Canopy Development, Yield, and Fruit Quality of `Empire' and `Delicious' Apple Trees Grown in Four Orchard Production Systems for Ten Years

A field planting of 'Empire' and 'Redchief Delicious' apple trees (Malus domestics Borkh.) was established in 1978 to evaluate four planting systems: 1) slender spindle/M.9, 2) Y-trellis/M.2 6, 3) central leader/M.9/MM.111, and 4) central leader/M.7a. During the first 5 years, yields per hectare for 'Empire' were positively correlated with tree density. In the second 5 years, the Y-trellis/M.26 trees produced the highest yields while yields of the other systems continued to be related to tree density. Cumulative yields were highest with the Y-trellis/M.26 trees. With 'Delicious', the Y-trellis/M.26 yields were greatest during all 10 years despite lower tree density than the slender spindle/M.9. Yields of 'Delicious' with the other three systems were a function of tree density during the 10 years. At maturity, canopy volume per tree was greatest on the central leader/M.7a trees and smallest on the slender spindle/ M.9 trees; however, there were no significant differences in canopy volume per hectare between the systems despite large differences in yield. Trunk cross sectional area (TCA) per hectare was greatest with the Y-trellis/M.26 trees and smallest with the central leader/M.7 trees. Yield was highly correlated to TCA/ha. Yield efficiency with 'Empire' was greatest for the slender spindle/M.9 system, followed by the Y-trellis/M.26, central leader/M.9/MM.111, respec- tively. With both cultivars, the central leader/M.7a system had the lowest yield efficiency. With 'Delicious', there were no differences in yield efficiency for the other three systems. The greater yield of the Y-trellis/M.26 system was the result of greater TCA/ha and not greater efficiency. 'Empire' fruit size was largest on the central leader/M.7a and the central leader/M.9/MM.111 trees and smallest on the slender spindle/M.9 and the Y-trellis/M.26 trees. With 'Delicious', fruit size was larger with the Y-trellis/M.26 trees than the other systems. When fruit size was adjusted for crop density, there were no significant differences due to system with 'Empire', but with 'Delicious' the Y-trellis/ M.26 trees had larger adjusted fruit size than the other systems. Crop density calculated using TCA correlated better to fruit size than did crop density calculated using annual increase in TCA, canopy volume, or land area. Fruit color and quality with 'Redchief Delicious' were not influenced by system. With 'Empire', average fruit color and soluble solids content were lower for the Y-trellis/M.26 and slender spindle/M.9 in some years when canopy density was allowed to become. excessive. The need to improve orchard productivity and profitability has led to a worldwide interest in new orchard planting systems (Jackson, 1978, 1981, 1986; Jackson and Palmer, 1989). Work on this topic has produced several important concepts regarding orchard system productivity and profitability. First, preplant de- cisions of scion and rootstock cultivars, as well as spacing and arrangement of trees, limit the choice of system and thus are extremely important. Second, preplant decisions of tree number/ ha and tree support establish the level of capital investment that must be recovered. Higher capital investments require propor- tionately higher productivity in the first years of orchard life to achieve similar break-even times. Once an orchard system is established, its productivity and profitability depend on yield and fruit quality (i.e., fruit value) and costs of management and harvest. The horticultural and economic merits of orchard Production svstems must be eval- uated over at least a significant part of the lifetime of the orchard to give sound recommendations to fruit growers. However, long- term comparative field plantings of orchard systems have been few due to the expense and time commitment required. From the wide range of comparisons made over the last 30 years, it is apparent that no one system is optimum for all scion/rootstock combinations, economic situations, or climates (Barritt, 1987).