Published 2020-10-19
Abstract
The huanglongbing (HLB) causative agent, Candidatus Liberibacter asiaticus, lowers tree performance by reducing
water and nutrient uptake as a result of root loss. HLB-affected trees have a fibrous root loss of about 30 to 80%, which
increases as HLB symptoms develop in the canopy. Investigating optimal nutrient concentrations in citrus roots thus
improves our understanding of HLB dynamics concerning root nutrition and fertilizer application methods. This study
sought to evaluate nutrient uptake of HLB-affected orange trees via soil fertilizer applications for 5- to 6-year-old Citrus
sinensis ‘Valencia’ orange trees on Swingle rootstock at Ridge and Flatwoods sites. Macronutrients and micronutrients
were applied at varying fertilization rates of standard fertilization via fertigation according to the University of Florida
Institute of Food and Agricultural Science guidelines. For macronutrients, the rates were: a) standard fertilization +
40 lb/acre Ca + 40 lb/acre Mg + 220 lb/acre K and b) standard fertilization + 90 lb/acre Ca + 90 lb/acre Mg + 440 lb/
acreK. For micronutrients, the rates were: a) standard fertilization + 5 lb/acre Fe, 5 lb/acre Mn, 5 lb/acreZn+ 1 lb/acre
B; b) standard fertilization + 10 lb/acre Fe, 10 lb/acre Mn, 10 lb/acreZn + 2 lb/acre B; and c) standard fertilization +
20 lb/acre Fe, 20 lb/acre Mn + 20 lb/acreZn + 4 lb/acre B. Soil and leaf samples were collected for nutrient concentration analysis in Spring and Fall 2019 and Summer 2020. No significant differences among treatments (P < 0.05) were
observed for tissue and soil nutrient concentrations due to nutrient interactions. Fruit yield between the 2019 and 2020
harvest seasons increased with increased nutrient availability. Therefore, at higher fertilization rates of (standard fertilization + 40 lb/acre Ca + 40 lb/acre Mg + 220 lb/acre K + 20 lb/acre Fe, 20 lb/acre Mn + 20 lb/acreZn + 4 lb/acre B),
HLB-affected trees showed increased nutrient uptake, improving overall tree performance.