Every laboratory has a different format for displaying soil sample results. When you’re deciding where you’ll send your soil samples, ask what type of sampling method the lab uses.
For example, Midwest Laboratories uses the DTPA test. If you’ve previously had soil samples using the Mehlich-3 test, the amounts of nutrients and recommendations will differ from your DTPA results. Always ask what sampling method a lab is using for analysis.
At ST Biologicals, we send some of our soil samples to Midwest Laboratories for analysis. This is an overview of how to read a Midwest Labs Soil Analysis Report.
Midwest Labs Soil Test Metric #1: Cation Exchange Capacity (CEC)
The first metric on a Midwest Labs DTPA test is the CEC (cation exchange capacity). That measures the soil’s ability to retain essential nutrients for plant health. It measures the positively charged cations such as calcium, magnesium, potassium, and ammonium.
The CEC is a good indication of soil type. Soils with higher CEC values are usually clay or clay loam. They hold nutrients longer. Soils with lower CEC values are sand or sand loam. The usually have low organic matter and do not hold nutrients or water very well. Sand or sand loam often requires more amendments and different farming practices than clay or clay loam.
Soil Test Metric #2: Soil Organic Matter
After CEC, the second most important soil component on a Midwest Lab report is soil organic matter. Crop residues, animal manures, and green manures supply many micronutrients and macronutrients. This test does not measure biological activity per se as in the Haney test (1), which measures the nutrients made available through microbial activity. For more information on the Haney test, read our blog.
Recommendations for field nutrient applications take into account the potential nutrients that don’t show up on the test but are tied up in the organic matter and rock forms. The higher the organic matter, the less supplemental nutrients the field will need.
Sandy fields that are low in organic matter are prone to nutrient leaching, drought, and drying issues. We recommend always having soil covered with growing roots, leading to higher amounts of green manures and less erosion.
Soil Test Metric #3: pH Measurement
No soil testing is complete without a pH measurement. Your soil pH depends on the crops you’re growing, farming practices, and the soil bedrock. If you’re a corn and/or soybean grower, you’re hoping for a pH of 6.2–6.5. A rancher with alfalfa/grass pastures wants 6.8–7.5. And if you’re a blueberry, strawberry, or cranberry farmer, you’ll like an acidic pH below 6.0.
Berries are high-value, specialty crops. What do you do if you’re a corn or soybean farmer and your soil test comes back acidic? The short, simple answer is to add lime. The Midwest Lab Soil Analysis gives you an estimation of how liming can change your pH with the pH buffered information.
Soil pH determines the availability of many nutrients. Most nutrients are more plant-available in the neutral pH level of 6.5-7.5. But soil is more complex than just CEC, organic matter, and pH.
The Complexity of Soil
The CEC, soil pH, and organic matter are interrelated. They are also related to micronutrients, microbial activity, past farming and ranching practices, weather patterns, and more.
An example of the complexity of soil is all the different forms of nitrogen. All forms, including ammonium, anhydrous ammonia, and urea must be converted to nitrate by soil microorganisms.
On average, the normal background levels of nitrates in soil range from 5-10 ppm (2). Fertilizers supply the difference for the crop need. The Midwest Labs soil report only gives the nitrate-nitrogen levels. This is what the test’s recommendations are based on.
Every farmer and rancher knows there are more variables in producing a profitable crop year than can possibly be accounted for. In agriculture we control what we can, but we know nature has the final say.
When you’re looking at a soil test and everything is lining up with past soil results and your soil is becoming healthier, you know you’re on the right track. But what about those outliers? Perhaps this year’s test results show your soil’s metrics are dramatically higher or lower than in previous years.
You have to ask yourself why. What was different this last year than previous years? What crops, structures, livestock, or other variables can be accounted for? If you can’t figure out why, it’s best to take another sample in that grid space.
Reading soil analyses can be overwhelming. If you’ve been reading them for a long time, you look for specific patterns. But you may be missing some key indicators simply because you’ve never thought they were important. Soil is complex. Everything is related and impacts all other aspects of soil. At ST Biologicals our team of crop consultants is trained to look for the nuances that make the difference between OK and optimal. Contact us. We’re here to help you succeed. When soil speaks, we listen.
