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Make the most of manure nutrientsMake the most of manure nutrients

Test manure to know nutrient levels so you can avoid unnecessary supplemental fertilizer.

Rod Swoboda

September 2, 2016

4 Min Read

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 Jim Friedericks, AgSource Laboratories’ outreach and education adviser, based at Ellsworth, Iowa.


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.

What do you test for?

“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 N, P and K along with moisture, and Friedericks says testing for ammonium (NH4) can be very useful as well.

He says ammonium is a measure of the amount of immediately available N.

“The ammonium levels can help determine how to best apply and treat your manure. For example, manure from a swine pit with high ammonium levels should only be injected into the soil when soil temperatures are at 50 degrees F [at 4-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 an N or P limit that must be followed.

Calculate application rate

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

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

Testing for manure nutrients should be done prior to application. If your farm only applies manure in the fall, once-a-year testing is adequate.

“Accurate analysis is dependent on correct sampling procedures,” Friedericks says. Sample collection, preparation and shipping can influence the results. Instructions on how to take a representative sample can be found at agronomy.agsource.com.

The University of Minnesota has developed guidelines for manure nutrient availability and determining what manure is worth. Go online and learn more about calculating rates at extension.umn.edu/agriculture/manure-management-and-air-quality/manure-application/calculator.

For information on manure management, visit extension.umn.edu/agriculture/manure-management-and-air-quality/about.

Basic manure sampling tips

Here are some tips on how to sample manure:

1. 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.

2. Use the proper container. No glass containers! Call the lab to order your plastic sample jars.

3. 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.

4. Handle samples carefully. Remember, manure is a biologically active material. It is best to collect the samples, cool or freeze them 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. Label all containers clearly, and include a laboratory identification sheet with each sample.

AgSource is an ag and environmental lab analysis and information management services company. A subsidiary of Cooperative Resources International, AgSource provides services to clients in the U.S. and across the globe. Learn more at agsource.com.

Source: AgSource Services

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