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Swine & U column: Proper manure management

 By Diane DeWitte, UMN Extension swine educator

Originally printed in The LAND - as March 1, 2024, Swine & U column

Spring’s coming and a young farmer’s heart turns to …..manure?!? Maybe your manure plan involves fall application, but as the soils thaw and the tiles begin to run, it’s a good idea to review a few environmental protection habits that will help keep nutrients where they belong.  

Manure broadcaster spreading manure on a field.

University of Minnesota Extension provides good resources for nutrient application calculation and groundwater and shoreland protection at its manure management website.

Extension’s manure management specialist Melissa Wilson and manure management crops educator Chryseis Modderman provide the latest best management practices for manure application in our Land of 10,000 Lakes and 8.9 million pigs.  


The best time to apply manure is dependent on farm logistics, weather, soil conditions and a producer’s willingness to take risks. UMN Extension recommends applying manure in the fall only after the soil temps are below 50 degrees and if soil textures are not coarse. When applying manure in the spring, wait until the snowmelt is complete and soils are thawed and drying. Springtime application will provide nutrients closer to the time growing crops will use them with a lower chance of nutrient loss. Conversely, if springtime soil conditions are poor, planting may be late after delayed manure application.

Summer application is also an option. Dr. Wilson’s research has shown that directly applying liquid hog manure into growing corn can be successful; Injecting manure between the young rows provides maximum nutrient value, but specialized equipment is needed.


Before planning for manure applications, consider how the nutrients will be managed for the upcoming crop. Will all the nitrogen (N) be supplied from manure? This will require a higher application rate and will overapply phosphorus (P) and potassium (K) for the crop year. If done too often, there could be environmental consequences when excess P enters waterways. A lower rate can be used to supply all the P the crop needs. This will allow the manure to be spread over more acres but will require additional N and possibly K to be applied as a commercial fertilizer.

Once you choose a strategy, use the following steps to determine application rates:

Step 1: Find the nutrient needs of the crop
Step 2: Calculate the actual nutrient availability in the manure
Step 3: Divide the answer from Step 1 by Step 2

While this sounds simple, there are slight differences in calculations depending on whether you are basing your applications on N or P needs of the crop or are using liquid or solid manure. When using liquid swine manure, the chance of over-applying Phosphorus is critical to remember. Dr. Wilson provides the latest application rate guidelines based on N or P in the Guidelines for manure application rates on the UMN Extension website.


UMN Extension Crops educator Chryseis Modderman addresses the manure pathogen issue in this discussion of how to reduce common microorganisms in manure.

Livestock manure is a valuable source of crop nutrients, but it can also come with pathogens that may cause livestock and people to become ill. The number and type of pathogens in manure vary based on animal species, feed, and animal health. There are many different types of pathogens in manure, so using multiple best management practices at once will give the best results.

Pathogens can infect humans directly through contact with manure or indirectly through contaminated water and food. Children, the elderly, and those with compromised immune systems are at the highest risk for infection.

Common manure pathogens include bacteria, protozoa, and viruses. These pathogens can cause fever, diarrhea, nausea, abdominal pain, vomiting, and in the worst-case scenario, death. Over the years, there have been several disease outbreaks from manure exposure in the United States.

Common bacteria found in livestock manure include Campylobacter, E.coli, Leptospira, Salmonella and Yersinia. Rotavirus is the most prevalent virus found in manure, and Cryptosporidium and Giardia are protozoa found in livestock manure and pet feces.

Modderman points out three main areas of focus where livestock producers can reduce pathogens:

1) In the animal: Stressed, unhealthy livestock are more likely to excrete pathogens than healthy animals. Therefore, keeping livestock healthy needs to be a priority to reduce the amount of pathogens in manure. Just because an animal appears healthy, does not necessarily mean that their manure will be pathogen-free. Some animals are carriers of disease without ever showing symptoms, themselves. Below are a few ways to keep livestock healthy:
    • Clean feed and waterVaccinations
    • Barn ventilation
    • Appropriate space allowance per animal
    • Temperature regulation
    • Biosecurity & sanitation measures
    • Slotted floors or prompt manure removal from barn
    • Fly and vermin control
Another way to decrease pathogens in manure is through feed selection. Adding antimicrobials to feed will reduce the number of pathogens in manure. Organic acids and yeast extracts added to feed have also been effective at lowering the number of pathogenic bacteria in manure. Replacing finely-ground feed with coarsely-ground feed can reduce Salmonella content in swine manure. Livestock producers should talk to their veterinarian before drastically changing feed.

2) During manure collection and storage: Using vegetative buffers near storage and areas of runoff will filter out pathogens before they reach a waterway. The effectiveness of a buffer strip depends on many factors, and the ideal buffer will have the following qualities:
    • Loam-textured soil for good infiltration
    • Soil with high organic matter and adsorption rate
    • Thick vegetation with deep, fibrous roots
    • Shallow slope
    • No rill or gully erosion for even flow
    • At least 15 feet wide (MN law requires 16.5 ft along ditches, and 50 ft along lakes, rivers, and streams)
    • Time of year (buffers will be relatively ineffective during the winter and at snowmelt)
Storing manure under anaerobic (no oxygen) conditions, like deep pits below livestock housing, will also reduce pathogens. Though some bacteria can survive anaerobic conditions, most pathogens will be killed within 30 days. Using anaerobic digesters can accelerate the destruction of pathogens.

High temperatures combined with aeration also kills most pathogens. Composting is a good way to do this. A compost pile consists of organic material such as manure, bedding, and dead livestock. Temperatures within a compost pile can reach 150⁰F. We recommend two cycles of temperatures of at least 131⁰F to kill pathogens. Aeration and uniform heat distribution are mandatory for the breakdown of a compost pile into dark, soil-like material.

The following are a few other, more costly treatment options to reduce pathogens. Lime added to manure can reduce pathogens and odors, and when it is land-applied, it also reduces soil acidification. Ozone destroys bacteria, though the high organic matter content in manure can reduce its effectiveness. Ultraviolet (UV) light and Pasteurization at 158⁰F for 30 minutes are also effective at killing most pathogens. Chlorine disinfects drinking water but should not be applied directly to manure. Because manure has high organic matter content, it will be generally ineffective and can produce toxic and carcinogenic byproducts.

3) During land application of manure: The main concern with pathogens at application is runoff and loss through tile drainage. People are at the greatest risk for pathogen infection when manure runoff reaches resources like waterways or food crops.

Pathogen concentrations decrease when exposed to UV light and drying. Since that naturally occurs when manure is surface applied, delaying manure incorporation will reduce pathogen numbers. However, waiting to incorporate manure can have adverse environmental effects as nitrogen is lost to the atmosphere and runoff risk is increased. Flies and vermin are also more likely to pick up and carry pathogens from manure that is left on the surface. Therefore, the recommended method is to incorporate manure soon after application.

To further reduce manure runoff, follow proper application methods to avoid over application. Test soil and manure for nutrient content to determine how much manure to apply. Calibrate equipment carefully for the intended rate. Avoid applying manure onto frozen ground where it cannot be incorporated.

Reducing pathogens in manure is important for livestock operations of all sizes, and the practices listed above will help do that. Before using each management practice, take into consideration the costs and benefits. Will these practices be economical? Will the social and environmental cost be too high if management action is not taken? All in all, reduction of pathogens at the agronomic level helps protect the health of people everywhere.


The Minnesota Department of Agriculture (MDA) has teamed up with the National Weather Service to design a tool that helps farmers and commercial applicators determine the best time to apply manure. The Runoff Risk Advisory Forecast tool uses past and predicted National Weather Service weather data like precipitation, temperature, and snow melt.

It predicts the likelihood that applied manure will run off fields in daily, next day, and 72-hour increments. Farmers and commercial applicators use an interactive map to locate their field and find the forecasted risk. MDA offers a ‘sign-up’ for Runoff Risk Alerts.

Alerts will be sent via email or text when conditions are likely for a runoff event.

Content of this article courtesy of Melissa Wilson, and Chryseis Modderman, , UMN Manure Management team. Diane DeWitte can be reached at
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