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What should I know about taking soil samples and testing my soil?

Answer

Taking soil samples and testing is a good idea every few years to track if your soil fertility program is moving in the right direction. These tests are one way to prove to your organic certifier that inputs, such as micronutrients, are necessary.

While numerous testing laboratories are available, give some thought to how you will use these tests and what your soil fertility program will require. If you are planning on using the test results to justify a government-approved Nutrient Management Plan, make sure you use a lab that is approved. Tests from an “unapproved” lab cannot be part of an NMP.

It is worth the extra dollars to go beyond testing only nitrogen, phosphorus and potassium (NPK). Get a full analysis, including Cation Exchange Capacity (CEC), which gives you an idea of the nutrient transfer capability of the soil to your plants. Organic matter (OM) helps you track if you are building soil structure and nutrient-holding capacity. All of the micronutrients plus pH are important to help you understand imbalances that can result in certain types of weed or pest problems, as well as depriving your crops of some nutrients.

To take soil samples, walk your fields in a zig-zag or wide “W” pattern, taking 6-10 samples at a minimum, depending on the size of the field. You will then mix these together in a bag and take a smaller amount of this composite sample to send to the lab. Use a soil probe or a trowel to dig about 4-8 inches deep. Try to avoid putting vegetation into the bag. Send if off to the lab in a timely manner.

Depending on your field(s), you may need to take numerous samples. If the soil type changes in the field—more clay on one end, sandy on the other—send in two samples so you can understand what is going on in these different areas. Also, make sure you have composite field samples for each of the fields that are growing different crops, so you can plan for your yield goals based on the needs of the crop and what the soil currently offers. Soil testing can be a good tool in helping you plan your crop rotations for both building soil health as well as crop yields.

Lastly, start a file for your soil tests so you don’t lose this information and can track, over time, the effectiveness of the soil amendments you might purchase and apply. Do not take your soil samples right after applying minerals or manure—the test would not give you a true picture of your soil composition.

Posted: Nov 2016
Answer By: Joe Pedretti