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Why Digest Poultry Litter? In 2003 the United States produced 8.49 billion broilers. The Mid-Atlantic region alone (PA, WV, MD, DE, and VA) produced over 1 billion broilers, mostly in areas that are located within the Chesapeake Bay watershed. (Data obtained from the USDA NASS). Assuming a five pound bird that produces 0.6 pounds of litter per pound of bird, the total chicken litter (bedding, feathers and manure) production associated with grow out of broilers was calculated to be 1.5 million tons in 2003 in the Mid-Atlantic region. Typical nutrient composition of a ton of chicken litter (70% dry weight) from wood chip based bedding in West Virginia is 60 pounds nitrogen (N) and 40 pounds phosphate (P2O5). Litter also contains E. coli and Salmonella bacteria that can be harmful to humans if ingested. The Mid-Atlantic region, within the Chesapeake Bay watershed, has a limited agricultural land base and cannot utilize all of the litter produced in the region for fertilizer without overloading the soils with phosphorus and increasing the likelihood for eutrophication of the waterways and bacterial contamination of wells and streams. Regulations in these states are beginning to limit the use of chicken litter in areas with high soil phosphorus levels and/or near waterways. Transportation costs limit the distance the litter can be economically transported. Therefore, the litter must be utilized within the watershed or value must be added to the litter so it can be economically transported out of the watershed. Anaerobic digestion not only adds value to the litter by producing methane gas, but also reduces pathogens, reduces total solids and partitions the majority of the phosphorus into the solids, while converting the nitrogen in the liquid into ammonium. Poultry litter slurry (6-10% total solids) can be used as the sole source of feed for a thermophilic anaerobic digester. Typical gas yields from one ton of litter with wood chip based bedding (70% dry matter and 80% volatile solid) at the thermophilic CSTR Pilot Plant at WVSU are as follows:
Large-scale regional digesters need large amounts of material within a small radius to reduce transportation costs. In the Mid-Atlantic, poultry litter may be a more suitable feed source than dairy or hog waste for regional digesters because of the intense concentration of houses in small areas and the high dry matter content of litter compared to flushed dairy and hog systems, thus eliminating the need to transport large amounts of water with manure from farms to the digester. From a nutrient management perspective, digestion of poultry litter could help reduce soil phosphorus levels over time while providing nitrogen for grasslands and row crops. Digested poultry liquid contains 1.8 lbs N per 100 gallons and only 0.49 lbs P2O5 per 100 gallons. Results of fertilizer trials on vegetable crops, turf grass, and hay indicate very little loss from N volatilization after surface application of digested liquid. Therefore for each pound of N added, only 0.3 lbs P2O5 is added. So for example if one acre of corn needs 150 lbs N and 60 lbs P2O5 and digested liquid is used as the sole fertilizer source to satisfy the 150 lbs of N required, only 40 lbs of P2O5 would be applied. In phosphorus saturated soils, application of digested liquids to meet corn nitrogen requirements could result in a net loss of soil phosphorus over time. The solid fraction of the digested poultry litter contains most of the phosphorus. This material can be composted, reducing the total solids and concentrating the nutrients. Since this is a woody material, it can be used for mulch or as a soil amendment for urban or residential landscaping. It has also been used as a substrate for potting soil and mushroom production. If organic certification can be obtained, it can be sold to organic farms at a premium price. These uses may allow the material to be used in a sustainable manner within the area or transported out of the watershed. |
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