River Action study looks at nitrogen, phosphorus run-off

With funding from the Scott County Regional Authority (SCRA), River Action initiated a study of phosphorus and nitrogen run-off from corn production in the Mississippi Watershed.

A local farmer volunteered his production fields for this study, and Solutions in the Land, LLC (SITL), an agriculture consulting firm, was enlisted to collect data and summarize the results.

The farm participating in this study had already adopted a number of practices to prevent leakage from the corn production system, including cover crops, enhanced waterways, reduced/no-till systems, livestock manure and a bio-reactor to reduce nitrogen run-off.

The farm operator also used manure from the hog-feeding operations to provide most of the fertility for his corn production. An additional 50 pounds of nitrogen was added with the corn planter. Using rye cover crops, the ground is never exposed to the rain and wind without some protective cover.

SITL installed an on-site weather station to accurately record temperatures and rainfall events. Excessive rains contribute to nitrogen leaching, causing decreased yields and water contamination.

Site specific weather information is critical to measure environmental impacts for nitrogen leaching.

The rainfall chart shows that 27.70 inches of rain fell during the growing season for corn. This is normal for total rainfall. However, for a 48-day period from July 29 to September 16, only .53 inch of rain fell. This long dry period had a negative impact on corn yield, but a beneficial impact on nitrogen leaching.

During that 48-day dry spell, corn reached maturity and heat degree units were nearly normal. Although heat unit accumulation was normal, night time temperatures were unusually cool, which contributing to poor dry down of the corn.

SITL monitored two different corn fields.

One was no-till corn into rye cover crop, and the other was minimum tillage following soybeans.

Both fields had the same treatment of applied nutrients: around 12.5 tons of liquid from the hog manure pit per acre were injected for the bulk of the nutritional requirements of the corn.

A very stable form of nitrogen was added to complete the nitrogen requirement. The two sites were aerial monitored with drone flights, and infra-red images were used to assess nitrogen levels in the growing fields.

The July 11 flight shows adequate nitrogen in most of the field as is indicated by the darker green color. Lighter areas are lacking nitrogen and are mainly around the waterways.

Both fields reflected similar nitrogen values indicating that the no-till and minimum-till were holding nitrogen equally.

Two sites were chosen to take water samples.

One location was at the outlet of the bio-digester and the other in a combined stream where the water from both fields converge.

Water samples were sent overnight to the State Hygienic Laboratory at the University of Iowa for testing of both nitrogen and phosphorous. We correlated rainfall events to the flashing of water flow coming out of the bio-digester.

The Results

• Nitrogen leaching into the fresh water is negligible from this farm operation.

• Phosphorous is slightly over the target level, but not excessive by any measure.

• Corn stalk nitrate test indicate both fields were short on nitrogen by the time the corn matured.

• Corn yields were disappointing in both fields but lower in the no-till following the cover crop.

• It is not possible from the study to draw linear relationships between specific practices and outcomes.

The study will be continued next year with a solid baseline of information collected this season.

It is evident from the study so far that the farmer is sacrificing some corn yield to protect the environment.

Contact Us

River Action, Inc.
822 E. River Drive
Davenport, Iowa 52803
Phone: (563) 322-2969
Email: riveraction@riveraction.org

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