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