Nitrate Loss in Subsurface Drainage from a Corn-Soybean Rotation as Affected by Nitrogen Rate and Nitrapyrin

Area of Science:

• Agricultural Science
• Soil Science
• Environmental Science

Background:

• Nitrogen (N) management is crucial for optimizing crop production and minimizing nitrate-nitrogen (NO₃-N) losses in the US Midwest.
• Subsurface tile drainage systems are common in the region, making water quality a significant concern.
• Understanding the impact of N application timing and additives on crop yield and water quality is essential for sustainable agriculture.

Purpose of the Study:

• To evaluate the effects of nitrogen (N) rate, application timing (fall vs. spring), and the nitrification inhibitor nitrapyrin on corn production.
• To measure the impact of these N management practices on nitrate-nitrogen (NO₃-N) concentrations in subsurface tile drainage water.
• To provide data for optimizing N management in corn-soybean rotations in Minnesota, considering both yield and environmental impact.

Main Methods:

• Field study conducted over a 5-year period in a corn-soybean rotation in Minnesota.
• Anhydrous ammonia applied at various rates (90, 134, 179 kg N ha⁻¹) with and without nitrapyrin.
• Application timings included fall and spring; however, drainage water monitoring was restricted to fall-applied treatments.

Main Results:

• A significant portion of annual drainage (71%) occurred during April-June, with minimal drainage (<1%) during winter months due to frozen soil.
• Fall-applied N at higher rates (134 and 179 kg N ha⁻¹) resulted in lower corn grain yields compared to spring application at 134 kg N ha⁻¹.
• Increased fall N application rates correlated with higher NO₃-N concentrations and loads in tile drainage water; nitrapyrin did not significantly impact yield or water quality.

Conclusions:

• Fall application of nitrogen requires higher rates to achieve optimal corn yield compared to spring application in Minnesota's cold soils.
• Higher rates of fall-applied nitrogen significantly increase nitrate-nitrogen (NO₃-N) losses to tile drainage.
• Nitrapyrin did not demonstrate a benefit in improving corn yield or reducing NO₃-N losses under the conditions of this study.