Development of Root Nutrient and Fertilization Guidelines for Huanglongbing (HLB)-Affected Orange and Grapefruit

Development of Root Nutrient and Fertilization Guidelines for Huanglongbing (HLB)-Affected Orange and Grapefruit

Report Date: 08/06/2021
Project: 18-042C   Year: 2021
Category: Horticultural & Management
Author: Davie Kadyampakeni
Sponsor: Citrus Research and Development Foundation

Progress report for the third quarter of the 2020/2021 project year

The purpose of the project is to develop new guidelines for restoring root health and improving overall tree nutrition for Florida oranges and grapefruits. 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. All sampling for the third quarter of the third year of the project are 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. Yield and fruit quality data were collected in February and are being analyzed.

Graduate student Lukas Hallman completed his MS program under the supervision of Dr. Rossi. Portions of his work will be published in peer reviewed journals. PI Kadyampakeni and graduate student Tanyaradzwa Chinyukwi published a review article in the Journal of Plant Nutrition.

Plans for Next Quarter

The 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. Former graduate student Tanyaradzwa Chinyukwi and graduate student Lukas Hallman will present their works at the Florida State Horticultural Society Meeting in Daytona Beach, FL in September 2021. Lukas will also present his work at the American Society of Horticultural Science in Denver, CO in August 2021.

Dr. Ferrarezi departed from IRREC this quarter and his tasks will be completed by co-PI Dr. Alan Wright to make sure all project milestones are completed as planned.

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