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Source: U. of Illinois natural resources and environmental sciences researcher Lowell Gentry

U. of I. natural resources and environmental sciences researcher Lowell Gentry describes the pros and cons of various strategies to reduce nitrate runoff from agricultural fields.
Agricultural runoff from Midwestern farms is a major contributor to a vast "dead zone" in the Gulf of Mexico. Nitrogen, phosphorous and other farm nutrients drain into the Mississippi River, which empties into the Gulf, spurring algae to overpopulate and suffocating other aquatic life. Illinois is a main culprit in this ongoing environmental blight. News Bureau life sciences editor Diana Yates spoke with U. of I. natural resources and environmental sciences researcher Lowell Gentry about possible solutions.

How big is the Gulf of Mexico dead zone today and how much does Illinois agriculture contribute to the problem?

Last summer, researchers at Louisiana State University measured the dead zone in the Gulf at 6,334 square miles, which was larger than its historical average. The largest ever measured was 8,776 square miles in 2017. In Illinois, nonpoint sources (of which, agriculture is, by far, the greatest) contribute 80% of the nitrogen and about half of the phosphorus to our rivers and streams. Illinois and Iowa are the greatest contributors of nutrients to the Gulf and both states have developed nutrient loss-reduction strategies, with the goal of reducing nitrogen and phosphorus losses by 45% by 2035.

We've known about this problem for years. Why is Illinois still struggling to reduce nutrient runoff from farms?

The answer is complicated. Many people think that nutrient losses from farm fields are simply a matter of excessive fertilizer application and that farmers just need to use less. In one of our tile-drainage studies, we used only 75% of the full nitrogen fertilizer rate on corn. This reduced grain yield by 10% but had little effect on tile nitrate losses over the course of the study.

There is no doubt, however, that the timing and method of nutrient application can have a great effect on nutrient losses in the tile-drained regions of the state. For example, our studies show that much more nitrate is lost to the tiles when nitrogen fertilizer is applied in the fall rather than in the spring, just ahead of corn planting.

Soybean production also aggravates nitrate losses to tile-drainage systems. We believe this nitrate forms as a result of microbial decomposition of crop residues and soil organic matter when the soil microbial community runs out of easily accessible carbon. The nitrate that forms during the nongrowing season is susceptible to leaching losses. This is a leak in the system that is not being addressed.

There are many state programs to encourage farmers to address the problem. Do some programs work better than others?

It's way too early to see an effect of conservation efforts on the Mississippi River Basin as a whole. Closer to home, we have been sampling the Embarras River at Camargo, Illinois, for 30 years and see little evidence of water quality improvement during this time. However, we are still in the baseline phase of this long-term monitoring project because there are few conservation practices on the ground here in central Illinois that could bring about the dramatic change sought.

Three programs here are moving farmers toward greater adoption of conservation: Fall Covers for Spring Savings, the Illinois Department of Agriculture's cover crop program; Saving Tomorrow's Agriculture Resources, a Champaign County Soil and Water Conservation program that teaches farmers about nutrient stewardship; and Precision Conservation Management, a program developed by the Illinois Corn Growers Association that aims to help farmers reap the economic benefits of engaging in conservation practices.

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