DIFFERENTIAL NITROGEN UPTAKE DURING GROWTH CYCLE IN YOUNG 'ROCHA' PEAR TREES

New ‘Rocha’ pear plantings involve higher tree densities, the use of fertilization with irrigation and the adoption of soil conservation systems, demanding a rational use of fertilizers. Knowledge about nitrogen (N) uptake patterns by the trees during the growth cycle can help in decisions regarding N formulations, amounts and dates of application, and contribute to more efficient N use. Two-year-old ‘Rocha’ pear trees grown in pots received 2 g N/tree, at dates corresponding to active shoot vegetative growth, shoot growth cessation and beginning of leaf fall, in the form of either NH₄¹⁵NO₃ or ¹⁵NH₄NO₃. N was preferentially absorbed as NH₄⁺ in all sampling dates, ranging from 62 to 66% of the total labelled N recovered in the trees. The fertilizer N use efficiency was also higher for ammonium treatment than for nitrate treatment in all sampling dates.