Determination of Nitrate Nitrogen in Soil Based on K Ratio Spectrophotometry

The content of nitrate nitrogen in soil directly reflects the short-term supply ability of soil nitrogen, which is the crucial factor affecting the growth of crops. For the correction factor method of ultraviolet spectrophotometry can´t effectively remove the interference of nitrite, this paper proposes a dual wavelength of K ratio spectrophotometry to detect nitrate nitrogen in soil in order to effectively eliminate the interference of the nitrite. The spectrum scanning was made for soil extract obtained by saturated calcium sulfate solution, selecting 205 nm and 230 nm as measuring wavelength and reference wavelength, to determine the coefficient K. Furthermore, the linear regression equation of standard curve on the relationship between concentrations of nitrate nitrogen and the corrected absorbance could be derived by regression analysis. Therefore, the quantitative model of nitrate nitrogen was established using dual-wavelength of K ratio spectrophotometry. Compared with correction factor method of ultraviolet spectrophotometry by soil sample experiments, the fitting correlation coefficient (R² = 0.9996) of this method is higher than the latter (R² = 0.9988), which showed its repeatability precision was better than the latter and the feasibility and validity of this method were proved.