After you have collected and sent off your soil sample for testing, you anxiously wait for your results. But when they arrive, do you know how to interpret those?
Above is an example of what a soil test report looks like. Let’s go through it by sections and talk about what it means.
SAMPLE ID: The first section is composed of the information you filled out when you sent in the soil sample and forms — name, contact, crop and sample information. If sending multiple samples, be sure to name them something that let’s you know to what area they correspond.
RESULTS: Here is the measured soil fertility levels- phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), zinc (Zn) and the pH. These elements are essential plant nutrients that are important for proper plant growth, development, maintenance and health. pH measures the acidity or alkalinity. Levels will range from 0-14, with <7 indicating an acidic pH, 7 a neutral pH, and >7 a basic pH. Different plants like different levels of pH. For example, most grasses prefer a neutral pH between 6-6.5, while blueberry bushes prefer pH levels that are more acidic (between 4.5 – 5.5).
You’ll notice that the levels of these nutrients are listed as a numerical value and a bar chart describing the levels as adequate or needed. The concentration of nutrients extracted from the soil sample is called an index. The soil test index is an indication of the soil’s nutrient-supplying capacity and its expected relative yield. The total amount of a nutrient in the soil is of little importance in determining fertilizer recommendations, because only a portion of a nutrient may be available for plant use during the growing season.
You may notice that nitrogen (N) is not measured. Although nitrogen is a macro plant essential nutrient, required in larger quantities and is often the limiting factor in plant growth, it is very difficult to measure in the soil and make accurate assumptions on how much will be available for crop use. Nitrogen is a very dynamic nutrient, moving very quickly in the environment from one form to another. If we measure nitrogen when you take soil tests, typically done in the fall through early spring, the value reported doesn’t mean much. By the time your plants are planted and actively growing, that pool of nitrogen measured might have leached, run-off, or left the soil in another form. In the recommendations section, you will find nitrogen recommendations and those are based off average plant uptake of nitrogen.
Recommendations: See what fertilizers and soil amendments are recommended in the text below “Recommendations”. If the pH is too low (meaning the soil is acidic), then the appropriate amount of limestone is listed to bring the pH back to the recommended level. The fertilizer rates listed are based on the soil test results in the bar graph to make it easy. The amount of fertilizer will depend on the crop being produced.
Reading soil test results can be overwhelming and can be hard to digest all this information. Hopefully this will help take some of the pressure off, but if you have any concerns, comments, or questions about soil testing, please don’t hesitate to contact the Madison County Extension Office at 706-795-2281 or uge1191@uga.edu.
