By CELESTE BAUMGARTNER
COLUMBUS, Ohio—Heidelberg University has been monitoring Maumee River water, which flows into Lake Erie, for 45 years. Last April, something weird was going on which could affect harmful algal blooms (HABs). It will be a topic for discussion at the March 3-4 Conservation Tillage and Technology Conference in Ada.
When Laura Johnson, director of the National Center for Water Quality Research at Heidelberg, started looking at the numbers, she was puzzled.
“We were getting a lot of storm events,” Johnson said. “Looking at the raw data, the (phosphorus) concentrations weren’t getting as high as they normally do during storm events. Typically, every summer, the dissolved phosphorus (DRP) concentration increases, and then it comes back down.”
Something is weird, Johnson told a colleague. Particulate phosphorus was high because the rain caused plenty of erosion, but the DRP was lower than expected.
Particulate phosphorus is phosphorus associated with the soil particles, Johnson said. DRP is the phosphorous that one can’t see, but it is easy for algae to use because it’s like the “sugar” of the phosphorous world.
“Flow was high; particulate phosphorous was still really high because we had plenty of erosion,” Johnson said. “But the dissolved phosphorous was lower than expected. This information might be important. Our forecasting has been biased towards dissolved phosphorous.
Based on flow, researchers expected last year’s bloom to be around 10 on a scale of 1 to 10. Instead, it was from 7 to 7.5. Still high, but not as high as expected, Johnson said.
Meanwhile, Greg LaBarge, Ohio State University Extension field specialist, did some surveys. He found that much less fertilizer was applied in the region from October 2018 through the end of May 2019.
“A lot less nutrient went on the soil,” LaBarge said. “Some of our ag practices, such as fertilizer application, even crop reduction had to be a part of that reduction we saw in DRP. But we still had enough phosphorous going down that there was a significant bloom.”
This indicates that there’s still phosphorous available in the soil, in addition to phosphorus stored in ditches, stream banks, the whole watershed system, which ends up in Lake Erie.
“It is going to take other practices than just thinking about nutrient management,” LaBarge said. “We need to think about water management practices; drainage water management, filtering phosphorus out of the water at the edge of field, wetlands and other practices that change the water leaving fields.”
Johnson agrees that more creative thinking is needed. Many farmers are applying maintenance phosphorus, just as much as the crop will use. Yet studies show that even then, soil test levels don’t vary much from year to year.
“Some farms haven’t applied phosphorus in 5 to 10 years, yet there is just a tiny decrease in soil test levels,” she said. “Why would dissolved phosphorus have gone down so much (last year)? I don’t think it is because suddenly the pool of phosphorus in the soil is depleted.”
Instead, Johnson thinks it is a placement issue. The evidence here and from other places has shown that with conservation tillage, paired with broadcast applications of fertilizer, researchers see reductions in DRP. Subsurface fertilizer injection, or getting the nutrient deeper into the soil in the row where the crop needs it, may be the way going forward.
LaBarge and Johnson will be talking more about this topic at the March 3-4 Conservation Tillage and Technology Conference at the McIntosh Center. They are among 65 presenters. For information visit fabe.osu.edu/CTCon.