Leaf uptake and subsequent partitioning of urea-N as affected by the concentration and volume of spray solution and by the shoot leaf position in apple (Malus domestica) trees

摘要

In a field experiment on 'Golden Delicious' apple trees, different combinations of labelled (10 at. % N-15) urea concentrations (4, 20 and 40 g l(-1)) and spray volumes (1500, 300 and 150 1 ha(-1)) were used in mid summer to foliar apply 920 mg N per tree by the following treatments: 1) low concentration-high volume, 2) medium concentration-low volume, 3) high concentration-ultra low volume. The fate of urea-N sprayed on leaves was followed during a 5 d period from spraying by determining N-15 concentration on leaf samples collected at different timings and on entire branches, previously girdled. Basal and apical leaves were sampled 1, 5, 24, 48 and 120 h after spraying. Leaves intercepted on average 24 mg labelled N per m(2) of leaf area, regardless of treatment and leaf age. Leaf N uptake within 48 h was highest when urea was sprayed at low concentration-high volume. At the end of the experiment (120 h), however, no significant effect of treatments on leaf uptake was recorded. Urea-N penetrated at higher rates on apical than basal leaves. While about 50% of the intercepted urea-N was recovered in the leaves sampled 120 h after application, the sum of fertilizer N recovered in the different organs of the girdled branches accounted for 84% of the estimated amount of N intercepted. The discrepancy between these two estimations can be explained considering that part of the N taken up from the leaves was rapidly exported and recovered in the fruits. Application of low volume with a high concentration of urea should be considered as a tool to decrease costs while maintaining a high N use efficiency.