What you’ll learn in this post about using manure in your garden:
- Benefits and drawbacks of manure in the garden
- Types of manure you can use in the garden
- Fresh vs. composted manure
- Nutrient availability of manure
- How to apply manure to your garden
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Manure has been used to fertilize farms and gardens for centuries. It is a prime source of slow release nutrients and adds organic matter to the soil. As long as you use the proper methods, you can safely take advantage of its many benefits.
Benefits and Drawbacks of Manure
Adding manure is an excellent way to improve your soil. It promotes the growth of soil life such as earthworms and beneficial microbes, which in turn creates better tilth and soil structure. When you amend sandy soils with it, you’ll increase your soil’s water-holding capacity. Amending clay soils will increase drainage. As the soil life works, the rich humus left behind will create dark, spongy topsoil.
The soil life will make a majority of the nutrients available the first year, with the rest feeding the plants over the next one or two years. As time goes on, and nutrients build up in the soil, you will need to add manure on a less regular basis. This is especially true in a no till garden as the soil life builds up.
“Adding manure to your soil promotes the growth of soil life such as earthworms and beneficial microbes, which in turn creates better tilth and soil structure.”
In fact, you need to be careful not to add too much manure to your garden. If you do, you may experience excessive vegetative growth, salt build up, nutrient runoff, and nitrate leaching. Proper application rates are essential when using manure.
Application techniques are also important, especially when using fresh manure. Incorrect methods can spread E. coli, Salmonella, Campylobacter bacteria, and Giardia or Cryptosporidium protozoa.
My chickens pooping, scratching and creating compost using the deep litter method.
Types of Manure to Use
Typical manures used in the garden are from poultry, cows, sheep, and horses. Never use manure from cats, dogs, or pigs (unless composted properly) as they are more likely to spread parasites to humans.
Manures may or may not have bedding mixed in. The more bedding mixed in, the more diluted the nutrients are. You can also choose from fresh or composted manure.
“If broadleaf herbicides have been used on lawns, pastures, or hay that animals have eaten, their residues can pass through their digestive system to the manure and remain even after being composted.”
It’s important not to use manures that have been contaminated by herbicides. If broadleaf herbicides have been used on lawns, pastures, or hay that animals have eaten, their residues can pass through their digestive system to the manure and remain even after being composted. The herbicides will break down eventually, but they can cause damage in the meantime. If you use contaminated manure or compost, your crops will experience poor germination rates, seedlings will die, and vegetation will be twisted and malformed.
Fresh vs. Composted Manure
Fresh manure can cause more problems than it solves, so composted manure is generally recommended. However, you can use fresh manure if you take certain precautions.
Fresh manure contains high levels of ammonium, or soluble nitrogen, compared to composted manure. Poultry manure specifically will likely cause nitrogen burn in plants if it has not been composted. Fresh manure must be incorporated 6 to 8 inches deep within 12 hours of application, or else the majority of the ammonium will be released into the atmosphere.
Fresh horse manure is notorious for containing weed seeds, which can lead to major weed problems in your garden.
Human pathogens are easily transmitted through fresh manure. E. coli, Salmonella, Campylobacter bacteria, and Giardia or Cryptosporidium protozoa can live in manure and contaminate crops. For this reason, organic standards dictate that fresh manure must be applied 120 days before planting to give pathogens time to die off.
“Many commercial operations will pasteurize their compost to destroy pathogens, however beneficial microorganisms are also killed in the process.”
You can avoid these issues by using composted manure. To guarantee harmful pathogens have been killed, the compost pile must reach 131 to 140 degrees for several weeks. The pile must be turned regularly to ensure all of the manure had been exposed to hot enough temperatures.
Many commercial operations will pasteurize their compost to destroy pathogens, however beneficial microorganisms are also killed in the process.
This is the compost my chickens make for me. All I have to do is feed them food scraps and yard waste, add some “browns” like straw or woodchips to their run every now and then, and screen the compost when I’m ready to use it. Chickens make composting easy.
While you can estimate the nutrients available in manure, the only way to get an accurate analysis is to test it in a lab. When collecting your sample, be sure to collect several subsamples and mixed them together to get the most accurate results.
If you are buying your manure commercially, you can request the nutrient analysis from the seller for N (nitrogen), P2O5 (phosphorous), and K2O (potassium) content. The analysis will show you the nutrient content, but availability depends on the microorganisms in your soil breaking the nutrients down into a form plants can use.
If you don’t want to take on the expense of lab tests, you can approximate the nutrient content. For example, the Livestock Waste Facilities Handbook says that horse manure with bedding will contain 4 lbs/ton of soluble, or readily available, nitrogen, and an additional 10 lbs/ton of organic nitrogen that still needs to be broken down by microbes. It will also contain about 4 lbs/ton of phosphorous and 14 lbs/ton of potassium.
Composted poultry manure will contain about 1 lb/ton of soluble nitrogen, 16 lbs/ton of organic nitrogen, 39 lbs/ton of phosphorous, and 23 lbs/ton of potassium. You can compare that to fresh poultry manure without bedding, which is estimated to contain 26 lbs/ton of soluble nitrogen, 7 lbs/ton of organic nitrogen, 48 lbs/ton of phosphorous and 34 lbs/ton of potassium.
“If the carbon to nitrogen ratio in your manure exceeds 30:1, the nitrogen will be tied up temporarily while it helps the carbon break down.”
While fresh manure can contain too much nitrogen for the garden and burn plants, composted manure contains organic nitrogen which is not available to plants until microbes convert N to NH4. This occurs over years.
Typically, 25 to 50% of the manure’s nitrogen will be available the first year, with less being available each subsequent year. In general, 70 to 80% of the phosphorous and 80 to 90% of the potassium will be available the first year.
If you get manure that contains bedding, it is important to be aware of the carbon to nitrogen ratio (C:N) in the manure. When the ratio exceeds 30:1, the nitrogen will be tied up temporarily while it helps the carbon break down. If this is the case, you may need to add nitrogen fertilizer to your plants until the nitrogen in the manure is released.
Our chicken coop is attached to the garden for easy access. All I have to do is screen my compost over my wheelbarrow, then dump it and spread it out wherever I need it.
How to Apply Manure to Your Garden
It is important to apply the correct amount of manure to your garden. If you don’t use enough, you’ll end up with nutrient deficiencies and poor yields. Too much can cause phosphorous run off, excessive crop growth, and nitrate leaching.
It is recommended that you test your soil and the manure you use to make sure your nitrogen and phosphorous levels are optimal. If you add manure every year, you risk building up excessive levels of phosphorous. By testing your soil, you can make the decision to use a different kind of fertilizer to allow the phosphorous levels to come back down.
However, if you don’t want to put up the money for these tests, the following application rates are recommended by the Wisconsin Master Gardener Program:
- For every 100 square feet, apply 75 pounds of cow manure without bedding, 95 pounds of cow manure with bedding, or 200 pounds of composted cow manure.
- For every 100 square feet, apply 40 pounds of sheep manure without bedding or 50 pounds of sheep manure with bedding.
- For every 100 square feet, apply 20 pounds of poultry manure without bedding, 30 pounds of poultry manure with bedding, or 70 pounds of composted poultry manure.
- For every 100 square feet, apply 65 pounds of horse manure with bedding.
A 5 gallon bucket holds roughly 25 pounds of manure or compost, so you can use it to measure instead of weighing your materials. For example, use a little less than one bucket full of poultry manure without bedding on a 10 x 10 foot garden, or a little less than 3 buckets full of composted poultry manure over the same space.
“It is ideal to spread fresh manure in the fall so that it is ready for spring, or in spring to plant a fall garden.”
When using fresh manure, there are a few extra guidelines you should follow. The USDA National Organic Program rules state that if the edible parts of vegetables have contact with the soil via rain or irrigation splash, that the manure must be applied 120 days prior to harvest. If the edible portion is not in contact with the soil, then manure must be applied a minimum of 90 days prior to harvest. This prevents harmful pathogens, such as E. coli and Salmonella, from spreading. It is ideal to spread fresh manure in the fall so that it is ready for spring, or in spring to plant a fall garden.
Fresh manures are high in salts, so be sure to wait 3 to 4 weeks after applying fresh manure to plant seeds to avoid salt damage. It needs to be incorporated into the soil within 12 hours of application, or else the ammonium will be released into the atmosphere.
With the proper application rates, techniques, and safety precautions, manure can be an excellent way to provide nutrients and build up the soil in your garden.
This article was originally published in the November 2018 issue of Maximum Yield Magazine.
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