Interaction of soil boron application with leaf B concentration, root length density, and canopy size of citrus affected by Huanglongbing

Abstract

Good and balanced citrus nutrition is important for high fruit yields and improved tree performance. A study was conducted for 2 years to investigate the effect of soil application of boron (B) on leaf nutrient content, canopy size, and root length density (RLD). The study was conducted on 10-year-old Candidatus Liberibacter asiaticus (CLas)-infected Vernia sweet orange on Rough Lemon rootstock in a commercial grove east of St. Cloud, FL planted at 375 trees ha−1 on a traditional soluble dry nutrition and spray programs. Treatments were supplied with various ground-applied controlled-release fertilizer treatments containing B. Boron was applied at 0×, 2×, and 4× current University of Florida recommendation where 1× = 1.12 kg ha−1. Data collected included leaf B nutrient content, soil B concentration, trunk diameters, canopy volumes, soil electrical conductivity, and soil pH. The 0×, 2×, and 4× application rates corresponded with leaf nutrient contents ranging from 56 mg kg−1 and 88 mg kg−1 in March 2017, 162 mg kg−1 and 288 mg kg−1 in September 2017, and 122 mg kg−1 and 320 mg kg−1 in May 2018. Temporary, RLD decreased with time from March to September 2017 by 13, 30, and 37% at the 0, 2.24, and 4.48 kg B ha−1 and increased by 309, 258, and 306% at the 0, 2.24, and 4.48 kg B ha−1, respectively, from September 2017 to May 2018. No consistent pattern was established between soil B application with canopy size.