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  • 1 University of Florida, IFAS. Citrus Research and Education Center, 700 Experiment Station Rd., LAKE ALFRED. FL 33850

The objectives of this greenhouse study were to determine the rate of nitrogen (N) uptake over a 30 day period, use efficiency and N partitioning within two citrus rootstock species. Sixteen-week old seedlings of Cleopatra mandarin (C. reticulata Blanco) and Swingle citrumelo (C. paradisi × P. trifoliata) were assigned to treatments (harvest day × rootstock species) in a completely randomized design, grown in a Candler fine sand for 6 weeks and fertilized weekly with a N:P:K (5:1:5) plus minor elements solution at 200 mg N · liter-1. A single application of 15NH4 15NO3 (20% 15N) was substituted for a normal weekly fertigation. Six replicate plants of each rootstock species were harvested at ½, 1½, 3½, 7½, 10½ and 30 days after I5N application. Uptake of 15N was more rapid in SC over the first 7½ days (17% of applied) than in CM (11%), but uptake over 30 days was similar (52-53%) for both species. A higher proportion of 15N was found in the photosynthetic tissues of CM (74%) than in SC (48%), whereas a lower proportion was found in the fibrous roots of CM (9%) than SC (22%).

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