Variation in the nutrient content of leaves and fruit with season and crown position for two apple varieties

Abstract

Leaves and fruit of Golden Delicious and Granny Smith apple trees, pruned by the Hawkes Bay tree-training method, were sampled at 2-weekly intervals from bloom time to leaf fall from the bulk of the top, middle and bottom thirds of the tree crown. Levels of calcium and magnesium per unit leaf area showed a general increase as the leaves aged, while nitrogen, phosphorus and potassium contents stayed relatively constant. With decreasing height in the crown, tree leaves had a markedly lower dry weight per unit area and lower contents of nitrogen, phosphorus, potassium, calcium, magnesium, chlorophyll and soluble carbohydrates per unit area, but the area per leaf was not significantly affected. The trends were more pronounced in the upright, bush-like Golden Delicious than in the spindly, open-centred Granny Smith trees. On a dry weight basis, differences in leaf nutrient content with crown height were not consistent or clear-cut, and therefore unlikely to affect leaf sampling for diagnostic purposes. The dry weight per fruit and the amounts of all nutrients per fruit increased throughout the season. With decreasing crown position, there was a decrease in fruit size, dry matter content and soluble carbohydrate concentration and an increase in green coloration, total nitrogen and free a-amino nitrogen concentration. The increased size of fruit from the upper crown position resulted in greater amounts of nitrogen, phosphorus, potassium, and magnesium per fruit in Golden Delicious but not in Granny Smith. Thus the self-shading nature of the Hawkes Bay training method may be detrimental to the production of large, highly coloured fruit. The largest dry weight and nutrient accumulation of both leaves and fruit was in the middle crown position of the trees followed by the lower and then the upper regions. The quantities of nutrients removed in the fruit crop at harvest time, as calculated from 2 years' data, were (kg ha-1 year-1): Golden Delicious: nitrogen, 23; phosphorus, 4; potassium, 120; calcium, 5; magnesium, 4; for Granny Smith: nitrogen, 13; phosphorus, 3; potassium, 57; calcium, 3; magnesium, 2. The quantities of nutrients returned to the orchard floor at leaf fall were (kg ha-1 year-1): Golden Delicious: nitrogen, 35; phosphorus, 3; potassium, 26; calcium, 45; magnesium, 7; Granny Smith: nitrogen, 35; phosphorus, 2; potassium, 25; calcium, 34; magnesium, 6.