Abstract
The accurate measurement of soil nitrate (NO3-) is critical for determining rates of nitrogen (N) cycling and potential N losses from ecosystems. Iron (Fe) can interfere with the colorimetric NO3- analysis of soil extracts to cause the appearance of anomalously low NO3- concentrations. To resolve the interference, imidazole or NH 4Cl-DTPA has been recommended to replace NH 4Cl-EDTA as the buffer in the analysis. Here we show that phosphate (PO43-) filtration can completely remove Fe interference whereas any of these buffers alone may not. Regardless of which buffer was used, 5.5-55mg FeL -1 ferrous iron (Fe 2+) interfered with NO3- determination in 0.3mg N-NO3-L -1 2M KCl solutions. Phosphate filtration removed all detectable Fe 2+ in 2M KCl anaerobic soil slurry extracts with high Fe 2+ concentrations (25.9±1.7mg Fe 2+L -1). With each of the three buffers tested, the measured NO3- concentrations in the anaerobic soil slurry extracts were significantly higher with PO43- filtration compared to without filtration. After filtration, the measured NO3- concentrations were similar across all three buffers, suggesting that NO3- concentrations were accurately measured in PO43- filtered soil extracts regardless of the buffer used. The Fe:N ratio of Fe interference with NO3- determination depended on Fe concentration, NO3- concentration, buffer, and cadmium column age, so that the amount of Fe interference that could occur can be difficult to predict. We suggest comparing measured NO3- concentrations for unfiltered and PO43- filtered soil extracts to determine the potential for Fe interference in colorimetric NO3- determination as standard additions may not detect all forms of Fe interference.
Original language | English (US) |
---|---|
Pages (from-to) | 123-128 |
Number of pages | 6 |
Journal | Soil Biology and Biochemistry |
Volume | 46 |
DOIs | |
State | Published - Mar 2012 |
Externally published | Yes |
Keywords
- Colorimetric analysis
- Griess-Ilosvay
- Imidazole
- Iron interference
- NH Cl-DTPA
- NH Cl-EDTA
- Nitrate
- Nitrite
- Phosphate filtration
- Soil extract
ASJC Scopus subject areas
- Microbiology
- Soil Science