Responses of Red Clover to Increasing Rates of Topdressed Potassium Fertilizer 1

Abstract High yields of legumes require large amounts of soil K. The purpose of this study conducted at Arlington, Wis. (43.7° N Lat) was to determine the amount of topdressed K needed to obtain maximum herbage yields from red clover ( Trifolium pratense L.). ‘Lakeland’ red clover was established on low K Typic Argiudoll (Plano silt loam) soil and topdressed during spring of the second year with 0 to 896 kg/ha of K as KCl. The three highest K rates also were applied in split applications with half topdressed in fall and half in spring. There was no advantage to splitting K rates between fall and spring. No significant differences in herbage yield were observed in response to the application rates of K. However, yields tended to decrease with the 672 and 896 kg K/ha spring applications. Analysis of the second‐year total herbage showed that concentrations of K and Cl increased with K topdressing rate, but concentrations of total nonstructural carbohydrates, N, P, Ca, Mg, Na, Cu, Zn, B, Sr, and Mn decreased. There was no effect of K fertilizer on concentrations of S, Fe, Al, and percentage of IVDDM. Residual herbage yields and stands in the third year, following a severe winter, increased steadily up to 336 (stand) or 448 kg/ha (herbage yield) of spring applied K. Alfalfa ( Medicago sativa L. cv. ‘Vernal’) with similar spring K applications on adjacent plots yielded less than red clover at all K rates. Even so, red clover yields were not increased as much as those of alfalfa by the topdressed K. Possibly red clover needs less K for maximum growth than alfalfa, or that at low soil K levels, red clover is better able to absorb K from the soil because of its profuse surface rooting.