Nitrates in Minnesota drainage water

While artificial drainage offers tremendous benefits for crop production, it can also potentially transport nitrates from the soil to surface water. Here, we share strategies to help you avoid these nitrate losses, which can help protect the environment and reduce fertilizer costs.

Understanding nitrate loss

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Influencing factors

The well-documented increase in the amount of artificial drainage in significant portions of Minnesota can be attributed to the practice’s overall profitability, as well as the increased efficiency of farmers’ time.

This has been accompanied by scrutiny about potential negative impacts, including nitrate loss. Minimizing nitrate loss via artificial drainage is in everyone’s best interests, as it makes sense from both an environmental and economic standpoint.

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Best management practices: N fertilizers

The University of Minnesota established best management practices (BMPs) for applying N fertilizer in the early 1990s, which were updated in 2008.

These detailed guidelines are designed to help producers efficiently use N fertilizer to maximize profit, while minimizing N loss to the environment:

Apply nitrogen at the right time

Red tractor applying Nitrogen to young green crop.
Figure 5: Ultimately, you may need technology and methods to reduce nitrate in surface waters. While you can fine-tune rates and timing, this is limited by time, climatic and crop growth constraints.

The N cycle dictates that conversion of the various forms of organic N must occur before nitrate becomes present in the soil. This conversion, caused by the actions of microorganisms, depends on temperature and time.

Nitrate’s subsequent movement depends on the presence of water that exceeds field capacity. A growing crop’s water demand lessens the likelihood of a drainage event. Optimum application timing also corresponds with the plant’s need for N.

Guidelines

Applying N fertilizer would logically and ideally be as close as possible to when a plant needs the nutrient, to minimize the chance for loss into the environment. Best management practices dictate the minimum requirements to prevent excessive N loss (Figure 5).

You can lessen the chance of a significant leaching event by further delaying application to better correspond with planting or by split-applying so some of the application occurs to a growing crop.

However, take caution when late sidedress (in-season) applications are surface-applied and not incorporated. If meaningful rainfall doesn’t occur for 10 to 20 days, you could lose this N to the atmosphere. In addition, it could become positionally unavailable to roots. In either case, yields will suffer due to lack of available N.

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Brad Carlson, Extension educator; Jeff Vetsch, researcher, Southern Research and Outreach Center and Gyles Randall, emeritus soil scientist, Southern Research and Outreach Center

Reviewed in 2018

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