Nitrogen-inorganic forms

Most soils contain inorganic nitrogen (N) in the form of ammonium (NH₄ ⁺) and nitrate (NO₃ ^-). Although methods have been described to determine exchangeable NH₄ ⁺, NO₃ ^-, or NO₂ ^- in soils without extraction, most methods for these determinations involve the preparation of extracts, which are easily stored for later analysis. To prevent loss of NO₂ ^--N through chemical decomposition of HN0₂ formed under acidic conditions, a neutral or alkaline reagent is normally employed in extracting soil for determination of NO₃ ^- or NO₂ ^-. The steam-distillation procedures described for determination of NH₄ ⁺, N0₃ ^-, and NO₂ ^- in soil extracts developed from the finding that interference by alkali-labile organic-N compounds in alkali-distillation methods of determining NH₄ ⁺is eliminated if the distillation is performed with steam for only a short period using a small amount of MgO. The duplicate distillation procedure for estimating nonexchangeable NH₄ ⁺ in soils was originally proposed by I. Barshad.