By Davie Kadyampakeni, Muhammad Shahid and Alisheikh Atta
Current citrus nutrient guidelines are based on studies of healthy citrus trees conducted in the pre-huanglongbing (HLB) era. These guidelines may no longer be valid for the present situation where 100% of mature citrus trees in Florida are HLB-affected.
Scientists at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) are conducting research on different nitrogen (N) and phosphorus (P) rates for young and mature citrus cultivars. This includes sweet oranges (Hamlin and Valencia), grapefruit and Satsuma mandarins. The project is evaluating five rates of N (100, 150, 200, 250 and 300 pounds per acre per year) and five rates of P at 0, 10, 20, 40 and 80 pounds of P2O5 per acre per year. The objective is identifying the appropriate site-specific rate of N and P for HLB-affected citrus trees. Scientists are using site soil characteristics and production practices to determine if the current guidelines for N (200 pounds per acre) or P2O5 (15 pounds per acre) need to increase or decrease.
Using conventional and controlled-release fertilizer sources, researchers should be able to develop and provide site-specific N and P guidelines for young and mature citrus trees of sweet oranges in Central and Southwest Florida, grapefruit in the Indian River district and satsumas in North Florida.
Early results show no differences in fruit yield and juice quality, though nutrient levels appear more concentrated in the upper 6 inches compared to lower depths (Figure 1). In satsumas, high P levels have been observed in the Panhandle (Figure 2). More data are being generated on water quality, canopy size and costs/revenue. Optimal fertilizer rates should be determined after a few years of this work, and updates will be shared at the Citrus & Specialty Crop Expo, Florida Citrus Show and Florida Citrus Growers’ Institute.
Davie Kadyampakeni is an associate professor, and Alisheikh Atta is a postdoctoral associate, both at the UF/IFAS Citrus Research and Education Center in Lake Alfred. Muhammad Shahid is an assistant professor at the UF/IFAS North Florida Research and Education Center in Quincy.
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