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Understanding the Importance of Nitrogen in Soil

August 24, 2023
Corn with signs of nitrogen deficiency at the Dixon, IL, Grow More™ Experience Site

Corn with signs of nitrogen deficiency at the Dixon, IL, Grow More™ Experience site

Nitrogen (N) is a crucial part of healthy plant growth. It’s among the most important for corn and soybeans, as they need more nitrogen than any other nutrient and have a high potential for deficiencies. When managed properly, appropriate N levels can result in substantial potential economic returns. To better protect your crop, you should have a solid understanding of the role nitrogen plays in soil, the ways nitrogen loss occurs and the need for supplemental N to combat nutrient deficiencies.

Importance of Nitrogen

  • Key Function: Nitrogen is a major component of amino acids, which are the building blocks of proteins. It’s also a key component of chlorophyll, which is used in photosynthesis and fuels plant stem, leaf and ear structure growth.
  • Corn Deficiency Symptoms: Corn plants deficient in nitrogen will have a yellow “V” that runs down the midrib of lower leaves to the center of the plant. Nitrogen is mobile in plants, so symptoms will begin on the lower leaves.
  • Soybean Deficiency Symptoms: For soybeans, deficiency symptoms often result because of poor nodulation. The lower and older leaves often turn pale or yellow-green.

Nitrogen Loss in Soil

Nitrogen deficiencies are common after heavy rainfalls. The fields at the most risk for N loss following wet conditions are the ones where nitrogen was applied in the fall, followed by fields that had an early spring nitrogen application.

It’s important to consider nitrogen’s mobility factor in soil when evaluating environmental triggers and developing fertility programs. Leaching may occur in sandy soils, while heavy, poorly drained soils may lose N through denitrification. The following are the 4 types of nitrogen loss that can occur:

  • Leaching: Movement of nitrogen by water deeper through the soil profile. Nitrate and urea are both susceptible to leaching, and if rain and wet weather continue, nitrogen can move deeper through the soil profile and become unavailable to plant uptake.
  • Volatilization: Soil surface loss when the nitrogen source contains urea forms that were not incorporated into the soil.
  • Runoff: Movement of nitrogen by water to off-target areas. Nitrogen applied to the soil that was not incorporated either through tillage or a gentle rainfall are at risk of loss due to excess rainfall and runoff.
  • Denitrification: Gaseous loss due to reduction of nitrates to nitrous oxide or nitrogen gas. Saturated soils create an anaerobic environment, and the microorganisms will obtain oxygen by removing it from the nitrate, creating the gaseous forms of nitrogen, both of which are unavailable to plants. Temperature can affect the microbial activity in soil, with cooler temperatures slowing the process and warmer temperatures increasing the rate of nitrogen loss due to denitrification.

Reducing Nitrogen Loss

The best way to avoid nutrient deficiencies is a well-planned fertility program. Nutrient deficiencies may potentially impact corn and soybeans at any time during the season and can often look like other field issues. Identifying deficiencies, especially early in the season, may help with management practices to help mitigate the nutrient issues in the future. Managing for better nitrogen efficiency requires understanding your nitrogen program, the environment and weather forecast in order to select the appropriate nitrogen stabilizer to protect against potential loss and maintain adequate N availability.

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