Manganese (Mn) is a nutrient that is often overlooked in the Great Lakes region since it rarely tests as low or deficient in our soils. In fact, nearly 90% of soils tested at ALGL test at adequate or higher levels. However, this is not the case for corn and soybean plant tissue tests. It is quite common for plant tissues to test low or deficient in Mn.
Where does this discrepancy between soil and tissue tests come from? The simple answer is that just because the Mn is present in the soil, does not mean that it is in a form that the plants can uptake. Manganese availability is highly dependent on soil pH, it is most available when the pH is around 6.5. As the pH approaches 7.0 or higher, the availability is greatly reduced. Another factor that reduces the availability of Mn is organic matter. Manganese is highly reactive with organic matter and forms bonds with it making it impossible for plants to access it.The good news is that there are options available to manage Mn. The best option is to maintain your pH around 6.5. However, this is not always possible, many areas in the Great Lakes region have naturally alkaline soils. In these areas, both soil applied, and foliar applied Mn fertilizers can be used successfully. In areas with high organic matter, foliar applied fertilizers tend to be more successful. If the pH and the organic matter are both high, a chelated form of Mn is the best option to maintain availability.