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:In order to compare the effects of early versus late / sustained fertilization on health and fruit production of Hamlin and Valencia trees, the following completed treatments were evaluated:Treatments: 1. T1: Control I: 50% during spring and 50% in fall season (applied linearly up to September (Ham.) and October (Val.)2. T2: Control-II: 50% during spring and 50% in fall ( 25% each split, Mar, Jun, Sept, October) 3. T3: 75% spring fertilization (Sigmoidal) and 25% application in August4. T4: 75 % spring fertilization (Sigmoidal) and 25% fall application in September (Ham.) or October (Val.)5. T5: 75 % spring fertilization (sigmoidal) and 25% two equal splits 6. T6: 75 % spring fertilization (sigmoidal) and 50% (25% extra) in August 7. T7: 75 % spring fertilization (sigmoidal) and 50% (25% extra) in Fall , two equal splits8. T8: 100 % spring fertilization (25% extra) and 25% application in August9. T9: 100 % spring fertilization (25% extra) and 25% application in September (Ham.) or October (Val.)10. T10: 100 % spring fertilization (25% extra) and 50% (25% extra) application in fall, two equal splitsThe first fertilizer of the season was applied to the Hamlin and Valencia trees in February, and the second in April. During the first quarter of 2023, the trees in the experiment were still recovering from substantial damage caused by hurricane Ian in 2022, but spring flush and bloom looked good until a heatwave and drought set in during March, which halted growth and increased post-bloom fruit drop. Oxytetracycline injections were applied to all 400 Hamlin and Valencia project trees during April, using the approved methods for Florida citrus with HLB. The Sugarbelle trees were not treated with OTC. Annual soil sampling and frequent lysimeter leachate sampling, leaf nutrient sampling, processing and analysis resumed with the spring growth in the first quarter. In Feb/Mar the roots of the Hamlin and Valencia trials were sampled at two soil depths by collecting and sieving soil samples taken around the driplines of trees. Root mass, frequency, and length were measured or estimated with digital scans.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):In the first year of the experiment (2022), comprehensive fruit quality recording was not done due to hurricane effects on fruit during maturation and ripening phases where Hamlin variety was extensively damaged (not enough fruit to measure on all plots). None of the fruit external and internal fruit qualities (diameter, fruit weight, TSS, TA and Ratio) were significantly different among the fertilizer application (rate and timing) treatments in Valencia variety. However, fruit diameter and fruit weight was greater in treatment T5 ([75-12.5-12.5]: early 75% and 25% split twice in fall) and T8 ([100*-25-0]: 100 % spring fertilization (25% extra) and 25% application in August). Similarly, treatment T5 and T9 recorded higher TSS and TSS:TA ratio, and lower TA.B) New developments: OTC was applied by injection to all trees in the experiment. It was judged essential to keep the trees alive for the duration of this research by suppressing HLB.C) Issues: The severe damage caused by hurricanes in 2022 will likely cause longer-term setbacks to the trees during 2023.2. Please state what work is anticipated for next quarter:Routine lysimeter sampling, leaf sampling, processing and analysis will be ongoing, as will tree size and fruit measurement. In early June the trees in plots will be measured with an aerial drone survey. There are three flights per year. The third fertilizer application will be applied at about the beginning of phase 2 of fruit growth, end of May. 3. Please state budget status (underspend or overspend, and why): Spending rate is approximately on track.