BACKGROUNDThe application of high frequency infrared carbon-sulfur analyzer to determine the organic matter in agricultural soil samples avoids the traditional method of sample liquid conversion. The method has a high measurement efficiency, but has problems such as low electromagnetic induction of soil samples and greater influence of the matrix.

OBJECTIVESTo solve the problems of low electromagnetic induction and large matrix effect in the determination of organic matter in agricultural soil samples.

METHODSThe iron and tungsten flux was optimized for the sample size. An accurate and efficient method for the determination of soil organic matter content was established by high frequency infrared carbon-sulfur analyzer.

RESULTSWhen the conditions set for a sample size of 0.05g, the flux iron content was 0.40g, and the tungsten content was 1.50g, optimum results of organic content were obtained. The method was verified by soil standard materials. The detection limit of this method was 0.003%, the relative standard deviation (RSD, n=7) was less than 4%, and the error between the analytical result and the standard value was less than 5%. There was no significant difference between the results of different analytical staff. The proposed method and potassium dichromate volumetric method were used to analyze soil samples in farm land of Gansu Province. The absolute error ranges of this method and potassium dichromate volumetric method were from -0.25% to 0.28%. The positively linear correlation between the determination results (R²=0.9736) indicated that the two methods were in good agreement.

CONCLUSIONSThe detection limit, precision and accuracy of the established method meet the requirements of the soil samples of farm land.