AGRONOMIC NEWS ITEMS
From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335
Spring 1997, No. 3
Potash is sold on the basis of its oxide, or K2O equivalent. That's confusing because potash does not contain any K2O and plants do not take up K2O. A fertilizer with an analysis of 0-0-60 would contain 60 percent K2O equivalent by weight. There has been interest in expressing the potassium in potash as percent K rather than percent K2O, but for now, the oxide form is the standard. Fortunately, converting K2O to K and vice versa is a simple calculation:
% K = % K2O x 0.83
% K2O = % K x 1.2
Potash fertilizers contain from 22 to 62 percent K2O equivalent, and all are water soluble. They consist of potassium in combination with chloride, sulfate, nitrate and other nutrients. Common potash fertilizers include:
Muriate of potash is the most widely used potassium fertilizer. It is applied directly to the soil or used in blends with nitrogen, phosphate and other nutrients. Potassium sulfate is used most often on potatoes, tobacco, turf grass and other crops which may be sensitive to large amounts of chloride. Potassium nitrate is also good for chloride-sensitive crops and is most widely used for fruit trees and high cash value crops like cotton and vegetables. Potassium-magnesium sulfate is routinely used wherever soils are deficient in at least two of the three nutrients in the products.
In most situations one potash fertilizer is as effective as another if the material is being used for its potassium content alone. Accompanying elements can be important and should be considered in choosing among the various sources.
Regardless of source, potash supplies potassium, an essential plant nutrient. Potassium is often deficient in the soil, making potash fertilizer necessary to grow high yielding, high quality crops.