Potassium fertilizer trials with potatoes on coarse-textured soils in southeastern Idaho

Abstract

Potassium fertilizer needs of potatoes were evaluated with a set of research plots established on coarse textured soils in southeastern Idaho. Over the seven-year period that these trials were conducted, tuber yields indicated no response to potassium fertilization. Specific gravity of tubers decreased with increasing rates of potassium fertilization, with greatest reduction in specific gravity resulting from the use of potassium chloride. Plots were established on land brought under cultivation for the first time in 1968. Under a potato-grain rotation, the plot area was planted to potatoes every other year beginning in 1968. At the conclusion of the trials in 1976, the check plots had not received any potassium fertilizer. Potassium fertilizer was applied to designated plots only in 1970 and 1974. Each plot received the same treatment in both of the years with rates of 150, 300, and 600 lb K2O/A (168, 335 and 670 kg/ha) using two different forms of fertilizer (KCl and K2SO4). Petiole samples were analyzed for levels of K. Soil K levels were determined annually from samples taken prior to planting the potato crop. Petiole K levels decreased as the season advanced. A petiole level of 6.5 to 7.5% K (45 to 75 days after planting) was sufficiently high for maximum yields. Soil test levels (sodium bicarbonate extraction) of 140 ppm K were sufficiently high for production of a 350 cwt/A (40 T/ha) yield.