Vis/Near- and Mid- Infrared Spectroscopy for Predicting Soil N and C at a Farm Scale

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a. In spectroscopic analysis, visible (Vis), near infrared (NIR) and mid infrared (MIR) ranges are often used as they include plenty of information on physical, chemical and biological properties of objects. Commonly, wavelengths ranges are from 350 to 760 nm for Vis, 760-2500 nm for NIR, and 2500 to 25000 nm for MIR (often used in its wavenumber form 4000 to 400 cm-1). Frequencies in the Vis are due to electronic transition while those in the NIR are generally overtones and combination bands from the fundamental vibrations occur in the MIR, mainly O-H, N-H, and C-H bonds (Viscarra Rossel, et al., 2006). When NIR and MIR radiations are focused onto a sample, the molecules in the sample will increase their vibration energy by absorbing energy at specific frequencies depending on the molecular geometry, bond strengths and atomic masses. The resulting Vis, NIR and MIR lights are thus modified, creating a spectrum or ‘signatures’ of the targeted object with peaks at the absorbing frequencies. b. The combined contributions from the various soil components can result in a very complex spectrum, difficult to analyze visually, but multivariate calibration models can be built to derive useful qualitative and quantitative relationships or models between the spectral signatures and many soil properties. Spectrometry is the combination of spectroscopy and chemometric (multivariate statistical) methods. It should be noted that the Vis-NIR-MIR spectrometry technique can predict multiple soil properties simultaneously. c. Recently, there is an increasing interest in the development of timeand cost-effective methods for the measurement of soil nitrogen (N) and carbon (C), due to the growing concerns about the effect of excessive use of N fertilizer in the environment and the increase of atmospheric C content, which could be limited through soil C sequestration. In order to manage N and C in soils in an efficient manner detailed information about these properties is needed. Previous reports confirm the presence of within-field variability of soil properties including N and C, which requires analysis of large number of soil samples (Mouazen, et al., 2007). Due to the fact that standard procedures for the measurement of soil N and C are time-consuming and expensive (Sinfield, et al.,