Managing Potassium for Organic Crop Production

Abstract

An adequate potassium (K) supply is essential for both organic and conventional crop production. Potassium is involved in many plant physiological reactions, including osmoregulation, protein synthesis, enzyme activation, and photosynthate translocation. The K balance on many farms is negative, where more K is removed in harvested crops than is returned to the soil. Although various organic certification agencies have different regulations governing allowable sources of K, the behavior of soil K is largely governed by its solubility. The slow release of K from soil minerals is generally insufficient to meet the peak nutrient demand of high-yielding crops, but they can contribute to the long-term improvement of soil fertility. There are many excellent K sources allowed for organic crop production, including soluble minerals such as langbeinite, sylvinite, and potassium sulfate. Potassium sources such as wood ash, greensand, and seaweed can also supply K but require special management because of their low nutrient content, their effect on soil pH, low solubility, or bulky nature. The concentration of K in manures and composts is highly variable, but it is generally quite soluble and available for plant uptake. Some rock minerals may supply a portion of the K requirement of plants, but many are too insoluble to be of practical significance.