Response of four potato varieties to potassium fertilization in a seed growing area of eastern Idaho

A soil test value of 112 ppm K in the 0 to 8 in (0 to 20 cm) depth was sufficient to produce a 250 cwt/A (28 T/ha) yield with no response to K fertilization. With a 93 ppm soil test value, potassium fertilizer increased yields in all four varieties tested. These results were obtained from trials at two locations in a seed-growing area in eastern Idaho where soil tests indicated low potassium levels (90 to 100 ppm K). Russet Burbank, Targhee, Nampa, and Butte varieties were included in the study at one location and only Russet Burbank at the second location. Potassium fertilizer treatments included K2O rates of 0, 250, and 5001b/A (0, 280, and 560 kg/ha) for each of the two forms of potassium fertilizer (KC1 and K2SO4). At the time of tuber initiation, a petiole content of 7% K in Russet Burbank was sufficient to produce maximum yields while a petiole content less than 6% K was insufficient. Analysis of petiole samples taken during the season showed that the K content declined rapidly as the season progressed. Potassium chloride generally resulted in higher petiole K levels than did potassium sulfate. Varieties appeared to differ in petiole K levels.