The iron, copper and boron soil tests are not accredited under the OMAF & MRA Soil Laboratory Accreditation Program. Since they are included on a soil test report, it is often asked why they are not accredited. They are not accredited because of challenges in the methodology or correlation between reported soil test value and crop response.
- Iron is not accredited because the soil test does not correlate well with plant uptake or fertilizer response.
- Copper deficiency is rarely observed on mineral soils. It may occur on muck soils but these soils are unique having more than 35% organic matter. And like the iron soil test, copper is also poorly correlated with plant uptake and fertilizer response.
- Soil test boron levels are often less than 1 ppm, making it difficult to get an accurate measurement. As well, boron is also mobile in the soil and its concentrations will change over the season depending on leaching and mineralization.
Although these three soil tests are not accredited, they can still be useful if you keep in mind the following four points:
- Stick with one soil laboratory for your soil analysis. This will ensure that the same extractant is used, consistency in the laboratory procedures, and that reported critical ranges reflect that extractant.
- Check the reported soil pH and make sure it is correct for the crop. Soil pH affects micronutrient availability.
- Complete a tissue analysis along with your soil test. Plant analysis can be a much more reliable indicator of micronutrient availability and uptake.
- Build a history of both plant and soil test results for each for your sampled fields.
More information on micronutrients and soil testing can be found in the Soil Fertility Handbook.