Over the past few months, many winter meetings in Indiana, Ohio, and Michigan have included presentations that previewed some of the possible changes in the Tri-State university fertilizer recommendations. One of the more publicized changes is the change in the chemical solutions used to extract soil nutrients in the laboratory from Bray to Mehlich III for phosphorus and from ammonium acetate to Mehlich III for potassium. While change can be challenging and concerning, this one is easy.
A&L Great Lakes Laboratories, like most leading soil labs, has been using Mehlich III as a universal extractant since the 1990s. Mehlich III is a slightly stronger acid and results in soil test values that are 10-20% higher depending on the nutrient. However, in order to facilitate interpretive guidelines, such as the current Tri-State soil fertility recommendations, which require Bray P1 and ammonium acetate K values, we employ a calculation to convert the Mehlich III value to a Bray P or ammonium acetate K equivalent.
Updated Tri-State fertilizer recommendations will reflect the use of the Mehlich III extractant, and will base recommendation calculations on the M3 values rather than the Bray P1 and ammonium acetate K values. During this transition period, it will be important to ensure that the soil extractant indicated in soil test data matches the fertilizer recommendation chart or equation being employed. With soil samples collected every 2 to 4 years, there will be a transition period were both data values may be part of this process.
Here at A&L Great Lakes Laboratories, we offer a wide range of reporting options to meet various customer’s needs. We will not be changing any soil test report formats to Mehlich III data until it has been requested by the customer. If you have any questions or need assistance once these university recommendations are released, please contact your ALGL agronomist or call the lab directly at 260-483-4759.