Excessive use of K fertilizers can greatly reduce the uptake of Ca and Mg. For these reasons, the tri-state K recommendations for alfalfa and corn silage do not follow the maintenance plateau concept above the critical K soil test level. Potassium recommendations above the critical level are less than crop removal so as to discourage luxury consumption of K and improve Mg uptake. Sulfur is taken up as sulfate by plants. Sulfate sulfur is supplied primarily by microbial decomposition of soil organic matter.
Sulfate is a negative ion and easily leaches in soils.
Most soils in Indiana, Michigan and Ohio will adequately supply needed sulfur for plant growth. Sandy soils low in organic matter that are subject to excessive leaching may not supply adequate sulfur. Crops such as wheat and alfalfa that grow rapidly at cool temperatures when mineralization of S is slow are most likely to be S deficient. If elemental sulfur is used, it should be applied at least 2 months before the crop is planted. This would allow time for the S to be converted to the plant-available sulfate form by the soil bacteria.