661 Influence of Irrigation and Fertilization on Performances of Young Apple Trees S. Tojnko Z. Cmelik Faculty of Agriculture Faculty of Agriculture University of Maribor University of Zagreb 2000 Maribor 10000 Zagreb Slovenia Croatia Keywords: Malus × domestica, growth, yield, internal and external fruit quality Abstract Investigations on the effect of irrigation with ‘Polyfeed’ fertilizer were compared with broadcast ‘Polyfeed’ fertilization without irrigation on the tree performance of ‘Golden Delicious’ and ‘Pinova’ apples grafted on M9 rootstock. Two orchard experiments were conducted, one with ‘Golden Delicious’ in the 2 nd and 3 rd year after planting, and the other with ‘Pinova’ in the 2 nd season. Orchard spacing was 3.2 x 0.7 m and trained to a slender spindle. The results showed no significant effect of applied irrigation treatments on tree vegetative performance and internal fruit quality attributes (firmness, soluble solid concentration and starch index) on both cultivars. However, irrigation did improve fruit size and yield per tree. Results indicated positive effects of irrigation on tree performance in high density apple orchards during tree establishment. INTRODUCTION In high density orchards rapid vegetative growth is needed during the first years after planting in order to build up the tree habit and thereby prepare the tree for early production. Controlled vegetative growth is needed to induce fruit bud formation. This problem maybe solved with adequate fertilisation with N, especially if N fertiliser is added in irrigated water periodically throughout the growing season. Fertigation is more efficient as compared to conventional methods of fertilisation due to the close contact between the roots and the nutrient solution in the soil, which provides opportunity for easier control of the growth and yield of plants (Kipp, 1992; Bravdo and Proebsting, 1993). Beneficial effects of fertigation on the growth and mineral composition of apple trees have been reported (Klein et al., 1989) or not observed (Hornig and Bunemann, 1996). Although fertigation with nitrogen gave a higher leaf N concentration and increased growth, in fertile soils these effects decreased with time (Wolf et al., 1990). Also, an increase of yields with fertigation was evident (Kodde et al., 1992), was not consistently affected by various rates of N applications (Fallahi et al., 2001), or was not observed (Hornig and Bunemann, 1995). Our objectives were to determine the effects of irrigation with application of ‘Polyfeed’ fertilizer in comparison with broadcast ‘Polyfeed’ fertilization without irriga- tion on tree performance of young apples ‘Golden Delicious’ and ‘Pinova’. MATERIALS AND METHODS The orchard site was located at ‘Pohorski dvor’ Agricultural Centre of the University of Maribor in Slovenia. The experiment was conducted on a soil that contains 39% sand, 46% silt and 15% clay from 0 to 30 cm depth. This soil containing 3.2% organic matter, 3.5 mg P2O5/100 g soil, 47.2 mg K2O/100 g soil; the pH (in KCl) was 5.3. Climatic conditions in the orchard site were favorable for apple growing. Long-term average temperature in Maribor is 9.7 °C. Annual precipitation is about 1045 mm, and during growing season is about 638 mm. Experiment was conducted on apple (Malus domestica Borkh) cultivars Golden Delicious and Pinova, grafted on M9 rootstock, grown at a spacing of 3.2 x 0.7 m (4,464 trees/ha) and trained as a slender spindle. Vegetation in the tree row was controlled over a 0.6 m width with herbicide. IV th IS on Irrigation of Hort. Crops Ed. R.L. Snyder Acta Hort. 664, ISHS 2004