[Advance and prospect of spectroscopy applied in grassland soil inspection]

Infrared spectroscopic measurement, especially near infrared spectroscopy, was widely used in grassland soil inspection. Recently, visible and ultraviolet diffuse reflectance spectroscopic techniques also were used in this field. Spectroscopy method is a rapid, timely, less expensive, non-destructive, straightforward analytic method. Furthermore, a single spectrum allows for simultaneous characterization of various soil properties and the techniques are adaptable for "on-the-go" field use. In the present paper, the authors reviewed the use of the techniques to inspect the water content, organic matter, nitrate content, available phosphorus, exchangeable potassium and soil texture classes of soil. The thermal infrared remote sensing assisted method for monitoring soil water content mainly includes thermal infrared method, thermal inertia method and temperature/vegetation index method. The content of organic material is strongly correlative with absorption features of soil spectrum in ultraviolet wave band (around 376,795 nm), visible radiation wave band (around 616,506 nm), and infrared wave band (around 724,975 nm). Mid-infrared Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy could be used to determine nitrate concentration in soil pastes. When visible (Vis) (400-700 nm), near infrared (NIR) (700-2500 nm) and mid infrared (MIR) (2500-25000 nm) were used to predict a number of different soil properties, more accurate predictions were obtained using the MIR for available phosphorus and electrical conductivity and the NIR produced more accurate predictions forexchangeable AL and K. Vis-NIR-FDA (the factorial discriminant analysis) is an efficient technique to classify soil into three main groups, sandy (light soils), loamy (medium soils), and clayey (heavy soils), and the classification models could be used for an on-the-go measurement system of soil properties. A standard penetrometer cone was modified to collect near-infrared reflectance and estimate soil moisture, density, and clay content. Because the techology can get useful soil datum, it can effectively improve grassland management. Nowaday a question that needs to be answered is how to examine the belowground biomass by the technique, so the authors can base on the data to forecast the grass growth. It is also needed to to invent more portable and "on-the-go" field use spectroscopy apparatus.