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This article in AJ

  1. Vol. 63 No. 3, p. 497-500
    Received: Nov 17, 1970



Levels and Sources of Potassium for Alfalfa as Influenced by Temperature1

  1. Dale Smith2



Studies were conducted with KCI and K2SO4 as K sources (0, 336, and 672 .kg/ha of added K) for alfalfa (Medicago sativa L.) grown to first flower in growth chambers at 21/15 C day/night temperatures. Growth and mineral composition of alfalfa at first flower in three temperature regimes (27/21, 21/15, and 15/10 C) also were studied in low-K soil with 0, 168, 336, and 672 kg/ha of K added as K2SO4.

KCI applied at high rates (672 kg/ha of K) to soil containing 205 kg/ha of exchangeable K caused damage to alfalfa plants grown in pots, presumably from the C1 ion. No injury was noted with K2O4.

K2SO4 applied (168, 336, and 672 kg/ha of K) to soil containing 120 kg/ha of exchangeable K increased herbage, root, and total plant yields, plant heights, and shoot nmnbers at the first flower growth stage. Largest increases occurred with the first increment of K and when grown at cool temperatures. Percentage of K in the herbage was highest at all rates of applied K in the warmest temperature regime (27/21 C day/night temperatures) and lowest in the coldest regime (15/10 C). Percentages of K in the herbage grown at 15/10 C were all below K-sufficiency (2.20%) at all rates of K. Higher levels exchangeable K are needed in the soil under cool than under warm temperatures in order for the plant to obtain sufficient K for maximum growth and production.

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