Graphic Courtesy UF/IFAS

Michael Dukes: Effectiveness of Fertilizer Ordinances | Guest Column

February 9, 2024

In the 2023 legislative session, UF/IFAS was tasked with the following: “…evaluate the effectiveness of the timing of seasonal fertilizer restrictions on urban landscapes toward achieving nutrient target objectives for waterbodies statewide.” In addition, the legislature imposed a moratorium on new fertilizer ordinances through June 30, 2024. There are at least 134 local governments that have fertilizer ordinances. These ordinances are also called fertilizer "bans", "restricted periods", "blackout periods", or similar. The main idea for most of them is that fertilizer application is restricted in periods where loss of fertilizer is more probable, for example summer rainy periods. However, there have been a couple instances of winter fertilizer bans. The final report can be found HERE.

Nine CLUE faculty and staff scoured the scientific literature for studies related to landscape fertilizer and water quality. A total of 111 sources were cited in the report; however, only six studies (5 in peer-reviewed scientific literature) were identified as directly reporting on the efficacy of fertilizer ordinances in Florida. Thus, this topic has been largely unstudied as to the effectiveness of fertilizer ordinances on water quality outcomes.

While the ordinances are well intentioned, landscapes and aquatic systems are dynamic and complicated with respect to nutrient dynamics. In addition, there are many sources of nutrients ranging from natural, such as in rainfall or in plants, to those attributed to man, such as fertilizer and septic systems. Plant and animal life need nutrients to survive; however, when nutrients, either nitrogen or phosphorus, are present in excess, negative water quality responses can occur such as algae blooms. Linking landscape fertilizer to water quality effects is complicated by the many sources of nutrients in a watershed, hydrology of the watershed, varying conditions over time as land development changes and weather variability.

Though, some critics have said that the report is not concerned with nutrient pollution or that the report says that nutrients are not a problem, they could not be further from the truth. It’s likely that there are multiple sources of nutrient runoff that contribute to nutrients leaching into groundwater and contributing to a negative effect on aquatic ecosystems. However, the extent of that nutrient runoff being linked to landscape fertilizer is not known. Furthermore, whether this loss of nutrients impacts aquatic ecology is not known as well. The outcome of not having evidence to answer the question of fertilizer ordinance effectiveness does not mean there is no concern or that nutrients are not a problem. It just means that we don't have adequate information to tell whether fertilizer ordinances have a specific effect on water quality.

The authors of the report recommend a detailed study of this topic. Such a study would ideally encompass a comprehensive monitoring program across multiple watersheds. This study would quantify nutrient sources, transport, and fate as well as ecological response. Our team would welcome a discussion with funding agencies to scope out this type of project.

Michael Dukes is the Director of the UF/IFAS Center for Land Use Efficiency (CLUE), which focuses on social, environmental, and economic issues affecting urban landscapes and agriculture in Florida.  

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