Phosphorus is an essential nutrient for plants, but too much can mean trouble for waterways.
Phosphorus is critical to plant health and growth by helping the development of root and increasing resistance to disease.
Pastures normally get phosphorus through fertilization because “the natural weathering of rock is not sufficient to assure the high crop yields necessary,” said Dirk Philipp, an assistant professor for the University of Arkansas System Division of Agriculture.
In pastures, phosphorus tends to be concentrated in areas where grazing animals spend more time such as travel lanes, ponds, shade and hay-feeding areas, he said.
When excess phosphorus washes into streams can cause eutrophication, Philipp said. In eutrophication, excess phosphorus promotes the growth of algae and oxygen depletion in lakes, leading to fish kills, he said. Other impacts of eutrophication include the decline of biodiversity, change in species dominance and toxicity of the water.
Philipp suggested a couple methods that farmers and producers can do to retain phosphorus on the farm and pastures.
The levels of phosphorus need to be monitored closely, he said. Testing different parts along the site is helpful because some parts need higher phosphorus levels than other.
“Levels above 100 pounds per acre are considered high,” he said.
Avoid applying phosphorus fertilizer before heavy rains.
Keep heavily used areas away from sites prone to get run-off. Install buffer zones along streams to slow runoff.
“Those buffer zones don’t have to be fancy,” Philipp said. “A single polywire will work and cattle can still graze those areas when the soil is dry.”
In order to filter out sediments and hold back runoff, grass strips can be used. These strips can be established in low-laying areas of pastures where runoff after heavy rains would naturally occur.
Avoid overstocking and muddying up of grazing grounds, he said. Keep forage canopy at 4 inches or more to prevent bare soil.
Moving feeders and hay rings regularly can help distribute phosphorus. Managing the distribution of phosphorus for grazing pastures is important because the ingested phosphorus will be excreted in a concentrated fashion, he said.
For more information about pastures, soil test, and water pollution, visit www.uaex.edu, or contact your county extension office.