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Make the most of Manure Nutrients this Fall

Manure is a very important nutrient resource. With proper management, it can also improve soil health by supplying nutrients to microorganisms and improving water infiltration and retention by increasing the amount of organic matter in the soil.

But before heading to the fields and applying manure this fall, consider submitting a manure sample.

“If you don’t test, you won’t know the value of the nutrients you’re applying,” says Dr. Jim Friedericks, AgSource Laboratories’ outreach and education advisor.

Friedericks explains although there are “general book values” on the nutrient content of manure, there are many factors that affect the numbers, including animal species, rations, production management and facility type. Even the bedding type makes a difference. The type of storage, handling and agitation system can all move numbers as well.  

“Two neighboring barns with the same design and management could even have a wide variation of nutrients in their manure,” he says. “It’s important to test to see exactly what you have.”

The minimum recommendation suggests testing for total nitrogen, phosphorous, potassium and moisture. Testing for ammonium (NH4) can also be very useful since it is a measure of the amount of immediately available nitrogen.

“The ammonium levels can help determine how to best apply and treat your manure,” says Friedericks. “For example, manure from a swine pit with high ammonium levels should only be injected into the soil when soil temperatures are at 50 [Fahrenheit] (at four-inch depth) and cooling, which will slow the denitrification process. Manure with low ammonium content can be broadcast with fewer risks. In general, if ammonium numbers are high the manure should be incorporated into the soil quickly.”

Manage manure as a crop nutrient resource. Manure application rates should be based on soil testing and the crop fertilization requirements of your next crop. Typically on most farms with a manure management plan, there will be a nitrogen or phosphorous limit that must be followed.

Friedericks also says it is beneficial to know about “manure nutrient availability” when calculating application rates. Some portion of the nutrients in manure cannot be utilized by the plant immediately. For example, in dairy manure, only 30 to 50 percent of the nitrogen and 80 to 100 percent the phosphorous can be used by the growing crop right away.

“Take the nutrient availability into account when determining application rates,” he says.

Most states have developed guidelines for manure nutrient availability:

• Iowa – https://store.extension.iastate.edu/Product/Using-Manure-Nutrients-for-Crop-Production
• Nebraska – http://extensionpublications.unl.edu/assets/pdf/g1335.pdf
• Wisconsin – http://learningstore.uwex.edu/assets/pdfs/A2809.pdf (see page 73)

Testing for manure nutrients should be done prior to application.

Basic Manure Sample Tips:

• Plan Ahead, Sample Early: Collect and submit samples before the busy harvest season starts to reduce stress and headaches. It takes time to agitate and sample manure, especially from multiple locations. But manure in storage is relatively stable, so sampling a few weeks before application will give you reliable results. Allow enough time for the sample to get to the lab and be tested.
• Use the Proper Container: No glass containers! Use plastic sample jars, typically available at the lab.  
• Label Samples: Full sample jars look very similar. Be sure to label and record sample numbers on the container and on the information sheet. When shipping the samples, seal the sample jar in a plastic bag but place the information sheet outside the bag. This will help keep the info sheet clean in case of a leak.
• Handle Samples Carefully: Remember, manure is a biologically active material. It is best to collect the samples, cool or freeze immediately, and send them to the laboratory the same day. Do not let manure samples sit in hot areas, such as a dashboard of a truck, for any period of time. Clearly label all containers and include a laboratory identification sheet with each sample.

Courtesy of AgSource Laboratories