Farming
Manure is one of the potential sources of ammonia and greenhouse gas emissions contributing to global warming. Hence, strategies are needed to mitigate ammonia and greenhouse gas emissions from manure to achieve environmental sustainability.
Several mitigation strategies, such as physical, chemical, and dietary manipulation techniques, have been investigated for their potential to reduce the emissions from manure. Amending manure with biochar is gaining attention due to its ability to reduce ammonia and greenhouse gas emissions. However, biochar produced from different feedstocks will have different physical and chemical properties that might impact its mitigation efficiency. Here, we present a case study on using biochar to reduce ammonia and greenhouse gas emissions from poultry manure.
What Are Greenhouse Gases, and How Do They Regulate the Earth’s Temperature?
Carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4), and halogenated compounds present in the atmosphere are called greenhouse gases. These gases absorb heat waves from the sun and prevent them from escaping the earth’s surface, thereby maintaining the planet’s temperature and ensuring that it does not drop to levels when life would be unsustainable. This effect is known as the greenhouse effect. Greenhouse gases are produced by various natural and human activities, such as agriculture, livestock, deforestation, burning of fossil fuels, and industrial development.
Even though greenhouse gases maintain the temperature on earth in a habitable range, an increase in the concentration of greenhouse gases leads to a rise in temperature, a phenomenon known as global warming. For example, the carbon dioxide concentration monitored at Hawaii’s Mauna Loa Observatory indicated the concentration of carbon dioxide in the atmosphere increased from 320 parts per million (ppm) in 1960 to 430 ppm in 2024. This warming effect is responsible for environmental changes, such as rising sea levels by melting glaciers, flood events in coastal plains, acidification of oceans, seasonal fluctuations, and ecosystem imbalance. Among all greenhouse gases, carbon dioxide is the most abundant in the atmosphere. However, when considering the ability of a gas to trap heat (also referred to as global warming potential), nitrous oxide is 298 times more potent than carbon dioxide. Similarly, methane has a heat-trapping capacity 24 times greater than carbon dioxide.
How Do Ammonia Emissions Affect Air and Water Quality?
Ammonia is a reactive form of nitrogen and plays a significant role in degrading both air and water quality. Ammonia reacts with compounds such as nitrates and sulfates present in the air and forms particulate matter, namely PM. This particulate matter has a diameter of 2.5 micrometers and causes respiratory problems in humans. Additionally, its deposition on water bodies leads to acidification of lakes and promotes algal growth, leading to degradation of water quality.
How Does Manure Produce Greenhouse Gas and Ammonia?
Manure produces greenhouse gases through various biological processes. The decomposition of manure in the presence of oxygen emits carbon dioxide. Methane is produced under anaerobic conditions (when oxygen is not available) by methanogenic bacteria. Nitrous oxide emissions from manure are controlled by the processes of nitrification and denitrification. During nitrification, ammonium present in the manure is converted to nitrate by the action of a group of microbes (nitrosomonas and nitrobacter) and releases nitrous oxide as a byproduct. When the oxygen levels in the manure fluctuate due to the moisture, denitrifying bacteria (pseudomonas, paracoccus, agrobacterium) convert the nitrate to nitrogen by releasing nitrous oxide as an intermediate product. This process is called denitrification. Besides greenhouse gases, manure also produces ammonia through bacterial activity. In poultry manure, ammonia is produced as a result of uric acid decomposition in the presence of oxygen. The ammonia is then released into the atmosphere through volatilization.
The amount of greenhouse gases and ammonia emitted from manure depends on various factors such as management practices, storage method and duration, temperature, moisture content, composition of manure, and environmental conditions.
What Strategies Are Currently Employed to Mitigate Greenhouse Gas and Ammonia Emissions from Manure?
Several strategies have been shown to reduce greenhouse gas and ammonia emissions from manure. These include physical, chemical, and dietary abatement techniques.
Table 1. Greenhouse Gas and Ammonia Mitigation Strategies Categorized in Three Groups
| Mitigation Category | Abatement Used |
|---|---|
| Physical | Physical mitigation strategies reduce emissions by altering the conditions that promote the release of greenhouse gases and ammonia. Some of the physical strategies are covering the manure, field incorporation, manure pile turning, aeration, bulking agent addition, and altering the storage methods. |
| Chemical | Chemical amendments decrease the emissions from manure by changing the composition of manure via chemical reactions. Some of the chemical strategies are mixing manure with Ferix -3, biochar, poultry litter treatment (sodium bisulfate), aluminum sulfate (alum), AlCl3, alum mud litter amendment (AMLA), superphosphate, lactic acid, and zeolite. |
| Diet Manipulation | Diet manipulations focus on altering the feed composition. For example, chicken diets are rich in protein and various amino acids. Chickens have limitations in digesting all the protein they consume. When the protein intake through the feed is greater than the chicken’s digestive ability, a significant portion of the nitrogen is excreted in the manure. So, manipulating the crude protein levels in the diet of poultry birds reduces nitrogen excretion and ammonia emissions. Some of the diet manipulation strategies are EcoCAL, corn dried distiller grain (DDGS), reduced emissions diet, and dietary crude protein. |
What Is Biochar? Can It Be Used as a Mitigation Strategy to Reduce Greenhouse Gas and Ammonia Emissions from Manure?
Biochar is a carbon-rich material produced by pyrolysis (heating organic material in the absence of oxygen) from various biogenic materials, such as wood, agricultural residues, and manure. The pyrolysis process can be slow, intermediate, or fast depending on the pyrolysis time. Biochar has been proposed as a potential strategy to reduce greenhouse gas and ammonia emissions due to its unique properties, such as high surface area, porosity, surface functional groups, and alkaline pH. However, due to the wide variability in biochar properties, be cautious in selecting the type of biochar to reduce greenhouse gas and ammonia emissions from manure.
Why Careful in Selecting Biochar as a Mitigation Strategy for Controlling Greenhouse Gas Emissions?
Figure 1. Comparison of nitrous oxide emission rates from untreated and biochar-treated poultry manure.
Biochar has the potential to mitigate emissions, yet care should be taken in choosing the right type of biochar. The properties of biochar can vary widely depending on the feedstock material and the conditions of its production. Different types of raw materials and pyrolysis processes can result in biochar with varying levels of stability, nutrient content, and capacity for carbon sequestration. Biochar produced from plant materials at higher temperatures is optimal for reducing methane and nitrous oxide emissions, while biochar made at lower temperatures is more effective at mitigating ammonia emissions. The particle size of biochar also plays an important role in specific surface area. For example, powdered biochar with a high surface area is better at reducing ammonia emissions, whereas granular biochar is more effective in mitigating methane emissions.
Efficacy of Biochar in Reducing Ammonia and Greenhouse Gas Emissions from Poultry Manure
Figure 2. Comparison of ammonia emission rates from untreated and biochar-treated poultry manure.
A laboratory study was conducted to explore the role of biochar on nitrous oxide and ammonia emissions from poultry manure. The study consisted of two treatments: poultry manure with and without biochar amendment. The biochar used in this experiment was produced from pine. Biochar was evenly applied on the surface of poultry manure, with an application rate of 10 percent (w/w). Gas monitoring was done in real time continuously every hour for 8 days. Results showed that although biochar reduced the cumulative nitrous oxide and ammonia emissions by 10.5 percent and 42.6 percent, respectively, during an 8-day monitoring period, compared to untreated poultry manure, the effect was short-term (figures 1 and 2). The biochar helped reduce nitrous oxide emissions from poultry manure for the first 5 days, after which no difference was observed between biochar-treated and untreated poultry manure. Similarly, biochar reduced ammonia emissions during the first 2 days, after which no difference was observed between biochar-treated and untreated manure. The study indicated that biochar could help reduce nitrous oxide and ammonia emissions, but the effect is short-term. Long-term impacts and interactions with environmental conditions need further research.
Conclusion
The use of biochar to reduce emissions is an emerging topic that requires further research. It is important to select the appropriate type of biochar, as its reduction efficiency depends on its properties and can vary based on pyrolysis conditions. Additionally, the application rate of biochar is another crucial factor to consider.
References
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- Anderson, K., Moore, P. A., Martin, J., & Ashworth, A. J. (2020). Effect of a new manure amendment on ammonia emissions from poultry litter. Atmosphere, 11(3)
- Chakraborty, D., Prasad, R., (2024). Phosphorus Basics: Phosphorus Species Disruptive to Freshwater Systems. ANR-3057.
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- Naylor, T. A., Wiedemann, S. G., Phillips, F. A., Warren, B., McGahan, E. J., & Murphy, C. M. (2016). Emissions of nitrous oxide, ammonia and methane from Australian layer-hen manure storage with a mitigation strategy applied. Animal Production Science, 56(9), 1367–1375.
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- van Emous, R. A., Winkel, A., & Aarnink, A. J. A. (2019). Effects of dietary crude protein levels on ammonia emission, litter and manure composition, N losses, and water intake in broiler breeders. Poultry Science, 98(12), 6618–6625.
Shruthi Koneti, Graduate Research Assistant, Crop, Soil and Environmental Sciences; Debolina Chakraborty, Research Assistant Professor, Biosystems Engineering; and Rishi Prasad, Extension Specialist, Associate Professor, Crop, Soil, and Environmental Sciences, all with Auburn University
New March 2025, Mitigation Strategies for Ammonia & Greenhouse Gas Emissions from Manure, ANR-3141