Potassium (K) is an essential plant macronutrient taken up in large quantities, like nitrogen. In plants, K does not become part of complex organic molecules. It moves as a free ion and performs many functions. Plants that are supplied with adequate K are better able to withstand stress, insect damage, and many plant diseases compared with plants low in K. Exchangeable K is measured by soil tests and is considered readily available for plants. Potassium can become “fixed” thereby not being available to the plant. Fixation and release of K by these minerals is dynamic throughout the year.
Right Source: The most commonly used K fertilizer source is potash. Compound fertilizers containing chloride, sulfur and/or magnesium are appropriate when soil supplies of these other nutrients are limiting. Liquid products or solid products can both provide adequate K to the soil.
Right Rate: Recommended rates of K application are based on both soil testing and crop removal. “Maintenance rates” are those equal to the quantities of K removed and are used to maintain soil fertility.
Right Time: Timing of P typically has little to no impact on crop use efficiency. Fall applications every year or every other year are common in our region.
Right Place: Potassium sources vary widely in their effect on the soil solution. Potassium fertilizer sources with a lower salt index may be used at higher rates when placed near or in direct contact with seed. Subsurface bands of K can provide benefits over broadcast applications when subsoil fertility is lower and when drier growing conditions exist.