Abstract
Among the factors affecting leaf penetration of urea, its concentration in the sprayed solution likely plays a major effect. The present study aimed to (1) asses the leaf absorption of nitrogen deriving from different combinations of carrier water volume and concentration of 15 N labeled urea and (2) test the hypothesis that basal and apical leaves have different abilities to take up urea. The experiment was carried out in July 2000, under field conditions in an apple orchard-cv. Golden D. on M9, 3000 tree/ha-located in the upper Adige Valley (South Tyrol, Italy). Different combinations of labeled (10% atom 15 N) urea concentration (4, 20 and 40 g L-1) and sprayed volumes (1500, 300 and 150 L ha-1) were used to apply similar amounts of N per tree in all the treatments (0.925 g N tree-1). Basal and apical leaves were sampled at: 1, 5, 24, 48 and 120 hrs after treatment and analyzed for total N and 15 N. Leaves intercepted on average 24 mg labeled N m-2 , regardless of the treatment and leaf age. Leaf N uptake within 48 hrs was highest when urea was sprayed at the lowest concentration. At the end of the studied period (120 hrs), however, no differences in the percentage of intercepted N recovered in the leaves was recorded. Apical leaves were more effective in taking up N than basal ones so that at the end of the investigated period they had absorbed as much as 32% more N than basal leaves.