Effects of Shade on the Growth and Cropping of Apple Trees. I. Experimental Détails and Effects on Vegetative Growth

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Abstract
Cox’s Orange Pippin apple trees on M.26 rootstock were shaded so as to receive 37, 25 or 11 % of full daylight during the post-blossom growing season in either or both 1970 and 1971 and their growth compared with that of control trees. Shading had direct and also residual effects, the latter in the year following treatment. It reduced the number and weight of new shoots, the fresh weight per unit length of shoot, girth increment and leaf thickness and weight per unit area, but increased the concentrations of K and Mg in the leaves. Residual effects included a reduction in the number of shoots but increases in girth increment, in weight per unit length of shoot and in leaf dry weight per unit area and per unit fresh weight. These latter results are thought to be a consequence of reduced competition for assimilates as a result of a drastic residual effect on the number of fruits carried. In the year after shading the concentrations of N, P, Mg and Ca in the leaves were reduced and that of K increased.