Influence of potassium fertilization on alfalfa leaf and stem yield, forage quality, nutrient removal, and plant health

Authors: Heuschele, Deborah - Jo; Gamble, Joshua; VETSCH, JEFFERY - University Of Minnesota; SHAEFFER, CRAIG - University Of Minnesota; COULTER, JEFFERY - University Of Minnesota; KAISER, KANIEL - University Of Minnesota; LAMB, JOHN - University Of Minnesota; LAMB, JOANN - Retired ARS Employee; Samac, Deborah - Debby

Submitted to: Agrosystems, Geosciences & Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/6/2023
Publication Date: 2/1/2023
Citation: Heuschele, D.J., Gamble, J.D., Vetsch, J., Shaeffer, C., Coulter, J., Kaiser, K., Lamb, J., Lamb, J., Samac, D.A. 2023. Influence of potassium fertilization on alfalfa leaf and stem yield, forage quality, nutrient removal, and plant health. Agrosystems, Geosciences & Environment. 6(1). Article e20346. https://doi.org/10.1002/agg2.20346.
DOI: https://doi.org/10.1002/agg2.20346

Interpretive Summary: Alfalfa uses high quantities of potassium for plant growth. Fertilizing alfalfa with potassium on deficient soils has shown to increase yields. However, there are conflicting studies on the quantity of additional potassium needed to improve production. We tested different potassium fertilizer rates on an experimental alfalfa where soil potassium levels were already sufficient. The alfalfa continued to absorb potassium without increasing yields, but plants decreased in animal digestibility. Therefore, potassium fertilization on sufficient soils does not lead to any additional economic benefits and may reduce field productivity. This information will reduce producers costs from use of fertilizers on soils with sufficient potassium concentrations.

Technical Abstract: Potassium is an essential nutrient for plant growth. In K deficient soils, fertilization has been shown to increase herbage yield of alfalfa. The purpose of this study was to determine the effects of K fertilization on alfalfa leaf and stem yield, forage quality, nutrient removal, and plant health of a nonlodging experimental germplasm. Five alfalfa rotations had potassium fertilizer applied at three rates (0, 186, and 372 kg K ha-1) to soils already containing sufficient soil test K (223 µg/g). No overall yield differences were found related to K application rates, though K removal in total herbage increased by 30% - 58% with K fertilization, depending on alfalfa stand age. Leaf:stem ratios were not impacted by K fertilization. The concentrations of B, Ca, and Na decreased with K fertilization, while K concentrations increased, which may have resulted in B deficiencies. Leaf in vitro digestibility decreased significantly with the K application of K. There was no benefit to crown rot disease resistance with increased K fertilization. This study supports that the addition of K to already sufficient soils does not lead to any additional economic benefits and may reduce productivity due to the reduction of B and in vitro digestibility.