What Is Manure? Why Is It Such an Environmentally Valuable Material?

Manure is an organic fertilizer made from the dung of domestic livestock including horses, cows, and poultry. It may also contain urine and bedding material like straw or sawdust.

Manure is an environmentally valuable resource because it contains nutrients like nitrogen, phosphorus, and potassium. These nutrients help boost the growth of plants and vegetables in farms and in your home garden. Besides adding nutrients to the soil, the organic matter within manure helps soil retain moisture, allows for better gaseous exchange, and adds beneficial microbes.

The organic content in manure can also be used to produce renewable energy, which has the added benefit of preventing the release of the greenhouse gas methane into the atmosphere.

What Exactly Is Manure?

Manure is made from animal dung. It can also contain bedding material like straw or sawdust and urine. The most common types of manure found for use in gardens as a fertilizer come from cows, horses, and poultry.

Manure contains five main components, all of which have useful applications across a range of industries.

• Nutrients. Primarily nitrogen, phosphorus, and potassium. These can be used in compost or fertilizer to improve soil quality. These nutrients can also be converted via biomass processes into soil amendments and animal feed.
• Organic matter. These carbon-containing compounds help improve soil structure and its ability to retain water. Adding carbon from manure to the soil may also help reduce atmospheric carbon. Soil with a higher percentage of organic matter helps improve crop yield and is also more resistant to erosion from both wind and water. Organic matter also increases gaseous exchange and adds beneficial microbes to the soil.
• Solids. Fresh manure has a high water content and once this is removed, the solid manure portion can be repurposed as a bedding material for farm animals.
• Energy. The energy within manure can be used to generate biogas, bio-oil fuels, and syngas.  
• Fiber. Manure contains a lot of fiber, both from undigested food and bedding materials. Manure fiber can be used to create products like seed starter pots and building materials.

Historically, manure has been a valuable resource for farmers and smallholders, although on an industrial level it seems to have fallen out of favor compared to inorganic fertilizers. According to the USDA, only 5% of U.S. cropland is fertilized with manure.

The nutrient level of manure will vary depending on the species of animal it comes from, as well as factors like the type of food the animal eats and its overall health. Additions like bedding material or urine will also affect the nutrient levels, as will whether the manure is fresh or composted.

Uses of Manure

Manure can be used as a fertilizer for your plants and vegetables. If you collect the manure of your own animals, or those of a neighbor, then this is far more cost-effective than buying commercially produced compost or inorganic fertilizer. It also drastically reduces costs when compared with the production and transportation of commercial fertilizer.

Research from the University of Wisconsin-Madison found that compared to inorganic fertilizers, manure offers better results when it comes to both soil quality and crop yield.

If you have your own small farm or homestead, then the manure that your own animals produce can be put to work fertilizing your vegetable patch. Once your manure has been fully composted it can be mixed with your existing topsoil.

How to Compost Manure

Due to the high nitrogen content of mature, it’s best to compost it before adding it to your soil. Without this step, your plants may become damaged.

Manure from poultry and sheep is especially high in nitrogen and other nutrients, so these always need to be composted first. Fresh manure can decrease seed germination and burn seedlings.

Another downside to fresh manure is that it has a stronger odor and as a result, attracts flies. It may also contain pathogens and seeds from plants that you may not want growing in your garden. To solve these issues, leave the manure to break down for 1-6 months. You’ll want to use the hot composting method, as the high temperatures will help kill fly eggs, pathogens, and weed seeds as well as reduce odors.

When composting manure, follow the same instructions used for backyard composting. Consider manure a "green" organic material. If the manure doesn’t contain bedding material like straw or sawdust, you will need to add "brown" material like leaves, shredded paper, or grass clippings to balance out the levels of nitrogen and carbon.

Composted manure should look more like soil, with a dark and crumbly texture. It will have lost any unpleasant odor and instead have a pleasant organic smell.

Types of Manure

Using manure as a fertilizer instead of a commercially prepared organic or inorganic fertilizer is a great way to add nutrients and organic matter to your soil in an environmentally friendly way. Synthetic fertilizers can add nutrients to your soil but they cannot add organic matter that helps improve soil quality and water retention.

There are a few different types of manure that are commonly available, each with its own pros and cons. The type you choose to use will depend on what's available in your area and whether you have the means to transport it to your home.

Unless you test the manure, you won't know the exact nutrient content, but as a general rule, poultry manure is highest in nutrients, followed by cow manure, and then horse manure.

Cow Manure

Manure from cows is a very popular organic fertilizer. It may be difficult to obtain fresh cow manure as most farms will keep it for their own use, but you can buy pre-composted bags in most garden centers.

Horse Manure

Horse manure is suitable for most plants, and fresh manure can usually be obtained from local barns and composted at home.

Chicken Manure 

Chicken manure is very high in nitrogen, so should always be composted until it’s fully broken down.

The manure from sheep, goats, pigs, and other poultry can also be used but these are less widely available.

Manure for Energy Production 

As well as adding valuable nutrients to the soil, the elements within manure, including carbon, can also be used to produce fuels for transport, heating, or to generate electricity.

A process called anaerobic digestion is used to turn manure into biogas. This fuel can be used directly at the site of production to generate electricity or heat or sold to the power grid.

Using a process called gasification, manure can be converted into syngas, which can then be used to power fuel cells, turbines, and engines.

Generating energy using a natural organic matter like manure helps to reduce our reliance on unsustainable fossil fuels. Farmers can save money by switching to fuel or electricity produced using these methods.

The USDA recommends expanding the use of manure for energy production, and notes that this shouldn't affect the amount of manure available for use as a fertilizer, as the important nutrients are leftover as a byproduct of energy production.

Environmental Impact of Manure and How to Prevent It

If used improperly, manure can negatively impact the environment, so it’s important to take steps to reduce the following risks:

Nutrient Runoff

This is usually a concern when manure is placed on areas near rivers or streams. When it rains, the manure can be washed off into the waterway. When manure (or any other fertilizer) enters waterways like this, the additional nutrients cause a spike in the growth of undesirable aquatic plants like algae, a process known as eutrophication. This can affect water quality and lead to the death of fish and other wildlife in the area.

If you live near a waterway, follow best management practices, including leaving a buffer strip of vegetation along waterways and avoiding applying manure just before rain or wind is forecast.

Pathogens

Fresh maure can contain pathogens including bacteria, viruses, and protozoa. When handling fresh manure, wear gloves and make sure to wash your hands afterward. Using the hot composting method to break down manure kills off any pathogens found in fresh manure.

Odor

Fresh manure can have an unpleasant odor and be attractive to flies. These can both be solved by composting manure. When adding fresh manure to your compost heap, make sure to cover it with a layer of brown material to help reduce both odor and flies.