Yield and pungency of eight onion varieties and their response to sulfur fertilizer on fine-textured soil

Onions are notable for their pungency, caused by sulfur-containing compounds. Fine-textured soils high in organic matter, or soils fertilized with organic amendments, are unlikely to require additional sulfur for maximum onion yield. We were interested in the impacts of additional sulfur (in such a situation, unlikely to be sulfur-limited) on pungency, soluble solids, and yield in eight onion varieties. We carried out a study in 2024 in southern Minnesota, designed as a split-plot (onion variety as the whole-plot) with four replicates. Heavy rainfall caused substantial unmarketability in our trial, with ‘Ringmaster’ suffering the most loss (11% of planted ‘Ringmaster’ were marketable). ‘Blush’ and ‘Red River’ yields were greatest. ‘Blush’ and ‘Redwing’ had the highest pungency, and ‘Patterson’ and ‘Sterling’ had low pungency. Soluble solids were highest in ‘Blush’, ‘Redwing’, and ‘Patterson’. Additional sulfur (gypsum) did not increase yield or change pungency or soluble solid content in the varieties studied, and yield was slightly lower when additional sulfur was applied. We found no benefit of sulfur fertilizer applied to onions in high-sulfur soils.