Evaluation of nitrogen-fertilizer uptake, nitrogen-use and water-use efficiency in sweet cherry (Prunus avium L.) on dwarfing and standard rootstocks

Optimum management of nitrogen (N) and water is of critical importance in order to maintain growth and high production of fruit trees in modern orchards. The objectives of this dissertation were to evaluate in sweet cherry on dwarfing and standard rootstocks: (1) the N-fertilizer uptake efficiency, and nitrogen-use efficiency (NUE), at different phenological stages; (2) the water-use efficiency (WUE) under non-limiting water availability and water deficit condition, and (3) the effect of water deficit on growth and physiological parameters. N-fertilizer uptake efficiency, NUE, and WUE were evaluated five times during the growing season on one-year-old potted sweet cherry cv. 'Rainier', grafted on the dwarfing rootstock 'Gisela 5', the semi-dwarfing rootstock 'Gisela 6', and the standard rootstock 'Mazzard'. Also the same rootstocks without scion were compared. N-fertilizer uptake was influenced by the accumulation of dry matter and was higher from rapid shoot growth until the beginning of leaf senescence. Overall, there were no differences in N-fertilizer uptake between dwarfing and standard rootstocks. NUE was significantly higher in 'Mazzard' compared to either the dwarfing or the semidwarfing rootstocks without scion. Values of NUE were similar for 'Mazzard', and cv. 'Rainier' grafted on dwarfing, semi-dwarfing, and standard rootstocks, in all the periods considered. WUE was higher in the standard rootstock without scion, compared to both dwarfing rootstocks without scion. N-fertilizer uptake and NUE were also evaluated in field-grown, five-year-old sweet cherry cv. 'Sam' grafted on 'Mazzard' and 'Gisela 5'. K15NO 3 was applied at full bloom, rapid shoot growth, and at the beginning of leaf senescence. N-fertilizer was absorbed in greater amounts when applied at bloom or at rapid shoot growth than at the beginning of leaf senescence. When N-fertilizer was applied at bloom, the percent of N-fertilizer was higher in leaves of sweet cherry on dwarfing than standard rootstocks indicating that N-fertilizer contribute more to the total N of dwarfing trees than standard trees. NUE, as well as N retranslocation from senescent leaves, did not differ between the rootstocks. Plant growth and gas exchange parameters, water-use efficiency and leaf carbon isotope composition were evaluated on one-year-old potted sweet cherry cv. 'Rainier' grafted on 'Mazzard' and 'Gisela 5' under two different water treatments: (a) well-watered (control), which received 100% of the amount of water lost by ET, and (b) water deficit treatment, which received 50% of the water applied to the control. Gas exchange parameters were affected earlier than growth parameters. Growth parameters measured in sweet cherry on standard and dwarfing rootstocks were affected similarly. Cumulative leaf area was the first growth parameter to be affected by water deficit. WUE was not significantly different between rootstocks, and did not appear to increase under water deficit condition, indicating that irrigation should be considered as an important practice in sweet cherry orchards, especially when dwarfing rootstocks are selected.