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UF research: Recycle phosphorus before it goes into public waters – and save millions

IMMOKALEE, Fla. — Recycle phosphorus while it’s still on the farm, and you can help prevent the nutrient from flowing downstream — where it could pollute water bodies — says a University of Florida scientist.

Reusing phosphorus using on-farm ponds can cost the state less than $40 per kilogram compared to $355 to $909 to treat the phosphorus before it goes downstream, according to a new study led by Sanjay Shukla, a UF/IFAS professor of agricultural and biological engineering.

The study was published recently in the journal Science of The Total Environment. The idea is to harvest the plants inside ponds, compost them and provide them to the growers for use at no cost. This recycling treats phosphorus at 90% less cost compared to what the state is spending to meet the phosphorus concentration goals in the Everglades.

Farmers need compost to grow crops, and the compost contains nutrients such as phosphorus and nitrogen. Farm-pond, considered a water quality best management practice, is required for croplands in South Florida to reduce downstream flooding. The nutrient has been building up in those ponds for years, and in some cases, it is ready to flow downstream. Making compost from plants helps keep the nutrient within the farm.

“The idea is to close the loop on nutrients,” said Shukla, a faculty member at the UF/IFAS Southwest Research and Education Center in Immokalee, Florida. “You apply fertilizer containing phosphorus to grow crops. Regardless of how good of a job you do at farming, there will always be some nutrients lost with the farm drainage that ends up in the pond, and part of it will eventually go downstream.”

“Using this system, phosphorus lost to drainage is brought back to fields as organic fertilizer,” Shukla said. “Moreover, when you apply compost you also increase a farm’s water- and nutrient-holding capacity to further reduce nutrient losses.”

To come to their conclusions in the new study, Shukla and his colleagues collected data from two farms in Hendry County – one grew sugarcane, the other, vegetables — in Florida’s Everglades basin. Researchers estimated nutrient treatment and costs by using results from their previous studies to evaluate how effectively the on-farm ponds treated farm drainage emptying into the pond.

Findings from the new UF/IFAS research show compost can increase the phosphorus retention rate in these ponds from 50% to 77% for farms that produce fresh vegetables.

So, as he moves forward, Shukla says what is needed is to field-verify the recycling concept through a pilot project for larger adoption.

“Using these farm ponds to provide additional environmental services through a public-private partnership is a win-win and sustainable option,” Shukla said. “We hope the state can pay farmers to treat nutrients economically, using existing infrastructure.”

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The above image was taken prior to national guidelines for face coverings and social distancing.

The mission of the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS)
is to develop knowledge relevant to agricultural, human and natural resources and to make
that knowledge available to sustain and enhance the quality of human life. With more than
a dozen research facilities, 67 county Extension offices, and award-winning students and faculty
in the UF College of Agricultural and Life Sciences, UF/IFAS brings science-based solutions
to the state’s agricultural and natural resources industries, and all Florida residents.

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