Incorporating liquid manure via injection. Photo by OSU Extension.

Livestock manure properties and pollution prevention

By Harold Keener, Fuqing Xu, Mary Wicks

Land application of livestock manure provides nutrients such as nitrogen, phosphorous and potassium (NPK) to field crops and is generally the most accepted and economical use for recycling these nutrients. However, land application of manure has been a contributor to severe outbreaks of harmful algal blooms in the Western Lake Erie Basin and Grand Lake St. Marys. The algal blooms have generated health concerns for those using these lakes as sources of drinking water or for recreation. Runoff of total and dissolved reactive P (DRP) is often the limiting nutrient for freshwater algal blooms. Previous studies have shown that the concentration of water-extractable P (WEP) in manure (expressed as lb WEP/lb dry matter) can help predict DRP in runoff.  Thus, for a given level of P application per acre, reducing the WEP/P level in manure would reduce total WEP application, thereby reducing the potential for P runoff from land applied manure and associated algal blooms. 

Previous studies at OSU and by others on WEP in manure indicate that WEP can be affected by manure storage conditions, such as temperature, storage time, and agitation frequency. During 2018-2019 OSU researchers conducted lab and on-farm studies to evaluate the effect of storage conditions and time on WEP/P ratios for liquid swine and dairy manure (moisture 85-98.5%). For solid poultry manure (moisture less than 70%) only on farm studies were done.  These studies showed the following:  

  1. WEP/P for dairy manure was higher than for swine manure or poultry (0.40 vs. 0.22 and 0.14).  This corresponded to previous results of a study by Kleinmen et al.  (2004/2005), which showed ratios of 0.70 vs. 0.28 and 0.19, respectively.  
  2. Liquid swine manure had higher WEP/P levels after storage for 90 days under closed storage (i.e., anerobic conditions) compared to manure stored in open storage. 
  3. Moisture and P levels had minimal effects on WEP/P in liquid swine manure.    
  4. Between 90 and 180 days of storage, WEP/P of liquid swine manure and dairy manure decreased more than 25% and 50%, respectively. No chemicals were added to manure during storage.  Dry matter loss was 8% and 34% (swine) and 28% and 37% (dairy) over the 180 days.  

Earlier bench scale studies by other researchers have evaluated the effect of incorporating dairy, swine and poultry manure into the soil before rainfall. Those studies showed that the DRP (i.e., WEP) runoff potential for incorporation of surface applied manure was not significantly different compared to soil with no manure application. 

Management implications 

Results of the 2018-19 Ohio studies indicate that long term storage of liquid swine and dairy manures can reduce the WEP/P of manure, but it does not eliminate the potential for DRP in runoff from surface applied manures. Results also showed that liquid dairy manure would result in the highest levels of WEP/acre for a given application rate of P/acre for the livestock manures investigated.  Previous research by others tells us to incorporate manure, especially liquid swine and dairy, to reduce the risk of nutrient runoff. Note that Ohio regulations provide guidelines for manure application during winter months as well as restrictions for impaired watersheds, such as Grand Lake St. Marys or the Western Lake Erie Basin, and for permitted livestock or poultry facilities. For more information, go to and click on ‘Conserving Resources.’ Dr. Harold Keener is a Professor Emeritus, Fuqing Xu was a Research Scientist, and Mary H. Wicks is a Program Coordinator in the Department of Food, Agricultural and Biological Engineering of The Ohio State University.  E-mail: Phone: (330)202-3533.  This column is provided by the OSU Department of Food, Agricultural and Biological Engineering, OSU Extension, Ohio Agricultural Research & Development Center, and the College of Food, Agricultural and Environmental Sciences.

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