Manure

Manure is a vital form of organic matter used as fertilizer in agriculture.

It provides essential nutrients to the earth to help plants thrive. Most manure consists of animal feces, but other forms exist. These include compost, which is decomposed organic material, and green manure. Green manure involves growing specific crops, such as clover, just to plow them into the soil.

This process incorporates organic matter and nutrients directly into the ground. By doing this, farmers can increase the fertility of their land.

The mechanism of manure relies on a complex soil food web. When manure is added to the earth, it provides organic matter and nutrients like nitrogen. These elements are utilized by tiny organisms such as bacteria and fungi.

These microbes act as the foundation for larger organisms in the soil. This chain of life helps improve soil aggregation, which is the soil structure. Better aggregation allows the soil to hold more water and nutrients. This improved structure makes the land much more fertile for growing crops. Manure also encourages microbial activity, which promotes the supply of trace minerals.

There are three main classes of manure used in modern soil management. The first is animal manure, which is the most common type. This includes farmyard manure, which often contains straw bedding used for animals. It also includes slurry, a liquid form of manure. Slurry is common in intensive livestock systems where animals live on concrete or slats.

The second class is compost, made from decomposed plant remnants or animal dung. The third class is green manure, which uses living plants to fix nitrogen. For example, legumes use Rhizobia bacteria in root nodes to fix nitrogen in the soil.

Different animals produce manure with very different chemical properties. Sheep manure is high in nitrogen and potash, which is a type of mineral. In contrast, pig manure is relatively low in both of those nutrients.

Poultry manure, such as chicken litter, is highly prized because it is concentrated in nitrogen and phosphate. Cattle manure provides a good source of both nitrogen and organic carbon. Horse manure is unique because horses do not digest seeds as well as cattle do. Because horses eat mostly grass and weeds, their manure can contain undigested seeds. Even guano from seabirds and bats serves as a potent form of manure.

History shows that humans have used animal manure for centuries to support farming. People have used cow dung and chicken manure to improve their harvests for a very long time. Today, manure is used in many ways, including commercial composting and bagging for sale. In some parts of the world, dry animal dung is even used as a fuel. In 2018, Austrian scientists discovered a new way to use this resource. They found a method to produce paper from the manure of elephants and cows.

Using manure also presents several environmental and health challenges. One major issue is the unpleasant odor caused by compounds like skatole.

In intensive pig farming, slurries can be very smelly due to anaerobic fermentation. To manage this, farmers may use a method called knifing, where they inject manure directly into the soil. There are also risks regarding pathogens, which are organisms that can cause disease. These can be carried by flies or rodents and might affect food safety. Additionally, manure can emit nitrous oxide, a greenhouse gas that contributes to climate change.

Another complex issue involves the presence of antibiotics in the soil. A 2007 study from the University of Minnesota found that crops can accumulate these drugs. Specifically, foods like corn, lettuce, and potatoes were found to contain antibiotics from manure. This happens when livestock are treated with drugs that end up in their waste. Organic farming standards, such as those from the Soil Association, manage this risk. Some organic farmers use their own manure to avoid drug residues. Others ensure that any nonorganic manure is fully composted to degrade residues and eliminate bacteria.