Adaptation and Validation of Colorimetric Methods in Determining Ammonium and Nitrate on Tropical Soils

Abstract

Inorganic nitrogen (N) determination in soil extracts is a useful tool in studying soil–N interactions. The main method used worldwide is the steam distillation, but colorimetric methodologies show advantages of being quick, simple, sensitive, and higher yield. However, they are subject to disruption when the extract has interfering organic N, limiting its application in tropical soil. The aim of this study is to evaluate colorimetric methods for the determination of NH4+ (through Berthelot reaction) and NO3− + NO2− (through Griess-Ilosvay reaction) in saline extracts of tropical soils by addition of activated charcoal during the extraction process. It is recommended to use extraction solution of 2 mol L−1 potassium chloride (KCl) and reaction time of 30 min. Validation parameters confirmed the best performance of the colorimetric methods, revealing results favorable to the addition of the activated charcoal in the extraction process to increase the accuracy and precision of the colorimetric methods.