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

Potassium (K) 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 K fertilizer applied at three rates (0, 186, and 372 kg K ha⁻¹) to soils already containing sufficient soil test K (223 mg kg⁻¹). 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 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 uptake and in vitro digestibility.