Effect of spring nitrogen fertilization on bearing and branching behaviors of young apple trees.

The total aboveground biomass production, nutritional status, bearing and branching behaviors of the central leader and one year old shoots of young apple trees have been analyzed. The shoots were further characterized according to the length, shoot demography, and the production of terminal and lateral flowers. All the characteristics are described in connection with nitrogen supply and cultivar. Nitrogen represents one of the major macronutrients involved in the growth and development of the fruit trees. The understanding of the effect of nitrogen supply for flower bud formation can be further improved by detailed analyses of tree architecture. While the biomass production was cultivar specific, the trees within particular cultivar were characterized by almost similar growth with respect to the nitrogen supply. Cultivar ´Rubinola´ exhibited similar branching pattern, but higher vigor than ´Topaz´. As a result of higher apical dominance, ´Rubinola´ produced higher proportion of long shoots, but a lower quality of short shoots than ´Topaz´. Consequently, cultivar ´Rubinola´ produced only few terminal flowers on short shoots and lateral flowers dominantly in the distal zone, while ´Topaz´ was characterized by intensive terminal flowering, but the lateral flowers were more abundant in the median zone. Even a lower dose of spring nitrogen improved the flower bud formation on both terminal and lateral positions extending the flowering zone on one-year-old shoots. This further changed the branching and bearing behavior of the apple trees, which particularly allows to optimize their fertilization management. However, this effect appears to be further regulated by mechanism connected with apical dominance.