Abstract
Potatoes require high potassium (K) fertilization for good yields, especially in Oregon’s Columbia Basin, but little is known about how K rate and source affect potatoes. This study aimed to evaluate the effects of different K fertilizer rates and sources on the yield and quality of various potato cultivars. Two-year trials (2020 and 2022) were conducted as a split-plot, randomized complete block design with four replications in a producer’s field near Boardman, Oregon. The study tested two K fertilizer sources (potassium sulfate—K2SO4 and potassium chloride—KCl, at five application rates from 0 to 896 kg K2O ha−1, on three potato cultivars: Clearwater Russet, Russet Burbank, and Umatilla Russet. Among cultivars, Umatilla Russet, with 56.5 t ha−1, had the highest total yield. Potassium fertilizer application, regardless of the rate, significantly increased tuber yield, resulting in an average 10% increase in total yield and a 12% increase in US No. 1 yield compared to the control. Although total yield differences among K application rates from 224 to 896 kg K2O ha−1 were generally not significant, the linear-plateau model identified a breakpoint at 251 kg K2O ha−1, indicating that applying rates beyond this level does not result in a significant yield increase. Additionally, higher K application rates were linked to a reduction in tuber-specific gravity. In terms of K sources, both K2SO4 and KCl produced similar yields. Further studies in diverse environments are needed to better understand how K fertilization affects potato yield and quality and to develop best practices for maximizing productivity.