Long-term leaf mineral nutrition in ‘Pacific Gala’ apple (Malus × domestica Borkh.) as affected by rootstock type and irrigation system during six stages of tree development

Summary

Use of an efficient rootstock and irrigation system are essential to establish a high-density orchard with a high production potential. High production becomes more important as World population increases and the availability of usable agricultural land and irrigation water decrease. Rootstock vigour and irrigation method are among the most important factors that affect the uptake of mineral nutrients and thus tree growth, fruit yield, and fruit quality attributes in apple (Malus × domestica Borkh.). The effects of four rootstocks and two irrigation systems on leaf size and mineral nutrition, and on the interaction between leaf nutrient concentrations, growth, and fruit quality attributes were studied over 4 years in ‘Pacific Gala’ apple. Evapotranspiration (ET_c)-based irrigation scheduling, adjusted for the percentage of ground shading, was used for both the sprinkler and drip irrigation systems. Leaf calcium (Ca) concentrations decreased, but leaf potassium (K) concentrations increased with increasing rootstock vigour, resulting in the highest leaf Ca, but the lowest leaf K concentrations in trees on ‘Budagovsky 9’ (B.9) dwarfing rootstock. On average, trees supplied by drip irrigation had larger fruit and higher leaf magnesium (Mg) and manganese (Mn), but lower leaf Ca, K, zinc (Zn), and copper (Cu) concentrations than those irrigated using the sprinkler system. A significantly lower volume of water was applied to trees using drip irrigation than by sprinkler irrigation. Highlynegative correlations were found between leaf K concentrations and leaf dry weight percentages (DW%), between starch degradation pattern (SDP) and fruit firmness, between leaf K and leaf Mg concentrations, and between leaf K and leaf Mn concentrations. Highly-positive correlations existed between leaf N and leaf Fe concentrations, between fruit yields and leaf N concentrations, and among the concentrations of most leaf micro-nutrients.