LEAF MINERAL-COMPOSITION OF APPLE TREE - SAMPLING DATE AND EFFECTS OF CULTIVAR AND ROOTSTOCK

Leaf mineral composition of cvs. 'Red Delicious' (strain 'Clear Red') and 'Golden Delicious' (strain B) apple (Malus domestica, Borkh) on M 27, M 9 and MM 106 rootstocks was determined six times at 15-day intervals, beginning 50 days after full bloom from 1986 to 1990. 'Clear Red' had significantly higher foliar concentrations of N, P, Mg, Fe and Cu and lower levels of K and Ca. The M 27 dwarfing rootstock increased leaf N, Ca, Mg and Zn but depressed K concentration. Decreasing concentrations of N, Ca and Mg were associated with an increase of cultivar vigour, suggesting a dilution effect of these elements in larger canopy. Because of its preferential capacity to accumulate K in the scion, MM 106 could be useful in reducing K deficiency. Except for Fe, Cu and Zn, mineral content of leaves varied according to sampling date. Generally, concentrations of N, P and K, expressed as dry weight, decreased and those of Ca, Mg, Mn and B increased from the first to the last sampling. Expressing data as dry weight and leaf area led to comparable results for all nutrients except N. For this element, the leaf area method appears more reliable for comparing concentrations sampled over the growing season.