Potassium Fertilization for Soybean in the Mid-Atlantic United States.

Next to nitrogen, potassium (K) is required in the greatest amount for soybean.  Potassium deficiencies are common in the Mid-Atlantic and could relate to insufficient amounts of K being applied to high-yielding crops.  Potassium requirements for full season and double cropped soybean need reassessment and recommendations may need revision for the Mid-Atlantic, United States. It is my goal to determine the optimum rate of K fertilizer needed for soils in Virginia and to utilize that information throughout the Mid-Atlantic. Nineteen experiments were conducted throughout the Coastal Plain and Piedmont of Virginia on low, medium and high testing K soils during the summer of 2013.  Within two weeks of planting, soil samples were collected at depths of 0-15, 15-30 and 30-60 cm across each replication.  Six K rates (0, 28, 56, 112, 168, and 224 kg K₂O ha^-1) using granular Muriate of Potash (0-0-60) were hand-applied to soybean two to three weeks after planting.  Experimental design was a randomized complete block with four replications.  Soybean were harvested at full maturity and yield, moisture, and seed weight determined.  Soil test reports indicated K levels ranging from 15 to 217 mg K kg^-1.  Results are under analysis and will be presented at the meeting.