Rebsie just did a post on this here. Before that it appeared on the Green Lane Allotments site.
The issue seems to be a new hormone based weed killer called aminopyralid. While it’s not approved for use on food crops, it’s applied to pasture land used to graze cattle. It’s very persistent, and residues are contaminating gardens and allotments where the resulting manure was applied.
It’s really part of a very deep seated tradition here in northern Europe, as well as other places in the world, to use manure on gardens. There are really a lot of reasons why this is not a good idea, and this contamination is just the latest example.
If you keep your own animals this is a completely different story, but modern farm animals are simply not a safe source for garden manure. There are also several other reasons why it’s not a good idea to apply fresh manure to your garden, under any circumstances.
Contamination
Modern farm animals consume a wide range of chemicals, foods and medicines that persist in their manure that you really don’t want in your garden. This is true in even so called organically raised animals. These things range from hormones and antibiotics, to GM animal feeds, as well as pesticides like in this case. Farmers are really quite often very detached from what they are doing, and have been known to feed really outrageous things to their animals.
We like to think there is some quality control, but in fact there is very little almost anywhere in the world. A very small percentage of our food is tested in any way. Even with organically raised animals, there’s often little in the way of quality control other than the paperwork that went along with the certification.
The other very important type of contaminants are the biological ones. New strains of Ecoli that have emerged in recent years are really quite scary. These can make you very sick, and are spread by animal manure. The recent contamination in the US of packaged lettuce is suspected to have come from cows on a neighboring field, and this contamination was spread all through the country. Even if you have access to manure that didn’t come from factory farm animals, the risk remains because these diseases now infect livestock worldwide.
The majority of these contaminants will survive both composting and ageing of the manure, and apply not just to cows but other animals like sheep and horses as well.
If you have an organic garden, and you apply manure obtained from a third party, you probably don’t really have an organic garden after all.
Free or Soluble Nitrogen
The other problem with manures is they are high in nitrogen that is not fixed, but rather soluble.
With all nutrients it’s not only an issue if they are in the ground, but if they are actually in a form that can be used by your plants.
The issue with manure is almost all of the nitrogen can be used immediately, and is water soluble as well. What this means is you will have a hard time regulating how much your plants absorb. In the short term it will probably make your plants grow quickly, and in the longer term it will wash away so you’ll have to add more. For many plants the stress of this will just kill them, especially very young plants. For other plants, you may make them vulnerable to various diseases or other problems. A good example is garlic rust that I recently posted about.
Fixed Versus Soluble
The other issue, that I am suddenly noticing in my community garden complex, is that using soluble nitrogen in the form of manure or fertilizer can prevent the establishment of fixed nitrogen, and actually deplete long term nitrogen levels.
Having fixed nitrogen in your garden is the best possible thing, because generally it becomes available at the rate your plants need it. All nitrogen you add in the form of fertilizer or manure is soluble. While there are several ways of getting fixed nitrogen into your garden, the most efficient is to grow nitrogen fixing plants like beans or peas.
The issue is that nitrogen fixing plants do this according to their own needs. This means, if you apply soluble nitrogen in the form of fertilizer or manure, any nitrogen fixing plants in your garden probably won’t need to fix much of their own nitrogen. Since whatever soluble nitrogen you’ve applied will eventually wash away, this will leave your garden without any long term benefit.
The only way to fix nitrogen in manure is to compost it first. Since composting requires a good balance between nitrogen and carbon, you will need to mix the manure with a very large quantity of high carbon material like straw in order to get good quality compost in the end. An alternative to composing manure is to age it for a year or two, in which case the soluble nitrogen will wash away or dissipate into the air.
Trusted Animals
If you have animals you raise yourself or otherwise get manure from a trusted source, there is little harm in composting or ageing this first and adding it to your garden. Perhaps when all is said and done, there is not a great benefit to this either. This will provide a source of organic material and compost to your garden, but perhaps there are easier ways to do this.
Permaculture Principles
This is another very good example why it’s best to apply permaculture principles to your garden, and avoid inputs and outputs where possible. With a properly run garden or farm, you won’t need anything except a couple of garden tools.
History
The reason why there is a culture of adding manure to gardens is because a long time ago some farmers realized they could avoid some crop rotations if they added manure or other materials to their garden. This turned out to be a short term solution to a longer term problem, but the idea stuck. This in turn led to the idea that somehow adding manure or other fertilizers or chemicals to your garden was a good thing to do.
