Microbial conversion of poultry manure to partly oxidized products that have more desirable characteristics has been undertaken in recent years with methods that exert some control over the biological processes involved. Such products may be more desirable because they have greater stability, contain more organic nitrogen, have fewer odors, and may have wider usage than plant fertilizer. These products are produced by controlled composting but require poultry manure to be mixed with a carbon source which provides energy for the microorganisms and a physical matrix for oxygen penetration into the fermenting mixture. The composition and usefulness of such composts varies with the fermentation, the freshness of the manure and the nature / amount of the carbon source employed. In addition to the manure, a readily available carbon source is required to make this process feasible. Crop residues would be the most likely materials to be used as sources of carbon; however, food processing plant wastes might also be used. The potential uses for stabilized composts made from poultry manure include animal feedstuffs, specialized plant fertilizers and soil conditioners. While these products might be recycled on the poultry farm, the greatest benefit would be from transport to other areas not involved in concentrated animal production.
The technology for anaerobic conversion of poultry manure to biogas and sludge in liquid systems as well as high solids anaerobic fermentation to produce methane has also been developed. Sustaining the microbial reaction, storage and reuse of the biogas as a fuel have all received research effort. Major problems with biogas production include maintaining adequate reaction temperatures, keeping the microbial gasification and liquification reactions in balance and utilization or storage of the gas as it is produced. Outputs of 1.5 to 2.0 cubic feet of gas per day per pound of manure in the digester have been reported. Both aerobic and anaerobic fermentation of poultry manure have the potential for generating new useful products that are more stable and have market potential, as well as potential for reuse on the poultry farm. Clearly, any system for converting poultry manure to other products must be biologically sound, of appropriate engineering design, economically feasible and socially acceptable to succeed. There is a great need to improve the fermentation process, to determine the economic feasibility of fermentation systems, and for pilot plant testing to improve design before investments in commercial scale systems are made. In addition to broad opportunities for converting poultry manure through specialized fermentation processes, limited opportunity also exists for using poultry manure for ruminant feeding by direct incorporation into diets or indirectly by ensiling it with crop residue where cattle or sheep are grown near to or as part of large poultry enterprises. This is a common practice on some farms. Research has shown that corn silage stability is improved by the addition of cage layer manure.