Managing Nitrogen After a Cover Crop

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This past year led the way in prevented plant acres since the USDA’s Farm Service Agency started sharing the report in 2007. With a record-breaking number of unplanted acres, many growers turned to cover crops to prevent erosion, alleviate compaction and improve soil health. As growers start heading to the field to begin the process of terminating cover crops and start fieldwork for spring crops, they need to give careful thought to several aspects of nitrogen management.

COVER CROP RESIDUE INCREASES VOLATILIZATION RISK

After cover crop termination, there will be crop residue left behind which can be valuable for soil health. But that organic matter could ultimately lead to the immobilization of surface-applied nitrogen. Nitrogen immobilization occurs when there is temporary loss of available nitrogen as microbes use nitrogen to degrade high carbon residue. Immobilized nitrogen becomes unavailable to the crop for uptake and may take several weeks or months to once again be plant available. To counteract the effects of immobilized nitrogen, additional nitrogen may be necessary to overcome the agronomic impact when using high carbon cover crops, like cereal grains.

High residue cropping systems are also known for increased volatilization risk due to greater urease enzyme activity, additional moisture, and reduced soil contact. Losses due to volatilization, which is when nitrogen is lost to the atmosphere, can be as high as 40% when nitrogen is not adequately incorporated into the soil and may be an additional 10% greater in high residue systems.

Protecting your nitrogen from volatilization is critical, and one way to ensure more nitrogen is available for the crop is to utilize a urease inhibitor. Urease inhibitors, such as ANVOL™ nitrogen stabilizer, can protect against ammonia volatilization. Next-generation stabilizers from Koch Agronomic Services slow the conversion of urea-based fertilizers (including granular urea and UAN), allowing more time for incorporation by rainfall or other means. This can give growers peace of mind and confidence that more nitrogen will be available for uptake by the crop.

COVER CROP RESIDUE CAN TIE UP NITROGEN

Soil microorganisms thrive in the presence of organic residue. Soil microbes use carbon as an energy source and utilize the soil nitrogen to build proteins, immobilizing the nitrogen intended for the crop. Even though cover crops help build organic nitrogen in the soil, it’s not immediately released when plants need it for early growth stages.

Because of this, the University of Missouri Extension recommends injecting a nitrogen source like UAN or anhydrous ammonia to avoid contact with crop residue and prevent it from being tied up. These applications can be protected with the nitrogen stabilizer CENTURO™, which is designed to protect against below-ground losses or to use a urea granule which could potentially fall through the residue. Using an enhanced efficiency fertilizer, such as SUPERU™ premium fertilizer, growers can get both above- and below-ground protection. The urea-based granule fully incorporated with both a urease and nitrification inhibitor, not only provides the nitrogen that the crop needs but also offers protection from volatilization losses when conditions turn dry or leaching and denitrification losses are caused by spring rains.

Start the season off right - contact your KAS representative or visit your local retailer to learn more and how we can help you make the spring season a successful one.

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