When I saw the headline “Tile drains a major path for phosphorus loss” in a respected Agronomy Society journal, I cringed. Nitrates are a big enough challenge, and previous research showed that phosphorus in tile lines was at extremely low levels — like 1% of the amount applied to fields, which was not an issue.
Well, according to recent USDA-ARS research studies in Ohio and Indiana, what has changed is the understanding of what happens in lakes at those low phosphorus levels. Research shows that a tile system carries away as much phosphorus as surface runoff. The report states that “90% of that low 1% to 2% concentration of phosphorus exceeded 0.03 parts per million, the recommended limit for curtail- ing blooms of toxic and nuisance algae.”
However, the researchers also caution that P transport in tile is NOT the “smoking gun” in Lake Erie’s algae problems.
Farmers, from an agronomic perspective, are doing great keeping phosphorus loss as low as 1% to 2%. The challenge, according to University of Arkansas phosphorus expert Andrew Sharpley, “isn’t so much the magnitude of the losses, or even the tile system itself; it’s the extent to which tile drainage has been implemented by farmers.”
Tile drainage is important, as 48.6 million acres are drained by tile, accoring to the 2012 USDA census. As Ohio USDA researcher Kevin King states in the story, “If we don’t have tile drainage, we cannot farm this landscape. So what we have to do is figure out how to work with it.”
The solution is the tricky part, because little amounts add up to larger amounts. Soil has a natural ability to bind P, so when surface-applied, it binds to the top half-inch of soil, but can be eroded on particles without good soil cover. If P is mixed or injected into the soil, surface loss is reduced.
There are a few innovative practices being tested to manage drainage water and reduce nitrates and P. Saturated buffers show big promise
(tile water filtered by stream buffers: see stories at bit.ly/1seoO2R and bit.ly/ Leoy4C). And an inline water level control structure that holds tile water shows potential in fields without much slope, at bit.ly/1x3R0cW.
There are no easy or inexpensive solutions. It’s not a perfect science where one solution fits all. Sediment comes from other sources (a large percent comes from streambank erosion). Reductions using less tillage or more tillage don’t fit everywhere. There’s a lot of leased land with landowners who only expect revenue, not spending. And the list goes on.
Farmers are willing to do what’s right. We just need to find the right fit for the myriad of soil and watershed environments that exist.
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