Phosphorus is one of the most essential nutrients for plant growth. It also is one of the most challenging to manage responsibly. When applied efficiently, it supports lawns and landscapes as well as healthy crops. But when it moves off-site through runoff or drainage, it can contribute to harmful algal blooms and impair water bodies.
There are many pieces of the phosphorus puzzle. Agriculture, golf courses, residential lawn fertilization, urban stormwater, and septic systems can all contribute phosphorus loads to sensitive watersheds. The bigger issue is not who is applying it, but whether application rates reflect the soils and hydrology of a given region.
UF/IFAS research plays a key role in shaping state nutrient management guidelines, best management practices (BMPs), and grower recommendations. Recent research from the UF/IFAS Department of Soil, Water, and Ecosystem Sciences (SWES) makes a strong case for soil-specific phosphorus management.
Soil type matters
Florida is not dominated by one uniform soil type. Instead, it contains a wide range of soil orders, from sandy Entisols to highly acidic Spodosols to organic Histosols. Each one has a very different phosphorus chemistry. In some soils, it binds strongly to iron and aluminum minerals. In others, phosphorus can precipitate with calcium, becoming less soluble. And in organic soils, biological cycling can dominate phosphorus availability.
“Bioavailable phosphorus varies greatly across Florida soils,” said Vimala Nair, SWES research professor. “That means the same fertilizer practice can produce very different outcomes. It depends on the soil’s mineralogy, organic matter content, pH, and its capacity to retain phosphorus.”
Nair, along with Dinesh Phuyal and Lilit Vardanyan, conducted the research in her environmental soil chemistry lab. It is part of the work the state-funded UF/IFAS Nutrient Management Program has underway.
“In Florida, soil order matters,” said Phuyal, a postdoctoral research associate. “The same phosphorus number can mean different things depending on the soil system.”
Soil testing
Soil testing remains one of the most practical tools for nutrient management. But they measure the phosphorus that dissolves under specific chemical conditions; not necessarily the phosphorus plants will access throughout the growing season. That difference matters in Florida. A soil test that works well in one soil order may underpredict or overpredict plant-available phosphorus in another. This can lead to fertilizer recommendations that are not ideal for crop performance or for environmental protection.
“A soil test value is not universally meaningful unless you understand the soil context,” said Vardanyan, a biological scientist and lab manager.
She added that there are bioavailable phosphorus indicators which better relate to plant uptake than traditional soil tests such as the Mehlich procedures. Those include the iron oxide strip method and the Haney test.
Why “one-size-fits-all” fails
The review in 2025 by Phuyal and Nair provides an example of why universal phosphorus testing and management approaches often struggle in real-world conditions. Muck soils (Histosols) are highly productive, organic-rich soils used for high-value agriculture. However, they often contain large pools of legacy phosphorus, accumulated over decades of fertilization and cultivation. These soils behave differently because of microbial mineralization and immobilization, so traditional tests may not capture these seasonal processes well.
Phuyal and Nair also note that acidic extractants (such as Mehlich methods) may be chemically disrupted in organic soils. Also, commonly used tests such as water-soluble P or Olsen P may not accurately predict crop phosphorus needs.
“In muck soils, phosphorus availability is not static,” said Phuyal. “Biology plays a major role in what becomes available during the growing season.”
Environmental risk in systems
Both papers reinforce that phosphorus management is ultimately about balancing productivity with stewardship. When phosphorus moves into canals, lakes, rivers, and estuaries, it becomes a water quality concern. That is true regardless of whether it originated from agriculture, turfgrass systems, residential neighborhoods, or wastewater.
Additionally, some soil tests, such as Mehlich-3, may be weak indicators of immediate dissolved phosphorus loss risk. The issue is that those tests do not directly represent the soluble fraction most associated with runoff-driven eutrophication.
“The goal is not simply measuring phosphorus,” Nair points out. “It’s understanding which soils can retain it and which soils allow it to move.”
Path forward
Better phosphorus management not only protects water quality but can also reduce fertilizer costs and improve crop efficiency. The research points to the need for regionally calibrated assessment tools. Those must incorporate key soil properties such as pH, organic matter, and P-binding elements like iron, aluminum, and calcium. Another tool, the Soil Phosphorus Storage Capacity (SPSC) is a promising environmental indicator but also requires local validation.
“Applying phosphorus is not the problem—some plants require it,” Phuyal said. “The challenge is understanding a soil’s chemistry and its ability to retain phosphorus. Then you can determine application rates.”
“The future of phosphorus management is not a single test or a single recommendation,” Nair added. “It’s understanding how each soil system behaves.”
You can read the two journal articles here:
The dynamics, analysis, and sustainable management of phosphorus in muck soils: a review. Frontiers in Environmental Science.
Featured image of a potato field soil sampling site in Hastings, FL, by Vimala Nair.
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