Manure Management on Organic Farms
Manure Storage Systems
Whether animals are raised on the farm or manure is brought in from an outside source, organic farmers will likely need to store manure on the farm prior to application. Livestock manure should be stored in an environmentally sound manner until it can be applied to land. Manure can be handled and stored as a liquid (less than five percent dry matter), slurry (5 to 10 percent dry matter) and/or solid (greater than 15 percent dry matter). Typically, beef cattle and poultry manure are handled as solid manure, whereas dairy and swine manure are stored and handled as a slurry or liquid manure. Manure storage facilities must be designed and managed to contain manure and contain runoff; if not designed or managed properly they can be a potential source of groundwater contamination. Dry manure can be stored in solid form in stockpiles, and liquid or slurry manure can be stored in tanks or earthen basins, or stored and treated in anaerobic lagoons. Storage allows the farmer the opportunity to apply manure when it’s best for the crop and during appropriate weather conditions.
Storage of Livestock Manure—Solid Systems
Manure should can be stockpiled on a concrete pad or compressed clay pad a safe distance from wells and surface waters. This prevents water from flowing down through the manure pile and contaminating the water. Concrete floors will prevent water from seeping from the manure into the soil where it may contaminate groundwater. A packed clay floor will also minimize seepage into the soil from solid manure structures, such as those used to store dry litter or manure scraped from feedlots. Sandy soils are generally very susceptible to contamination from seepage.
Manure that is stored in piles may lose much of it nitrogen and potassium. Nitrogen is lost by leaching, by gaseous losses of ammonia by volatilization, and by gaseous losses of nitrates by denitrification. Leaching losses can be minimized if the pile is covered and on a hard surface, whereas losses of nutrients from shallow, flat uncovered piles will be very high by leaching.
Storage of Livestock Manure—Slurry and Liquid Systems
Many types of facilities are used to store manure in the slurry form. One type is the under-floor pit in which manure is deposited directly into the pit through slatted floors. Slurry manure storage facilities not located under the production buildings may be fabricated or earthen structures. Slurry manure may also be stored in earthen structures or basins. Liquid manure storage facilities (lagoons) are generally used when some treatment of the manure is desired to facilitate handling or reduce odors. Lagoons are designed with a permanent “treatment volume” facilitating the growth of bacteria that degrade and stabilize manure organic matter. They are earthen structures but are larger than those designed for slurry storage due to the additional treatment volume.
Government regulations generally require lagoons and storage pits to have clay or synthetic liners if the existing soil on site is not suitable for preventing waste seepage from the structure. Pits or lagoons that are not sealed may allow wastes to seep into the underlying soil, especially if the lagoons or pits were built in sandy soils. Groundwater contamination will result if the subsurface earth materials do not have sufficient ability to break down contaminants contained in the seepage.
NOP Manure Storage and Handling Requirements
National Organic Program (NOP) requires farmers to handle and store biological soil amendments of animal origin in a way that does not contaminate covered produce; food-contact surfaces; areas used for growing, harvesting, holding, and packing; and water sources and distribution systems. Farmers must also make sure that treated amendments are not contaminated by untreated or “in-process” amendments.
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Topics Within This Chapter:
- Introduction to Manure Management on Organic Farms
- National Organic Program Standards for Manure
- Benefits and Limitations in Using Livestock Manure
- Managing Nutrients in Livestock Manure
- Timing of Manure Application
- Manure Application Rates
- Manure Application Methods
- Manure Storage Systems