DETERMINATION OF EXCHANGEABLE BASES IN SOILS OF DIFFERENT pH VALUES BY ICP-AES

Exchangeable base is an important index to evaluate soil fertilizer supply, fertilizer conservation and soil buffering ability. There are some problems such as large matrix interference, cumbersome analysis steps and poor reproducibility by traditional measurement method, which uses direct determination after ammonium acetate/ammonium chloride-ethanol extraction. To improve the test precision and efficiency, the extraction solutions of soil with different pH values are optimized, through desalting and redissolving at a high temperature after being dried in a water bath, no ammonium acetate/ammonium chloride matrix matching required for standard curve. The contents of exchangeable K, Na, Mg and Ca are determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) using the same standard curve. The method is used to analyze 4 standard substances for available nutrients of soil, including ASA-11, ASA-14, ASA-16 and ASA-20. The measurement results are all within the range of uncertainty, with the relative error between the measured value and standard value of the 4 elements from -1.32% to +7.27%, the relative standard deviation less than 3.50%, and the maximum relative difference of 9.92%(< 10%), which meets the requirements of analytical test. The method has good reproducibility for soil samples with different pH values, overcoming the shortcomings of being too simple or cumbersome in the traditional analysis process with poor reproducibility, completing the on-line detection of K, Na, Mg and Ca simultaneously, shortening the analysis steps, and improving the analysis efficiency and saving costs.