Effects of fertigation on yield, fruit quality and return bloom of young apple trees

When establishing an apple orchard it is important to stimulate the growth of young trees to fill up their allotted space in the row and minimize the time to come into full production with high quality fruit. In May 2012 two-year-old 'Summerred'/'M.9' knip trees were planted at the experimental farm at NIBIO Ullensvang, western Norway. The planting distance was 4×1 m (2500 trees ha^-1). Three fertigation schemes were established (zero; low NDASH 0.15 g N m^-1 row day^-1, and high nitrogen NDASH 0.30 g N m^-1 row day^-1) and two crop loads allowed (low and high). In the year after planting the crop loads were limited to zero and five apples tree^-1, respectively. In the third leaf the crop loads were adjusted by hand to 15 apples and 30 apples tree^-1, respectively. The experimental design was a randomized blocks with four replications and 10 trees treatment^-1. No significant effects of N-fertigation on soil NO₃^-, NH₄⁺ or N-min contents were found. However, N-fertigation increased the leaf nitrogen content the whole season and leaf N were ≥ than the standard adequacy range (1.5-2.0%). Trees reached the desirable height of 3 m in the third leaf. Trunk circumference and number of branches per tree increased from second to third leaf, but were not significantly influenced by the N-fertigation. In the third leaf the high crop load trees yielded 7 kg tree^-1 (17.5 t ha^-1) and the low crop load 4 kg tree^-1. Fruit weights were negatively correlated with the crop loads. Small differences in fruit quality attributes were found. Return bloom was not affected after the second leaf. However, the high crop load in the third leaf clearly reduced the amounts of return bloom in 2015, irrespective of the amount of N-fertigation.