Nitrogen (N)

  • One of the 13 essential elements for plant growth and is one of the 6 Major Elements, based on concentration required
  • amount required for healthy plant growth: 14,000 ppm, 1.4%, dry soil matter
  • Principle form of uptake: ionic forms ammonium, (NH4+) and nitrate (NO3)
    • the preferred form changes from NH4 to NO3 as the plant approaches maturity
  • Nitrate moves through the soil primarily by mass flow, but also by diffusion
  • soil conditions related to deficiency of nitrogen:
    • sandy soils leached by heavy rainfall or irrigation
    • mineral soils low in organic matter
    • long history of crop depleting because not enough N added
  • soil factors that affect plant uptake:
    • Temperature
    • the level of decomposition of organic matter
      • plowing under highly carbonaceous materials (cover crops or straw) when still being decomposed by soil organisms will reduce available N, since microorganisms are better competitors than plants for resources
  • plant factors that affect uptake of nitrogen:
    • hybrid or variety of plant
    • stage of growth
    • interactions among the other elements
      • molybdenum is required for converting nitrate to nitrogen – if the form of nitrogen supplied to the plant is NH4, then the amount of molybdenum required is greatly reduced

Nitrogen functions in plant:

  • combines with carbohydrates and sometimes sulfur to form amino acids, amino enzymes, chlorophyll, alkaloids, nucleic acids, and purine bases

Sources for Nitrogen:

  • organic debris, plant residues, and microorganisms are the major sources of nitrogen

Nitrogen Deficiency Symptoms:

  • pale yellow-green leaves (can be confused with sulfur deficiency)
  • Nitrogen is very mobile within the plant, so deficiency symptoms will first show in the older leaves, since the plant is moving N from older leaves to newer growth to supply growing points
  • Nitrogen content in leaves naturally declines with maturity of the plant, so some symptoms of deficiency are normal in those older leaves, as the plant ages

Nitrogen Excess Symptoms:

  • too much nitrogen will bring down brix levels
  • excessive nitrogen in acidic soil (pH < 7) can result in iron (Fe) deficiency

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