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

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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 magnesium chloride sprays to three, but applying them over the same time interval, resulted in similar' crop responses even though less magnesium was taken up and symptoms were slightly less effectively controlled.

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