Available research-based information continues to verify that the soil test potassium (K) level of 125 ppm as a critical level for K application is adequately high for agronomic crops of Nebraska. The probability of profitable response to K application is very low if soil test K is above 125 ppm.

In three studies of corn response to applied K involving over 50 trials, there was a 2-4 bu/ac average decrease in yield during the year of application. The decrease was not greater with application of 86 compared with 43 lb/ac of K₂O. The cause of the decrease has not been well determined. There is no evidence for such a decrease with other crops or of the reduction effect for corn persisting beyond the year of application although this has not been well-studied. These results suggest that

• fertilizer K should not be applied if not needed;
• infrequent higher rate applications are better than annual lower rate applications; and
• K may be better applied to another crop in the rotation rather than corn.

The UNL K recommendations are available in the Nebraska Extension publication, Nutrient Management for Agronomic Crops of Nebraska (EC155). We realize that some advisors recommend K rates in excess of UNL recommendations, but available research-based information indicates that these higher rates reduce profit potential.