How To Interpret Manure Nutrient Test Results

How To Interpret Manure Nutrient Test Results

ISU Extension has new publication that complements existing manure management resources. "How to Interpret Your Manure Analysis" explains the value of manure testing to indicate nutrient concentrations.

Iowa State University Extension recently released a new publication that complements existing extension manure management resources. How to Interpret Your Manure Analysis, PM 3014, explains the value of manure sample analyses that indicate nutrient concentrations. Such analyses help define application rates that increase the potential of manure as a crop nutrient source.

"Having your manure analyzed is the best way to determine its nutrient concentration for crop fertility and manure application purposes," says Tom Miller, ISU Extension swine specialist. "This new publication explains the numbers producers see in the analysis results they get back after they send manure samples to the testing lab. The new ISU publication also tells producers how to use those numbers in the nutrient management planning process."

New publication makes interpreting manure nutrient analyses easier

The ISU publication explains how frequently to sample, what tests to request, what the manue test results mean and how to use those results in a nutrient plan. How to Interpret Your Manure Analysis  also provides examples of lab reports and a list of common conversions.

"Viewing the publication online allows readers to click on highlighted text and reach Web pages that have additional nutrient planning information," says Angie Rieck-Hinz, the ISU Extension manure management program specialist in the Agronomy Department at Ames. The publication can be viewed online or downloaded from https://store.extension.iastate.edu/ItemDetail.aspx?ProductID=13669. The print version of the publication can be ordered by contacting the ISU Extension Online Store at 515-294-5247 or emailing [email protected].

Why and how often should you sample manure and have it tested?

Manure analysis is a critical component of proper nutrient management planning, says Rieck-Hinz. "Using table or book values of manure nutrient concentrations can serve as a starting point for planning purposes, but actual manure sample analysis provides a better indication of manure nutrient concentrations and will help better define your application rates. Using manure testing will help achieve the potential as a crop nutrient source, and result in reduced chance for misapplication of manure that could lead to lower crop productivity or increased environmental risk."

How often should you sample manure and have it tested? What about the history of manure application to a field?

Collecting manure samples for nutrient analysis should not be a one-time event, says Rieck-Hinz. Manure samples should be taken and tested at least yearly, and near the same time every year, to account for any seasonal changes, and preferably they should be taken near or during the time of land application of the manure. "Once manure samples have been collected and tested for at least three years, and if you have no significant changes due to feed inputs, management or storage, the sampling frequency can be reduced. However, if your feed inputs, management, storage or land application frequency changes very often, then the manure sampling should continue on a yearly basis," she says.

Suggested sampling strategies can be found in another ISU publication

Sampling strategies are explained in PM 1558, How to Sample Manure for Nutrient Analysis. One recommendation is to collect samples as the manure is being land applied. Sampling during land application will prevent you from having a nutrient analysis available to determine application rates, but this method ensures you have a well-mixed sample of manure and you will know what nutrients were applied (along with the known application rate).

By sampling yearly, you will build a history of analyses allowing you to determine your application rates, says Rieck-Hinz. You can further refine your nutrient applications by using the results of samples collected at application and adjusting your nutrient rates with fertilizers, if needed.

What information should you submit along with a manure sample for analysis?

When collecting and submitting a sample it is important that you provide as much information about the sample as possible. In addition to your name, address, phone number and email if available, you also need to provide a sample identification name or number so you can remember where and when the sample was taken.

It is also recommended you record the species of animal, how manure is stored, if there is bedding, type of bedding and how the manure is land-applied.

What nutrient analysis should you request when you send the sample to a lab?  As a minimum, all manure samples should be tested and analyzed for total nitrogen (N), total phosphorus (P), total potassium (K)  and moisture content—or dry matter. You may choose to have your manure sample analyzed for ammonium-N as well. Other tests may include micronutrients and total salts.

What about secondary nutrients and micronutrients? Manure contains all of the secondary and micronutrients necessary for growing crops, she says.  "Having manure analyzed for secondary and micronutrients is not necessary unless you think you are experiencing a specific deficiency," notes Rieck-Hinz. "This analysis will help you determine how much of that nutrient you are applying."

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