Seasonal Uptake Rate Dynamics and Partitioning of Mineral Nutrients by Bourse Shoots of Field-grown Apple Trees

Strategies to improve the nutrient use efficiency in the orchard should allow a synchronization of the dynamics of nutrients demand by trees with their availability in the soil. In the present study we assessed the dynamics of nutrient accumulation along a vegetative season into the bourse shoot (including one apple attached at its base) in two apple cultivars ('Golden Delirious' and 'Nicoter'). This model tree organ accounted for about three quarters of the fruits and for more than half the leaves present on the trees. On June 10, July 24, August 28 and October 8 (ripening stage for both cultivars) 2008, randomly-chosen shoots were removed, separated into leaves, shoot axis and fruit and their dry weight and nutrient content were determined. The bourse shoots of the two varieties differed in their dry matter allocation, the fruit being a stronger sink in 'Golden Delicious' than in 'Nicoter'. Nutrient uptake and biomass increases were partially decoupled. For all macronutrients except potassium (K) the accumulation rate peaked between June and July and decreased thereafter. The accumulation of K, on the contrary, occurred at highest rate until the end of August, and diminished only dose to fruit harvest. All nutrients, with the exception of calcium (Ca), increased in the fruit until harvest. At harvest, more Ca and magnesium were found in the bourse shoots of 'Nicoter' as compared to 'Golden Delicious', which in turn accumulated more K. The two genotypes did not differ for the total amounts of nitrogen and phosphorus accumulated in the bourse shoot.