Nondestructive Analysis for Nitrogens of Soils by near Infrared Reflectance Spectroscopy

Traditional wet analytical method such as the gravimetric, Kjeldahl or Walkley-Black method are still the most widely used for determining the organic matter (OM), moisture and notal nitrogen (T–N) content of soils. However, these are time-consuming, high in cost and labour intensive as well producing harmfull pollutants making the method undesirable for field measurement. Over three years we have been working on the development of a non-destructive on-site analyser for measuring OM, moisture and T–N. In this research we investigated the possibility of using near infrared (NIR) spectroscopy for the non-destructive analysis of T–N, inorganic and available nitrogen in domestic soil samples.85 soil samples of upland over the Kyungpook prefecture were colledted to make a calibration and validation. Dried soil samples were packed in the closed-cup and the NIR spectra data was measured from 1100–2500 nm using a scanning type NIR instrum, InfraAlyzer 500 and filter type NIR instrument, InfraAlyzer 400, which has a modified sample compartment. Multiple linear regression analysis between the content of soil properties determined by the traditional method and the NIR spectral data were conducted to develop an non-destructive analysing equation for T–N, inorganic and available nitrogen. In the case of the scanning type, the standard error or prediction were 0.028%. 1.7 mg⁻¹ and 1.1 mg⁻¹ for T–N, inorganic and available nitrogen respectively. The prediction results in the filter type appeared to have the same accuracy as the scanning type. It is concluded that NIR spectroscopy could be used to predict soil nitrogen compounds such as total nitrogen, inorganic and available nitrogen non-destructively.