The Manure Analysis Proficiency (MAP) Program, administered by the Minnesota Department of Agriculture, began in the mid-1990s to assist US Midwest analytical laboratories to verify the accuracy (including both bias and precision) of laboratory manure analyses. In 2003, the program expanded nationally and continues today. With an annual enrollment of 60 to 74 labs each year over the past two decades and the analysis of 120 manure proficiency samples of 12 test parameters, trends in laboratory methods and performance have arisen. The presentation will cover inter-laboratory bias and precision of the primary manure analysis parameters: total solid content, nitrogen, ammonia nitrogen (NH3-N), phosphorus and potassium.
What Did We Do?
The MAP Program was designed to follow international standards under the ISO/IEC 17025 general requirements for the coordination of a proficiency testing program. This includes development and use of standard protocols for the preparation of manure proficiency testing (PT) samples, the use of blind sample replicates for the assessment of intra-lab precision, and the implementation of robust statistical measures for the assessment of data for the evaluation of both laboratory accuracy (bias) and precision.
Since 2002, the MAP program has sent PT samples to laboratories twice per year. Each cycle includes three manure types with each type having three replicates (for a total of nine manure samples). The PT samples are selected based on source animal type and a range of total solids (2-90%). Samples are thoroughly ground and homogenized and then packaged and frozen prior to overnight shipping to program participants. Each participating laboratory completes the required tests and sends back their results along with their analytical methods used to the MAP program. With the results tabulated from all laboratories each cycle, method bias is assessed based on the inter-lab (or between lab) median and 95% confidence limits (using the median absolute deviation). Precision is assessed based on the intra-lab (or within lab) relative standard deviation of PT sample replicates. Participating labs are provided graphical reports illustrating method performance as well as lab bias and precision.
One-hundred twenty-nine manure PT samples from dairy, beef, swine, and poultry operations have been evaluated since 2002 and each sample was analyzed by 60 to 74 labs participating in the MAP program (depending on the year). The samples ranged from 3.1 to 91% total solids, 0.02 to 2.71% total nitrogen, and 0.05 to 0.48% total phosphorus. With this wide range of manure types and conditions, plus the ability to pair data with manure analysis methods and accuracy ratings, we can evaluate the efficacy of certain methods and discuss their pros and cons.
What Have We Learned?
MAP program results for nitrogen have shown the dry combustion method to be unsuitable for manure samples with total solid content less than 10%. Results for four different ammonia methods indicate generally good agreement between methods in the median concentrations, but methods varied in precision. Across samples, intra-laboratory precision decreased with decreasing analyte concentration, often associated with decreased manure total solid content. In general, total solids, phosphorus and potassium methods were of high precision with intra-lab precision < 5%. Manure test parameters exhibiting poor intra-lab precision were EC, pH, and NO3-N.
The MAP program continues to operate under the Minnesota Department of Agriculture in partnership with Central Lakes College in Brainerd, MN. The team is currently working with the USDA-NRCS (who provided funding), the University of Minnesota, and laboratory directors of public and private laboratories to update the “Recommended Methods of Manure Analysis” manual which is expected to be released and printed in 2022.
Robert Miller, Technical Director, Agricultural Laboratory Proficiency Program
Corresponding author email address
Jerry Floren, MAP Program Director (retired), Minnesota Department of Agriculture
Larry Gunderson at the Minnesota Department of Agriculture
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