Not All Manure Is the Same – Poultry Litter

The nutrient characteristics of a manure is dependent the species of animal, the diet of the animals, and how the manure is handled. In recent years poultry litter has been elevated to a unique value status among the manures. It has gone from a waste product to a commodity of value, in some cases, garnering a premium over an equal amount of nutrient in the form of commercial fertilizer. This has been supported with poultry litters relatively nutrient dense high organic matter content, and litter applications resulting in yield responses.  This makes hauling manure away from the production barn to fields that traditionally do not receive manure applications an economically viable option.

The as-applied nutrient content of poultry litter is much higher than other manures, primary due to its low moisture content.  For example, swine lagoon manure is often 97% or more water, where poultry litter is most often 20-40% water. If you were to dry swine manure down to 20-40% moisture, it would exceed the nutrient content of poultry litter. The moisture or bedding dilution of most other manures leads to a lower nutrient density. The low moisture content of poultry litter is primarily due to the fact that birds do not urinate, rather they excrete uric acid in a dry form with the manure. The uric acid crystals are the white coating on the manure. The higher moisture content in some poultry litter is usually from high protein diets, excess water from watering systems, humidity, and other environmental factors. Since bedding is normally used to absorb excess water and urine, the naturally low moisture content of poultry manure reduces the need for bedding materials. Low moisture means high organic solids content, witch with routine application, has been shown to have a positive increase soil organic matter content over time.

Litters from layer barns tend to have a greater soil pH impact than other manures. Layer birds are often fed a high calcium diet to promote proper eggshell development. Most commonly that calcium source is calcium carbonate or course ground ag lime. Excess calcium carbonate from either feed waste or excess excreted by the birds can lead to an elevated calcium carbonate content in layer manure. Broken eggshells can also add calcium carbonate to the littler. Repeated application of layer manure is equivalent to repeated light lime applications and can lead to unwanted increases in soil pH over time. Because of the low water solubility of the calcium carbonate in layer manure, soil pH increases can continue for a couple years after layer little applications are halted. Effective management includes routine soil sampling so monitor soil pH.

The moisture and nutrient content of poultry little can vary by the type of poultry, and therefore impact the as applied nutrient content of the manure.

  Source: K-State Agronomy 2017

70 to 80% of the nitrogen in poultry litter is in an organic form with the remainder primarily in ammonium forms. Poultry litter has as overall higher ammonium content than other manures. The dry excretion of urine containing nitrogen as urea will convert to ammonium. Other species that excrete urine as a liquid increases the potential for water-soluble nitrogen to leach from the manure. The handling of the poultry litter prior to application can impact the retention of the ammonium fraction. If the litter is stirred or exposed to rainfall, more of the ammonium fraction is lost. The loss of ammonium leads to increased odor. With the stock piling of litter under a roof by larger poultry operations, ammonium loss and ammonium smell are reduced.

The ammonium fraction of nitrogen is immediately available for plant uptake, while the organic N fraction can take up to 2 years to become available. Some researchers estimate as much as 10% can be retained for release in year 3. Slower than swine, yet slightly faster than bovine manure. 50 to 60% of the total nitrogen is available in the first year, with 15-20% available in the second year. The extended period of nitrogen release fits well in a corn-soybeans rotation when applied ahead of corn.

Figure 1. Response of crop yield to poultry litter application. Dotted blue line represents crop response to inorganic fertilizer. Blue dotes indicate a yield increase (+) or decrease (-) from poultry litter relative to inorganic fertilizer. Source: Yara Lin, Agronomy Journal, 2018

The dry nature of poultry manure leads to the retention of phosphorus and potassium in organic forms. High moisture, especially liquid manures, encourages the conversion of nutrients to water soluble forms. The mineralization of the phosphorus and potassium is delayed until application to the field leading to a slower release of P and K compared to a liquid manure. It is estimated that up to 50% of the P and K is available shortly after application, with 90-100% available within the first year.
Figure 1. Response of crop yield to poultry litter application. Dotted blue line represents crop response to inorganic fertilizer. Blue dotes indicate a yield increase (+) or decrease (-) from poultry litter relative to inorganic fertilizer. Source: Yara Lin, Agronomy Journal, 2018

Poultry litter has been shown to have the greatest yield impact on medium textured soils (silty clay loams, loams, sandy loams) while showing a yield reduction on course textured soils. Often this yield improvement is attributed to season long nutrient release, the timing of nutrient release corresponding to favorable growing conditions given that microbes thrive in similar conditions. Long term involvements are attributed to more diverse soil microbial populations and increased soil organic matter content leading to increased water holding capacity and improved soil structure.

Figure 2. Response of crop yield to poultry litter based upon soil type. Dotted blue line represents crop yield for inorganic fertilizer. Blue dotes indicate an average yield increase (+) or decrease (-) from poultry litter relative to inorganic fertilizer. Source: Yara Lin, Agronomy Journal, 2018

The key to proper use of poultry litter as part of a nutrient management plan is to have current soil tests and manure analysis to determine the proper application rates. Contact your local ALGL agronomist with any questions you might have on manure analysis, or incorporation of manure into your overall nutrient management plan.

Sources:

Jacobs, J., Pescatore, T.. “Avian Digestive System ACS-203. University of Kentucky Extension.  Nov 2013.

Koelsch, Rick. “Poultry Litter’s Agronomic and natural Resource Benefits.” 23 Dec. 2019, https://water.unl.edu/article/animal-manure-management/poultry-litter%E2%80%99s-agronomic-and-natural-resource-benefits

Lin, Y., Watts, D., Van Santen, E., and Cao, G.. 2018. Influence of Poultry Litter on Crop Productivity under Different Field Conditions: a Meta-Analysis. Agronomy Journal.

Zhang, H., Hamlton, D. W., and Josh Payne. “Using Poultry Litter as Fertilizer.” Apr. 2017, https://extension.okstate.edu/fact-sheets/using-poultry-litter-as-fertilizer.html

Tomlinson, P., Shoup, D., and Ruiz Diaz, D. “Nutrient Availability in Poultry Manure.” – Agronomy eUpdate21 Dec. 2017, https://webapp.agron.ksu.edu/agr_social/m_eu_article.throck?article_id=1635