Most fraction of nitrogen in soil belongs to organic matter present in soil, but soil contains other fractions like nitrate, nitrite and ammonia form together. Then how organic bound nitrogen can be determined?
The sediments and soils concentrations of the organic carbon are correlated very well with organic contaminants and for this reason can be used as a tool for the estimation of the level of contamination - toxicity . The sediments TOC and TN ratios can be used as biomarkers, to distinguish the marine or terrestrial sources of organic matter as well as aerobic/anoxic and sulfate reduction conditions and thus give a qualitative indication of the redox status . Moreover, organic matter and nitrogen content ratios have been used widely as biomarkers for the reconstruction of sedimentological depositional environments and the environmental changes of the past .
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Nitrogen in the soils occur in both organic and inorganic forms, a major part is intimately associated with organic matter. Total soil N (mainly organic N) is generally measured after wet digestion using the well-known Kjeldahl procedure. It involves three stages namely, digestion, distillation and titration. The soil samples/sediments are digested in concentrated H2SO4 with a catalyst mixture to raise the boiling temperature and to promote the conversion from organic-N to ammonium-N. Ammonium-N from the digest is obtained by steamed distillation, using strong alkaline (40% NaOH) to raise the pH. The distillate is collected in saturated boric acid solution containing mixed indicator, and titrated with standard acid.
The sediments and soils concentrations of the organic carbon are correlated very well with organic contaminants and for this reason can be used as a tool for the estimation of the level of contamination - toxicity . The sediments TOC and TN ratios can be used as biomarkers, to distinguish the marine or terrestrial sources of organic matter as well as aerobic/anoxic and sulfate reduction conditions and thus give a qualitative indication of the redox status . Moreover, organic matter and nitrogen content ratios have been used widely as biomarkers for the reconstruction of sedimentological depositional environments and the environmental changes of the past .
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OK Sirs, but if ammonia in free form in sediment is present , it also undergoes distillation in Kjeldahl estimation.
@ Phani, the N present in free form in soil, you may determined using 2M KCl as the extracting solution in 1:5 ( soil:KCL) ratio. Ammonium and nitrate plus nitrite are determined by steam distillation of ammonia, using MgO for ammonia and devardas alloy for nitrate. The distillate is collected in 2% boric acid and titrate with dilute acid.
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