Impacts of Oak Mulch Amendments on Rhizosphere Microbiome of Citrus Trees Grown in Florida Flatwood Soils.

Rhizosphere interactions are an understudied component of citrus production. This is even more important in Florida flatwood soils, which pose significant challenges in achieving sustainable and effective fruit production due to low natural fertility and organic matter. Citrus growers apply soil amendments, including oak mulch, to ameliorate their soil conditions. Thus, the aim of this research was to evaluate the effects of oak mulch on citrus nutrient uptake, soil characteristics, and rhizosphere composition. The plant material consisted of 'Valencia' sweet orange (Citrus × sinensis) trees grafted on 'US-812' (C. reticulata × C. trifoliata) rootstock. The experiment consisted of two treatments, which included trees treated with oak mulch (300 kg of mulch per plot) and a control. The soil and leaf nutrient contents, soil pH, cation exchange capacity, moisture, temperature, and rhizosphere bacterial compositions were examined over the course of one year (spring and fall 2021). During the spring samplings, the citrus trees treated with oak mulch resulted in significantly greater soil Zn and Mn contents, greater soil moisture, and greater rhizosphere bacterial diversity compared to the control, while during the fall samplings, only a greater soil moisture content was observed in the treated trees. The soil Zn and Mn content detected during the spring samplings correlated with the significant increases in the diversity of the rhizosphere bacterial community composition. Similarly, the reduced rates of leaching and evaporation (at the soil surface) of oak mulch applied to Florida sandy soils likely played a large role in the significant increase in moisture and nutrient retention.

Root-Shoot Nutrient Dynamics of Huanglongbing-Affected Grapefruit Trees.

With huanglongbing (HLB) causing a reduction in fine root mass early in disease progression, HLB-affected trees have lower nutrient uptake capability. Questions regarding the uptake efficiency of certain fertilizer application methods have been raised. Therefore, the goals of this study are to determine if nutrient management methods impact nutrient translocation and identify where in the tree nutrients are translocated. Destructive nutrient and biomass analysis were conducted on field grown HLB-affected grapefruit trees (Citrus × paradisi) grafted on 'sour orange' (Citrus × aurantium) rootstock under different fertilizer application methods. Fertilizer was applied in the form of either 100% soluble granular fertilizer, controlled release fertilizer (CRF), or liquid fertilizer. After three years, the entire tree was removed from the grove, dissected into eight different components (feeder roots, lateral roots, structural roots, trunk, primary branches, secondary branches, twigs, and leaves), weighed, and then analyzed for nutrient contents. Overall, application methods showed differences in nutrient allocation in leaf, twig, and feeder root; however, no consistent pattern was observed. Additionally, leaf, twig, and feeder roots had higher amount of nutrients compared to the other tree components. This study showed that fertilization methods do impact nutrient contents in different components of HLB-affected trees. Further research should be conducted on the impact of different fertilizer application methods and rates on HLB-affected trees.

Impact of a Soil Conditioner Integrated into Fertilization Scheme on Orange and Lemon Seedling Physiological Performances.

Growers in Florida face unique challenges regarding maintaining proper citrus nutrition.Poor draining soils with low fertility, low C.E.C., and high rates of leaching are common in thisregion. In response to these challenges, interest has grown in products labeled as soil conditioners.Using a completely randomized experimental design, this greenhouse study tested the effects of 5different combinations of a traditional fertilizer (TF) and a new soil conditioner (SC) on lemon andorange seedling physiology. Eight-month-old 'Bearss' lemon and 'Valencia' sweet orange graftedon sour orange rootstocks were employed, and five repetitions were used for each treatment. Plantbiomass (dry weight), height, stem diameter, chlorophyll content, stomatal conductance andnutrient uptake were analyzed after 120 days of treatment. The results show that SC has a positiveimpact upon both chlorophyll levels and stomatal conductance values in both orange and lemonseedlings. However, based on dry weight growth data, we can only conclude that the SC waseffective for orange seedlings at 50% TF and 0.5% SC. Based on this short 120-day evaluation, theSC achieved positive growth promotion for orange (50% TF) but not for lemon seedlings.