Magnesium nutrition of apple trees I. Kit eel of K and Mg fertilization and comparison of soil and foliar treatments with magnesium sulphate

In an experiment, performed in 1968-1970 on young Bancroft and Mclntosh apple trees on sandy loamy soil, Mg fertilization at the dose of 400 kg of MgO per year, in the form of epsomite increased available Mg content in both 0-20 and 20-40 cm soil layers. After 4 years only 20-29% of the Mg applied remained in these layers. K fertilization at the dose of 300 kg of K2O per ha in the form of potassium salts increased available K2O content, and 85–97% of additionally applied potassium remained in the top soil layers. K fertilization decreased leaf Mg content, increased leaf K content, increased Mg deficiency symptoms and in the absence of Mg reduced tree growth. Fruit set and fruit storage quality were adversely affected by the K fertilizer dose of 300 kg of K2O as compared with 60 kg of K2O per ha. Mg fertilization to the soil increased leaf Mg content, decreased Mg deficiency symptoms and counteracted the negative effect of high doses of K2O on growth. It did not have any effect on growth when K fertilization was moderate; no effect on yield was found. Four sprays of 2% epsomite applied each season were less effective in increasing leaf Mg content and in controlling Mg deficiency symptoms than soil dressings of this compound. Foliar sprays increased fruit set and early yields (in the 4th year after planting). Mg applied to the soil or to the leaves increased the green skin colour of Bancroft apples; it did not affect bitter pit incidence