Relationships between yield, crop density coefficient and average fruit weight in 'Lobo' apple trees under various planting systems and irrigation treatments

'Lobo' apple (Malusxdomestica) trees grafted on Malling 26 (M.26) were planted on flat ground or on raised beds covered with black polyethylene. In both planting systems trees were drip irrigated to maintain soil water potential within the range of 0 to 0.02 MPa (0 to -0.3 lb/inch(2)) or were left without irrigation. Planting methods and irrigation influenced tree growth. Standard planted trees and irrigated trees grew stronger, whereas planted on beds less vigorously, irrespective to irrigation. The yield of all trees increased with time until the fourth year of production. Fruit size decreased as yield increased. Also lack of irrigation considerably reduced average fruit weight. Yield and trunk cross-sectional area (TCA) measurements were used to calculate crop density coefficient (CD). CD values varied considerably between the treatments showing their dependence on planting method, irrigation and tree age. In most cases, the correlation coefficient between CD and average fruit weight were negative, indicating that the weight of individual fruit decreased with increasing numbers of fruit per unit of TCA. We question whether CD coefficient may be universally used under wide range of environmental conditions and cultural practices.