Using Near Infrared Spectrometry in Agriculture

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NIR in Food Production

The pressure to increase food production is mounting as the world’s population grows. Moreover, consumers are ever more discerning and demand good quality produce and food. To improve both the quantity and quality of food produced, it is necessary to be able to make fast, frequent, and cheap measurements in individual farms. This can help farmers and growers make proper and timely decisions during crop management and harvesting. The right technology can prevent costly mistakes, improve profit margins, and save time. Of all the new technologies available, the most promising one is near infrared (NIR) analysis, which has many important applications in agriculture.

What is Infrared Light?

Infrared light, which is invisible to the human eye, is a form of electromagnetic radiation. It is the part of the light spectrum that is next to red light. All light with wavelengths above ≈ 700 - 800 nanometers (nm) fall into this category. Infrared light is emitted by any object which has a temperature above -450 degrees Fahrenheit, or -268 degrees Celsius; it is therefore also called heat radiation.

Infrared light is present around us but is perceived as heat rather than light. When objects get very hot, they can also emit visible light, as in the case of fires. The warmth from living organisms is not so high, and so the radiation lies in the infrared region. For example, this is the light spectrum which is used to capture images in night-vision goggles.

The infrared region in the spectrum has four further divisions, the near infrared, short wavelength infrared, mid-wavelength infrared, and long wavelength infrared. The near infrared region is right next to red in the light spectrum and is on the fringe of human visibility. The near infrared radiation ranges from ≈750 - 2,500nm or (12,500 - 4000 cm−1, when expressed as wavenumber).

Measuring Near Infrared Light

Infrared light makes up 50% of the radiation that reaches earth. The properties of NIR make it the most suitable range in the analysis of agricultural purposes. In astronomy, other parts of the infrared spectrum are also used. Moreover, NIR has wavelengths which are longer than light in the visible spectrum; this allows it to pass through dense air with less scattering than light with shorter wavelengths, making them ideal for use.

NIR is absorbed and reflected by the earth and its vegetation. So, changes in it can be used to study the growth of crops, changes in vegetation, and soil conditions. Instruments analyze the NIR absorbed and reflected by plants or soil, which indicates plant and soil health.

Though it can’t be seen by humans, instruments can detect NIR and are used for accurate quantitative analysis. NIR analysis depends on measuring either the amount of NIR:

• Absorbed by a material, i.e. its transmission, or
• Reflected by the object, i.e. reflectance.

Another important aspect to consider for analysis is that different wavelengths are needed to measure different substances. Thus, protein analysis will need a NIR wavelength that differs from that needed to measure fats, etc. The wavelength used will also depend on whether the transmission or reflectance of NIR is being measured.

Using NIR

There are many different ways to detect and measure NIR. Some are simple, while others are more complex. The most common methods are discussed here.
Satellite Imagery

Plants look green because they reflect green light. At the same time, they also reflect near infrared light, which we can’t see. Healthy plants with more chlorophyll are known to reflect more NIR, so by analyzing the difference in its reflection, it is possible to get a picture of a crop’s health. Healthy crops will appear as red in the satellite imagery, while yellowish areas show unhealthy crops.

Credit: Jeff Carns, NASA (https://science.nasa.gov/ems/08_nearinfraredwaves)

Infrared Cameras

Another way to measure NIR is with infrared cameras that can provide NIR images of plants.

Near Infrared in Agriculture & Plant Research

Spectroscopy measures the photons that are released and absorbed by NIR interaction with different compounds in plants, food materials, or compost. The results can provide information on many chemical and physical parameters in crops, fruit, soil, and processed food. NIR spectroscopy, which is a non-destructive technique, has several applications in agriculture:

• Fertilizer application can be regulated by qualitative analysis of soil fertility and plant tissues. Here, the amount of different nutrients, such as nitrogen, phosphorus, and organic matter in the soil, is quantified. Alternatively, the concentrations of the nutrients can be measured in leaf tissues to check for their absorption by the plants. If there is a need for more nutrients, the correct amounts can be applied.
• Irrigation schedules can be optimized by determining moisture content in soil through NIR analysis. Irrigation can be provided as and when necessary to maintain crop health and prevent excess water use.
• Harvest time can be determined by measuring fruit ripeness or quality. This is done by measuring different compounds and the water content of the fruit. For example,
  • The F-750 Produce Quality Meter measures total soluble solids, dry matter, acidity, the internal and external color of many fruits, such as apples, grapes, kiwis, mandarins, mangos, pears, and persimmons, to provide information that determines if the fruit is ripe enough to harvest.
  • The F-751 Avocado Quality Meter is specially designed to measure ripeness based on dry matter content, allowing harvests to be scheduled.

Advantages of NIR Spectroscopy

While many other methods of NIR are also non-destructive, NIR spectroscopy is by far the most popular method used. It can be easily applied through the use of handheld instruments that take thousands of measurements a day. Its ability to be used in the field increases the number of uses. NIR spectroscopy has the advantage of being swift, cheap, and accurate, with instruments like F-750 and F-751 in a price range affordable by even small farmers. Moreover, NIR analysis is environmentally friendly, as it involves no use of chemicals and entails no occupational hazard for farmers or laboratory personnel. It is therefore not surprising that it is replacing traditional analytical methods in agriculture and the food industry.

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Vijayalaxmi Kinhal
Science Writer, CID Bio-Science
Ph.D. Ecology and Environmental Science, B.Sc Agriculture

Sources

Garcia-Sanchez, F., Galvez-Sola, L., Martínez-Nicolás, J. J., Muelas-Domingo, R., and Nieves, M. (2017). Using Near-Infrared Spectroscopy in Agricultural Systems. In K. G. Kyprianidis and J. Skvaril (Ed.) Developments in Near-Infrared Spectroscopy. Intech Open publishers. Retrieved from DOI: 10.5772/67236

Paschotta. R. (2008, October). Infrared light. In Encyclopedia of Laser Physics and Technology, 1. edition October 2008. Wiley. Retrieved from https://www.rp-photonics.com/infrared_light.html

National Aeronautics and Space Administration, Science Mission Directorate. (2010). Reflected Near-Infrared Waves. Retrieved from NASA Science website: http://science.nasa.gov/ems/08_nearinfraredwaves

Lucas, J. (2015, Mar 26). What Is Infrared? Retrieved from https://www.livescience.com/50260-infrared-radiation.html

Persechini, L. (2018, May 14). Near-Infrared: A fact sheet. Retrieved from http://blogs.nature.com/onyourwavelength/2018/05/14/near-infrared-a-fact-sheet/.

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