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Plan for when plants need nitrogen most.

Agronomy Bulletin 102 ─ Nitrogen Management

Situation

Nitrogen (N) can be lost from the soil between application and crop uptake. By managing applications, you can maximize yield by making sure N is available when corn plants need it most.

Factors to Consider

  • Crop stage
  • Application timing
  • Soil moisture and temperature
  • Yield goals
  • Amount of nitrate present
Figure 1. Corn has the highest nitrogen needs after the V8 stage.

Action Plan

  1. Know the nitrification process. Upon application, N sources applied as ammonium (NH4+) are converted to nitrite (NO2–) and subsequently to nitrate (NO3–) via the nitrification process. Because soil bacteria are responsible for nitrification, rate of nitrification is heavily dependent on soil temperature and moisture. It typically begins when soil temperatures reach 50 F. Once soil temperature exceeds 50 F, nitrification rates increase with temperatures. Under optimum conditions, the process occurs in as little as two to four weeks. Once in the NO3– form, fertilizer N is subject to significant loss.
  2. Understand N loss. Peak in-season N losses occur from May to July, or anytime up to 75 days after crop emergence (see Figure 1). Because NH4+ carries a positive charge, it binds to the negatively charged soil. N losses, such as leaching and denitrification, occur when fertilizer N is converted to the negatively charged NO3– form.
    • Leaching. Due to negative charge, NO3– moves with water through the soil profile and subsequently out of the root zone.
    • Denitrification. This is the microbial process of converting NO3– to gaseous forms of N due to saturated soil conditions.
  3. Estimate N available in your fields. N deficiency usually appears as a V-shaped yellowing of the lower, or older, leaves of the plant. Visual scouting may not be enough for an accurate diagnosis of deficiency. In-season soil samples can determine N concentration. Another option is leaf tissue sampling.
  4. Choose the application method and N source.
    Injecting N into the soil by deep banding anhydrous ammonia or coulter injecting UAN is one of the best applications. It minimizes volatilization and reduces foliar damage.
    Broadcast or top-dress applications of urea, ammonium nitrate or UAN are great alternatives. Urea causes the least foliar damage for all growth stages. Apply with an inhibitor or into irrigated soils as it becomes volatile within three to four days. Ammonium nitrate is not volatile but may cause slightly higher levels of foliar damage in later growth stages. UAN causes the greatest foliar damage. Take caution applying it on corn more than 6 inches in height and in high-residue situations.
    • Surface banding or dribbling of UAN is another option. It is useful on fields with substantial residue cover because it reduces tie-up of the solution.
  5. Stabilize N. Remember that adding Instinct&#174; nitrogen stabilizer to urea, UAN and liquid manure and adding N-Serve&#174; nitrogen stabilizer to anhydrous ammonia helps keep N in its preferred form, NH4 +, ensuring N is available in the root zone between the V8 and VT stages when plants need it most.

Summary

Successful N management maximizes yield and profitability while minimizing N losses. Think long term and develop a program that addresses fall applications and corrective action during the season. For more information, contact your local Mycogen Seeds customer agronomist or trusted agronomic adviser.

Resources

Published on Wednesday, January 14, 2015