The area under citrus production in Florida is 332 000 ha, with a production of 10 to 12 million metric tonnes of fruit annually. Nutrient management recommendations are needed to increase N uptake efficiency and to minimize nitrate leaching below the root zone. The objectives of this study were (i) to evaluate biomass distribution of 6-yr-old 'Hamlin' orange trees [Citrus sinensis (L.) Osbeck] on 'Swingle citrumelo' [Poncirus trifoliata (L.) Raf. x C. x paradisi Macfad.] rootstock grown in a sandy soil under low volume irrigation, and (ii) to estimate partitioning of 15N fertilizer applied to the soil during early spring into different tree components. We evaluated biomass of tree components (leaves, twigs, trunk, taproot, roots, and fruit), and N recovery and distribution of 15NH415NO3 (AN) and 15N-urea (UR) (10 atom % 15N) applied to the soil surface. About 70% of dry matter biomass of trees was aboveground (AG). Length density of feeder roots was concentrated at a depth of 0 to 15 cm below the soil surface and varied from 1.87 to 0.88 cm cm-3 at 0.5- and 1.5-m distance from the trunk, respectively. Total recoveries of 15N by trees were 25.5% for UR and 39.5% for AN at fruit harvest, 280 d after fertilization. Mean accumulation of applied 15N in recent leaf flush was 4.2% and that of older leaves was 2.5%. Accumulation of 15N was low in woody tissue. Since fruit represented a large sink for N (10.2 and 18.4% recovery of 15N applied as UR and AN, respectively), we confirmed the importance of N fertilization before fruit development.