Measurement of Organic Carbon and Nitrogen Content in Soil by Infrared Absorption-Thermal Conductivity Method

The organic carbon and total nitrogen in soil are the key factors for evaluating soil fertility. Rapid and accurate determination of organic carbon and total nitrogen in soil is of great significance for evaluating soil fertility, studying the relationship between carbon and nitrogen and plant growth metabolism, and further improving crop yield and quality. To solve the current problem of long measurement time and low efficiency batch testing of organic carbon and total nitrogen in soil, the infrared absorption-thermal conductivity method was adopted to simultaneously measure the content of organic carbon and total nitrogen in soil, further improving the analysis efficiency. The effects of sample size, combustion catalyst, and inorganic carbon interference on the determination of organic carbon and total nitrogen were discussed. The results showed that the optimum conditions were 0.12 g of sample mass, 0.04 g of copper oxide as combustion catalyst and 4 mol/L hydrochloric acid to eliminate inorganic carbon interference. When the instrument standard curve was established with soil standard samples, the limits of quantification for carbon and nitrogen were 0.008 2% and 0.043%, respectively. The method was applied to measure actual soil samples, with a precision of less than 3.0%. Compared with the standard method, the measured values of this method were within the allowable error range of the standard.