Influence of Rootstock and Irrigation On Mineral Nutrition, Growth, Fruit Quality and Yield In 'Gala' Apple

The increasing trend in the world population and decreasing trend in the availability of suitable land for fruit production, combined with the water shortage, mandate the use of more efficient methods of irrigation and the establishment of high density orchards that require size-controlling rootstocks.  The method of irrigation and vigor of rootstock are among the most important factors affecting mineral nutrients, and thus tree growth, fruit yield, and quality attributes of apples.  In a long-term experiment, the effects of two irrigation systems and four rootstocks on water use, tree growth, fruit quality, and mineral nutrients were studied in young and mature ‘Pacific Gala’ apples grown under conditions in southwest Idaho that represent the high desert conditions of the Intermountain West region of the United States. Evapotranspiration-based irrigation scheduling, adjusted by the percentage of ground shading was used for sprinkler and drip systems. Significantly less water was applied to the trees with drip irrigation than those with sprinkler irrigation systems. Fruit weight and yield per tree in ‘Pacific Gala’ on RN29 rootstock was higher than those on Bud 9 and GC30 rootstocks. ‘Pacific Gala’ on Bud9 rootstock had smaller trees and fruit size but higher fruit starch degradation pattern (SDP), suggesting an earlier fruit maturity in this rootstock. Trees on Bud9 rootstock were more precocious than those on other rootstocks.  ‘Pacific Gala’ trees with drip irrigation had more soluble solids concentrations and SDP but slightly lower firmness when trees were young, but the differences were not significant when trees matured.  In ‘Pacific Gala’, leaf calcium (Ca) and magnesium (Mg) decreased but leaf potassium (K) increased with the rootstock vigor, resulting in the greatest Ca but lowest leaf K in trees on Bud9.  ‘Pacific Gala’ with sprinkler irrigation had  higher Leaf  nitrogen (N), Ca, and K than those with drip system when trees were young, but differences were not significant for leaf N and Ca when trees were mature. The opposite situation occurred in leaf Mg due to K-Mg antagonism. The relationships between tree growth, overall fruit quality attributes, yield, and mineral nutrients will be discussed in more detail.