Determination of inorganic nitrogen in soil

Investigations were conducted to find the most suitable conditions for extraction and subsequent determination of nitrate in soils by the xylenol method. Errors were caused by two main factors: (1) When using methods of nitrate analysis based on the formation of highly coloured nitro‐compounds, low recoveries of nitrate were obtained if even small amounts of soil organic matter were present at the time of nitration. the nature and extent of this loss were investigated and a satisfactory method devised for eliminating this interference. (2) With aqueous soil suspensions, biological loss of nitrate occurred after a few hours and progressed rapidly unless sterile or bacteriostatic conditions were maintained. Extraction of soil with 0.02N‐copper sulphate solution, precipitation of copper from the decanted supernatant as hydroxide and subsequent filtration gave solutions on which nitrate could be determined, and these interferences were obviated. Use of a solution containing sodium sulphate (N) and copper sulphate (0.02N) as extractant permits determination of both ammonium and nitrate in the same extract.