The down and dirty on manure and food safety
Manure can be a valuable plant nutrient source and a potential food safety hazard.
Manure can be a significant benefit to growing fresh produce or a potential threat to food safety when applied on produce farms. Raw manure should never come into contact with harvested produce and, in all cases, produce in the field. Proper application and storage of manure near produce farms is essential to ensure a reduced risk of contamination. Improper application can result in costly recalls or worse.
In general, manure should be stored at least 100 yards from the produce growing area. Care should be taken to ensure that no runoff from the storage facility enters the production area. If you choose to periodically check the manure storage area to ensure this, it should be written as part of a Standard Operating Procedure and the periodic monitoring should be recorded on a manure storage log sheet.
Either an annual calibration of the application equipment to ensure an effective rate of nutrient application or a manure nutrient test with applications in each field in tons per acre can serve to validate your rate of application based on crop removal. In either case, include any documentation or record the date of calibration in your Food Safety Manual.
It is also important to be aware of what some food safety auditors may consider to be raw manure. In some cases, food safety auditors have considered fish emulsion to be raw manure. If using fish emulsion, be sure you have documented assurance from the supplier that it contains no detectable generic E. coli. This documented assurance should be in the form of an analysis report. As an additional precaution, Michigan State University Extension recommends delivering the fish emulsion through a drip line or other means where there is no direct contact of the fish emulsion with the edible portion of the plant.