Manure: Definition, types, uses, benefits and more

Manure refers to the organic waste produced by livestock animals and serves as an invaluable fertilizer for crop production.

Animal manures contain essential macronutrients such as nitrogen, phosphorus, and potassium that are vital for plant growth and soil health.

There are two main types of manures: hot manures from omnivores and carnivores like pigs and chickens, and cool manures from herbivores like cows and horses.

• Hot manures are high in nitrogen and need composting before application to avoid burning plants.
• Cool manures can be directly applied but benefit from some aging.

When used appropriately, manures can enrich soils by returning nutrients, enhancing soil structure, and supporting microbial activity.

What is manure?

Manure refers to animal excreta or animal bedding that can be used as an organic fertilizer for crops and plants. It contains nutrients such as nitrogen, phosphorus, and potassium that are essential for plant growth.

Manure is produced by livestock animals like cows, horses, sheep, goats, pigs, and chickens. It consists of animal feces and urine, along with bedding materials like straw and hay. Over time, microorganisms act on the manure to break down its organic matter. This releases nutrients in forms that plants can absorb and utilize.

The use of manure provides the following benefits:

• Improves soil structure and fertility
• Supplies organic matter and nutrients for plant growth
• Enhances moisture retention in soil
• Promotes soil microbial activity
• Reduces the need for synthetic fertilizers
• Aids sustainable farming practices

With proper management and application, manure can serve as an excellent organic fertilizer source.

Notes:

• Data shows a steady increase in manure nutrients recycled as fertilizer in the U.S., from 90.4 million tons in 2012 to 104.1 million tons in 2022.
• Cropland acreage receiving manure as fertilizer also rose from 22.5 million acres in 2012 to 25.5 million acres in 2022.
• Statistics estimate annual manure fertilizer use and application in the United States.

Types of Manure

There are many types of manure produced by different animal species. The nutrient content in each manure type also varies. The major types of manures used in agriculture include:

Cow

Cow manure is one of the most commonly used manures. It has moderate amounts of nitrogen, phosphorus, and potassium. Cow manure contains about 0.5-0.7% nitrogen. Fresh cow manure has a nitrogen-phosphorus-potassium ratio (N-P-K) of 0.6–0.2–0.5.

With composting, most cow manure reaches an NPK ratio of 2-1-1. Cow manure also contains good organic matter to improve soil structure. It has a carbon-to-nitrogen ratio between 15:1 and 25:1.

Horse

Horse manure has high amounts of nitrogen and potassium. Its typical NPK ratio is 0.7–0.3–0.6. Horse manure contains more bedding materials, like straw, relative to the manure. It has a carbon-to-nitrogen ratio between 25:1 and 50:1.

Pig

Pig or hog manure can have very high nitrogen levels. Fresh pig manure may contain up to 2% nitrogen. The NPK ratio of pig manure is around 0.5–0.3–0.5. Pig manure requires proper composting before field application to avoid burning plants.

Sheep and Goat

Sheep and goat manures have relatively higher amounts of nitrogen, with an NPK ratio of 0.7–0.4–0.9. Sheep manure, in particular, has very high nutrient levels. However, their droppings are usually mixed with bedding materials, which increases their carbon content.

Poultry

Poultry litter, or manure, comes from chickens, turkeys, and other domestic birds. Poultry manure is very rich in nitrogen and phosphorus. Its NPK ratio can be 1.1–0.8–0.7 or even higher for nitrogen. Fresh poultry manure may contain 4 to 6% nitrogen. Proper composting is essential before using poultry manure.

Rabbit

Rabbit manure has among the highest nutrient levels. Its NPK ratio can range from 2.4 to 1.4 to 0.6. Vermicomposted rabbit manure provides balanced nutrition for plant growth. Fresh rabbit urine and droppings can damage plants, so composting is a must.

Green

Green manures are cover crops that are grown and then plowed under the soil. Common green manures include legumes like clover, vetch, and peas. As legumes fix nitrogen, they increase soil fertility. Grasses and forbs can also be used as green manures.

Uses of Manure

Manure has served as a vital natural fertilizer for crops for centuries. Both conventional and organic farms utilize manure to meet crop nutrient needs through the following methods:

Raw Manure Application

Raw or fresh manure can be directly applied to agricultural lands. Solid manures like cow, horse, sheep, and poultry manure may be spread unprocessed on fields. Liquid manures like swine effluent are sprayed on land. Direct raw manure application is suitable for non-edible crops.

Composted Manure

Composting stabilizes nutrients in manure and kills pathogens. Well-composted manure does not burn plants. It releases nutrients slowly over time for long-term benefits. Composted manure is ideal for vegetable crops, gardens, and landscaping uses. Only aged or finished compost must be used.

Manure Teas

Manure teas involve extracting nutrients from composted manure into a liquid solution. Compost is soaked in water for days or weeks, which releases soluble nutrients. The filtered manure tea provides an immediate fertilizer source upon foliar application to plants.

Manure Pellets or Granules

Dehydrated and pelletized manure provide concentrated nutrients in an easy-to-use form. Manure pellets break down gradually to supply nutrients when needed by crops. Pellets allow wider manure distribution through broadcast spreaders. Granular forms also reduce manure odors.

Blended Fertilizers

Manures are often mixed with other organic materials to create custom blended fertilizers. The addition of rock powders, fish emulsions, seaweed, etc. balances nutrients in manure. Such value-added organic fertilizers cater to specific crop needs.

Anaerobic Digestion

Anaerobic digestion of manure produces biogas for renewable energy generation.[1] The nutrient-rich digestate byproduct serves as a biofertilizer. Manure processing via biodigesters reduces pollution while harnessing its fertilizer value.

With its excellent nutrient profile, manure finds extensive usage as organic fertilizer across diverse agricultural systems.

Notes:

• Manure makes up 13% of fertilizer used in the U.S.
• The most widely used synthetic fertilizer is urea, at 31%.
• Other major synthetic fertilizers used include DAP, MAP, potash, and NPK blends.
• Ammonium nitrate has declined in use due to regulations.

Sources:

• USDA ERS
• IFDC Fertilizer Outlook 2022

Benefits of Using Manure as Fertilizer

Using manure and manure-based fertilizers provides multiple agronomic and environmental advantages:

Improves Soil Fertility and Health

Manure adds major plant nutrients like nitrogen, phosphorus, and potassium. Other nutrients like calcium, magnesium, and sulfur are also supplied. Continued manure application improves soil organic matter. It supports diverse microbial populations in the soil.

Enhances Nutrient Use Efficiency

Unlike synthetic fertilizers that readily leach out, nutrients in manure are released more slowly over time. Manure enhances soil cation exchange capacity (CEC), which retains nutrients. Greater nutrient retention also reduces pollution from fertilizer runoff.

Supports Sustainable Agriculture

Using locally available manure decreases reliance on external synthetic fertilizers. Manure-based farming allows for the creation of a self-sufficient closed nutrient cycle on farms. Sustainable crop production is achieved without chemicals.

Sequesters Carbon

Applying manure adds carbon to the soil, which improves its structure. Increasing stable soil organic carbon supports long-term carbon storage and sequestration. This offsets greenhouse gas emissions.

Reduces Erosion

Adding organic matter through manuring improves soil aggregation and water infiltration. It prevents soil compaction and surface sealing. Manured soils are more resilient to erosion losses from wind and water.

Increased Crop Yields

Adequate fertility availability from manure results in higher crop productivity. The diverse nutrients in manure also support better crop development compared to chemical fertilizers with limited nutrients.

Safe for Food Crops

Properly composted manure is free of harmful pathogens. It poses no health risks and can safely be used to fertilize fruits, vegetables, and other human food crops. This offers a natural alternative to chemical pesticides.

Low-cost source

Using animal manure available on or near farms reduces the need to purchase expensive synthetic fertilizers. Although some processing, like composting, may be needed, manure is still a low-cost organic fertilizer option.

With its multifaceted benefits, manure is an invaluable organic resource that can support both sustainable agriculture and natural ecosystem balance in the long run.

How to Compost Manure

For safe and effective use as fertilizer, fresh manure must be composted first. Here are some key steps for proper composting of different types of manures:

• Site: Select a well-drained, shaded site to prepare compost piles or bins. Avoid proximity to water sources.
• Aeration: Turn manure piles regularly and maintain porosity for oxygen ingress needed by compost microbes. Moisture should be 40–60%.
• Bedding: Bulk up manure by mixing with high-carbon bedding or crop residue. A 30:1 carbon-to-nitrogen ratio is ideal.
• Moisture: Water piles as needed to keep lightly moist but not saturated. Excessive wetness causes anaerobic conditions.
• Size: Piles should be at least 1 cubic yard (3′ x 3′ x 3′) in size to allow self-heating for sanitization.
• Time: Actively compost manure for 4 to 6 months minimum to stabilize nutrients and eliminate pathogens.
• Testing: Sample finished compost to verify safety regarding acceptable pathogen levels before field application.
• Storage: Cure mature compost for 3-6 months before use. Store in a covered area to prevent nutrient leaching from rainfall.

Proper manure composting converts raw animal waste into a stabilized soil amendment that nourishes plants as well as the environment.

How much manure per acre?

Recommended manure application rates vary based on the type of manure, crops grown, and soil conditions. Some general manure application rate guidelines per acre are:

• Cow manure: 10 to 15 tons per acre
• Horse manure: 8 to 10 tons per acre
• Pig manure: 5 to 10 tons per acre
• Sheep manure: 5 to 8 tons per acre
• Poultry manure: 2 to 5 tons per acre
• Rabbit manure: 500 to 1,000 lbs per acre

For gardens and landscaping, around 2 to 3 inches of composted manure can be applied and incorporated into the soil annually before planting. Excessive application of fresh manure can burn plants, so it is best to consult local agronomy resources for specific rate guidelines based on soil test results.

Manure application rates also depend on the carbon-to-nitrogen ratio of each manure type. Manures with narrow C:N ratios (10–15:1) can be applied at higher rates for meeting crop nitrogen needs compared to manures with wide C:N ratios. Wider C:N ratio manures are also best applied in the fall or before planting cash crops. Soil testing helps determine the actual plant-available nutrients supplied by applied manures.

When should I apply manure?

The timing of manure application depends on the form of manure used—raw, aged, or composted. Some general guidelines on when to apply different manures include:

• Raw manure: Apply just before planting non-edible cover crops to prevent food contamination. Incorporate immediately into the soil to retain nutrients.
• Aged or partially composted manure: best to apply in the fall, several months before growing the actual crop. Aged manure releases nutrients more slowly.
• Finished composts can be applied 1-2 weeks before planting spring crops or in the fall for next year’s crop. Well-cured composts can be used anytime.
• Manure teas: Apply as a foliar spray during the growing season to provide a nutrient boost to plants.
• Pellets or granular fertilizer can be applied at planting or as a side dressing mid-season when crops need more nutrients.

Spreading manure when plants are actively growing should be avoided, as it can burn and damage crops. Proper timing allows the nutrients in different manured materials to be available when crop demand is high.

Storing Manure

Raw manure decomposes quickly, so short-term storage is needed before field application. For aged or composted manures, following storage guidelines helps retain nutrient quality:

• Store manure in a covered area or shed to prevent exposure to rainfall, which can cause the leaching of soluble nutrients.
• Place compost piles on an impermeable base like concrete and use barriers to avoid nutrient runoff contamination.
• For stack storage, cover the pile sides with straw bales and tarpaulin. Place piles far from water sources, ideally downhill.
• Construct a three-sided storage bay or bunker with concrete flooring to hold large manure piles.
• Build a roofed manure pad that allows for collecting leachate, which can be redistributed back onto the piles.
• Store in piles less than 6 feet tall to minimize compaction and loss of aeration. Turn piles or aerate as needed.
• Test stored manure periodically for organic matter and nutrient levels. Discard manure if it turns anaerobic.

Following best practices for manure storage preserves its fertilizer value while also protecting the environment.

Manure Management Considerations

Some important aspects to consider for proper and sustainable manure management include:

Potential Pollution

Raw manure can contaminate water resources through surface runoff and leaching. Adequate storage and timely soil incorporation are vital. Vegetative buffer strips help prevent manure from being transported from fields into waterways.

Odor Nuisance

Manures emit gases like ammonia, hydrogen sulfide, and volatile organic compounds that cause offensive odors. Composting reduces smell, but covered storage and a minimum distance from inhabited areas are advised.

Pathogen Risks

Fresh manure contains disease-causing organisms like E. coli that may persist for months. Heating during composting kills pathogens. Allowing ~6 months before manure use prevents contamination.

Nutrient Variability

The nutrient content in manure varies with animal feed rations, bedding, moisture, storage, etc. Regular lab analysis provides current nutrient data for adjustment of field application rates.

Land Base Requirements

Applying large manure quantities year-round necessitates sufficient farmland. Factors like the number of animals, manure collection efficiency, and crop areas determine the land base needed for recycling the nutrients.

Treatment Costs

Additional costs may be incurred if facilities and equipment for manure handling, storage, composting, etc. are required. However, long-term fertility improvements compensate for these initial investments.

With careful attention to such factors, manure use can be planned to maximize agricultural benefits while minimizing any environmental risks.

Future Outlook

Manure is gaining recognition not just as an agricultural fertilizer but also as a valuable renewable resource that links crop production with sustainable natural cycles[2].

Some emerging trends in manure use include:

• Specialized manure composting systems to create customized fertilizers for different crops, soils, and conditions.
• Vermicomposting via earthworms is emerging as a technique to process manures into a superior plant growth material.
• Anaerobic digesters to produce renewable energy from manure are becoming more common on animal farms.
• Manure processing is advancing from basic compost to fortified organic fertilizers using techniques like biochar additions and nutrient enrichment.
• Application methods are improving via technologies like GPS-guided spreaders and sub-surface manure injections to enhance use efficiency.
• Struvite recovery from liquid manure streams helps recycle phosphorus, a finite nutrient resource.
• Manure management is being integrated into carbon farming models and regenerative agriculture systems.
• Legislation, incentives, and funding for technology adoption are promoting sustainable manure recycling practices.

With its comprehensive benefits for crops, soils, sustainability, and the environment, manure is now emerging as a key natural resource rather than just an agricultural waste product. Continued research, technology transfer, and farmer education will further maximize the role of manures within holistic nutrient management that nurtures both agriculture and the planet.

Conclusion

Manure is an integral component of organic farming systems that has been traditionally used to enhance soil fertility. Different animal manures each have unique nutrient profiles that can address crop requirements. Raw manure needs proper composting to stabilize nutrients and eliminate pathogens before field application. Aged, composted manures and manure-based products serve as safe, environmentally sustainable fertilizers for crop production. When managed appropriately, manure offers multiple benefits for not just plant nutrition but also overall soil quality, resource conservation, and an ecologically integrated circular farming economy. With its high potential to support both food production and a healthy environment, manure is truly a natural wonder!