Abstract: A innovative method for the determination of contents of the ammonium in the soil by gas phase molecular absorption spectrometry （GPMAS） was proposed. The orthogonal experiment was used to optimize the extraction conditions of ammonia nitrogen in soils such as extraction temperature, extractant concentration and extraction time. The effects of extraction conditions on the amount of ammonia nitrogen extracted from soil were studied. The results showed that the optimum conditions for ammonia nitrogen extraction in soil were as follows： KCl extract concentration was 2 mol/L, extraction temperature was 25℃, and extraction time was 30 min. The standard sample was recovered by gas phase molecular absorption spectrometry. The recoveries of the actual samples were 88.0%~105.5%, and the relative standard deviations were 3.8%~4.3%. Compared with the current industry standard methods, there was no significant difference in the results of the test by t test. The determination method is simple and easy, and can meet the requirements of large-scale determination contents of soil ammonia nitrogen, and has practical promotion value.

Key words: soil, ammonium, gas-phase molecular absorption spectrometry