By Clint Thompson
It is time for petiole-sap testing or leaf tissue analysis for watermelon producers in North Florida.
Bob Hochmuth, University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Regional Specialized Extension agent in Live Oak, Florida, discusses the testing service that UF/IFAS Extension provides to growers.
“We collectively provide a service of going out and running petiole sap test for all of the watermelon farmers. They’ll pull the samples. Sometimes we’ll pull the samples, but the service that we’re providing is the actual running of it,” Hochmuth said. “It’s geared only towards nitrogen and potassium. Those are the two nutrients that once (growers) start doing fertigation, those are the two nutrients they are going to be fertigating with. They don’t apply any more phosphorous or micronutrients during the season unless something goes wrong.
“From the BMP (Best Management Practice) world, it’s a really good way for us to help them not apply nitrogen or potassium unless they absolutely need it. Let’s say you’ve got some bed fertilizer put down, and with these leaching rain events that we don’t really know how long that’s going to last before you would start your fertigation program … this process will tell them you don’t need to start yet. Or once they start, we have a program that tells them how many pounds per acre per day they need to be thinking with their liquid fertigation program.”
UF/IFAS recommends nitrogen levels be between 1,200 and 1,500 ppm and potassium levels be between 4,000 and 5,000 ppm at first flower for plant petiole sap tests.
For whole leaf analysis at first flower, nitrogen levels should be between 2.5% and 3.5%, while potassium levels should be between 2.7% and 3.5%.
Sample collection is the most significant part of the process. Samples should not be taken from areas that are suffering through disease, cold, disease or a drought. UF/IFAS recommends samples of the most recently matured leaf. Collect between 15 to 20 full leaf samples to be submitted in paper bag.
Once petioles are collected, remove the leaf blade from the petiole only, put in plastic bags and immediately test. If not testing until later, samples should be stored with a little ice or refrigerated.
