Errors in the measurement of extractable soil inorganic nitrogen caused by impurities in the extracting solution

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Abstract
The potassium salts used as extracting solutions to determine soil inorganic nitrogen contain nitrogen impurities which could introduce a small error into the analysis. Ammonium nitrogen can be removed from the extracting solutions by raising the pH of the solution to pH 11.0 by the addition of 1 Molar potassium hydroxide and then boiling and stirring for a period of 15 minutes to expel all the ammonia. The pH can be readjusted to 6.0 with an appropriate dilute acid depending on the potassium salt being purified. As there is no simple method for the removal of nitrate it is suggested that the potassium salts are tested and a batch with a low level of nitrate selected for use where soil nitrate levels are expected to be low.

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