Photo by Alisheikh Atta
By Davie Kadyampakeni, Noor Basar, Alisheikh Atta, Muhammad Shahid, Shahid Iqbal and Alan Wright
Citrus trees in Florida impacted by HLB have limited nutrient uptake largely due to limited root mass, compromised physiology and extremely sandy soil. The state’s current nutrient management guidelines were developed based on data prior to the spread of HLB, when trees had dense canopies and healthy root systems. There was a growing need to update nutrient recommendations based on field research. The key objectives of a University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) multisite study was to assess the different rates of nitrogen and phosphorus in oranges, grapefruit and satsuma mandarins and to assess the timing of nitrogen applications in satsumas grown in the Florida Panhandle.
UF/IFAS researchers compared rates varying from 100 pounds/acre to 300 pounds/acre of nitrogen and 0 to 80 pounds/acre of phosphorus. They also compared three, five and seven splits of nitrogen application in satsumas.
A key finding is that one size does not fit all. For example, soil phosphorus levels were noted to be in the sufficiency or excess levels in the soil and leaf analysis in the Florida Panhandle. This suggests that depending on the test, phosphorus might have to be omitted or reduced in grower nutritional programs. The split application suggested that more frequent application splits work best in promoting nitrogen-use efficiency, confirming earlier observations with healthy citrus trees.
In Central, Southeast and Southwest Florida, researchers observed elevated or high phosphorus levels in the soil but low concentrations in the leaf tissues, suggesting limited acquisition. This scenario is expected where there is low pH. The remedy is to apply lime to raise the pH to a desirable range of around 5.8 to 6.5. When the pH is high, it is typically recommended to apply some acid, elemental sulfur or acid-forming fertilizers to lower the pH.
While the fruit yield trends and quality have been inconsistent due to hurricanes and diseases, UF/IFAS researchers are working on assessing the economics and fruit quality and will share the results in the near future.
Acknowledgment: The authors are grateful to the Florida Department of Agriculture and Consumer Services for financial support of the project.
Davie Kadyampakeni is an associate professor, Noor Basar is a graduate student, and Alisheikh Atta is a postdoctoral research associate — all at the UF/IFAS Citrus Research and Education Center in Lake Alfred. Muhammad Shahid is an assistant professor, and Shahid Iqbal is a postdoctoral research associate — both at the UF/IFAS North Florida Research and Education Center in Quincy. Alan Wright is a professor at the UF/IFAS Indian River Research and Education Center in Fort Pierce.
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