Potassium (K) is one of three macronutrients that all plants require for growth. Potassium is needed to move sugars and other forms of energy throughout the plant, allow gas exchange with the atmosphere through the stomata, and aid in cell wall strength. In dry conditions, potassium helps the plant stay rigid and upright. Adequate potassium fertility is essential to maximizing crop yields.
Analyses of potassium fertilizers are typically reported as percent K2O (potassium oxide), a potassium form that is not actually present in fertilizers but is used as an industry standard measure. In a standard fertilizer analysis, the third number is the percent of K2O by weight in the fertilizer. To convert amounts of K2O to K+, use the following equations:
KCl – Muriate of Potash (0-0-60)
K2SO4 – Sulfate of Potash (0-0-50)
K2SO4 MgSO4 – Sulfate of Potash-Magnesia (0-0-22)
KNO3 – Potassium Nitrate (13-0-44)
KOH – Potassium Hydroxide (0-0-70)
Biennial potassium applications can be equally as effective as annual applications, as long as the biennial application rate accounts for the nutrient needs of two crops.
Spring application is just as beneficial as applying in the fall, unless soil test levels are in the very low range. Soils with a low CEC may benefit from K application closer to planting to reduce the amount of fertilizer leached.
When starter N+K2O fertilizer is used, do not apply more than 80 lbs/acre to prevent salt injury. If more K2O is needed, broadcast and incorporate before planting.
Nutrient removal due to silage harvest or stover removal should be considered when determining fertilizer rate recommendations, as both will remove more potassium than grain harvest alone. Delaying harvest and removal can reduce nutrient removal rates.
Author: Samantha Reicks