SEASONAL VARIATION IN LEAF AND SOIL POTASSIUM

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Abstract
A study of seasonal variation in potash content of selected leaves from red raspberry, black raspberry, Boysenberry and gooseberry plants, together with changes in exchangeable K levels of treated and untreated soils, is reported. K content of leaves was greatly influenced by treatment and stage of growth. Excepting in black raspberries, the K content was highest in the blossom stage. With both red and black raspberries, the lowest leaf K was found in the post-harvest period. Gooseberry leaves contained minimum K during the fruiting stage; the K content of Boysenberry leaves varied widely with treatment and stage of growth. Any attempt to set a level of leaf K below which it would prove advantageous from a yield standpoint to make K applications must be based on the stage of growth. Visible symptoms such as bronzing or leaf scorch were found wherever leaf K was much lower than 1% prior to the fruiting stage. Bronzing is also accompanied by increased Mn absorption. K absorption from the 6- to 12-inch soil layer was found to approach completion during the blossom state of growth of both red and black raspberries. This suggests greater emphasis on fertilizer placement with such crops.