What is Manure?
Manure can be considered the original fertilizer and an important component for those wishing
to practice organic gardening. The most common sources of manure are cows, horses, sheep,
pigs, goats, and poultry. By using manure you will be adding important micro and
macronutrients to your soil that will be slowly released over time, improve soil aeration and
water retention thereby building good soil structure and texture. Having good soil also offers
supportive system for beneficial soil organisms and earthworms. Furthermore using manure
means you are recycling which removes dependency on chemical fertilizers.
Soil Nutrients and Manure Types
Manures differ from each other based on source, age, how they were stored (piled, spread,
turned over or not), and the animal
Manure Nitrogen Phosphorus Potassium bedding material, which may be
type
(N)
(P)
(K)
mixed in. For that reason it is
Chicken
1.1
0.8
0.5
difficult to provide precise guidance
about how long manure should be
Cow
0.6
0.2
0.5
aged before use, how much to use,
Duck
0.6
1.4
0.5
or the expected nutrient content. In
Horse
0.7
0.3
0.6
general all of these processes affect
Pig
0.5
0.3
0.5
the nutrient content of manures.
Rabbit
2.4
1.4
0.6
The general breakdown in nutrient
Sheep
0.7
0.3
0.9
content can be found in Table 1
Steer
0.7
0.3
0.4
which describes the approximate
levels of total nitrogen (N),
Table 1: Manure types and approximate NPK percentages
phosphate (P), and potassium (K)
that should be found in specific manures.
The relatively high nitrogen content makes manure extremely valuable in composting, where
it activates soil bacteria and contributes to rapid
decomposition of organic matter. This macronutrient
also has the greatest potential for soil and water
pollution. Nitrates and ammonium can build up in the
water
table
and
contaminate
water
course.
Understanding how nitrogen is released into the soil is
key to ensuring it is used mindfully.
Important to keep in mind is that not all the nitrogen in
the manure is available at the same time. Some benefit
will be obtained in the second and third years following
application. Taking into account residual release of
nitrogen in subsequent years should help to avoid
excessive applications. Figure 1 shows a great example
of how the nitrogen cycle works within the substrate.
Figure 1: Nitrogen cycle and its components
General rules of thumb for nitrogen are that organic
nitrogen released during the second and third cropping
years after initial application will be 50% and 25% of that mineralized during the first cropping
season. Remember that some manures and composts contain high levels of phosphorus, so
if organic nutrient sources are regularly applied at rates to meet crop nitrogen demands, the
amount of phosphorus in the soil can build up to excessively high levels. Regularly sampling
the soil to determine nutrients needs for the year will help ensure that nitrogen is not overapplied.
Keep in mind that the more nitrogen you have in your amendment the more potential it has
of burning your crops. Best to add it to the soil during the off season of planting or when a
portion of the plot is resting. When to apply for different application can be found below in
Table 3.
Type of Garden
Best
manure
source
When to
apply it
Concerns and Considerations
All manures can contain pathogens
such as salmonella, listeria, E.coli
0157:H7, bacteria and parasites like
Flower
Cow or horse
Early spring
roundworms and tapeworms. While
Vegetables
Cow, horse, or
Fall or spring
bacteria and fungi already living in
chicken
the soil will complete most of these
Potato or root crop Cow, horse, or
Fall or spring
risks we recommend that raw manure
chicken
not be used in any of the Community
Acid loving flowers
Cow or horse
Early fall or not Garden beds unless prior
and vegetables
at all
conversations have been had
between garden staff and plot renters.
Table 3: Types of gardens and best manure sources
This is for the protection of yourself
and others who use the garden. Food safety and potential concern for contamination are
both concerns for the organic gardener. Always remember to wash your hands after working
with soil that has manure added to it. This also goes for any root of leafy vegetables. If you
are still concerned about potential pathogens rest assure that cooking vegetables will kill
them. Furthermore it is not recommended that gardeners use any manure from dogs, cats,
or other meat-eating animals, since there is risk of parasites or disease organisms that can
be transmitted to humans. Finally a way to further protect yourself is to not use fresh
manure. That also means do not make compost tea from any manure period.
Where and How to Source Manure
If you are looking for cheap manure it can be found in bags for sale from farmers in Saanich
near Keating Cross Road for a few dollars. Manure can also be found by making connections
with a local farmer. If you are able to drive directly to the farm and haul your own manure to
your garden it is often free. Try checking out Used Victoria for suppliers. Once you find a
supplier feel free to ask questions about the quality of the manure such as if the animal is on
antibiotics or medicines, what types of food it eats, it it’s been cured, bedding material
content, and so on. These questions will help you figure out if the manure is in contact with
any chemicals or pesticides and any potential weed sources.
Sometimes it is difficult to determine whether a purchased compost product may pose a
contamination hazard. The organic standards require a specific time period and temperature
for composting, in order to ensure that any pathogens are eliminated. Compost that does not
meet these requirements is considered to be the same as raw manure. Please refer below for
information on the use of raw manure.
Using Composted or Raw Manure
Raw
While using raw compost is not recommended if composting is not available there are ways
to add it to the garden while not causing harm. Here are some tips:
o
Do not place raw manure directly on the soil or in the garden. This action will release
highly soluble nitrogen compounds and ammonia which can burn plant roots and
interfere with seed germination.
o
If you must apply fresh manure do it before you garden is planted as a soil
conditioner. The U.S. Department of Agriculture recommends an application window
of 120 days prior to harvesting and eating any vegetable where the edible part
comes in contact with the ground. That includes anything grown below the ground
(beets, carrots, potatoes, radishes...) as well as anything sitting on the ground, like
lettuce, spinach and even vining crops like cucumbers and squash. The logic behind
this window is that pathogens will likely be rendered unviable by soil microorganisms
after a certain time period, and will no longer pose a threat to food safety.
o
It is very common for farmers and gardeners spread fresh manure in the fall or
winter, and till or turn it in at spring planting time.
Composted
As mentioned above manure can contain pathogens, bacteria, parasites and weed seeds.
The only way to effectively remove most of these contaminants is through composting. The
process of composting will allow better access to the nitrogen, potassium, phosphorus, and
bacteria that is good for the soil. For direct use in the garden, first aging manure for 4-6
months is a good rule of thumb.
When manure is spread in the spring, even if aged, it is safest to wait for at least one month
before planting crops, since the microbial activity it stimulates may interfere with seed
germination or plant growth before that time. Ideally composted manure is spread directly
over the soil, it is helpful to add about 40 lbs. per 100 square feet, turned into the top 6 to
9 inches.
A hot composting system (when the pile reaches between 130-155 degrees F) destroys
most weed seeds, but many composting systems are inexact and seeds can come through.
For that reason, those who use manure usually plan on weed-control techniques such as
mulching, interplanting (growing cover crops between rows), and hand-weeding. Please
refer to the supplement 1 that further describes what a hot composting system would look
like.
References
Alberta, G. o. (2005, January). Manure Composting Manual. Retrieved from Alberta Agriculture and
Rural Development: http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex8875
Almanac, T. O. (2015, Feburary). When to Spread What. Retrieved from The Old Farmers Almanac :
http://www.almanac.com/content/manure-guide
Carl J. Rosen, P. M. (2015, February). Using manure and compost as nutrient sources for fruit and
vegetable crops. Retrieved from Univeristy of Minnesota: Commercial Fruit and Vegetable
Production: http://www.extension.umn.edu/garden/fruit-vegetable/using-manure-andcompost/
Charles Mazza, S. C. (2014, May 06). Using Organic Matter in the Garden. Retrieved from Cornell
University: http://www.gardening.cornell.edu/factsheets/orgmatter/
Fernandez-Salvador, L. (2014, September 19). Mother Earth News. Retrieved from How to Use Manure
in Organic Growing: http://www.motherearthnews.com/organic-gardening/how-to-usemanure-zbcz1409zdeh.aspx
Gardening, O. (2015). Manure. Retrieved from Organic Gardening:
http://www.organicgardening.com/learn-and-grow/manure
Iannotti, M. (2015, February). Is Manure Safe to Use in Your Vegetable Garden. Retrieved from
About.com: http://gardening.about.com/od/fertilizer/a/Is-Manure-Safe-To-Use-In-YourVegetable-Garden.htm
Paige, J. (2015, February). A Guide to Composting Horse Manure. Retrieved from WSU Cooperative
Extension: http://whatcom.wsu.edu/ag/compost/horsecompost.htm