CONICET | Buscador de Institutos y Recursos Humanos

Sweet cherry is a fruit of increasing economic importance though it is less significant than other stone fruit species such as peach. Cherry has receive little attention about nitrogen (N) uptake and dynamics in mature trees. The aim of this work was to determine N uptake and partitioning in 7-year-old sweet cherry trees cultivated in a cold region (Los Antiguos, Santa Cruz, Argentina; 71°38 W, 46°32 S), as influenced by the timing of fertilizer application. Nitrogen (95 kg ha-1) was applied as ammonium nitrate to a soil with sweet cherry trees (Prunus avium Bing) grafted onto P. mahaleb rootstocks. Fertilization was split into two equal applications per treatment: (1) the commercial product and (2) the product labelled with 15N isotope (10% atom.). Treatments consisted of one early spring (full bloom, October 2005) or one summer (January 2006, after harvest) application of 15N ammonium nitrate to three replicate trees. Fruit were harvested in January and leaves were collected at both full canopy and leaf fall. All trees were excavated in winter (August 2006) and partitioned into their components. Those components were dried and analysed for total N and 15N content. Total N per tree was 158.73 and 134.22 (p=0.240) g for spring and summer treatments respectively. Nitrogen content derived from the fertilizer was similar in both treatments (57.62 ± 9.89 g and 39.65 ± 5.05 g respectively per tree; p=0.1285). Summer postharvest 15N application partitioned not only to structural components (trunk and roots) but also to buds and leaves. Uptake efficiency was significantly (p=0.0113) higher in the spring than in the summer application (65.7% versus 37.44%). Nevertheless, 52.5% of N applied in spring is usually lost due to harvest and summer pruning. This emphasizes the importance of the postharvest N fertilization which increases N accumulation in both reserve organs and buds though, according to our data, it is more inefficiently used at this moment. The extent of nitrogen uptake, efficiency of use and partitioning in the following growing seasons are still open questions that deserve further research.