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Where and when to apply fall nitrogen fertilizer

The Minnesota Department of Agriculture is advising farmers to avoid spreading nitrogen fertilizer in areas with high leaching potential and to wait to apply until the soil is cooler than 50 degrees.

Farmers and applicators should check soil temperature and delay fall application of anhydrous ammonia and urea fertilizer until soil temperatures stay below 50 degrees, the state said.

The agriculture department provides real-time soil temperatures at 25 locations across the state. The website includes a map of soil thermometers.

Applying nitrogen fertilizer in the fall poses a risk to groundwater in certain areas, such as where coarse soils that drain quickly. Waiting to apply anhydrous ammonia and urea increases the availability of nitrogen to next season's crop and decreases the amount of nitrate that could potentially leach into groundwater or tile drainage, the state said.

The department also recommends delaying the application of manure. Research from the University of Minnesota at Waseca showed liquid dairy and hog manures injected in November produced yields 10 bushels per acre higher than manures injected in September and October.

If approved, a proposed Groundwater Protection Rule would restrict fall nitrogen fertilizer application in areas vulnerable to groundwater contamination beginning in January 2020.

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