Effect of Cu Application Rate on Citrus Trees Roots and Shoots Development.

Understanding citrus tree root development dynamics is critical in determining crop best nutrients management practices. Relatively small numbers of studies have examined root responses to nutrient additions in citrus trees. The role of copper (Cu) in root development of healthy and HLB affected trees in Florida is not well documented. Thus, the objective of this study was to determine citrus trees roots and shoots development in healthy and HLB affected sweet orange (Citrus x sinensis (L.) Osbeck) trees. The study was initiated in July 2016 on a fine sand soil texture (Sandy, siliceous, hyberthermic Arenic Alaquods). Twenty-four soil lysimeters were divided into HLB affected and healthy trees in a randomized complete block. Four Cu rates including 0, 0.5x, 1x, and 2x kg yr^-1 were replicated three times from July throughout October 2016. One vertically mini-rhizotron tube (CI-600, CID Bio-Science) was installed per lysimeter at 30 cm soil depth. Roots densities were measured bi-weekly for 26 weeks. Also, leaf area, stem diameter and trees height were measured during July and October. Results showed significant effect of Cu rate on root development. Average root length under the control treatment (0x Cu) increased by 84 % and 61% in the healthy and HLB affected trees, respectively. In contrast, average roots length under the highest Cu rate (2x) decreased by 63% and 57% in the healthy and HLB affected trees, respectively. Our results indicated that the root systems of healthy trees developed faster than HLB affected trees, and that roots of trees not receiving Cu developed faster than trees receiving higher Cu rate. Indicating that, HLB and increasing Cu application rate are suppressing factors for roots development. Furthermore, average leaf area declined with higher Cu rate (2x) by 25% under HLB affected trees. Above and below-ground systems responded negatively to higher Cu rates.