Lake Erie often garners national attention for its algae blooms. The Great Lake, which is near David Myerholtz’s farm, constantly weighs on his mind. In fact, it was a driving force in his decision to address the levels of accumulated phosphorus (P), also known as legacy P, on his Gibsonburg, Ohio, farm.
Myerholtz has cut overall P use at least 20% in the last decade by tapping into legacy P and adhering to the 4R principles: the right fertilizer source, at the right rate, at the right time and in the right place.
“This legacy P issue haunts us,” he says. “We’d like to use even more, but the soil doesn’t readily release it for crop uptake.”
There are two types of phosphorus in soils: Bray P1 and Bray P2. The former is quickly taken up by crops and can dramatically boost yields. Bray P2 is not readily available to crops as it tends to bind tightly with soil particles.
Both forms will show up in nutrient runoff, an issue that perplexes farmers, says Anne Cook, senior environmental, health and safety manager for The Andersons.
“Farmers and retailers know they’re using less P, so there’s sometimes a gap of understanding about why it’s still coming out of the drainage tiles at the same levels as before,” Cook explains.
No Silver Bullet
Unfortunately, there is no silver bullet to fix legacy P, says Lamonte Garber, Watershed Restoration Coordinator for the Stroud Water Research Center, Avondale, Pa. “A farmer’s ability to draw down the nutrient requires multiple strategies that work together,” he notes.
Some strategies include growing cover crops to extract nutrients and sequester organic material and using soil tests to identify where accumulated P is located so farmers can more accurately tap into it.
Patience with Phosphorus
The draw-down process takes time, however. “You should be able to detect and quantify the amount of phosphorus dropping in your soil in a three- to five-year period,” says Adam Lovelace, director of farm centers for The Andersons.
Better phosphorus management can help protect the long-term viability of farms, Garber notes.
“We don’t know where regulations will go in the future,” he says. “We don’t want farmers backing themselves into a corner with high soil phosphorus levels that could become one of those things a future buyer might look at.”
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