Split application of nutrients improve growth and yield of Huanglongbing‐affected citrus trees

Citrus production in Florida declined steadily because of Huanglongbing (i.e., HLB, citrus greening) caused by the bacteria Candidatus Liberibacter asiaticus. The objectives of the study were to determine whether leaf tissue nutrient concentration, tree growth, fruit yield, and juice content were improved with split applications of essential nutrients on selected rootstocks on Florida sandy soils. The treatments were arranged in a split‐split plot design where the nitrogen (N) was fertigated in 20 splits and the Ca + Mg nutrients were also split three times coinciding with the spring, summer, and late summer flush seasons on trees budded on two rootstocks of ‘Hamlin’ citrus trees [ Citrus sinensis (L.) Osbeck]. A significant difference in leaf N, calcium (Ca), and magnesium (Mg) concentration were detected between rootstocks when trees received the highest N rate and remained within the optimum range of critical nutrition concentration even with the lowest N rate, suggesting a lower N requirement with split N applications. Yet, leaf Mg concentration remained in the minimum range implying a low soil Mg pool. For Ca, Mg, and Ca + Mg treatments, we recorded 1.41×, 1.23×, and 1.23× and 1.22×, 1.26×, and 1.30× greater tree canopy volumes (TCV) on Cleopatra and Swingle rootstocks, respectively, as compared with control trees. Significantly greater fruit yield was detected for trees budded on Cleopatra rootstocks that received either Ca or Ca + Mg treated trees with 59.7 and 63.0 kg tree –1 as compared with the control trees (36.9 kg tree –1 ), respectively. A magnitude of 1.14× more average fruit weight than control trees was noted for trees budded on Swingle rootstock in response to Mg nutrition. Therefore, the application of essential nutrients has a positive impact to ameliorate tree growth and nutrient deficiency associated with Candidatus Liberibacter asiaticus‐induced problems, thereby improving tree growth and yield.