Managing Potassium in Potato Production Systems of Idaho

Historical soil test information for southern Idaho surface soils (0-12") shows that extractable K concentrations declined from 400-plus ppm in the late 1960's to 100-200 ppm today. Potatoes, silage corn, and alfalfa can remove nearly 400 lbs K/A-yr when high yields are achieved. Many irrigation waters contain 28-56 lbs/A-ft soluble K which is not sufficient to maintain soil test K concentrations with high K removal rates. Recent data on the K fertilizer requirements of alfalfa, dry beans, Russet Burbank potatoes and soft white winter wheat supported the use of soil K concentrations recommended in University of Idaho fertilizer guides (Gaviak et al.,1989). For potatoes, K fertilization is not recommended when NaHCO 3 extractable K concentrations are greater than 158 ppm (McDole et al., 1987; Jones et al., 1970; Painter and Ohms, 1967; Iritani and Painter, 1963). Relatively high potato yields (over 500 cwt/A) are being achieved by many of Idaho's potato growers. This production level typically removes over 200 lbs K/A in the tubers. In addition, petiole K concentrations below suggested critical concentrations during mid- and late-season tuber growth are being reported. As a preventive or corrective measure, some growers are applying K solutions during tuber growth with their irrigation systems. Data from Wisconsin indicates that in-season K applications do not enhance yields or quality, or improve fertilizer-use-efficiency over preplant or side-dressing applications (Kelling et al., 1994). Plant tissue diagnostic norms for petioles are generally not available to determine when to recommend this practice. In addition, it is not known how late during tuber growth K solutions could or should be applied without affecting tuber quality. The objectives of this study were to a) evaluate the K fertilizer requirements of Russet Burbank potatoes, b) the efficacy of K-solutions applied during tuber growth, c) the relative effectiveness of K-sources, and d) the K dynamics in the potato plant as related to petiole K concentrations. This paper reports the tuber yield and quality responses obtained with potassium fertilization