Retailers and nonprofits in Illinois partnered for a second year of studies to measure the nutrients that are lost through tile drains. The group conducted tests in 37 sites across a nine-county geography.
“The data we collect 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) don’t want a mandate, and we’re voluntarily planning to decrease loss of nitrates and phosphorus from our soil by 45% by 2025. Our industry needs stakeholders that take ownership of the total environmental idea called ‘sustainability.’”
Each of the test sites drain directly into the Wabash River or Ohio River watersheds. Samples are pulled biweekly 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, iron, magnesium, boron, zinc, copper and manganese. Note that Environmental Protection Agency drinking water standards mandate no more than 10 parts per million (ppm) of nitrates, 0.1 ppm is maximum phosphorus for algae blooms, and it has no standard for phosphorus in drinking water.
“When you say you are going to decrease something by 45%, that seems like a huge number,” Wilson says. “But to meet that, we only have to manage 2% of the total nitrogen sold in the state. And when we look at nutrient loss, we need to look at all of the factors, including how nutrients work in the soil and in the plant.”
The group found that nitrate loss spiked 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.
Wilson says retailers and farmers should take note that this real-world study shows the value in split-nitrogen applications and nitrogen stabilizers.
Other notable observations from the study include:
- Spikes in nitrate levels and nitrogen applications are correlated, but nitrates were mostly below 10 ppm.
- Concentration levels of nutrients might be high even if there is a low flow rate entering the watershed.
- There needs to be a push for more nitrogen stabilizers and cover crops to minimize nutrient loss.
- The focus for phosphorus management should be on erosion control because phosphorus moves with soil.