December 1, 1996
Fertilization rate and growth response of young trees vary both in citrus nurseries and in new plantings. Experiments were conducted with 'Hamlin' orange trees [Citrus sinensis (L.) Osb.] on 'Swingle' citrumelo rootstock [C. paradisi Macf. × Poncirus trifoliata (L.) Raf.] rootstock to determine the optimum N rate for greenhouse nursery trees and the effect of N nutrition of greenhouse nursery trees on growth and fertilization response of trees in the field. Greenhouse nursery trees received 12, 50, 100 or 200 ppm N weekly via drip irrigation for one year. Optimum tree growth occurred at the two highest rates, while trees that received 12 or 50 ppm N were stunted and chlorotic. In another experiment from 0 - 0.75 Ib N/tree/year were applied for 2 years to young field trees with initial leaf N levels of 1.4 - 4.1% when planted. Preplant leaf N level had no effect on trunk diameter, height, shoot growth and number or dry weight of trees for year one and two in the field. Fertilizer rate in the field did not affect tree growth in year one but did in year two, with maximum growth occurring at 0.37 Ib N/tree/ year.