Water Use, Mineral Nutrition, Tree Growth, Yield, and Fruit Quality of 'Fuji' and 'Gala' Apples under Various Irrigation Systems and Rootstocks

Use of crop evapotranspiration (ETc), when a precise crop coefficient value (Kc) is used, provides a reliable tool (irrigation scheduling) for determination of water requirement. In this process, Kc should be modified by percentage of ground shade (GS) and tree canopy maturity (M). An experiment in Idaho with ET based irrigation scheduling, had either 'Autumn Rose Fuji' or 'Pacific Gala' trees with a full micro-jet sprinkler system each receiving an average of 6461.7 L (994 mm) or with a full drip system receiving 3996 L (614.1 mm) of irrigation water. Using a micro-jet sprinkler system, a partial root zone drying regime reduced fruit size but slightly improved fruit color in 'Fuji' apple. Application of water at 65% full drip rate, applied on both sides of the tree row (DD), reduced fruit size in 'Fuji'. However, when the 65% of full drip rate was applied to only one of the alternating sides of the tree every other week (PRD), fruit size was larger than with DD treatment. In 'Pacific Gala', leaf calcium (Ca) decreased but leaf potassium (K) increased with rootstock vigor, resulting in the greatest Ca but lowest leaf K in trees on Bud9. Fruit weight and yield per tree in 'Pacific Gala' on RN29 rootstock was higher than on Bud9 and GC30 rootstocks. 'Pacific Gala' on Bud9 rootstock had smaller trees and fruit size but higher fruit starch degradation pattern (SDP), suggesting earlier fruit maturity on this rootstock. On average, 'Pacific Gala' trees with drip irrigation had larger fruit and higher leaf Mg and Mn but less fruit color and firmness and lower leaf Ca, K, Zn, and Cu than those with sprinkler system.