Volume 2.5 Nitrogen
Nitrogen (N) constitutes (together with carbon, hydrogen and oxygen) the major part of the proteins of all living materials. Naturally, N in soils is found in organic and mineral forms. It is important to monitor the dynamics of N in soils because ammonia volatilization, leaching of nitrite and nitrate nitrogen to groundwater, ammonium fixation into soil clay minerals, and precipitation of nitrate and ammonium nitrogen can contribute to surface, subsurface and groundwater pollution, and increase greenhouse gas emissions.
Mineral nitrogen
Mineral (inorganic) N in the soil is always highly variable due to leaching, plants uptake, temperature changes, soil moisture content and aeration. Therefore, soil mineral N and soil organic matter analysis should be done together to determine their capacity in real time. Mineral N comprises ammonium ions (NH4+), nitrate (NO3-) and very little nitrite (NO2-). In general, many plant species prefer to absorb the nitrate form over the ammonium form. The ammonium form interacts with the soil’s cation exchange system and is therefore less soluble and mobile than the nitrate form. All these factors make the determination of mineral nitrogen forms in the soil very challenging.
The methods to quantify nitrogen content in soils already harmonized by GLOSOLAN are the following:
- Mineral Nitrogen by colorimetric method (available soon)
Total nitrogen
Soil total nitrogen (TN) is the sum of nitrate (NO3), nitrite (NO2), organic nitrogen and ammonia (all expressed as N). Analysis and quantification of TN is used to estimate nitrogen availability from the natural decay of organic materials. Testing TN in arable soils is useful for making nitrogen fertilization management decisions if local mineralization rates are known.
The methods to quantify nitrogen content in soils already harmonized by GLOSOLAN are the following: