Comparison of methods for determination of nitrogen levels in soil, plant and body tissues, and water

Abstract Four different methods to include all forms of nitrogen (N), especially nitrate (NO3), not usually measured in the analysis using the standard total Kjeldahl nitrogen (TKN) digestion procedure, were investigated. The methods compared were: total nitrogen determination by combustion using a LECO FP‐428 Nitrogen Determinator, salicylic acid modification prior to TKN digestion, a method of reduction of nitrate‐nitrogen (NO3‐N) to ammonium‐nitrogen (NH4‐N) before digestion using CrK(SO4)2, and the addition of phenyl acetate to the standard digestion mixture. Obtained results were compared to those obtained by the standard TKN digestion procedure. The tests were performed on air‐dried soil, oven‐dried plant and body issue, and a water sample. The purpose of the investigation was to ascertain which method provides the best recovery and is most easily incorporated into a laboratory setting. Acid digestion was done using a Tecator Block Digester with a forty 75‐mL tube capacity. All digestions beyond pre...