Effects of Plant Biostimulants on Onion Growth and Production Under Greenhouse and Field Conditions

The escalating impact of climate change on agricultural production underscores the need to investigate sustainable crop enhancement methods. This research explores the use of plant biostimulants to grow onion (Allium cepa L.) under varying environmental conditions. In the initial germination and greenhouse screening, seven biostimulants were tested on ‘Vaquero’ onion seeds: 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). Mighty Mycorrhizae, Continuum, and Myco Apply supported faster germination, while seeds treated with Spectrum and Seaweed took longer. The speed and uniformity of germination showed limited difference across the applied biostimulants. In the greenhouse test, cluster analysis identified Huma Pro 16 (humic) and Spectrum DS (spectrum) as the most effective biostimulants based seedling emergence, leaf area, and biomass. Following this, field trials were conducted with four onion cultivars: ‘Bridewhite’ (white), ‘Marenge’ (red), ‘Walla Walla’(sweet), and ‘Vaquero’(yellow), subjected to water [ conditions simulating Drought (75% reference evapotranspiration, ETr) or Wet (100% ETr)] or nitrogen [reduced (-N:100 lbs·ac-1) or recommended (+N:150 lbs·ac-1)] treatments. ‘Vaquero’ onions performed better under both water and nitrogen treatments. The total yield of ‘Vaquero’ onions was higher under Control Wet (no biostimulant), Humic Wet, and Spectrum Wet treatments compared with ‘Walla Walla’ onions which had lower yield under Spectrum Drought and Wet treatments. Similarly, under nitrogen treatments, ‘Vaquero’ onions produced the highest yield under Humic -N, Humic +N, and Spectrum +N compared with ‘Marenge’ onions under Control -N and Humic +N and ‘Walla Walla’ onions under Humic and Spectrum treatments. Although biostimulants, water or nitrogen treatments did not affect onion storage after harvest, ‘Walla Walla’ onions experienced the highest yield loss and rot, while ‘Vaquero’ had the lowest loss and more single centered bulbs across treatments. Biostimulant effectiveness varied by cultivar, water availability, and nutrient levels, highlighting the need for further research to optimize their use in onion growth and production under adverse environmental conditions.