Because of the wide range of variables associated with manure composition, preapplication storage, application, and incorporation, the United States Department of Agriculture National Organic Program (NOP) specifies a minimum manure application-to-harvest time interval necessary to provide adequate assurance of safety. Weather conditions, desiccation, soil type, predatory protozoan populations, and the degree of manure incorporation are all likely to have various effects on pathogen survival in manure-fertilized soil ( 5, 6, 8, 9, 18, 19, 21, 36, 40, 42, 51- 53, 59, 66). Further death of manure-borne pathogens occurs once the manure is incorporated into the soil. A variety of environmental and operational variables, including storage temperature ( 26) and the diet of the cattle ( 37), could affect the extent of pathogen decrease, and complete elimination of pathogens is not assured by this technique ( 20). An alternative to composting may be to passively age or store and digest the manure before application so that pathogen populations either decrease or disappear ( 31, 32, 37). Composting of bovine manure is not yet widely practiced in Wisconsin ( 1). Tailing of pathogen inactivation curves has been reported ( 29), as have apparent regrowth or recontamination and growth of bacteria in cooled compost ( 7, 38). However, the heat-induced death of bacteria in composted materials is a complex phenomenon ( 15, 28). Composting is an accepted manure pathogen reduction treatment ( 58), and compost-generated heat is believed to eliminate pathogenic bacteria ( 27, 34). However, bovine manure is a well-known source of food-borne pathogenic bacteria ( 31, 33, 41, 64, 67), and using it without prior treatment to destroy pathogens increases the likelihood of contaminating vegetables grown in manure-fertilized soils. Bovine manure is a good source of macro- and micronutrients, so using it as fertilizer is an important disposal method ( 35), particularly for organic farmers. In the North Central region of the United States, an estimated 10.4 million dairy and feedlot cattle produce between 23.6 and 35.5 kg of manure (feces and urine) per 454 kg (live weight) per day ( 16). Recent scrutiny of the role of agricultural practices in contamination of fresh vegetables with pathogenic microbes ( 47, 54) has led to concern about the safety of using animal manures as fertilizer in vegetable production. coli strains are, it appears that the risk of contamination for vegetables grown in Wisconsin soils would be elevated only slightly by reducing the NOP requirement to ≥100 days. Unless pathogens are far better at colonizing vegetables than indigenous E. coli from vegetables harvested from manure-fertilized Wisconsin soils may not be ensured solely by adherence to the NOP ≥120-day limit. The rapid maturation of radishes prevented conclusive evaluation of a 100- or 120-day application-to-harvest interval. coli on carrots (≥1 enrichment-negative result for 100% of the treatments). The current ≥120-day limit provided an even greater likelihood of not detecting E. For carrots and lettuce, at least one enrichment-negative sample was obtained ≤100 days after manure application for 63 and 88% of the treatments, respectively. coli generally persisted in manure-fertilized soil for more than 100 days and were detected in enriched soil from all three sites 132 to 168 days after manure application. coli in manure-fertilized soil generally decreased by about 3 log CFU/g from initial levels of 4.2 to 4.4 log CFU/g. Soil and washed (30 s under running tap water) vegetables were analyzed for indigenous Escherichia coli. Noncomposted bovine manure was applied to 9.3-m 2 plots at three Wisconsin sites (loamy sand, silt loam, and silty clay loam) prior to spring and summer planting of carrots, radishes, and lettuce. In this study we tested the validity of the National Organic Program (NOP) requirement for a ≥120-day interval between application of noncomposted manure and harvesting of vegetables grown in manure-fertilized soil.
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