The Response of Magnesium-Deficient Edward VII Apple Trees to Variations in the Timing and Composition of Foliar Sprays

Abstract

Magnesium-deficient Edward VII apple trees were used to study the effect of pre-blossom sprays of magnesium sulphate and urea, and to compare the efficiency of post-blossom sprays of magnesium sulphate and chloride.Two pre-blossom sprays of 2% Epsom salt (MgSO4·7H,O) prevented the development of early-season magnesium deficiency symptoms but did not increase fruit set. Similar sprays of 0· 5%urea had no effect on symptoms but increased the set of fruit.Five post-blossom sprays of 2% Epsom salt largely eliminated both early and late symptoms and produced consistent increases in the magnesium content of the leaves (% dry wt.). There was also a large increase in crop, due mainly to a greater fruit set which could be detected after the second spray application. Growth responses also were associated with this treatment.Five post-blossom sprays of 0·83% magnesium chloride, i.e. containing only half the amount of magnesium, produced similar responses, except that growth was not affected. Reducing the number of m...