Illinois Studies Nitrate and Phosphorus Loss from Tile Lines

A partnership of non-profits and retailers joined together for the second year in Illinois to determine just how much nutrients are lost through tile drains. The group tested in 37 sites across a nine county geography.

“The data we collected helped growers make decisions pertaining to the Illinois Nutrient Loss Reduction Strategy [a voluntary program],” says Mike Wilson, with Wabash Valley FS, a partner in the study. “We [Illinois] didn’t want to be mandated and we’re planning to decrease loss of nitrates and phosphorus from our soil by 45% by 2025.”

Each of the sites tested drain directly into the Wabash River or Ohio River watersheds, with samples pulled bi-weekly from March 16 to July 20. Farmers involved in the study kept their anonymity. Fields tested were mostly corn and soybeans with more subsurface tile than surface inlets, less than 40% used nitrogen stabilizers and only two of the 37 fields used cover crops.

Water from the tile lines was tested for ammonium, nitrate, phosphorus, potassium, calcium, sulfur, magnesium, iron, boron, zinc, copper and manganese. Note EPA drinking water standards say there cannot be more than 10 PPM of nitrates, .1 PPM phosphorus for algae blooms and has no standard for phosphorus in drinking water.

The group found that nitrate loss did spike past the 10 PPM threshold a few times, but not more than 14 PPM and that phosphorus has little to no movement through tile lines.

Other notable observations from the study include:

  • There is a noticeable correlation between spikes in nitrate levels and nitrogen applications, but for the most part stayed below 10 PPM threshold
  • Making multiple nitrogen passes, instead of just one, reduced overall loss and boosted nitrogen use efficiency
  • Tile flow rate should be considered, even though concentration levels of nutrients might be high if there is a low flow rate little enters the watershed
  • Those testing said there needs to be a push for more nitrogen stabilizers and cover crops to minimize nutrient loss
  • Study showed very little phosphorus loss through tile lines, indicating the focus for phosphorus loss management needs to be on erosion control since phosphorus moves with soil

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