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The Nitrogen Cycle

Understanding the Nitrogen Cycle is an important step in farming; it is one of the most important cycles that occurs on earth. Nitrogen not only makes up 78% of our atmosphere, but is also a building block for amino acids which make up all proteins. However, we can’t take the gaseous nitrogen from the atmosphere and use it instantly. Nitrogen must be converted to an inorganic form to be digested in our food systems.

Nitrogen can be converted to an inorganic form through a variety of processes, yet plants need Ammonium (NH4+) and Nitrate (NO3) for growth.

Within the cycle, these processes may occur to convert to an inorganic form of N.

Nitrogen Fixation

Definition: conversion of atmospheric N to a plant available form.

  •      Requires a lot of energy to transform.
  •      Occurs with lightning storms, because of the energy available.
  •      Legumes are a biological source of fixation.
  •      Haber Bosch process uses immense amounts of energy to create inorganic


Definition: A biological process of microbes decomposing organic N.

  •      Decomposed from organic matter, manure, and crop residue.
  •      Transition from inorganic N to ammonium.
  •      Depends on temperature of the soil, moisture, and aeration (oxygen in the soil) for the process to occur because it is biological.


Definition: the conversion of ammonium to nitrate for energy by microorganisms.

  •      Nitrate is the most plant available from of N after ammonium.

To return to an unusable state by plants, N can undergo one of these processes.


Definition: the loss of N to gases from the conversion of nitrate to nitric oxide, nitrous oxide, and dinitrogen gas.

  •      Occurs under saturated soils and when bacteria use nitrate as a source of oxygen.
  •      Occurs in poorly drained soils.


Definition: loss of N to the atmosphere through the conversion of ammonium to ammonium gas.

  •      Occurs in soils with a high pH, hot, and windy conditions.
  •      Losses are greater in urea fertilizers that are applied to the surface.


Definition: when nitrate and ammonium are taken up by soil organisms so they’re unavailable to crops.

  •      Opposite of mineralization, soil organisms are constantly competing with crops.
  •      Incorporating things with more carbon than nitrogen, like sawdust, increase biological activity so there’s a larger demand for N from soil organisms.

Check with the consultants at AgDynamic to get a soil health testing! Testing your soils for nitrogen content is important for the environment as well as the health of your plants.


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