The Big Florida Fertilizer Update

Web Admin Citrus, Fruits, Vegetables

By Frank Giles
Fertilizer recommendations
Sen. Ben Albritton spearheaded the legislation (SB 1000), which secured funding for the fertilizer updates.

Outbreaks of blue-green algae and red tide in recent years have put the spotlight on the use of fertilizer in agriculture. Environmental groups have blamed agriculture for being a main source of nutrient pollution that has caused water-quality problems. Folks in agriculture know it is more complicated than that and they need new data to support their cause.

Wrapped up in this debate has been the state’s best management practices (BMPs) program, which growers follow to be considered in compliance with water-quality standards. The Florida Department of Agriculture and Consumer Services (FDACS) administers the program.

With increased inspections and scrutiny of the BMPs program, FDACS has been reporting some growers have been applying more than the recommended amounts of fertilizer. Those recommendations come from the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS).

Recent legislation has directed FDACS to more frequently update the manuals that the BMPs programs for various crops are based upon. The research BMPs are based upon is decades old in many cases.


During the 2022 Florida legislative session, $8.8 million in funding was allocated to UF/IFAS to update fertilizer recommendations via Senate Bill 1000. These recommendations will be reflected in updated BMPs manuals.

Research in the first year will focus on five priority crops identified by the Legislature: tomatoes, potatoes,

citrus, grain corn and green beans. Hemp and forage grass will also be studied. Most of the work will be done with grower-cooperators in their fields, and it will cover production areas across the state, from the Panhandle to South Florida.

UF/IFAS is slated to begin this work in late summer. Tomato and potato research will build on work started in 2021, supported by previous FDACS funding. The new $8.8 million allows UF/IFAS to continue this research and expand it to additional crops at different locations across the state.

Thomas Obreza, senior associate dean for UF/IFAS Extension, is leading the project to update nutrient recommendations. He characterized the state’s funding as a shot in the arm for the needed research.

“The amount and purpose of the state financial assistance UF/IFAS will receive for soil fertility work is unprecedented in my 33 years with the university,” Obreza says. “Nutrient management work is usually on the back burner of funding agencies. We have received some funding of this type from FDACS in the last 25 years, and we thank them for that. What we are about to receive is an order of magnitude higher, in just one year. It has given us the ability to start or continue 14 unique projects covering several commodities across the state. This has never happened before.”

The research updates will focus on nitrogen and phosphorous. Both of those elements are important for successful crop production, but they are also linked to Florida’s water-quality issues. Obreza says UF/IFAS recommendations should consider the ability of a grower to achieve maximum economic production, but also to minimize nutrient losses by improving fertilizer-use efficiency.


The 4Rs concept of nutrient management has been a model for smart agriculture for many years. The Rs stand for: right source, right rate, right time and right place. The concept posits that growers following the 4Rs will maximize economic production while minimizing potential nutrient pollution.

Obreza says the new research will add a fifth R to the equation to include irrigation.  “Nutrient and water management are intimately linked in Florida crop production,” he says. “We have projects studying irrigation/nutrient management interactions and/or fertigation with tomato, potato, snap beans and citrus in Central and South Florida.”


One of the criticisms of the current BMPs recommendations is that they do not reflect the various conditions and soil types where growers plant their crops. SB 1000 funding specifically addresses this flaw. The legislation reads: “UF/lFAS shall analyze the use of site-specific nutrient management for Florida crops and shall develop a research plan and interim recommendations for implementation of site-specific nutrient management.”

“It is clear what the legislature wants. The tricky part is defining what site-specific means,” Obreza says. “Is it a row, a block, a field, a farm, a soil type, a watershed? FDACS will be involved with that determination. Whatever the answer is, it will be important to relate site-specific recommendations to zones a producer can manage in a practical sense. Some of our projects have elements that relate to site-specific nutrient management, particularly artificial intelligence.”


Thanks to funding from FDACS, some work is underway for tomato and potato. One year of research has been conducted already in growers’ tomato and potato fields on soil test phosphorus calibration and crop response to phosphorus fertilizer rates.

“Those data are still being compiled, but I can hint that there have been some interesting results we did not expect,” Obreza says. “We will have to wait until all data analysis is complete before we can report on these studies. Our new funding will allow us to repeat these studies starting in the fall. Additionally, we will start projects with citrus this summer, snap beans in the fall and grain corn next spring. We also will have work involving hemp, limpograss and cotton.”

Fertilizer recommendations
Updates to Florida’s citrus fertilizer recommendations are needed to reflect the influence of HLB on tree health. Current recommendations are decades old.


Obreza says the introduction of HLB changed the whole ball game when it comes to nutrition of citrus trees. That’s because all of the fertilizer recommendations were derived from work on healthy trees.

“It became clear that UF/IFAS must revisit management of all nutrients for HLB-affected citrus,” he says. “We have made some progress with calcium, magnesium and micronutrients, and changes to our recommendations for those nutrients are due soon. We need much more work on nitrogen, phosphorous and potassium nutrition. This summer, thanks to our new funding, we are starting a statewide project in commercial Ridge and Flatwoods citrus groves to do just that. We will also do similar work with cold-hardy citrus in the Panhandle, which is an entirely new area for us.”


As the new nutrient research comes in, that data will be converted into recommendations. UF/IFAS has a Plant Nutrient Oversight Committee (PNOC) composed of administrators, researchers and Extension specialists.

“Faculty who want to change a UF/IFAS recommendation bring their proposals to PNOC, which has final decision-making authority,” Obreza says. “Faculty share their research results with PNOC, providing unbiased, scientific evidence for new recommendations. Approved changes will be integrated into our recommendation literature. We are seeing some changes this year, with more to come in future years as research is completed. Nutrient management research typically takes at least two years to generate enough data, but three years is better.”