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Which Tests Do I Need?
Most labs have a basic manure test with the option to add other tests for an additional fee. Make sure the tests or the package you select includes at least the following analyses for nutrient management planning:
- % Moisture or % Solids,
- Total N,
- Ammonium-N (NH4-N),
- Total P, and
- Total K.
Other analysis that may be useful in some situations include: pH, Carbon:Nitrogen ratio (C:N), water extractable P, calcium carbonate equivalent, secondary nutrients (Ca, Mg, & S), and micronutrients.
Manure Test Results Can Be Reported Differently
Dry Matter or As-Sampled?
Manure analysis results can be reported in several different ways. It is important that you clearly understand how your results are reported. The first consideration is whether the results are reported on an as-sampled basis or on a dry-weight (dwt) basis. Most agricultural labs that do manure testing report the results on an as-sampled basis. If the results are reported on a dry-weight basis the analyses will have to be converted back to as-sampled to be practical for use in a nutrient management plan. Example calculations for converting analyses results from % dry-weight (% dwt) or ppm to “as-is” results (lb/ton or lb/1000 gal are at Common Manure Test Results Conversions.
Reporting Units
Another, issue with reporting manure test results in the units used. When results are reported on an as-sampled basis the most common units used are lb/ton for more solid samples and lb/1000 gal for liquid samples. However, carefully check the units on the manure test because other units are sometimes used. For example, some labs report liquid manure test results in lb/100 gal. Lb/acre-inch may be preferred by producers using irrigation systems. Also, particularly when results are reported on a dry-weight basis, percent (%) and parts per million (ppm) may be used. Example calculations for converting analyses results from % dry-weight (% dwt) or ppm to “as-is” results (lb/ton or lb/1000 gal) are at Common Manure Test Results Conversions.
Elemental or Oxide?
Results may be reported as the elemental form for example P and K, or in the oxide form as P2O5 and K2O. Most agricultural labs that do manure testing report the results in the oxide form since this is how fertilizer recommendations are made. If the results are reported in the elemental form, they will have to be converted to the oxide form for use in nutrient management planning. Example calculations for converting analysis results from elemental to oxide are at Common Manure Test Results Conversions.
Solid or Liquid?
Finally, there may be situations where the results are reported for a liquid ie. lb/1000 gal but the manure is spread on a ton basis ie. tons/acre. The density of the manure can be used to convert from liquid to solid analysis. Example calculations for converting analysis results from liquid to solid or solid to liquid at Common Manure Test Results Conversions.
For more information see Reporting Manure Analysis Results taken from the publication “Recommended Methods of Manure Analysis”.
Related Web Pages
- Overview of Manure Testing
- Step 1. Manure Sampling
- Step 2. Manure Test Results (you are here)
- Step 3. Total and Available Nutrients
- Step 4. Manure Test Record Keeping
Page Authors: Douglas Beegle, Pennsylvania State University and John Peters, University of Wisconsin