One of the most frequent criticisms or concerns I hear expressed about organic food is the suggestion that organic farmers “rely” on animal manures for fertility, so therefore, organic food is at higher risk of microbial contamination. The statement contains a number of assumptions, and I’d like to take some time to explore them.
1) Reliance on Animal Manures
The idea that organic farmers “rely” on manure and/or compost for fertility is a common misconception: there are a wide range of soil amendments available to organic farmers, especially when it comes to high-value crops like fruits and vegetables. Many of these are raw, unprocessed minerals like calcium carbonate (lime), rock phosphates, or potassium sulfate. Others are derived from plant or animal sources (seed meals and fish emulsions are two good examples).
In fact, I’ve developed a fertility plan for my own farm’s vegetable acreage that does not rely on any manure or compost (I am applying the small amount we do generate here to build and maintain fertility on permanent hay ground and fields I may eventually transition to vegetable production.) Furthermore, there are “vegan” farms that guarantee their customers that no animal products are used in the production of food on their farms.
Whether or not we can have a truly sustainable agriculture without incorporating livestock somewhere into the system is certainly a debate worth having, but for the purposes of this blog post, let’s simply acknowledge that organic farmers can produce crops without relying on animal manure. The next question to ask is, “for the sake of food safety, should they?”
2) Managing Manure Risks
To read some of the more radical critics of organic agriculture, you may be led to believe that organic farmers can apply manure to their crops without any regard whatsoever for microbial contamination or food safety – nothing could be further from the truth. There are, in fact, a couple of different manure management strategies in place on organic farms.
The preferred method is composting. Organic standards define compost as, “The product of a carefully managed aerobic process by which non-synthetic materials are digested by microorganisms. Organic materials for compost shall be managed appropriately to reach temperatures for the duration necessary to effectively stabilize nutrients and kill human pathogens.” (from the Canadian Organic Standard)
How this is accomplished is further defined in similar terms in the organic standards for both the Canada and the United States (quoting from the Canadian Standard again):
Compost produced on the farm . . . if made from animal manures or other likely sources of human
pathogens, compost produced on the farm shalla. reach a temperature of 55°C (130°F) for a period of four consecutive days or
more. The compost piles shall be mixed or managed to ensure that all of the
feedstock heats to the required temperature for the minimum time; orb. meet limits for acceptable levels (MPN/g total solids) of human pathogens
specified in the Canadian Council for Ministers of the Environment publication
Guidelines for Compost Quality; orc. be considered as aged or raw manure rather than compost (i.e. meet the
requirements specified in par. 5.5.2.5 of CAN/CGSB‑32.310, Organic
Production Systems — General Principles and Management Standards).
This last statement is particularly important: on most organic farms, it is practically impossible to meet the first of these requirements (which are actually taken from the requirements for commercial composting operations). Although it irks some organic farmers that the efforts they make to compost their manure (and all the associated benefits it brings) are not recognized by the certification bodies when it comes to the timing of application, it is an essential food safety consideration. Therefore, organic standards require that:
5.5.2.5 The non-composted solid or liquid manure shall be
a. incorporated into the soil at least 90 days before the harvesting of crops for human consumption that do not come into contact with soil,
b. incorporated into the soil at least 120 days before the harvesting of crops having an edible part that is directly in contact with the surface of the soil or with soil particles.
Organic farmers are required to keep records documenting manure application, and these records are reviewed during the annual inspection; farms can also be subject to random, unannounced inspections at any time. Interestingly, GAP (Good Agricultural Practices) food safety programs, which are quickly becoming a standard requirement for any grower wishing to supply large grocery chains, have the same 120-day standard for manure application.
3) Evidence of Contamination
I’ve done a fair bit of research and even challenged some critics to prove to me whether any microbial contamination issues in organic food have ever been traced back to manure applied to the growing area. The answer, to the very best of my knowledge, is no. Post-harvest handling appears to be the area of greatest risk, and whether the product is organic or not has little bearing at this stage in the process. However, organic standards require that any water used in post-harvest handling be routinely tested for potability and that these results are shared with the certification body.
Food safety and microbial contamination is a concern that every farmer, organic or not, needs to take very seriously, and I’ve never met a farmer who didn’t recognize this fact. As we can see, the standards for certified organic production also directly address these concerns in a manner consistent with recommended best management practices for all agricultural operations, and certification bodies verify and enforce these requirements. The bottom line is clear: consumers can trust the safety of organic produce.
Anastasia
April 4, 2013
I totally agree that manure is not necessarily a food safety threat, but that is only true if farmers properly treat the manure. There hasn’t been a ton of research on this but this study for example shows that manure treated produce has greater incidence of E. coli (although there also seems to be a climatic component), in large part due to improper treatment of the manure, and that cattle manure is a greater risk than other manures.
I don’t think it’s true that consumers can completely trust the safety of organic produce (or any produce for that matter) because there is some level of risk but it is true there are regulations in place to protect consumers. Organic is no guarantee against food borne illness. We all must be careful to use adequate food safety techniques for all food, especially when it comes to washing produce that will be eaten raw.
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songberryfarm
April 5, 2013
Thanks, Anastasia, for reinforcing the fact that manure needs to be handled carefully, and for reminding us that consumers also play an important role in ensuring food safety.
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songberryfarm
April 8, 2013
I just came across this article, providing yet another perspective on food safety and how we interpret risk. It’s worth a read: “Determining the ‘High Risk Foods’: Another Analysis Sees it Differently” http://www.foodsafetynews.com/2013/04/determining-the-high-risk-foods-another-analysis-sees-things-differently/#.UWLXGKJ23Vo
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Marjorie from bristol qc
August 27, 2013
Hello Rob,
If you don’t use any manure or compost on your vegetable field, what do you use to prevent the lost of organic matter content and structure of your soil. I am very curious…what is your fertility plan and routine???
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songberryfarm
August 28, 2013
Hi Marjorie,
Great question! We rely heavily on crop rotation and cover crops (“green manures”) on our vegetable acreage. The majority of the time, a year of vegetables is followed by a year of cover crop; if we grow vegetables on a piece of ground for 2 years in a row, it will go into cover crops for the next 2 years. For cover crops we’ve used buckwheat, oats, tillage radish, winter peas, rye, common vetch, hairy vetch, red clover, and sometimes just weeds (which we mow before seed set). This year, we started an experiment in our squash field of planting a spring cover crop before transplanting and letting it grow between the rows (I’ll share the results of that experiment in a later blog post!).
Along with some of the other soil amendments I mentioned above and by paying attention to the timing and type of tillage we do, these cover crops help build and maintain organic matter and soil structure in our fields. Our soil test results show that we have been able to raise the organic matter content of our soils by an average of 0.8 of a percentage point over 4 years, and I expect that rate to increase as we bring better mineral balance into our soils and fine-tune our cover-cropping and tillage systems.
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JD Mumma
July 9, 2016
How does “raise the organic matter content of our soils by an average of 0.8 of a percentage point over 4 years,” using “green manure” compare to those farms who typically use animal manure?
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Tamara, gardener in Colorado
January 29, 2015
Bonjour Rob!
I’m wondering about the necessity of researching ingredients in animal feed prior to application of their manure onto our gardens, as well as questioning the use of alpaca manure as a safe wet fertilizer application. I have asked the rancher for the type of feed given to their alpacas and have found questionable ingredients in both their feed as well as mineral supplements which are non-organic. (Ingredients below)
Wheat middlings, ground soybean hulls, cane molasses, thiamine mononitrate, salt, dehydrated alfalfa meal, biotin, monocalcium phosphate, dicalcium phosphate, calcium lignin sulfonate, calcium carbonate, dl-alpha tocopheryl acetate, yeast culture, dehulled soybean meal, soybean oil, vitamin D3 supplement, zinc methionine complex, choline chloride, artificial apple flavor, niacin supplement, zinc oxide, vitamin A acetate, copper sulfate, ferrous sulfate, potassium iodide, manganous oxide, cobalt carbonate, sodium molybdate, sodium selenite, zinc sulfate, manganese sulfate.
Monocalcium Phosphate, Salt, Processed Grain By-Products, Magnesium Oxide, Calcium Carbonate, Potassium Chloride, Zinc Sulfate, Dried Molasses, Soybean Oil, Vitamin E Supplement, Zinc Proteinate, Sodium Selenite, Manganese Proteinate, Vitamin A Supplement, Vitamin D Supplement, Ethylenediamine Dihydriodide, Copper Sulfate, Yeast Culture, Copper Proteinate, Organic Selenium, Cobalt Carbonate.
It’s unfortunate that all these ingredients are labeled as top-quality food for ranch livestock, and caretakers are led to believe this claims.
Would you be able to advise regarding the level of contaminants that could be transferred into the soil? Some organic gardeners consider them to be trace amounts and therefore negligible. I’m questioning that logic…
Additionally, is there another method you personally would suggest for nutrient replacement in soils other than rotation every other year with cover crops?
Thank you so much for any advice you can provide!
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songberryfarm
February 23, 2015
Hi Tamara,
Thanks for your comment and my apologies for the delayed response. Many of the ingredients you list (the oxides, sulfates, phosphates, and carbonates and others) are simply common forms of minerals, and you’d find exactly the same ingredients in an organically-approved livestock mineral – they are also already present in your soil. I don’t see anything in this list that I would consider a soil “contaminant” – anything like that is far more likely to make the animals sick long before it would make your soils sick or cause issues in the plants – a healthy soil biology is a pretty robust system!
I’m not real familiar with alpaca ranching, but one concern I’d have would be any products used against intestinal parasites – certain conventional de-wormers can have a negative impact on soil biology.
Finally, cover crops will keep nutrients cycling in soils and can also make minerals more available to plants, but they cannot replace the nutrients that are removed by harvest. If you keep harvesting vegetables without returning nutrients to the soil, you’ll eventually deplete those minerals, regardless of how much cover cropping you do.
Regular soil testing will help you evaluate the current levels and balance of minerals in your soils and allow you to track them over time. When you’ve identified what’s needed, there are actually a wide range of natural soil amendments available to address any deficiencies. The alpaca manure is providing a wide range of major and minor elements, with the major benefit of adding organic matter, so it’s a great option if your soils are already in reasonably good shape, and as long as you don’t overdo it!
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Wm Pilacinski
May 17, 2015
Are you aware of: Association of farm management practices with risk of E. coli contamination in pre-harvest produce grown in MN and WI by Mukherjee, et al, 2007. Int’l J of Food Micro?
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rob
May 21, 2015
Thanks for the comment. Yes, I’m aware of that paper and have discussed its implications with scientists on several occasions. Andrew Kniss brings it up in this blog post (http://weedcontrolfreaks.com/2015/04/stop-saying-organic-food-is-less-safe-unless-you-can-provide-evidence/), pointing to this conversation about it (https://twitter.com/songberryfarm/status/390650445930442752).
The bottom line is that this work conflated results from both certified organic and non-certified “organic” farms and used poor statistical analysis to reach their conclusions.
Finally, here is a much more recent (2013) presentation from that study’s lead author: http://bit.ly/1Ao93Ab His conclusion is very clear: “Not only scientific but as well as recall data support the idea that the safety of organic produce is equivalent to conventional.”
Thanks again for reading and commenting!
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Mallory
January 24, 2023
Thanks for tthis blog post
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