Rootstock and ET-Based Irrigation Effects on Mineral Nutrition, Yield and Harvest Quality over Different Seasons in 'Pacific Gala' Apple

Efficient use of land and water, and thus the use of dwarfing rootstocks with high yield efficiency and efficient irrigation systems become increasingly crucial as the world population grows. Method of irrigation and vigor of rootstock are among the most important factors affecting uptake of mineral nutrients, and thus tree growth and fruit yield and quality attributes of apples (Malus domestica). In a long-term experiment, effects of two irrigation methods and four rootstocks on leaf mineral nutrients, tree growth, and fruit quality at harvest were studied in 'Pacific Gala' apple. Evapotranspiration-based irrigation scheduling (ETc), adjusted by percentage of ground shading was used for sprinkler and drip systems. A significantly lower volume of water was applied to the trees with drip irrigation than those with sprinkler irrigation system. Leaf calcium (Ca) decreased but leaf potassium (K) increased with rootstock vigor, resulting in the greatest leaf Ca but lowest leaf K in trees on Budagovsky 9 (B.9). Fruit weight and yield per tree in 'Pacific Gala' on RN. 29 rootstock were greater than those on B.9 and Geneva 30 rootstocks. 'Pacific Gala' on B.9 rootstock had smaller trees and fruit size but higher fruit starch degradation pattern, suggesting earlier fruit maturity on this rootstock. On average, 'Pacific Gala' trees with drip irrigation had larger fruit and higher leaf magnesium and manganese but less fruit color and firmness and lower leaf Ca, K, zinc, and copper than those with sprinkler systems.