The escalating impacts of climate change on agriculture necessitate the exploration of sustainable crop enhancement methods. This research integrates greenhouse screening and field application to evaluate the efficacy of biostimulants in promoting the growth of onion (Allium cepa L.) under variable environmental conditions. In the initial greenhouse experiment, seven biostimulants were tested, including three bacterial products (Continuum, Spectrum DS, and Tribus Original), two mycorrhizal products (Mighty Mycorrhizae and Myco Apply), one seaweed extract product (Seaweed), and one product containing humic acid (Huma Pro 16). These were applied to assess their impact on seedling emergence and growth in a peat-based soilless substrate. Huma Pro 16 and Spectrum DS were identified as the most effective in increasing seedling emergence, leaf area, and biomass. Based on these findings, field trials were conducted with four onion cultivars (red, sweet, white, and yellow), subjected to conditions simulating drought and normal watering (75 % and 100 % evapotranspiration) or with nitrogen levels adjusted to low and high (75 % and 100 % of optimal 168 kilograms per hectare). The field trials assessed bulb diameter, weight, and leaf metrics. Results indicated that cultivars responded differently to varying conditions, with red and white onions showing consistent growth patterns, while sweet onions displayed more variability. Yellow onions benefited from the biostimulants, exhibiting improved growth under both drought and low nitrogen conditions. This study demonstrates that the application of certain biostimulants can significantly enhance crop growth and resilience. Huma Pro 16 and Spectrum DS show promise for improving onion yield in the face of climatic challenges. Keywords: biostimulants, drought stress, nitrogen availability, onion, and sustainable agriculture.
