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Alfalfa doesn’t need fall potassium fertilizer application to aid winter hardiness in Minnesota, research shows

Field of alfalfa crop

Minnesota alfalfa growers typically apply potassium (K) fertilizer in the fall to help with overwintering their alfalfa crop. New research from the University of Minnesota shows that a fall (K) application has no effect on alfalfa's winter hardiness.

There are two likely factors for the neutral effect of the potassium application. 

  • Modern alfalfa varieties have been bred for greater winter hardiness, so they don’t need as much K for overwintering as past varieties.
  • Previous research showing a benefit from fall K application was likely done on soils with much lower K levels than we have today. 

Fall K application may also lead to greater fertilizer loss via leaching in sandy soils and surface runoff on other soil types. “With the current economic situation, nobody wants to spend money on fertilizer and lose it to leaching and runoff,” says Dan Kaiser, Extension soil fertility specialist, who participated in the research.

Test soils and apply potash once during the growing season at recommended rates. The University also provides an alfalfa calculator to help farmers choose optimal phosphorus and potassium application rates.

The study was funded by Minnesota’s Agricultural Fertilizer Research and Education Council (AFREC) and the Midwest Forage Association. It was published in the Agronomy Journal (paywall) and is available on the AFREC website.

Learn more about alfalfa and potassium in this recent Minnesota Crop News post.

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