Pathogen die-off rates following manure application under Ontario field conditions
Project 11-012 - Head Researchers: Ann Huber, Keith Warriner
Researcher: Ann Huber, the Soil Resource Group, Keith Warriner, University of Guelph
Graduate student: Di Wang, MSc Food Science, University of Guelph, 2016
Summary:
The Soil Resource Group, a firm that completes applied research in the agricultural and environmental sectors, spent one year evaluating the rate of bacterial die-off after liquid manure applications using a novel container method which prevents run-off from affecting the results. The project goal was to determine manure management techniques which would reduce pathogen contamination of irrigation water or soils in which food crops are grown. In turn, this could help reduce the risk of food-borne illness.
The researchers applied liquid hog manure to the surface of different Ontario field plots in June, September and November. After application, they sampled the soil surface and soil at a depth of 15cm, to determine the levels of E. coli, Salmonella and Listeria in the soil. All of the bacteria of interest demonstrated a general pattern of stable or increasing numbers for the first few days after manure application, followed by a phase of rapid die-off which lasted approximately 3 weeks. 120 days after application (the post-harvest wait period after application) neither Salmonella nor E.coli 0157 were detectable, however Listeria and environmental E.coli were still found in small amounts.
No effect of soil type was observed for any of the pathogens and it is likely that climate (temperature and moisture) rather than season are factors in the rates of decline of pathogens in soil. A significant impact of application depth was demonstrated for the initial rapid die-off rate for E.coli, E.coli O157 and Salmonella for the fall trials.
With lower rates of decline of pathogens at depth, leaving the manure on soil surface for at least 12 days is a simple and cost-effective treatment for lowering pathogen levels (including E.coli and Salmonella) from liquid manure. However, applying manure during a dry week is required to prevent contamination in run-off, and the losses on nitrogen need to be considered in nutrient management for crops.