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Summary of Five UF/IFAS Controlled Release Fertilizer Studies in 2019 and 2020

By Robert Hochmuth, Regional Extension Agent- Vegetable Crops,

UF/IFAS, North Florida Research and Education Center- Suwannee Valley, Live Oak, FL

Research Trial Design

This summary report is for the two years of research on the use of controlled-release fertilizer in watermelon. The full reports are available on the FWA website. Funding for these trials was provided by Florida Watermelon Association and FDACS, Office of Ag Water Policy, as well as in-kind support from Harrell’s Fertilizer, Waters Agricultural Labs, Clifton Seeds, and Syngenta Seeds. The objective of this two-year project was to evaluate using a controlled-release nitrogen source of fertilizer as an alternative to conventional, more soluble, sources of nitrogen in-bed fertilizers. We measured the movement of nitrogen over time in these studies by taking multi-depth soil samples and analyzing for nitrate- N.


The performance of CRF was similar to or better when compared to the current BMPs for conventional watermelon yield. We saw slightly higher early yields in the two trials with a complete analysis, full-season CRF in the bed. We did not see any significant difference in total yield in any of the two trials where both fertilizer and irrigation rates varied. Both conventional and CRF treatments resulted in very low leaching of N at the lower depths below the root system in a well-managed drip irrigation schedule.

Overirrigation during the early part of the season typically results in the highest risk of leaching of soluble fertilizer below the root zone. During the end of the season, nitrate-nitrogen levels in all five studies were very low in the deeper samples indicating most residual nitrogen had been used by the crop and very little was left to be leached from the soil below 36 inches. The 2020 CRF and irrigation rate study tends to support the higher likelihood of leaching nitrogen when overirrigation occurs. The results of the single on-farm study indicate both conventional and CRF programs can be used in a well-managed production system and result in very little or no nitrate-N leaching below the watermelon root zone throughout the season, and at the same time, attain very high yield (over 60,000 lbs per acre).

This collective data verifies the effectiveness of well-managed BMP practices for irrigation and nutrient management implemented on this watermelon farm, whether using conventional or CRF sources of nitrogen when no leaching events occur. The additional cost of CRF will have to be considered in moving forward with a BMP program. But these five trials, combined, confirm there are environmental benefits in seasons when leaching rain events or when overirrigation occurs while still maintaining very high yields.

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