COMPARISON OF DIFFERENT PROCEDURES FOR THE DETERMINATION OF AMMONIUM IN SOIL EXTRACTS

Abstract

A laboratory experiment was set up to determine the ammonium concentration in 0.01 M Cacl₂, soil extracts by three different procedures: an NH₃- gas diffusion electrode, a Continuous Flow System (CFS) and High Pressure Liquid Chromatography (HPLC). The influence of time on the measured ammonium concentration when leaving the extracting solutions to stand was also tested. The NH *₄ -nitrogen concentration in soil samples extracted with 0.01 M Cacl₂ and measured by a continuous-flow technique and HPLC gave almost equal values. The values obtained by measurement with a gas-diffusion electrode was slightly lower than those obtained by CFS in the soil samples dried at 40 °C but slightly higher than the samples dried at 105 °C. The analytical problems in the measurement of low NH^*₄-nitrogen concentration using a gas - diffusion electrode is that these values do not differ statistically. The NH^*₄ - nitrogen concentration in the soil extracts does not change during storage for at least 5 hours. The same result was found when this soil was shaken for only 30 minutes instead of the conventional 2 hours. The concentration of measured NH *₄ was not influence by shaking time and standing time.