The concentration of livestock production facilities has contributed to excess nutrient loading, which has led to degraded surface water quality, increased algal blooms, and community concerns. Livestock manure applied to cropland can provide nutrients and improve soil conditions, but in areas with high livestock concentrations, the acreage needed to recycle manure nutrients may not be available due to excess nutrient loading. Alternative manure processing technologies (MPTs) that have the potential to utilize livestock manure for value-added products are available, but adoption has been limited because farmers lack objective data and a mechanism for comparing their effectiveness.
Under a USDA-NRCS Conservation Innovation Grant-funded project, information sheets for seven MPTs (Table 1) and an interactive MPT Decision Tool spreadsheet were developed by the Ohio Composting and Manure Management Program (OCAMM) at The Ohio State University’s OARDC in Wooster.
|Table 1. Manure processing technologies (MPT) for livestock manure.|
|Land Application||organic nutrients are applied to cropland|
|Separation||a portion of the liquids are removed|
|Composting||a microbial process in which organic materials are decomposed in an aerobic environment|
|Anaerobic Digestion||a microbial process in which organic materials are decomposed in an oxygen-free environment|
|P Recovery||a chemical process in which phosphorus is captured and directly removed from stored liquid manure|
|Pyrolysis||direct thermochemical conversion of organic material in an oxygen deficient environment at low moisture and high temperature|
|Hydrothermal Liquefaction||direct thermochemical conversion of organic material in an oxygen deficient environment at high moisture, pressure, and temperature|
|Key: A-fertilizer and/or soil amendment; B-renewable energy; C-raw materials|
The information sheets provide comprehensive objective information regarding the effectiveness of the seven technologies for managing and utilizing manure nutrients. They describe how the technology works, its benefits and limitations, and cost considerations. This information will help livestock farmers make decisions to adopt technologies that will improve the recycling and conservation of nutrients, especially N and P. Conclusions regarding the MPTs evaluated were:
- Land application is the best use of manure if an adequate land base is available.
- Separation and composting are viable technologies for reducing moisture and improving the economics of moving some or all manure nutrients out of a watershed.
- Anaerobic digestion is a viable technology that can reduce odors and generate energy; however, the moisture and nutrient content of the effluent is similar to the manure before digestion.
- P recovery, pyrolysis, and hydrothermal liquefaction (HTL) are viable technologies; however, they are not economically feasible for manure processing at this time.
Alternative manure processing technologies decision support tool
The MPT Decision Tool is an innovative computer program that facilitates the adoption of alternative technologies. It allows livestock farmers to quickly and accurately assess their nutrient balance and identify technology options that may be effective for improving management of manure nutrients. The MPT Decision Tool was validated by using input data from four farms in Ohio. Table 2 provides a summary of each farm’s inputs and the nutrient balances calculated. Table 3 describes the effect of these results.
|Table 2. Nutrient balance for four Ohio livestock farms using MPT Decision Tool.|
|Dairy||250 milk cows, 120 calves @150 #, 120 young stock @250#, 120 heifers @750#,||167 ton wheat straw||1000 ac: Sc,Sb,Ws,Af,Af,Af||N: + 26.7 tonP2O5: – 29.5 tonK2O: – 119.0 ton|
|Dairy & Beef||Dairy: 120 milk cows, 50 calves @150 #, 50 young stock @250#, 50 heifers @750#. Beef: – 60 @250#, 60 @600#, 60 @1000#||50 ton wheat straw||300 ac: Cg,Sb300 ac: Sc,Sb,Ws,Af,Af,Af||N: + 11.6 tonP2O5: – 11.1 tonK2O: – 38.9 ton|
|Swine (grower/finisher)||850 head (50# IN, 280# OUT), 95 days feeding, 5 days for clean out, 3% death rate||none||200 ac: Cg,Sb200 ac:- Cs,Sb,Ws||N: – 1.5 tonP2O5: – 1.8 tonK2O: – 10.2 ton|
|Layers||250,000 birds (4#), 365 days feeding||none||100 ac: Cg,Sb100 ac: Cs,Sb,Ws||N: + 152.6 tonP2O5: + 118.4 tonK2O: + 64.8 ton|
|Key: Af – alfalfa; Cg – corn grain; Cs – corn silage; Sb – soybean; Ws – wheat straw|
The decision tool also recommends which of the seven technologies may be effective. For example, the recommendations for use of anaerobic digestion for the dairy were:
“The moisture content of your manure + bedding is: 86 %. Your manure is within the moisture range for anaerobic digestion. The C:N ratio of your manure + bedding is: 10%. Your manure does not currently have the appropriate C:N ratio for anaerobic digestion. Target C:N ratio for anaerobic digestion is between 25 and 35. Consider the addition of high carbon content materials, such as fats, oils and greases to bring your C:N ratio into range.”
Based on feedback from each of the farm owners, projected nutrient balances were similar to what they were experiencing. The interactive decision worksheet, along with the fact sheets and other documents, are available on the OCAMM website: http://www.oardc.osu.edu/ocamm.
Funding for this project was provided by Federal and State dollars and a grant from the USDA-NRCS Conservation Innovation Grant program.
|Table 3. Summary of results for four Ohio livestock operations based on nutrient balance.|
|Nutrient||Dairy||Dairy and Beef||Swine||Layers|
|N||You have an excess of nitrogen. However, no accounting is made for losses or availability of organic N.||You have an excess of nitrogen. However, no accounting is made for losses or availability of organic N.||You are deficient in nitrogen||You have an excess of nitrogen. However, no accounting is made for losses or availability of organic N.|
|P2O5||You are deficient in phosphorous||You are deficient in phosphorous||You are deficient in phosphorous||You have an excess of phosphorous|
|K2O||You are deficient in potassium||You are deficient in potassium||You are deficient in potassium||You have an excess of potassium|