CUPS Irrigation and Fertilization for Grapefruit

Josh McGillCUPS, Nutrition, Tip of the Week

By Rhuanito S. Ferrarezi and Mark A. Ritenour

Citrus under protective screen (CUPS) is a modern production system that excludes the Asian citrus psyllid and, consequently, the devastating disease citrus greening (huanglongbing or HLB) from plants cultivated in screenhouses. A recent study investigated the effect of different irrigation management strategies on fruit yield and quality of grapefruit grown in CUPS. Additionally, the best fertilization strategy was identified by comparing granular fertilizer application and fertigation.


Ray Ruby grapefruit grafted on US-897 rootstock was used in the irrigation trial and on sour orange in the fertilization trial, both planted in September 2013 at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Indian River Research and Education Center (IRREC) CUPS in Fort Pierce. Evaluations took place during the 2020–21 and 2021–22 seasons.

Treatments for the irrigation trial included:

  • Two production systems (100 × 120 × 14 feet enclosed screenhouses and open-air plots with ¼-acre each)
  • Two planting systems (in-ground with Riviera sandy soil and potted in 10-gallon plastic containers with peat moss/perlite substrate)
  • Three irrigation scheduling methods (daily crop evapotranspiration and two soil moisture sensor-based irrigation using 33% and 50% of soil maximum allowed depletion)

For the fertilization trial, three fertilization methods (daily fertigation, weekly fertigation and controlled-release fertilizer applied to soil three times per year) were tested.

In the irrigation study, trees grown under screen were free of HLB and had significantly greater trunk diameters (71.7 vs. 66.9 millimeters), canopy volumes (5.9 vs. 3.4 cm3), fruit yield (19,058 vs. 356 kilograms per hectare) and salable fruit (72.2% vs. 2.3%) with higher total soluble solids (9.5% vs. 7.1%) than those grown in the open air. In-ground trees had significantly greater trunk diameters (87.6 vs. 51.0 millimeters), canopy volumes (8.0 vs. 1.3 cm3), fruit yield (15,437 vs. 3,975 kilograms per hectare) and salable fruit (46.3% vs. 28.2%) than potted trees. However, the different irrigation management strategies tested here did not significantly influence trunk diameter, canopy volume, fruit yield or the quality of grapefruit cultivated under screenhouses over the two seasons.

In the fertilization method study, the treatments had no significant effects on trunk diameter, canopy volume, fruit sugars or acids, but daily fertigation applied to in-ground trees inside the screenhouses resulted in the highest fruit yield and percentage of salable fruit.

In summary, while different irrigation management strategies did not result in any difference in the parameters evaluated, daily fertigation applied to in-ground trees inside the screenhouses increased fruit yield and quality.

Learn about more CUPS research here.

Rhuanito S. Ferrarezi is an associate professor at the University of Georgia in Athens, and Mark A. Ritenour is a professor at the UF/IFAS IRREC in Fort Pierce.

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