There has been an increase in the amount of potassium (K) deficiency in field crops being reported both around the state and locally.  Potential reasons for this have been well documented.  One of these has been the increase in use of liquid starter fertilizers, specifically 10-34-0.  Certainly we don’t see K deficiency in every situation where 10-34-0 is used as a starter.  In most if not all cases broadcast K is applied in the fall or spring to replace the amount of K removed by the crop.   

        The specific issue is how much of the positive “starter” effect is the result of having some K in the starter fertilizer and do we suffer some yield loss if it’s not there?  We may not have the research base in Wisconsin to say for sure just yet, but there is adaptive research evidence to suggest that some yield loss occurs, at least in certain situations.  Historically, Wisconsin recommendations for starter fertilizer have been founded on a minimum of 10 lbs. N, 20 lbs. P₂O_5, and 20 lbs. of K₂O per acre.  This minimum is applied even if soil test levels are in the excessively high range.  Further, the research has also shown that the odds of obtaining an economic yield response on high testing soils differs based planting date and corn relative maturity.  This same research also confirms that K is a key component in the starter mix to obtain the full “starter” yield effect in responsive situations.

        The dilemma occurs when options are explored to include K in the liquid starter.  Traditional liquid fertilizers that include K such as 7-21-7 are more subject to “salting out”, especially under cool temperatures.  Some producers seem to have more problems with this than others as evidenced by the fact that the product is routinely used by some.  Other forms of liquid K fertilizer, not subject to salting, are extremely expensive, if not cost prohibitive.  The second part of the dilemma is that liquid starter fertilizers are desirable from a handling and metering perspective compared to dry products and producers want to continue to use them.  They are especially popular among growers farming large acreages.  

        The “No-K starter dilemma” as described here is not reason enough to make drastic changes in your current management practice.  However, it does point to the need for some additional research to answer the following questions: 

·   How much, if any, yield loss occurs as a result of not having any K in the corn starter fertilizer? 

·   How is the yield loss impacted by K soil test, planting date, tillage system, hybrid maturity, and other management factors? 

·   What is the minimum amount of K needed in the starter to overcome the yield loss?