Florida citrus nurseries produce more than 2 million trees annually (Kessinger, 2005). Citrus trees were traditionally produced either in field nurseries (65% of total) or in greenhouses (35% of total). However, with the return of citrus canker (Xanthomonas axonopodis pv. citri) and the introduction of citrus greening (Candidatus liberibacter) to Florida, new nurseries now must grow trees in greenhouses in isolated areas. Nevertheless, field nurseries currently are still important sources of citrus trees in Florida.
Adequate nutrition is essential for production of high-quality citrus nursery trees, but application rates, frequencies of application, and nitrogen (N) sources vary greatly among citrus nurseries worldwide. For example, annual N rates in Florida citrus nurseries varied from 1174 to 3222 kg·ha−1, with less than 20% of the applied N being recovered in leaves (Castle and Rouse, 1990).
Optimum fertigation (liquid N) rates have been determined for the greenhouse, but not for field nurseries. Maust and Williamson (1991) found that critical N concentration ranged from 15 to 20 mg·L−1 applied daily in 1.0 L water, and high N rates actually decreased tree growth. In contrast, Guazzelli et al. (1996) observed that the optimum N rate in solution was 165 mg·L−1 or about 0.5 L N/tree annually. Differences in media types used likely resulted in differential responses in the two studies.
Only general guidelines are available concerning optimum N rates for field citrus nurseries. Recommended annual N rates for field nurseries range from 555 to 1110 kg·ha−1 (Bridges and Youtsey, 1977; Tucker and Youtsey, 1980), but some surveys suggested that rates as high as 2500 kg·ha−1 have been used in the past (Castle and Rouse, 1990).
The objective of this study was to determine the relationship between annual N rate and growth of ‘Hamlin’ orange nursery trees in the field. In addition, leaf samples were collected and N concentration analyzed to determine whether there is a correlation between N application rate, leaf N concentration, and growth in the field nursery.
Guazzelli, L., Davies, F.S., Ferguson, J.J. & Castle, W.S. 1995 Nitrogen nutrition and growth of Hamlin orange nursery trees on Swingle citumelo rootstock HortTechnology 5 147 149
Guazzelli, L., Ferguson, J.J. & Davies, F.S. 1996 Pre-plant leaf nitrogen effects on growth and fertilizer requirement of young ‘Hamlin’ orange trees Proc. Fla. State Hort. Soc. 109 72 76
Marler, T.E. & Davies, F.S. 1990 Microsprinkler irrigation and growth of young Hamlin orange trees J. Amer. Soc. Hort. Sci. 115 45 51
Maurer, M.A. & Davies, F.S. 1995 Reclaimed wastewater irrigation and fertilization of mature ‘Redblush’ grapefruit trees on spodosols in Florida J. Amer. Soc. Hort. Sci. 102 394 402
Maust, B.E. & Williamson, J.G. 1991 Nitrogen rate effect on growth of containerized citrus nursery plants Proc. Fla. State Hort. Soc. 104 191 195