nitratenitrogen

Nitrate nitrogen, commonly abbreviated as nitrate-N or NO3-N, is the portion of nitrogen present in nitrate (NO3−) ions. It is used as a way to express nitrogen content on a nitrogen basis, rather than by total nitrate mass, in soils, fertilizers, and water analyses. Because nitrogen in nitrate is 14 g/mol and nitrate as a whole is 62 g/mol, nitrate-N accounts for about 22.5% of the mass of nitrate. Consequently, to convert between nitrate-N and nitrate, the factor 4.43 is used (mg/L or mg/kg).

Sources and occurrence: Nitrate-N originates from microbial nitrification of ammonium, decomposition of organic matter, and from agricultural inputs such as mineral fertilizers and animal manures, as well as wastewater and atmospheric deposition. In soils and groundwater, nitrate can leach and migrate, contributing to eutrophication in surface waters.

Measurement and reporting: In practice, nitrate-N is reported in mg/L (water) or mg/kg (soil), but nitrate is also reported. Analytical methods include colorimetric assays for NO3− after reduction, ion chromatography, or spectrophotometric methods.

Applications and effects: Nitrate-N is used to estimate plant-available nitrogen and to assess water quality. High nitrate in drinking water poses health risks to infants (methemoglobinemia). Environmental concerns include eutrophication and algal blooms.

Regulatory notes: Drinking-water guidelines commonly cite 50 mg/L as nitrate (NO3−) or about 11 mg/L as nitrate-N (WHO). In the United States, the maximum contaminant level for nitrate as nitrate-N is 10 mg/L (≈45 mg/L as NO3−).