Getting a Soil Test Done

Whether getting a soil test done has crossed your mind or not, this is a must-do to get the best grasp on your soil needs. Not only will it benefit your future crop, but it will benefit your knowledge and understanding of the soil present in your own backyard!

Why should you get a soil test?

  • Test results are used to determine cost effective lime and fertilizer recommendations specific to the type of crop or plant and yield desired.
  • To better grasp your soil fertility needs

All About Tests:

The most common basic soil tests include pH, phosphorus, potassium, and nitrogen.  A lot of tests will also check for trace minerals like calcium, magnesium, zinc, manganese, iron, copper, sodium and boron. Testing is often offered through your state Extension offices for a small fee. All you need to submit is a soil sample.

There are also more in-depth soil tests you may opt for. While most of these are best for large farm operations, greenhouses, and the like, you may want to consider opting for a test of your Soil Organic Matter (SOM). SOM is a good indicator of the overall fertility of your soil. Healthy soils will have between 3-6% SOM, with more being better!  If your soil is low on SOM, you can add compost, use cover crops, and thick mulches to build it up.

Once you know the type of test you need, all you have to do is send in a soil sample and the fees associated, and you should receive your results in a week or so.

Collecting a sample properly is critical for getting a valid result on your test.  You will need to take soil from 10-15 spots and combine them together. Let it dry out and then fill up your test box or bag.  For more detailed instructions, check out these resources:

How to Sample a Farm Field:

Visit How to Sample a Farm Field for more information.

How to Sample a Lawn or Garden:

Visit How to Sample a Lawn or Garden for more information.

For more information about soil testing in TN, visit: https://extension.tennessee.edu/Lauderdale/Pages/Soil-Testing.aspx

Converting from Conventional to Organic

Many testing services will give you back nutrient recommendations using conventional fertilizer.  If you want to grow organically, you’ll need to do a little math (sorry!). For instance, let’s say your test tells you to add 30lbs of 10-10-10 per 1,000 square feet.  Those numbers stand for percentages of NPK (Nitrogen, Phosphorus, Potassium) contained in the fertilizer. So 10% of 30lbs is 3lbs of NPK each that you need to add to your soil.  

If your organic fertilizer bag says 5-4-3, then you know that it contains 5%-4%-3% of N-P-K.  To get 3lbs of actual nitrogen into your soil, you will need to use 60lbs of fertilizer per 1,000 square feet.  60lbs x 0.05 = 3lbs. Now, the Phosphorus and Potassium don’t match up, but for the most part, it’s fine to just focus on matching up the nitrogen when using a balanced organic fertilizer.  

If your test shows that you have a deficiency of a specific nutrient, then you will need to add a source of that nutrient.  For a detailed list of organic sources of major and minor soil nutrients, check out this article from Penn State Extension: https://extension.psu.edu/using-organic-nutrient-sources

And remember, you can always call the lab that tested your soil sample and get a detailed explanation of your results, if there’s anything you don’t understand!