Understanding Animal Manure Fertilizers

Compost results from the decay of organic matter, such as animal manure, into carbon and nitrogen elements. Nutrient type and abundance vary based on source material, time, moisture, mixing, temperature, and microbial communities present. Decaying plant matter, animal matter, and metabolic waste (feces and urine) can all provide good material for compost. Even small applications of compost can show significant improvement to soil structure quality and nutrient levels. In soils fertilized with compost or manure, macronutrient levels are higher than in synthetically fertilized soils. 

In outdoor growing systems, many basic biological factors are already present but soil may be enhanced through the addition of fertilizers like compost. Indoor growing systems like greenhouses generally lack environmental inputs and rely on fertilizers for nutrient addition. Products like worm castings, blood and bone meal, fish or crab meal, and bat guano in addition to compost provides biological benefits to indoor growing systems.

Benefits of Manure and Compost Fertilization

Higher concentrations of calcium, potassium, magnesium, and manganese have been observed in organic farms using manure than in farms using synthetic nutrients. Manure fertilizers are also beneficial to soil microbes, lowers populations of pathogenic microbes, increases organic matter content in the soil, produces higher levels of carbon in the soil, and gives soil better nutrient holding capacity and less bulk.
  • Compost and manure impart the same benefits to gardens, potted plants, and greenhouse plants
  • Composted manure can be mixed in equal parts with vermiculite, perlite, or pumice for use with potted plants
  • Compost bins in greenhouses help to heat the greenhouse and maintain warmth in cold months
  • In greenhouses, germination trays can be placed on compost bins to provide added warmth and encourage germination.
Manure Sources and Nutrient Levels
Farmyard animal manure is the urine, feces, and used bedding of livestock animals is stacked and turned to compost through microbial decay. When properly used manure and compost can replace the use of costly synthetic fertilizers. The nutrient content of manures depends on the animal source. In addition to nutrient enrichment, manure and compost add organic matter to the soil which improves soil texture and helps build and maintain beneficial soil microorganisms.

Approximate NPK Values of Farmyard Manures

  • Sheep and Goat Manure NPK: 1-0.5-1
  • Cow Manure NPK: 1-0 2-1
  • Pig Manure NPK: 0.5-0.3-0.5
  • Chicken Manure NPK: 2-1-1

How to Safely Use Manure

The degree of decomposition achieved by composting will influence manure nutrient availability to plants. Composting also allows time for potentially pathogenic microbes to die off. Manures can contain residual hormones, antibiotics, pesticides, pathogenic microorganisms, and other unwanted materials. These materials can be degraded through proper composting, but the use of un-composted raw manures may offer advantages by way of higher nitrogen levels, decreased costs, and increased convenience. And let's be honest, do you really want to use oh-so aromatic fresh manure?
  • Manure may be applied to soil ahead of planting a cash crop, or just before planting a cover crop
  • Nitrogen amendment is maximized when manure is mixed into the soil as soon as possible and does not spend time exposed on the soil’s surface
  • The 90-120- Day Rule must be followed for raw manure application on organic farms (reduces the risk of exposure to harmful residues/microbes)
  • For a simple compost tea, a shovel full of manure can be placed in a 5-gallon bucket; the bucket can be filled with water and left overnight, then the liquid can be applied to soil every 2-3 weeks to fertilize

Improper Use of Manure Can Lead to Nutrient Lock

Raw manure fertilization can be detrimental to the quality of produce crops when used improperly. Raw manure should not be applied directly to food crops because as it breaks down chemical compounds are released that can ruin the flavor of vegetables. The best use of raw manure is to spread it on cover crops being planted a season prior to planting produce. Overuse of raw manure is also problematic because it can create nutrient imbalances. If particular nutrients like phosphate build-up in excess, they can tie up other nutrients, making them unavailable to plants. Excessive levels of nitrogen can even burn the roots of plants. Excess nutrient levels impact the chemical composition of the soil. Along with nutrient imbalances, increased salinity and acidic pH can also reduce soil fertility.

What is Composting? How Does it Work?

Compost is one of the most used soil amendments. It is formed through the decomposition of organic waste and results in a nutrient-rich substance that bolsters soil texture and adds carbon to feed communities of beneficial soil microbes. Once the compost has cured and matured, the nutrients it contains are very stable and readily taken up by plants. A large variety of materials can be composted, from kitchen waste to farmyard manure, making it a highly sustainable process favored by organic producers.
Composting manures stabilized the nutrients and degrade compounds released during decomposition that can cause root burn and bad flavors. Many pathogens present in manure also degrade during composting, making composted manure much safer to use than raw manure. If weed seeds are present in manures composting will also degrade those and prevent them from being introduced to the crop.

Beware of Manure Contaminants

For farms that are certified organic, manures must be tested to ensure they do not contain chemical residues. If a farm does not have livestock and purchases manure from another farm, caution must be taken because manures from conventional farms can contain traces of genetically modified feeds and herbicides. Herbicide manure contaminants may not injure all crops but can be present in concentrations great enough to stunt crop growth. The herbicide residue aminopyralid (used to guard against broadleaf weeds) can be particularly harmful to tomatoes and peppers. Heavy metal contamination is also a concern as well when using manure from and industrial farms. Feed crops can be contaminated with heavy metals from synthetic pesticides and herbicides. Heavy metals can also contaminate crops from the use of biosolids, which are prohibited for use in organic farming. 
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