Potassium management effects on potato yield, tuber quality, and chloride cycling

Potatoes require large amounts of potassium (K) to promote yield and tuber bulking. Previous studies have also shown that K can have both positive and negative effects on tuber quality. While KCl is the most economical K source to apply, there is concern that the high chloride (Cl) content of this fertilizer may have detrimental effects on a potato crop. In addition, Cl is highly leachable, and Cl concentrations in groundwater have been increasing. The objectives of this study were to (1) evaluate the effects of KCl rate on tuber yield and quality, (2) determine whether banded KCl improves K uptake efficiency relative to broadcast application, (3) evaluate the effects of split KCl application on yield and quality, (4) determine whether K source (KCl vs. potassium sulfate) affects yield and tuber specific gravity. The study was conducted in 2023 and 2024 under irrigated conditions at the Sand Plain Research Farm in Becker, Minnesota. Twelve treatments were evaluated including five KCl rates ranging from 0 to 320 lbs K₂O/A at planting. In 2023, a dry year, potato yields increased with KCl up to 160 lbs K₂O/A and then declined. In 2024, a wet year, yields increased linearly with K₂O rate. Chloride excess may be a greater issue in a dry year like 2023 due to lack of chloride leaching.High concentrations of Cl in the irrigation water may have also exacerbated the Cl effect in the dry year. Banded KCl application at 160 and 240 lbs K₂O/A tended to decrease the yield of 6- to 10-ounce tubers compared to broadcast applications in both years. Tuber specific gravity decreased with increasing K rate regardless of K source. Chloride uptake increased with increasing KCl rate, with approximately 75% of the chloride taken up by the crop at harvest accumulating in the vines.