New research suggests that poultry litter-based soil amendments and weather conditions, specifically extreme weather events, may influence how long bacteria survive in agricultural soils used to grow sweet onions. The findings could help inform food safety risk management for produce growers.
In a two-year field study published in Risk Analysis, researchers found that soils amended with heat-treated poultry pellets and composted poultry litter supported longer survival of Escherichia coli compared with untreated soils.
"Organic produce growers increasingly rely on biological soil amendments to improve soil health and crop productivity," Kapoor said. "Our findings show that field environmental conditions and the type of amendment used can interact in ways that influence the survival of E. coli. This is important for risk-management approaches that account for local conditions."
Across two growing seasons analyzed, E. coli survived longer in soils amended with heat-treated poultry pellets and composted poultry litter than in untreated soils.
The influence of weather differed between the two growing seasons. Higher humidity was associated with greater bacterial survival, while stronger winds generally reduced survival. Researchers found that rain and warmer soil temperatures could promote bacterial persistence, whereas higher air temperature and wind speeds tended to reduce survival. The results suggest that extreme weather events, rather than average seasonal conditions alone, may play an important role in determining how long bacteria can survive in agricultural soils.
The findings are particularly relevant in Georgia, one of the nation's leading poultry-producing states, where approximately 2 million tons of poultry litter are generated annually. Poultry litter, a mixture of poultry manure, bedding material, feathers and feed residues, is widely used as fertilizer because it supplies valuable nutrients to crops.
Onions have been linked to several major foodborne illness outbreaks in North America, including outbreaks associated with slivered onions on the McDonald's Quarter Pounder burgers reported by the FDA as recently as 2024. Others include a 2020 outbreak of Salmonella Newport linked to red onions across the U.S. and Canada, and a 2021 outbreak of Salmonella Oranienburg tied to fresh onions imported from Mexico. These incidents resulted in thousands of reported illnesses and hundreds of hospitalizations, underscoring the importance of understanding how disease-causing bacteria persist in agricultural environments.
The authors note that regulators continue to seek data on the food safety implications of biological soil amendments of animal origin. Understanding how amendment practices interact with extreme weather events may help inform risk-based management approaches under field conditions.
