Determinations of Total Nitrogen

Content

Determination of Essentiality
Nitrogen Metabolism and Nitrogenous Constituents in Plants
  Nitrate Assimilation
    - Nitrate Reductase
    - Nitrite Reductase
  Ammonium Assimilation
    - Glutamine Synthetase
    - Glutamate Synthase
    - Glutamic Acid Dehydrogenase
    - Transamination
    - Amidation
  Proteins and Other Nitrogenous Compounds
Diagnosis of Nitrogen Status in Plants
  Symptoms of Deficiency and Excess
  Concentrations of Nitrogen in Plants
    - Concentrations of Nitrogen in Plant Parts
    - Ratios of Concentrations of Nitrogen to Other Nutrients in Plants
Nitrogen in Soils
  Forms of Nitrogen in Soils
    - Organic Nitrogen in Soil
    - Inorganic Nitrogen in Soil
Soil Testing for Nitrogen
  Determinations of Total Nitrogen
  Biological Determinations of Availability Indexes
    - Determination of Inorganic Nitrogen
      - Ammonium
      - Nitrate
      - Amino Sugars
Nitrogen Fertilizers
  Properties and Use of Nitrogen Fertilizers
    - Anhydrous Ammonia: 82% N
    - Aqua Ammonia: 21% N
    - Urea: 46% N
    - Ammonium Nitrate: 34% N
    - Ammonium Sulfate: 21% N
    - Nitrogen Solutions: 28–32% N
    - Ammonium Phosphates: 10–21% N
    - Other Inorganic Nitrogen Fertilizers
    - Organic Nitrogen Fertilizers: 0.2–15% N
References
 
The determination of nitrogen by the Kjeldahl method gives an estimation of the total nitrogen in soils (93,113). This test, often considered a chemical index, is essentially a test for total soil organic matter, since the nitrogen concentration of soil organic matter is relatively constant. This measurement does not estimate the rates of transformations of organic nitrogen into inorganic forms that are available for plants; hence, many irregularities in predicting available nitrogen occur in its use. However, considering that transformations depend on the type of organic matter, temperature, aeration, water supply, acidity, and other factors, total nitrogen is likely as informative as determination of other availability indexes.

Nevertheless, determinations of availability indexes have been investigated extensively (96).