Progress report for the fourth quarter of the 2019/2020 project yearThe purpose of the project is to develop new guidelines for restoring root health and improving overall tree nutrition for Florida oranges and grapefruit. The objectives of the project are to:1. Determine optimal nutrient concentrations in roots and leaves for multiple grapefruit and orange varieties.2. Compare and contrast fertigation, soil, and foliar fertilization to identify best application method for uptake of nutrients into both underground and aboveground components.3. Investigate the relationship between root and leaf nutrient contents to tree health, yield, and fruit quality as well as bacteria titer.4. Generate updated and new guidelines for optimal nutrient contents for roots and leaves for HLB-affected trees. Progress to date:The project is being conducted at three sites: Citrus Research and Education Center (CREC), Southern Gardens Citrus near Clewiston, FL and Indian River Research and Education Center (IRREC). Data collection continued during this quarter on root scanning, canopy size determinations and soil sampling on the central Ridge and southwest Flatwoods along with fertilizer treatment applications. Trends on soil and root nutrient levels in Valencia orange, for example, continue to follow the pattern of treatments e.g. 4x>2x>1x, for soil applied treatments in summer and fall 2020. Similarly, for foliar applied treatments, the pattern in leaf nutrient concentration follows 1x<2x<4x. All sampling for the fourth quarter is complete. The aim of the study at the UF/IFAS IRREC in Fort Pierce, FL was to relate nutrient concentrations in grapefruit leaves and roots to indicators of tree health and root growth. The research was conducted on flatwoods soils in a randomized complete block design field study on `Ruby Red' grapefruit. Micronutrients (B, Fe, Mn and Zn) were applied using three different concentrations (1x, 2x, and 4x current UF/IFAS guidelines) in the form of either dry granular water-soluble fertilizer, controlled-release fertilizer, or liquid fertilizer. A total of 600 trees divided in 40 experimental units were employed. We collected leaf and root nutrient concentrations, canopy volume and tree height twice a year. Mini-rhizotrons were installed at the beginning of the experiment and root images were taken four times a year. Results showed increased micronutrient concentrations in the leaves among all treatments. There were no significant differences in tree height, canopy volume, root length, and root diameter. Graduate student Lukas Hallman presented his research at the American Society of Horticultural Science virtual Annual Meeting on August 10-13, 2020: Hallman, L.; Ferrarezi, R. S.; Kadyampakeni, D.; Wright, A. L.; Lange, J.; Johnson, E.; Rossi, L. 2020. Micronutrient uptake and root growth and development in HLB-affected grapefruit on Florida Flatwoods soils. HortScience 55(9): S3 (Abstr.). Graduate student Tanyaradzwa Chinyukwi presented her research at the American Society of Horticultural Science virtual Annual Meeting on August 10-13, 2020: Chinyukwi, T., S. Kwakye, and D. Kadyampakeni. 2020. Response of HLB-Affected trees to differential foliar, and Soil Macro- and Micronutrient Applications. HortScience 55(9) (Abstract) Graduate student Tanyaradzwa Chinyukwi presented portions of her research at the Florida State Horticultural Society virtual Annual Meeting on October 19, 2020. She has submitted a conference proceedings paper that will be in print soon. Chinyukwi, T., S. Kwakye, and D. Kadyampakeni. 2020. Performance of HLB-affected trees to soil macro- and micronutrient applications. Proceedings of the Florida State Horticultural Society 133:xx-xx. Plans for Next QuarterThe team will continue with fertilizer treatments and data collection including HLB rating assessments, canopy size and root growth measurements and reporting on the progress of the project.