Time to Soil Test

This is definitely the time to be out in the field soil testing. I am a big proponent for taking your soil samples at the same time every year so that I can reasonably expect that the soil is at the same environmental condition as in previous years. I also like to keep my soil test results in a spreadsheet where I can place them side by side and see every year’s results. How can I monitor fertility unless I measure fertility? How can I know progress unless I can see the changes from year on top of year? Here are some test results I like to see.

Types of Soil Tests

Of course, a normal soil test or what you might call a Regular Soil Test is a must. These are not usually expensive, +/- $15 or more with micronutrients. This test is mostly meaningless unless I have previous year’s results to see what is going on. I have taken literally thousands of soil samples and often I will see something show up that is off the charts. I am not known to panic when I see a problem because I am not going to react to that test unless I know it has steadily been a problem that is just getting worse. For instance, we can see pH swings in sand from one year to the next. Before I lime a soil, I may take a second sample just to verify I need lime. $15 soil test is cheaper than $60 per acre lime application.

Second, I like to have a Haney Soil Test done. What does a Haney soil test give me? Here is a list of the tests done:

  • Soil Respiration CO2-C ppm
  • WEOC – Water Extractable Organic Carbon
  • WEON – Water Extractable Organic Nitrogen
  • %MAC – % Microbially Active Carbon
  • Organic C:N
  • Organic N to Inorganic N
  • Organic N Release
  • Organic N Reserve
  • Soil Health Score

If you thought it was cheap, guess again. Most labs charge $50 so you don’t usually just send everything in for a Haney Test. Again, the results are only good if you have several years’ worth of data to see if you are getting better.

Last, is the PLFA Test or Phospholipid Fatty Acid Test. This test measures the biomass of the microbes in the soil and is one of the tests that is currently being conducted to determine the microbial population of soil. Here’s an example:

Looking at this example you can see the microbial biomass, the diversity index with a rating chart, the different groups – bacteria, fungi, protozoa and undifferentiated (unknown). This test is not cheap either costing $75 per sample but it does help to know if you are putting in the right mix of crops and fertility to see microbes increasing.

The “take home” message is not soil testing only, but records of soil tests you can see over time!

Author: Bob Whitney, Regents Fellow & Extension Organic Specialist

Agriculturalist, extension educator and researcher, organic agriculture enthusiast and promoter, international program developer, Christian, husband, father and friend.

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