Soil Testing and Plant Diagnostic Services
Missouri Soil Testing Association accreditation program
The Missouri Soil Testing Association Accreditation Program (MSTA) is designed
to assure that results provided by participating public and private labs serving
the citizens of Missouri agree with allowable statistical limits. Based on this
premise, soil test results from MSTA approved labs will be accepted by the U.S.
Department of Agriculture and Farm Service Agency (FSA).
Beginning in 1999, MSTA combined its efforts with the North American Proficiency
Testing Program (NAPT). The NAPT coordinator sends soil test data from the labs
participating in MSTA program to the state coordinator.
The MU Soil Testing Lab director serves as the state program coordinator and
performs statistical analysis of the data as specified in the MSTA program. If
a lab's results fall within the allowable limits, the lab will be placed on the
Farm Service Agency's (FSA) list of approved labs. A lab that is not accredited
may re-apply after six months.
Approval procedures for MSTA labs
The labs that wish to participate in the MSTA program should send a formal
written request to the director of the University of Missouri Soil Testing Laboratory.
They also need to request the NAPT coordinator to send results to the MSTA program
Participating labs must use procedures of the Missouri Soil Testing
Program in current use as described in MU Extension publication EC923, Soil Testing in Missouri (PDF).
The lab will be approved for routine soil tests:
- Bray-I P; ammonium acetate extractable K, Ca, and Mg
- Organic matter
- pH in 0.01 M CaCl2
- Neutralizable acidity (using the Woodruff Buffer test)
Standard pH 7.0 and pH 4.0 buffers must be used to calibrate all pH meters.
It is suggested each laboratory set up two or more internal check samples.
One of these checks should be included with each twenty or thirty soil samples.
A log of the results of the check samples should be maintained.
The MSTA coordinator will receive results from the NAPT program coordinator
on the recommended tests and do the statistical evaluation.
Approval criteria for MSTA labs
The MSTA program uses the median and median absolute deviation (MAD) as used by the NAPT program as robust estimations of central values and variances of all data sets. This statistical approach is less sensitive to influence of extreme values (outliers) than the mean and standard deviation. The MSTA summary report lists the median and MAD values and the lab data. If the lab's data falls outside the range of +2.5x MAD (it is marked as Low or High) and considered to be out of the allowable limit. If the lab data falls outside the limits of +3.5x MAD they are marked as outliers.
Test results of 75 percent of the samples must fall within the above allowable limits for each test. Upon meeting these criteria a letter will be sent to FSA to add the requesting lab to the list of approved labs in Missouri.
If the lab fails the lab director may discuss with the MU Soil Testing Lab director ways to solve problems at the expense of the requesting lab.