By Gary Sliworsky
Ag rep, Emo
There are a number of misconceptions out there that keep us from getting the best value from soil testing.
In some cases, they mean that samples don’t get collected at all. This is a waste of valuable information you could use to improve your bottom line.
Myth—My farm is unique so a soil test can’t be relevant.
Fact—While it is true that there are differences from farm to farm in how effectively nutrients are used, the soil test is the only reliable way to get information about the concentration of nutrients in your soil.
You can manage your unique situation better if you have this information.
Myth—You have to grid sample to get good information.
Fact—We are more aware of within-field variability today, but the value of quantifying this variability is limited.
The first step always should be a good field scale sample (maximum 25 acres).
Myth—I grow good crops so I don’t need soil tests.
Fact—Good for you! This probably indicates that nutrient deficiencies are not a problem, but that there may be opportunities to save money with lower fertilizer rates on some fields.
Myth—Water is the best extract because it shows what is immediately available to the crop roots.
Fact—This is one of those attractive theories that just doesn’t work in reality. The water extract, despite the claims, is not at all the same as the concentration in the soil solution.
This is because it involves shaking a soil sample in a soil/water slurry, that is a much higher amount of water than a root could ever grow in.
It also ignores the contribution of exchangeable and slightly soluble nutrients from the soil, which account for most of the plant uptake during the growing season.
Myth—Other provinces/states use “better” extractants.
Fact—Soil test extraction is a complicated dance between the chemistry of the soil and the extractant, in an attempt to mimic the availability of nutrients to the crop over the growing season.
The extractants chosen for Ontario work well with our soil types. Others are better suited to the conditions in their particular areas.
Myth—Fertilizer recommendations from soil tests are only for average crops.
Fact—Soil fertility is only one small part of growing high yielding crops, and crops with a high yield potential will have large root systems that are very efficient at absorbing nutrients from the soil. Fertilizing using soil test recommendations will not limit crop yields.
Myth—The soil test reports are too hard to understand.
Fact—Soil test labs are trying to add more value to the soil test by including more interpretations of the results on each report.
Unfortunately, this does sometimes have the effect of making the important information harder to find.
School yourself to concentrate on a few key numbers (i.e., soil pH, extractable P, K, and Mg), and interpreting the test results becomes much simpler.