The primary source of potassium (K) fertilizer is KCl which contains 50% chloride (Cl) by
weight. Soybean yield decreases have been found during recent years and decreased
grain protein and increased oil have occurred for soybean within K trials conducted across
Minnesota. Purchasing inputs that may reduce the yield of a crop is problematic and
Minnesota soybean producers need better fertilizer guidelines to ensure greater profitability
of nutrient inputs. Potassium research and improved guidelines are needed as soybean
producers are increasingly focusing on inputs to further increase yield across the state, and
little guidance is available across the Midwest on maximum rates of potash fertilizer which
should be applied to reduce the risk of chloride (Cl) toxicity in soybean. Recent research in
Minnesota has demonstrated the need for S to be applied to soybean. Research in the
Midwest has indicated that the application of sulfur (S) may mitigate Cl impacts. Additional
research would be beneficial to study whether S can help mitigate yield decreases in
soybean due to high rates of Cl being applied to further increase yield potential of soybean
across the state. The effect of K and Cl on grain quality also must be assessed studying
protein, oil, and amino acid distribution as past research in Minnesota has shown that S can
increase cysteine and methionine content while K application decreased these two
essential amino acids. The proposed research will help better refine potassium and sulfur
guidelines for soybean maximizing grain yield and quality parameters.

Evaluate the long-term impact of potassium rate and timing in a corn/wheat-soybean rotation on soybean grain yield and quality. a) Quantify yield effects when K fertilizer is applied at different times and rates in a two-year rotation containing soybean.
b) Quantify changes in soybean protein and oil concentration based on long term K fertilization strategies.
c) Correlate K and Ca or Mg in plant tissue to determine impacts on soybean yield.
Determine if the application of Cl has negative effects of soybean grain yield and quality. a) Quantify yield impacts for K fertilizer sources applied with and without Cl on soybean varieties that vary in IDC (potentially salt) tolerance.
b) Track rates of Cl buildup in poorly drained soils.
c) Quantify plant tissue Cl concentration and correlate tissue Cl concentration to the concentration of other essential nutrients.
Determine whether sulfur should be considered as an essential nutrient and applied to soybean in Minnesota. a) Assess the impact of sulfur on soybean grain yield and seed quality.
b) Determine if the application of sulfur can reduce negative impacts of K or Cl on soybean seed quality or seed yield.
c) Further develop a set of sulfur guidelines for soybean production in Minnesota.