PO 17. Indicate how the following may cause variability in soil test results.

Number of samples taken depends on the size of the field, field characteristics, and field management, as discussed in PO 16 and PO 20.  One sample generally should not represent more than 10 acres, and should only represent one management unit, ideally a uniform soil-type area.  Samples should be taken at least once in three years, or twice per rotation.

Samples should be taken with clean equipment (probe or auger and plastic bucket), taken consistently (2-3 subsamples per acre on a uniform field), and selected to avoid misrepresentation (avoid fence rows, manure, stones, wood; sample between rows away from fertilizer; avoid sampling when wet).

The type of extraction method varies with the laboratory and with which tests are being done.  The laboratory you send to and the extraction type should remain the same.  Many different methods exist, and some are interconvertible, but not completely accurate.  Historical records cannot be developed with results from different labs.

Remember – your soil testing results and the fertility recommendation you make based on the soil test can never be more accurate than the soil sample you take!