Understanding the Causes of Odor in Organic Manure
Organic manure is an invaluable resource for organic farmers and gardeners, providing essential nutrients and improving soil structure. However, the strong odors associated with some organic manures can be a challenge, impacting farmworker comfort, neighbor relations, and environmental quality.
Why Does Organic Manure Smell?
The primary cause of odor in organic manure is the microbial breakdown of nitrogen-rich compounds, especially proteins and urea, which release ammonia (NH3), hydrogen sulfide (H2S), and volatile fatty acids. Anaerobic conditions (lack of oxygen) during manure storage or composting can increase the production of these odorous gases.
Key factors contributing to manure odor include:
– High nitrogen content: Manures rich in nitrogen, like poultry and pig manure, tend to produce more ammonia.
– Anaerobic decomposition: Poorly aerated manure piles create anoxic conditions that favor sulfur-containing compounds and other malodorous gases.
– Moisture content: Excess moisture promotes anaerobic zones, intensifying odors.
– Temperature: Higher temperatures accelerate microbial activity, increasing odor emission.
Types of Organic Manure Prone to Strong Odors
Not all organic manures smell equally. Understanding which types are more prone to strong odors helps in planning their use and management.
Poultry Manure
Poultry manure is high in nitrogen and moisture, making it prone to ammonia emissions and a strong, pungent smell if not properly managed. It is often the smelliest of common manures.
Pig Manure
Similar to poultry, pig manure has high nitrogen and moisture but also contains a high sulfur content, contributing to foul odors from hydrogen sulfide.
Cattle Manure
Cattle manure has a more balanced C:N ratio and is typically less odorous than poultry or pig manure, especially when mixed with bedding materials like straw.
Horse Manure
Generally less odorous, especially when dry bedding is present. However, fresh horse manure can still emit noticeable odors.
Compost and Vermicompost
Properly managed compost and vermicompost generally have minimal odor. However, incomplete composting or anaerobic pockets can cause unpleasant smells.
Health and Environmental Impacts of Smelly Organic Manure
Health Risks
- Respiratory issues: Ammonia and hydrogen sulfide gases can irritate the respiratory tract, causing coughing, wheezing, or asthma exacerbation.
- Pathogen exposure: Manure odors can indicate incomplete composting, increasing the risk of pathogens.
Environmental Impacts
- Ammonia volatilization: Loss of nitrogen reduces fertilizer value and contributes to atmospheric nitrogen pollution.
- Greenhouse gases: Anaerobic decomposition releases methane (CH4), a potent greenhouse gas.
- Neighbor complaints: Odor nuisance can lead to conflicts and regulatory challenges.
Techniques to Reduce or Manage Manure Odor
Organic farmers and gardeners can employ several strategies to minimize manure odors while maintaining its agronomic benefits.
1. Proper Composting
- Aeration: Regular turning of manure piles ensures oxygen availability, promoting aerobic decomposition and reducing anaerobic odors.
- C:N Ratio Adjustment: Mixing manure with carbon-rich materials (straw, sawdust, leaves) balances the carbon to nitrogen ratio, optimizing microbial activity.
- Moisture Control: Maintaining moisture at 50-60% supports aerobic microbes and limits odor.
- Temperature Monitoring: Compost temperatures between 55-65°C (131-149°F) kill pathogens and reduce odors.
2. Manure Storage Management
- Covered Storage: Using covers or shelters reduces odor dispersion and rainwater infiltration.
- Frequent Removal: Avoid long-term storage; apply manure promptly.
- Anaerobic Digestion: Biogas systems capture methane and reduce odor.
3. Additives and Amendments
- Biochar: Adding biochar to manure can adsorb odors and improve nutrient retention.
- Lime Application: Raising pH with lime reduces ammonia volatilization.
- Enzyme Additives: Commercial microbial inoculants can accelerate decomposition and odor reduction.
4. Application Techniques
- Incorporation into Soil: Immediate incorporation after application reduces surface odors.
- Timing: Apply manure during cooler parts of the day or seasons with lower temperatures.
5. Alternative Manure Processing
- Vermicomposting: Using earthworms to process manure produces low-odor, nutrient-rich vermicompost.
- Pelletizing: Drying and pelletizing manure reduces odor and facilitates handling.
Frequently Asked Questions (FAQs)
Q1: Can all organic manures be odorless?
No. While some manures have naturally low odor, proper management and processing (e.g., composting) are essential to minimize smell.
Q2: How long does it take to compost manure to reduce odors effectively?
Typically, 8-12 weeks of active composting with regular turning and moisture control is needed to significantly reduce odors.
Q3: Is it safe to use smelly manure on food crops?
Using improperly composted or fresh manure can pose health risks from pathogens and should be avoided. Fully composted manure is safe when applied following guidelines.
Q4: Does adding straw to manure reduce odor?
Yes, straw increases carbon content, improving the C:N ratio and aeration, which helps reduce odor emissions.
Q5: Are there legal restrictions related to manure odors?
Many regions have regulations to control odor nuisances from farming operations. Check local guidelines to ensure compliance.
Key Takeaways
- Odor in organic manure primarily arises from anaerobic decomposition and high nitrogen content.
- Poultry and pig manures are generally the most odorous, while properly composted manure has minimal smell.
- Odors can cause health issues, environmental pollution, and community conflicts.
- Effective odor management includes proper composting, storage, additives, and application techniques.
- Regular monitoring, balancing moisture and carbon content, and timely manure use are critical for odor control.
References
- USDA Natural Resources Conservation Service – Managing Manure Odors
- Paul, E. A., & Clark, F. E. (1996). Soil Microbiology and Biochemistry. Academic Press.
- Zhang, R., et al. (2012). “Odor control in manure management: A review.” Journal of Environmental Quality, 41(1), 1-11.
- EPA AgSTAR Program – Anaerobic Digestion Basics. https://www.epa.gov/agstar/anaerobic-digestion-basics
- Bock, B., et al. (2013). “Best management practices for manure odor control.” Journal of Extension, 51(3).
