NO3-N concentrations in 35-year-old ‘Hamlin’ orange (Citrus sinensis L. Osbeck) and ‘Marsh’ grapefruit (C. paradisi Macf.) trees on rough lemon (C. limon Burm. f.) rootstock were highest in the feeder roots (212-962 ppm), followed by the leaves (160-300 ppm) and trunk wood (0-304 ppm). Only in 3 of 10 orange trees and in 1 of 10 grapefruit trees was NO3-N detected in the bark. Nitrate-N concentration in the leaves and the wood and the percentage of NO3-N in total N in the wood were higher in orange than in grapefruit trees.
Received for publication 14 Oct. 1983. The author is grateful to Florida Citrus Groves Corp., Clermont, Fla., and Jack M. Smoot for technical assistance. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact.