1. Please state project objectives and what work was done this quarter to address them: The overall goal of the project is to develop fertilization strategies to best match nutrient supply and demand, and develop recommendations for optimal nutrient application timing as compared to a simple constant supply, which will improve fruit yield, quality, and reduce fruit drop. A)Objective 1) Test if a reduced N-P-K nutrient supply in the fall is safe for sustaining HLB-affected citrus, and whether it can improve fruit quality to facilitate earlier maturity / harvesting and reduce fruit drop:Trunk diameter, fruit growth, fruit drop measurement was done in Hamlin and Valencia during October to December. Additionally, routine leaf sampling was accomplished during October and December for leaf nutrient analysis. In the 2nd week of November, treatment-wise fruit was harvested from the Hamlin variety for yield data, fruit drop % calculation, and fruit quality measurement. Temporal treatment responses on different variables and results recorded during October to December were presented and interpreted below.1. Trunk Growth: There were no significant treatment differences on relative growth rate of trunk diameter (mm/cm/month) in both Hamlin and Valencia varieties during October to December 2023. However, overall trunk growth rate in approximately in two years of the experiment was significantly higher in Valencia variety in treatment T8 and T9 (fertilizer applied 125% RDF (recommended dose of fertilizers) with 100% in spring and 25% fall season).2. Fruit relative growth rate (RGR): Fruit diameter of tagged fruit was measured every two weeks to calculate the relative growth rate of fruit after physiological fruit drop in May in both varieties. In both years, fruit RGR was not significant after August in Hamlin and Valencia. Overall fruit RGR (mm/cm/month) was also statistically non-significant between treatments in both varieties in both years.3. Fruit drop: Fruit drop was extremely high, and started after physiological fruit drop in May. We counted dropped fruit every two-week intervals in both varieties. Treatment 6 (50% fertilization in August), Treatment 8 (125% fertilization in spring and 25% in August) and Treatment 2 ( linear fertilization with 25% in August) resulted in a higher numbers of cumulative number of fruit drop per tree in Hamlin in 2023. However, only Treatment 2 showed higher fruit drop in Valencia. Fruit drop percentage was calculated based on number of fruit harvested and number of fruit drops before fruit harvesting. In 2023, only 3 replications were used for calculation in Hamlin because the 4th replication was heavily affected by citrus canker in addition to HLB disease. The fruit drop rate was higher than 70% in all fertilization treatments which were not statistically significant between treatments in Hamlin variety.4. Fruit quality at harvest:a. Fruit size (diameter and weight): After harvesting, 10 fruits were selected to measure the fruit diameter and fruit wt. There was no treatment effects on fruit diameter and single fruit weight in Hamlin variety in 2023. b. Juice quality: The fertilization treatment did not affect the juice quality of Hamlin fruit. Total soluble solids (TSS), titratable acidity (TA), and TSS:TA ratio were NS. c. Fruit yield over time: Yield was very low in Hamlin due to perhaps severe HLB infestation and excessive fruit drop. The projected potential yield of these trees was only 153 boxes/acre if no fruit drops had occurred. However cumulative excessive fruit drop resulted in very low fruit retention and less fruit yield. Treatment 10 resulted in a higher yield (~58 boxes/acre) than other treatments which was still not likely profitable. Objective 2) Develop an optimized, practical fertilizer timing management profile to boost fruit quality and reduce fruit drop for HLB-affected citrus based in part on the sigmoidal nutrient demand curve defined by four physiological growth phases (0=bloom/fruit set; 1=cell division; 2=cell enlargement; 3=maturation):Due to the absence of significant differences to date, we have not made progress with this objective. The hurricanes of 2022 caused damage that takes years to repair, and the constant high pressure of citrus canker on the Hamlin trees in particular has been an additional source of noise that masks any treatment response.B) New developments: NoneC) Issues: None, except those mentioned above that are beyond our control.2. Please state what work is anticipated for next quarter:Routine lysimeter sampling, leaf sampling, processing and analysis will be ongoing, as will tree size, root growth and fruit drop and growth measurement.Plan for January to March:1. Sampling for leaf nutrient analysis2. Fruit diameter measurement (Valencia)3. Collection of leachates for nitrate N loss and analysis4. Scanning of the Minirhizotron for root growth5. Fruit drop count in every two weeks until harvesting in Valencia6. Harvesting Valencia variety for yield and fruit quality measurement 3. Please state budget status (underspend or overspend, and why):Spending rate is slightly below the target by about 10%. This is considered within the normal deviations of budgeting.