Composting animal manure
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EmailComposting animal manure is an effective soil amendment that enhances soil health, provides better organics storage options, reduces manure volume and offers greater flexibility for field application compared to raw manure.
Composting manure can provide more effective control of odors and flies compared to other handling methods. Additionally, applying composted manure to fields is more efficient and consistent than spreading solid or semi-solid raw manure. Increasing concerns about water quality and the cost of soil amendments have raised composting to becoming a preferred manure management approach for agricultural operations.
Beyond its environmental benefits, composting manure reduces its weight and volume, eliminates weed seeds and retains manure nutrients in a more stable organic form, aside from some airborne ammonia loss. Another advantage is that composted manure has market potential. Unlike raw manure, composted material can be used in various residential and horticultural applications, making it a practical value-added opportunity for off-farm sales. When properly processed, farmyard manure compost serves as an excellent garden fertilizer and when blended with other composts, soil or peat, it is particularly effective for starting seedlings. Given that many states now require farms to manage excess nutrients, marketing composted manure off-farm may be the most cost-effective way to keep its value while complying with nutrient management regulations.
Note: Before considering selling compost in Michigan as a value-added choice, check with Michigan Department of Agriculture and Rural Development (MDARD) about regulations for selling compost products, and with EGLE (Department of Environment, Great Lakes and Energy) for compost site permitting registrations. Compost facilities that have over 500 cubic yards of material on site at any time are required to get authorized by EGLE.
The composting process
Composting is a biological process in which aerobic microorganisms break down organic materials—such as manure and bedding—into a stable, soil-like substance. Successful composting depends on maintaining a balanced mix of carbon and nitrogen, which fuels microbial activity. The ideal carbon-to-nitrogen (C:N) ratio for composting ranges between 25-30:1, with an acceptable range of 20-40:1. Moisture content is equally critical, with an optimal range of 50-60% and an acceptable range of 40-65%. Most well-bedded manure packs naturally fall within these ranges. The On-Farm Composting Handbook (NRAES-54, Natural Resource, Agriculture, and Engineering Service, 1992) is a valuable reference for compost management practices.
Balancing carbon-to-nitrogen ratios in compost
Pure manure is often too high in nitrogen and too moist to compost effectively on its own. To achieve a balanced C:N ratio, it must be mixed with carbon-rich materials such as:
- Straw
- Corn stover
- Wood chips or sawdust
- Leaves
Average C:N ratios for common manures
Different livestock produce manure with varying carbon-to-nitrogen ratios, requiring different levels of carbon-rich amendments:
|
Animal |
Average C:N Ratio |
|
chicken |
10:1 - 15:1 |
|
cow |
18:1 - 25:1 |
|
pig |
10:1 - 20:1 |
|
horse |
20:1 - 25:1 |
|
goat |
15:1 - 25:1 |
|
sheep |
15:1 - 25:1 |
To adjust a compost pile's C:N ratio, mix high-nitrogen manure (like chicken or pig) with carbon-rich bedding (such as straw or sawdust). Regularly checking the pile’s moisture level ensures proper decomposition.
Managing the composting process
Once the compost pile is formed, aerobic organisms begin breaking down nitrogen and carbon compounds, producing organic matter, carbon dioxide and heat. As temperatures rise and oxygen levels decline, turning the pile is essential to release excess heat and replenish oxygen. Without adequate turning, microbial populations will die from excessive heat and oxygen depletion, slowing or halting decomposition. This can be done using:
- Windrow turners (specialized composting equipment)
- Tractors or end loaders with buckets
Time for composting
When managed well, composting typically takes 4-8 months, with an additional 2-12 months for curing to produce high-quality compost. The final product should be fully decomposed, soil-like and stable. However, for some operations, this timeline may not allow for full composting before winter. Partially composted manure can still be spread in the fall, though it will not provide the same benefits as fully cured material. Over the course of composting, material volume is reduced by approximately 30%, making transportation and spreading more efficient.
Advantages of applying composted manure
Composted manure offers several advantages over raw manure when applied to fields:
- Easier spreading on hayfields and pastures, as the finer texture allows grass to grow through the material more effectively.
- Reduced odor and fly issues, making it more suitable for applications near livestock grazing areas.
- More uniform nutrient distribution, improving soil fertility and reducing nutrient runoff.
- Increased grazing efficiency, as animals are more likely to graze after compost is spread compared to raw manure.
Composting is an effective and sustainable manure management strategy for livestock producers. By balancing carbon-to-nitrogen ratios, maintaining adequate moisture and oxygen levels, and allowing adequate time for decomposition, farms can produce high-quality compost that enhances soil health while mitigating environmental concerns. As more states implement nutrient management regulations, composting also presents an opportunity for cost-effective off-farm marketing of manure-based soil amendments. With the right approach, composting can transform manure from a waste product into a valuable resource for agriculture and beyond.
For more information on composting animal manure and its use, contact Eliza Hensel, Compost Systems Extension Educator, at hensele1@msu.edu, or visit MSU Extension to learn more today.
