Flushing phosphorus down the drain tile

Learn more about practices to keep phosphorus in your field and out of the water.

Sometimes we get wrapped up in borders, but water doesn’t honor these boundaries. Our neighbors in Canada have been great partners in the research and application of nutrient reductions to help with the cleanup of Lake Erie from harmful algal blooms. Recently, Merrin Macrae, from the University of Waterloo in Ontario, joined Michigan State University Extension educator Monica Jean and me on the “In the Weeds” podcast to discuss nutrient losses in field crops.

Cover crops can help hold on to nutrients

Macrae specializes in water quality in the Great Lakes and specifically the impacts of agriculture on water quality. She recommends the use of cover crops to hold soil in place and to prevent phosphorus from running off in sediment. This is in line with the recommendations of the MSU Extension Cover Crop Team and the Midwest Cover Crop Council.

Concerns have been raised that phosphorus loss occurs during the winter when cover crops freeze and thaw, contributing to water quality issues. Macrae clarifies the freeze and thaw cycles in the Great Lakes are not as severe as in the prairie where research has shown the freeze-thaw cycle to be an issue with cover crops. The Great Lakes region also has ample snow cover, a factor that protects cover crops. She suggests phosphorus loss can be reduced by using more hardy cover crops like rye and vetch. Leaching is also greater where cover crops are waterlogged, so providing proper drainage, or avoiding planting cover crops where it floods each year in the field can help prevent this.

Smart trade-offs

Stopping the practice of no-till in order to prevent loss in tile is not always the answer, warns Macrae. Although tillage can mix your soil, preventing nutrient stratification, and leaching through macropores, it also promotes erosion. Consider where you farm and each field’s unique properties. If you have rolling topography and lighter soils, most of your phosphorus loss may be from surface run-off so no-till and cover crops would be great practices to implement. Alternatively, if you farm where there are heavier soils and flat lands, your loss may be through tile drains, so different cover crops and reduced tillage may be in order. Choose the best practices to prevent nutrient loss based on your soil types.   

Wacky weather

The Great Lakes region should expect to have more extreme rain events due to climate change.  These large events spike phosphorus in our waterways and spur flooding across the watershed.  They also postpone field practices and cost money to repair fields and replace applications of nutrients. Adapting your farm practices now can help you deal with flooding in the future.  Conservation practices and utilizing the 4Rs, in particular - the right rate and right place, are critical in creating a resilient cropping system.

Take-away

  • Importance of management for both surface and sub-surface phosphorus loss.
  • Get the fertilizer underground. By putting the fertilizer underground in a band, you can reduce your losses from 70-90%.
  • Be precise with your management. Select cover crops, tillage practices, nutrient rates, and placement based on your field’s soil type and topography.

Podcast information: Listen to the Michigan Field Crops podcast channel for a new “In the Weeds” series exploring water quality farming. You will hear from farmers, agribusiness, and Michigan State University Extension educators. The podcast is available on Spotify, iTunes, and embedded on the Field Crops Team website. New podcasts will be posted every week for this series. To receive notification on podcast posts, please subscribe to our channel: Michigan Field Crops.

GLRI related articles : This project is supported by the Environmental Protection Agency’s grant #00E02802, awarded to the Institute of Water Research at Michigan State University in partnership with The Nature Conservancy, Michigan Department of Agriculture and Rural Development (MDARD), Michigan Association of Conservation Districts (MACD), Michigan Farm Bureau (MFB), and Michigan State University Extension.

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