Response of Two Alfalfas (Medicago sativa L. and M. falcata L.) to Time and Rate of Potassium Application in the Subarctic
1966
Klebesadel, L. J. | Brinsmade, J. C.
Annual topdressings of K at 0, 42, and 166 pounds per acre, applied either in spring or mid-summer, were compared with 2 alfalfas—Medicago sativa (var. ‘Vernal’) and M. falcata—for 3 seasons in Alaska's Tanana Valley. Stands of both alfalfas thinned rapidly during the study but stands and stand losses showed virtually no relationship to K treatments. Winterkill accounted for most of the reduction of stands and Vernal winterkilled more than M. falcata. K treatments resulted in large differences in yield. Both rates of K topdressing resulted in higher alfalfa yields than no topdressing; and 166 pounds of K per acre were superior to 42 pounds per acre. Crude protein content of forage was seldom influenced to a significant extent by K applications. Where differences existed, crude protein content was lowest with the highest rate of K application. M. falcata contained higher levels of crude protein than Vernal. K content of forage, virtually always lowest where no K was topdressed, was usually higher in alfalfa topdressed with 166 pounds of K per acre than at the lower rate. K content was lower in Vernal than in M. falcata. Highest percentage recovery in forage of applied K occurred with no topdressing. There, recovery exceeded the amount of K applied at planting. K recovery with the higher rate of topdressing was poorer than with the lower rate. M. falcata was superior to Vernal in K recovery. Amounts of available K in the soil did not differ among treatments until the third harvest season, when K levels were higher in most plots that had received the higher rate of K topdressing.
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