How to Interpret Your Soil Test Results

Jan 18, 2021

From the GreenPoint Ag Agronomy Team
While the holiday season always brings a feast to your table, the days following provide something completely different to digest: soil analysis reports. With harvest out of the way and the new season in mind, now is the time to focus on the results of your soil tests to determine what fertility steps you’ll need to take to give yourself the best chance for success in 2021.
At first glance, it might seem like you need a Ph.D. in agronomy to understand the soil analysis your lab provides, but if you break it down piece by piece, it’s easier to digest. So, here are some suggestions to help you interpret the reports you receive from the lab.
A basic soil analysis provides:
  • Soil pH level: The ideal pH range for most crops grown in our service territory is 5.5 to 7.5, but soils tend to be more acidic here – hovering in the high 5 range. If your soil pH is low, the lab will recommend a specific lime application to help you achieve a pH of 6.5.
  • Buffer pH: an indicator generated by the lab to determine how much lime is needed to adjust pH to ideal levels. The lower the buffer pH reading, the higher the lime requirement.
  • Cation Exchange Capacity (CEC): CEC is a measurement of your soil’s ability to hold nutrients. A higher CEC (>25) is desirable because it means your soil can hold more nutrients, usually indicating it is a silty clay loam with good organic matter levels. A low CEC (<5) means your soil is unable to hold nutrients or deliver them to the roots, likely indicating it is sandy and lacks organic matter. You can’t change soil CEC, so if yours is low, fall fertilizer applications are not recommended. In this case, you’re better off spoon-feeding nutrients to your crop via split in-season applications.
  • Phosphate (P) and potassium (K) levels: The amount of nutrients present in your soil is reported in either lbs./A or parts per million (PPM); 1 PPM equals 2 lbs./A In addition to this figure, the lab will also categorize the nutrient levels in your field as very low, low, medium, optimum or very high. It’s important to note that these designations often vary between labs. (i.e., what one lab might consider “low,” another might classify as “very low,” and so forth.) For that reason, we recommend you have the same lab analyze your soil samples year after year to avoid any discrepancies.
  • Soil fertility recommendations: The lab provides application rate recommendations based on the crop you intend to plant next season and the nutrient levels you currently have in your field. Sometimes application timing is also recommended. If you change your mind and decide to plant a different crop next season, your agronomist can log into the lab’s online portal and generate new nutrient application recommendations for the appropriate crop.
For an additional fee, a more detailed soil analysis can be ordered. This will contain the same information from a basic soil test, but can also include items like:
  • Secondary micronutrient levels: The levels of nutrients like calcium (Ca), magnesium (Mg), sulfur (S), boron (B), copper (Cu), iron (Fe), manganese (Mn), zinc (Zn), and sodium (Na) can also be tested. If you ordered them, they will appear right after your phosphorus (P) and potassium (K) levels.
  • Organic matter content and Estimated Nitrogen Release (ENR): The percentage of organic matter is a measurement of the amount of plant and animal residue in the soil. Darker soils are usually higher in organic matter. The organic matter serves as a reserve for many essential nutrients, especially nitrogen (N). During the growing season, a part of this reserve N is made available to the plant through bacterial activity. The ENR is an estimate of the amount of N (lbs./A) that will be released over the season. In addition to the organic matter level, this figure can be influenced by seasonal variation in weather conditions and physical conditions of the soil.
  • Soil texture analysis: You’re likely well aware of the types of soil that make up your fields, but analyzing the texture can be helpful when farming a new piece of land for the first time.
When looking at your soil analysis, you’ll likely notice that your field’s current nitrogen (N) levels are not included. Since N moves through the soil more rapidly than other nutrients, it’s difficult to measure in the fall and accurately assume how much will be available for crop use. Therefore, labs typically only test for N in spring or during the growing the season when a grower is preparing for a pre-plant or side-dress application. However, the lab still supplies a general N recommendation based on the yield goal and expected uptake of your intended crop.
As noted earlier, the fewer changes you make between labs, the more consistent your soil analysis will be. Most labs in our region use the Mehlich-III extraction method when performing soil tests, but they might use different buffering agents during the process, which can lead to differences in the nutrient applications they recommend.
So if you’re satisfied with the analysis your lab provides, it’s best to stick with them. Doing so makes it much more likely that you’ll be able to identify the fertility trends that take place in your fields when you have soil samples tested every two or three years. That said, GreenPoint Ag has built relationships with many of the top labs in our region, so if you’re unhappy for some reason, you can rest assured that we’ll refer you to a quality provider.
Reviewing soil test results can be a challenge, so don’t hesitate to contact your local Co-op crop specialist or GreenPoint Ag agronomist if you have any questions. Whether you need a quick phone conversation or an in-person visit, we’re happy to help. You can also rely on us to help you prescribe a customized fertility plan to ensure you supply your fields with the right amount of nutrients in the coming weeks and into the spring.

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