Jay Capasso, UF/IFAS Columbia County. Bob Hochmuth, UF/IFAS NFREC-SV. Luke Harlow, UF/IFAS Union County. Kelly Aue, UF/IFAS NFREC-SV.
Petiole Sap testing is an educational tool and service provided to vegetable growers in the Suwannee Valley region of North Florida by UF/IFAS Extension. Using portable meters, UF/IFAS Extension agents provide vegetable growers information on the current nitrogen and potassium nutrient status of their crop. This information is beneficial for growers and allows them to identify whether their crop nutrient status is deficient, adequate, or excessive. Adjusting nitrogen and/or potassium rates based on petiole sap test results prevents the limiting of yield from insufficient fertilizer use and unnecessary increases in input costs from excessive application of fertilizer. The information is also helpful from an environmental perspective, helping growers avoid the loss of excess nitrogen to the environment. The most common crop the petiole sap testing is implemented on in the Suwannee Valley region is watermelon.
The petiole sap testing methodology involves sampling petioles of the most recently matured leaf (usually the 5th or 6th leaf from the tip of a watermelon vine) from at least 5-6 representative locations of a field. The petioles are then squeezed in a garlic press to create a sap. The sap is analyzed using calibrated portable meters to determine the nitrate-nitrogen, and potassium content. The results are compared to optimum ranges for the current growth stage of the crop which have been pre-determined based on University of Florida research.
For more information on petiole sap testing see link to UF/IFAS Extension article and video below:
Plant Petiole Sap-Testing for Vegetable Crops: CV004/CIR1144
Watermelon Petiole Sap Testing Video: