Fertilization Rate and Growth of `Hamlin' Orange Trees Related to Preplant Leaf Nitrogen Levels in the Nursery

Abstract

Our objectives were to determine if leaf N concentration in citrus nursery trees affected subsequent growth responses to fertilization for the first 2 years after planting and how N fertilizer rate affected soil nitrate-N concentration. `Hamlin' orange [Citrus sinensis (L.) Osb.] trees on `Swingle' citrumelo rootstock [C. paradisi Macf. × P. trifoliata (L.) Raf.] were purchased from commercial nurseries and grown in the greenhouse at differing N rates. Three to five months later trees were separated into three groups (low, medium, high) based on leaf N concentration and planted in the field in Oct. 1992 (Expt. 1) or Apr. 1993 (Expt. 2). Trees were fertilized with granular material (8N–2.6P–6.6K) with N at 0 to 0.34 kg/tree yearly. Soil nitrate-N levels were also determined in Expt. 2. Preplant leaf N concentration in the nursery varied from 1.4% to 4.1% but had no effect on trunk diameter, height, shoot growth, and number or dry weight in year 1 (Expt. 1) or years 1 and 2 (Expt. 2) in the field. Similarly, N fertilizer rate had no effect on growth during year 1 in the field. However, trunk diameter increased with increasing N rate in year 2 and reached a maximum with N at 0.17 kg/tree yearly. Shoot number during the second growth flush in year 2 was much lower for nonfertilized vs. fertilized trees. Leaf N concentrations increased during the season for trees with initially low levels even for trees receiving low fertilizer rates. Soil nitrate-N levels were highest at the 0.34-kg rate, and lowest at the 0.11-kg rate. Nitrate-N levels decreased rapidly in the root zone within 2 to 3 weeks of fertilizing.