1. Multipurpose analysis: soil, plant tissue, wood, fruits, oils. Benchtop, portable Validation in-built, ISO compliant Little or no sample preparation. Rapid and easy technique. High repeatability and reproducibility Self serviceable Near Infrared Spectroscopy Contact: World Agroforestry Centre (ICRAF), P.O. Box 30677-00100 Nairobi, Kenya. Tel: +254 020 722 4000. www.worldagroforestry.org Near infrared (NIR) spectroscopy is a rapid non-destructive technique for analysing the chemical composition of materials. It is widely used in many pharmaceutical and industrial applications for quality control. A sample is illuminated and diffuse reflected light (electromagnetic radiation) is measured in narrow wavebands over the range from about 780 nm to 2,500 nm (Fig. 1). The resulting spectral signature summarize how much energy was absorbed at each wavelength (Fig. 2). Figure 2. NIR spectra of a soil (red) and a plant (green) sample. Spectral signatures respond to the soil organic and mineral composition. A wide range of agricultural inputs and outputs can be analyzed (soils, sediments, organic manures, feed and fodder, plant tissue, grain, tree products). NIR provides a rapid, versatile, low cost, high throughput analytical technique for a wide range of agricultural and environmental applications. Multivariate (multiple wavelength) calibration techniques (e.g. partial least squares regression) are used to calibrate standard reference analyses to NIR spectra (Fig. 4). Figure 4. Calibration of nitrogen concentration in a wide range of organic manures. The statistical model is then used to predict the composition of unknown samples that are part of the sample population. Samples that fall outside the population can be analyzed by traditional means and included in the new model. Careful development of calibration libraries is essential for reliable use of NIR methods. Prediction of soil properties (e.g. soil organic carbon, exchangeable Ca, cation exchange capacity, P sorption) and soil fertility capability. Digital soil mapping. Nitrogen content and decomposition characteristics of manures/composts. Leaf N concentration. Feed/fodder quality. Grain moisture, protein and germination rate. Wood density, moisture and carbon content. Biofuel moisture, ash and calorific value. Applications Materials are composed of molecules consisting of atoms linked together by bonds (e.g. C-H, O-H, N-H), which are constantly vibrating. Irradiation of materials by light energy excites molecules to change their vibrations from one energy level to another. Molecules that absorb near-infrared energy vibrate in two modes: Stretching and bending (Fig. 3). The resulting absorbance of light at different frequencies produces a characteristic spectrum of a substance. Working Principles Scanning soil samples with a Fourier Transform Near Infrared spectrometer. Air-dried 2-mm sieved soils are loaded into glass Petri dishes and scanned in 30 seconds. Figure 3: Stretching and bending vibrations Large sample required Cannot detect quartz in soils Direct spectral interpretation limited Wavenumber (cm -1 ) Absorption (Log 1/R) Increasing Frequency Increasing Wavelength X-RayVisNIRMIR FIR, Microwave UV 200 nm380 nm780 nm 2,500 nm25,000 nm 50,000 cm -1 12,820 cm -1 4,000 cm -1 400 cm -1 Figure 1: The electromagnetic spectrum InstrumentationIntroduction Spectral analysis Key Advantages/Limitations