Rapid and Inexpensive Steam Distillation Method for Routine Analysis of Inorganic Nitrogen in Alkaline Calcareous Soils

Determination of inorganic nitrogen (N) in soil is important in making N fertilizer recommendations for crops. To find a rapid, reliable, and economical method for the estimation of inorganic N in alkaline calcareous soils of Pakistan, three steam distillation methods were compared using soils varying in ammonium (NH₄) and nitrate (NO₃) N contents and other physicochemical properties. In the standard method, the soil sample is shaken with 2 N potassium chloride (KCl) for 1 h, and the extract is then analyzed by steam distillation. In the other two methods, the soil sample is distilled directly with either 2 N KCl or distilled/deionized water. Based on the results of the present work, a method that involves steam distillation with only distilled/deionized water and that requires half the quantity of magnesium oxide (MgO) of the standard method has been proposed, as all the three methods yielded identical results for NH₄- and NO₃-N contents. Being economical, the proposed method for inorganic N estimation by direct distillation of soil with distilled/deionized water deserves consideration for adoption by soil-testing laboratories.