Evaluation of potassium, boron, and sulfur application in alfalfa

Study author(s): Daniel Kaiser, University of Minnesota
Growing season(s): 2026, 2027 (continuation of multi-year trials)
Minnesota location(s): Rosemount

Note: Complete reports with figures and tables will be available for download.

What is this project about?

Alfalfa forage removes large amounts of nutrients from the soil, especially potassium. On soils with lower organic matter, such as those in southeastern Minnesota, crop yield and quality can also be limited by a lack of sulfur and boron. While previous research has confirmed the yield benefits of sulfur, less is known about how boron pays off on non-sandy soils or how potassium, sulfur, and boron interact with each other when applied together.

Additionally, standard air-dried soil tests on silt-loam soils may underestimate how much potassium is actually available to the crop. Led by Daniel Kaiser at the University of Minnesota, this project builds on research at Rosemount to determine the yield, quality, and soil testing benefits of targeted potassium, sulfur, and boron applications.

Key Project Goals & Farmer Benefits

  • Updated Guidelines: Update University of Minnesota fertilizer guidelines for alfalfa based on modern forage production demands.
  • Nutrient Interactions: Identify how potassium, sulfur, and boron interact to affect forage yield and overall crop quality.
  • Evaluate Boron Response: Provide practical data on whether boron applications are cost-effective for high-yield alfalfa production on non-sandy soils.
  • Better Soil Testing: Compare traditional air-dried soil testing against field-moist testing to see if field-moist methods give a more accurate picture of soil potassium availability.
  • Stand Longevity: Measure stem counts after the first cutting to track how different fertilizer programs impact stand persistence over time.

How the Study Will Be Conducted

  • Location: Conducted on an established alfalfa site at the Rosemount Research and Outreach Center.
  • Trial 1 (Potassium & Sulfur): 12 fertilizer combinations comparing various rates of potash (0-0-60), ammonium sulfate (AMS), K-mag, and polyhalite (Poly4).
  • Trial 2 (Potassium & Boron): Eight fertilizer combinations including potash (0-0-60), MES10, Aspire (a combination K and B fertilizer), and granular boron.
  • Measurements: The trial will be harvested four times during the season. Researchers will measure total forage yield, test crop quality and nutrient concentration using NIR and lab analysis, take post-cut stem counts, and collect soil samples (comparing field-moist vs. air-dried potassium levels).
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