Project overview
Many organic producers use manure to provide nutrients and improve or sustain soil health, and some integrate crop and livestock production to enhance nutrient cycling, farm functional biodiversity, and enterprise diversity. However, the use of manure in crop rotations that include specialty crops such as salad greens, tomatoes, and strawberries that are often consumed raw raises food safety concerns. Current food safety regulations utilize the NOP-required 120-day interval between manure application and crop harvest, but additional research is needed to determine if this is the best waiting period considering food safety, soil health, and farm management logistics.
This two-year study on 19 organic farms in the West, Midwest, and East examined different waiting periods for manure application (dairy, poultry, and horse). Researchers sampled manure, soil, water, and produce to check for foodborne pathogens.
Farmer takeaways
- Longer USDA-NOP (>120 days) wait periods or composting of animal manure may be necessary to protect organic vegetable crops from fecal pathogen contamination.
- Strategies to maximize the manure-to-harvest interval (e.g., applying manure at time of cover crop planting) are needed to minimize food safety risks in produce.
Project objectives and approach
Assess on-farm practices, environmental factors, and soil health associated with the persistence of of pathogens among organic farms using raw manure as a soil amendment
- A two-year study was conducted on a total of 19 certified organic farms producing at least one leafy green, root vegetable, or fruit in the West, Midwest, and East.
- Experimental field trials were conducted to determine appropriate application intervals for biological soil amendments of animal origin (dairy manure, poultry litter, and horse manure).
- Composite manure, composite soil, water, and harvested produce were sampled repeatedly in order to assess the prevalence and survival of foodborne pathogens (Salmonella, STEC, non-STEC, and L. monocytogenes), as well as indicators of contamination.
- Management and farm practices (demographics, size, irrigation, crop type, soil amendments, soil health, etc.) and environmental factors (climate and landscape data) were recorded for the duration of the study.
Determine the relationship between soil health and pathogen survival in organically grown fresh produce fields amended with raw manure
- Soil health was evaluated periodically at each of the farms via microbiome analysis, general soil chemistry, and a soil health self-assessment in order to discern any existing relationships between soil health and pathogen survival post-manure application.
Key findings
Farm management practices, environmental factors (temperature and precipitation), soil factors (moisture, organic matter, and micronutrients), and manure type may be associated with pathogen prevalence and persistence
- Soil samples amended with cattle or horse manure had lower concentrations of generic E. coli (gEc) compared to samples amended with poultry manure after 120 days.
- Higher levels of humidity, precipitation, temperature, micronutrients, and organic matter were associated with higher counts of E. coli.
Pathogens may persist in manure-amended soils and produce for longer than 120 days
- Generic E. coli persisted in manure-amended soil and transferred to spinach, carrots, and tomatoes for longer than the recommended wait-time of 120 days.
Region
North Central, Northeast, Western
Topic
Soil Health, Post-Harvest Quality and Safety
Category
Vegetables/Fruits
Year Published
2021
