Sustaining Healthy Soil

by Shari L. Plimpton, Ph.D.
August 21, 2006

When I speak of microbial Food Safety to a group of growers, few imagine that I will be focusing on the safety of their field practices, particularly the soil. Understandably, many assume that harvest and post-harvest practices will be the focus. For the greatest food safety success, the emphasis should be on prevention of microbial contamination, since it has been demonstrated repeatedly that washing does not eliminate pathogenic microorganisms (those microorganisms that cause foodborne illness.) Therefore, all practices that could be a source of contamination pre-harvest, including manure management, should be reviewed with foodborne illness in mind.

Sustainable agricultural practices are touted as methods designed to prevent contamination from chemicals, pesticides and microorganisms. It is not enough to assume that if you are building a soil based on sustainable practices, that you need not worry about pathogenic microorganisms. Attention must be paid to detail when handling manure to assure that the microorganisms that thrive in the resulting soil are not pathogenic. Pathogenic microorganisms do thrive in both soil (i.e. Listeria) and animal and human intestinal tracts (i.e. E.coli, Salmonella). Properly treated, manure can bean effective fertilizer. For this reason, Good Agricultural Practices (GAPs) have been developed for the entire farm operation to reduce the potential for foodborne illness from fruits and vegetables.

While most of this will be recognized as common sense, let’s review the GAPs that apply to manure management recommended by USDA and the FDA (not to mention the GAPs program itself).

Consider the source
We recommend that you segregate manure from young animals from that of mature animals. Young animals have been shown to have higher levels of potentially pathogenic microorganisms. Also, consult your veterinarian regarding the health of your herd as it pertains to using the manure they produce for horticultural crops.

Incorporate
Whether or not you are composting, be sure to incorporate manure into the soil so the soil’s microflora can act more effectively upon the organic material you are adding.

Timing
You do not compost, then either apply the manure to fields for crops not intended for human consumption. If you must use it for crops intended for human consumption, then incorporate the manure at least 120 days (90 days if you are certain the crop will not come in contact with the soil) before the harvest of a crop intended for human consumption.

Compost
Composting is the preferred practice when managing manure incorporation into the soil, because it is effective in reducing the presence of pathogenic microorganisms (we can’t say eliminate because of the chance of some survival.) Composting, of course has some recommendations of its own which I will mention a few:

• Maintain barriers to prevent leakage and tracking from both manure and compost piles.

• Minimize opportunities for cross contamination by excluding animals from the composting system.

• For a static aerated pile system or an in-vessel method maintain a temperature between 131 F to 170 F for a minimum of three days.

• For a windrow system maintain a temperature between 131 F and 170 F for a minimum of 15 days.

• Again, incorporate.

Record Keeping.

Practices to avoid are:

• Manure teas are not acceptable for use on crops intended for human consumption.

• Sidedressing with untreated manure is also to be avoided.

• Allowing runoff from manure piles or compost systems to leak to fields.

Remember that manure is not just from cattle, chickens and pigs. Dogs, cats, deer, birds, rodents and flies (flies are particularly noted for E. coli contaminaion) can all potentially be sources of microbial contamination. We recommend that you consider you practices for minimizing the potential for contamination from all animal and insect sources.

If you source manure or composted manure from another source, make it your business to know their practices and that they adhere to GAPs for handling manure and compost. Again, strive for minimizing the risk, since elimination is not a reasonable expectation.

Consultation for GAPs, developing food safety programs, and passing third party audits is available through CIFT. You can reach us by calling Shari L. Plimpton at 614-314-4627 or emailing us at foodsafety@eisc.org.

Good Agricultural Practices Articles...

• ABCs of GAPs

• Cleanliness is Next to Food Safety

• The Distant Sound of Drumming

• The Efficient Use of Chlorine and Other Sanitizers in Postharvest Fruit and Vegetable Operations

• The Elements of Produce Food Safety Programs

• GAPs in Organics: Fresh Produce Safety from Pre-planting through Production

• Handling Your Food Safety Risks

• Its Not All in the Bag

• Passing a Third Party Food Safety Audit

• Pest Patrol for Fruit and Vegetable Growers

• Planning for Prevention: Fresh Produce Safety from Pre-planting through Production

• So, Just How Clean is Your Water

• Sustaining Healthy Soil

• The Value of a Food Safety Plan

• Water, Water Everywhere

• Worker Hygiene Keeps Produce Clean