By Davie Kadyampakeni, Jonas Pereira de Souza Junior, Edilaine Istéfani Franklin Traspadini, Shankar Shrestha and Alisheikh Atta
Integrated nutrient management is critical for improved and sustainable citrus production. Typical practices include split fertilization applications, the use of leguminous cover crops and the incorporation of soil amendments. This article discusses the importance of using novel blends, including macronutrients and micronutrients, as well as using orange peel powder to enhance nutrient cycling in Florida sandy soils.
CONTROLLED-RELEASE FERTILIZER STUDY
University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) researchers conducted a study on mature orange trees to compare two new nutrition programs utilizing controlled-release fertilizer (CRF) to provide year-round elevated levels of secondary and micronutrients with a selected standard commercial nutrition program. The treatments were as follows:
1) CRF1: A four-time soluble dry application program where the second and fourth applications are the complex mix containing 180-day CRF products at about 150 pounds per year
2) CRF2: A four-time application of soluble dry program, designed to test the new Diamond R 5-1-5 CRF 180-day product along with a more affordable source of NPK at 150 pounds of nitrogen per acre per year
3) Control: Commercial grower standard applied as a granular fertilizer at 200 pounds of nitrogen per acre per year
Data collection will result in new recommendations for using CRF across Florida citrus-producing regions impacted by HLB. In the second-year data, fruit yield and juice quality were not different between treatments. There were also no differences in canopy size, but the study is continuing in its third year to determine responses with regard to fruit yield, juice quality and canopy size.
NITROGEN AND PHOSPHORUS STUDY
A multiyear study on nitrogen and phosphorus rates is still underway at 14 sites in Florida. Nitrogen (N) rates vary from 100 to 300 pounds per acre, while phosphorus (P) rates range from 0 to 80 pounds per acre. The work is being conducted at grower sites.
The study is being performed to determine the optimal N and P rates for improving citrus yields across different agroecologies. After three years of study, UF/IFAS researchers have not established significant differences in fruit yields and juice quality across rates, suggesting that even modest rates of N and P would be appropriate in citrus production systems impacted by HLB.
In addition, leaf levels for P were noted to be very high or excessive, especially in the Florida Panhandle. Therefore, growers can omit P in their fertilizer practices during select times of the year and apply when the P levels fall to low levels.
In all sites, most ammonium and nitrate nitrogen and phosphorus were observed to concentrate in the top 6 inches of soil, where 80% of the citrus roots are found. This showed that under current management, nutrient retention is significantly higher within the root zone than in the subsoil. However, lower subsoil concentrations suggest potential leaching beyond 18 inches, likely driven by high hydraulic conductivity. To monitor these potential losses, lysimeters have been installed below the root zone for future leaching assessment.
ORANGE PEEL POWDER BENEFITS
The application of orange peel powder as an organic fertilizer and soil conditioner constitutes a sustainable and effective strategy to enhance citrus plant development by promoting nutrient recycling and potentially improving orchard productivity (Figure 1). This residue is a source of primary macronutrients — such as nitrogen, phosphorus and potassium — and also provides secondary nutrients and micronutrients, including calcium, magnesium, sulfur, iron, zinc and manganese. Following soil incorporation, these elements are progressively released through microbially mediated decomposition and mineralization.
Moreover, orange peel powder can increase soil organic matter and cation exchange capacity, thereby enhancing nutrient retention and supporting longer-term nutrient availability to the root system. Effects are often more pronounced from the second application onward.
In addition to its nutritional contribution, orange peel powder may contribute to soil pH buffering and to improvements in soil physical and hydraulic properties, including increased water-holding capacity and enhanced aeration. This promotes a more favorable environment for root development.
Incorporation of orange peel powder can also stimulate the soil microbiota, increasing microbial biomass carbon and elevating the activity of enzymes such as catalase, urease and sucrase. Collectively, these enzymatic responses support nutrient cycling and the decomposition of carbonaceous organic matter.
In terms of vegetative development and yield, studies conducted in citrus groves have shown that the application of orange peel powder can result in up to a 30% increase in tree canopy volume, greater cumulative yield and improved average fruit weight at harvest.
Another relevant benefit is the natural biopesticidal and nematicidal action of citrus peels. Peels contain essential oils rich in limonene and other terpenoids with demonstrated toxicity against a range of pests and insects, thereby supporting ecologically-based phytosanitary management.
Orange peel powder optimizes the physiological performance of citrus plants and contributes to mitigating environmental problems caused by the improper disposal of industrial residues, promoting a more productive and resilient citrus production system.
CONCLUSION
The use of fertilizer blends should be considered for improving citrus production and fruit quality. Rate studies on N and P will help in determining the best rates for optimizing production and mitigating nutrient leaching. The use of soil amendments such as orange peel powder can improve nutrient cycling and availability in Florida sandy soils.
Acknowledgments: The authors are grateful to U.S. Department of Agriculture Hatch Projects 006185 and 006496, the UF/IFAS Citrus Initiative and the Florida Department of Agriculture and Consumer Services for support. Thanks also goes to the grower cooperators for conducting this research on their farms.
Davie Kadyampakeni is an associate professor; Jonas Pereira de Souza Junior, Edilaine Istéfani Franklin Traspadini, Shankar Shrestha and Alisheikh Atta are postdoctoral research associates — all at the UF/IFAS Citrus Research and Education Center in Lake Alfred.
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