Influence of fertigation with nitrogen on leaf mineral element composition and cropping of 'Jonagold' and 'Golden Delicious' apple trees

Two apple (Malus x domestica Borkh.) cultivars grafted on M.9 rootstock were grown at high density ('Jonagold' 2500 trees/ha, 'Golden Delicious' 3000 trees/ha). There were five treatments for each cultivar (fertigation with 45 kg N/ha, 60 kg N/ha, 120 kg N/ha, irrigation without fertilisers, and control - without irrigation and without fertilisers), and two timing variants (Variant A: treatments during vegetation period from I May to 20 June; and Variant B: treatments from I May to I August). The treatments were imposed beginning in the second year after planting and lasted seven years (1992-1998). Leaf mineral composition was determined over the 7(th) and 8(th) growing seasons. During the seasons 1997/98 effects of the applied treatments on leaf mineral concentration were notable, but these effects often were not consistent. There was no significant effect of timing on leaf nutrient concentrations of 'Golden Delicious', but there were significant effects on leaf Ca and Mg concentrations of 'Jonagold'. During the years of cropping (19931998) there were no consistent treatment effects for cumulative yield, however, treatments had significant influence on regularity of bearing. The control treatment on 'Jonagold' showed the least alternate bearing, while 'Golden Delicious' performed best when it was fertilised with 45 kg N/ba.