhanced yield by up to 71%, thousand-grain weight by 27%, and spikelets per square meter by 75% relative to the control, with responses influenced by genotype and environment. Grain fractions > 2.8 mm increased by up to 22% under UI + B, while GPC remained within the optimal malting range (9.5–11.5%). Early-stage applications produced strong benefits overall. Principal component analysis distinguished treatment effects, with UI + B samples clustering consistently apart from controls. These results demonstrate that combining biostimulants with urease inhibitors can simultaneously improve yield, quality, and sustainability in malting barley, supporting reduced nitrogen input in Mediterranean systems.

Barley (Hordeum vulgare L.) is a key cereal crop for malting and brewing, where grain plumpness and optimal grain protein concentration (GPC) are essential quality traits. This study investigated the combined effects of nitrogen fertilization strategies and a seaweed-based biostimulant (Ascophyllum nodosum extract) on malting barley produc-tion across four environments in Thessaly, Greece, over two growing seasons. Treat-ments included urea (U), urea with biostimulant (U+B), urea with urease inhibitor (UI), urea with urease inhibitor and biostimulant (UI+B), and a control (no fertilization). Applications were tested on genotype G20 at mid-development (Z30–33) and genotype G45 at an earlier stage (Z24–30). UI+B treatment consistently enhanced yield by up to 71%, thousand grain weight by 27%, and spikelets per square meter by 75% relative to the control, with responses influenced by genotype and environment. Grain fractions >2.8 mm increased by up to 22% under UI+B, while GPC remained within the optimal malting range (9.5–11.5%). Early-stage applications produced stronger benefits overall. Principal component analysis distinguished treatment effects, with UI+B samples clustering consistently apart from controls. These results demonstrate that combining biostimulants with urease inhibitors can simultaneously improve yield, quality, and sustainability in malting barley, supporting reduced nitrogen input in Mediterranean systems.