Nitrogen (N) is needed for the synthesis of amino acids, proteins, chlorophyll, nucleic acids and coenzymes.

Tomato plants cannot make their own nitrogen so there must be some present in the growing media for them to thrive. When fertilizing tomatoes this nutrient is usually the most needed.

Plants asborb nitrogen mostly as inorganic forms such as nitrate (NO₃^-) and also as ammonium (NH₄⁺) or amino (NH₂⁺) ions. Since most soil nitrogen is in the organic form, it must be oxidized first by soil organisms into the inorganic forms in order for the plant to use it.

Nitrogen fertilizers can also effect pH of the soil.

Various sources of nitrogen can be used when fertilizing tomatoes.

Inorganics ammonium nitrate ammonium sulfate anhydrous ammonia calcium nitrate potassium nitrate sodium nitrate urea

Organics alfalfa meal blood meal compost feather meal fish meal legumes (tilled in) manures

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Inorganics

Benefits quick release to the plant lower volumes required able to fertigate

Drawbacks can lead to salt build ups easier to "over-fertilize" can "burn" roots or foliage

Organics

Benefits slow release to the plant often adds organic matter most do not "burn" roots or foliage some can be used to temporarily repel animals (bloodmeal, hair)

Drawbacks over use of manures can lead to excessive salt build ups often larger volumes to apply some are "smelly" potential source for human pathogens (manures, blood meal, bone meal)

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Signs of Nitrogen deficiencies

• reduced growth
• uniform yellowing of the lower, older leaves progressing to younger
• reduced yields

Conditions which favor deficiencies

• leaching rains
• soils with little organic matter (little present or leaches quicker)
• soils with too much organic matter ("ties up" available N)
  • undecomposed mulchs or cover crops
• inadequate application(s)

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Nitrogen excess

• Generalized or complete necrosis (death of tissue) - excessive applications
• Much vegetative growth at the expense of fruit production or quality
• Fruit maybe poorly colored and/or puffy
• Flowers may prematurely drop or fail to form
• Higher chances of certain disease incidences (Fusarium, Early Blight, Pith Necrosis, Blossom End Rot)
• Excessive salt build up in the soil (over time)

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