K is for Potassium, Why soil K levels need monitoring.


Soil sampling for pH has become a staple in decision making on farms across the state that grow alfalfa. The second soil test nutrient that is monitored heavily is phosphorus, this is due to the need to maintain soil P levels for compliance and soil conservation. The forgotten tool in a routine soil sample is the soil K level. Potassium is the key nutrient that drives yields in corn silage, alfalfa, soybeans and grain corn.

The majority of potassium stays in the cells of plant tissue in the fall, meaning that any removal of Stover yields a large export of soil K from fields. Rock River Labs out of Watertown have followed trends in soil K levels. Their research has shown the levels of soil K have been increasing in the low and very low categories over the last 5 years for a total of an 8% increase in these categories. This paired with the research by UW Madison has shown a decrease level of 1.5ppm / year. This is problematic to crop production as the remedial process for soil K can be a 5-8 year adventure.

So my advice for you is to monitor your soil K levels before they become low or very low, and affect your yields for 5-8 years. Soil K removal for 60 bushel beans is 70lbs K , alfalfa at 5 ton is 245 lbs K, and corn silage at 20 ton is 145lbs K . Converted to Potash this is 115, 395, and 230 lbs respectively. This can become a huge amount of K removal from a field in a 4/5/or 8 year rotation. Ask yourself if your current rotation and fertility programs are able to address the yields that you have removed from the fields. If you feel that you have not replaced the soil K levels that have been removed, contact myself, or your CHS Larsen agronomist to talk about monitoring your soil K levels with soil testing and proper fertilization.

By Alex Yost, CHS Larsen Co-op YieldPoint Specialist 

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