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The basic principle of spectroscopy involves dissecting the light of a specific object into various wavelengths that represent different physical properties of the object, some of which include temperature, mass, luminosity and composition.
Some of the most commonly used analytical spectroscopy techniques include:
- Infrared Spectroscopy (IR)
- Near-infrared (NIR) Spectroscopy
- Nuclear Magnetic Resonance (NMR)
- Ultraviolet-Visible Spectroscopy (UV-Vis)
- Atomic Emission Spectroscopy (AE)
- Atomic Absorption Spectroscopy (AA)
For agricultural applications, spectroscopy offers a highly sophisticated way of performing quality control of food products, investigating chemical purity levels within the soil, maximizing harvest supplies, analyzing fertilizer properties and much more. This article will further discuss current agricultural applications of spectroscopy.
Determining Soil Quality with Spectroscopy
The quality of the soil being used in both farming and agricultural applications plays a major role in determining the overall rate of food production in these locations. Since mass production of food products and extended harvesting seasons can potentially deplete soil quality, farmers and agricultural managers must often supply their soil with supplemental nutrients, such as fertilizers, to promote optimal conditions and a continued growth of their cops. While useful for promoting crop growth, these nutrient additives must be closely monitored to ensure that the proper nutrient contents are supplied to the soil.
Most agricultural fertilizers contain excess concentrations of both nitrogen and phosphorus, both of which must be closely analyzed to ensure that healthy crops are produced in higher yields. Both phosphorus and nitrogen are essential elements that promote plant growth and sustainability.
One analytical technique that has been successful in a recent study to determine the concentrations of phosphorus present within sugarcane juice, water, fertilizer and detergent samples is a UV-Vis spectrophotometer1. Molybdenum blue is a commonly used technique that can accurately determine the concentrations of inorganic phosphate within a sample. During this specific experiment, the absorbance of phosphomolybdenum blue, which resulted from the reaction between molybdenum blue and any inorganic phosphates present within the sample, was measured from 800 to 900 nm to determine the lmax. The reaction requires about 35 minutes to complete, By utilizing this UV-Vis, agricultural workers can rapidly determine the presence of phosphates within their samples without requiring any analyte extraction or HPLC to be performed.
Since many different forms of nitrogen fertilizers exist, there is a significant need for agricultural workers to be able to quickly analyze and measure the presence of nitrates within their soil samples. Similar to the method which was utilized for the analysis of phosphorus, a simple technique can be used to detect the presence of nitrates within a fertilizer sample by initially adding several drops of concentrated iron sulfate (FeSO4) solution to the sample. X-ray absorption spectroscopic analysis can subsequently be conducted to quantify the purple hue of the sample and ultimately determine the nitrate levels present within a given fertilizer sample.
NIR Spectroscopy in Agriculture
NIR spectroscopy is a useful analytical technique that can provide users with a rapid method of determining the nutrient composition of food samples. The earliest agricultural application of NIR spectroscopy dates to 1989 when Karl Norris and colleagues utilized this analytical method to investigate protein and moisture levels in grains, as well as protein, oil and moisture levels of soybean samples2. Since its introduction into the agricultural industry, NIR continues to be a key analytical technique that is used for plant, animal and soil analysis. The major advantages associated with the use of NIR spectroscopy for these purposes is due to its ability to rapidly produce results at costs that are up to 80% lower than traditional laboratory analytical tools.
Several publications have recently emerged in which NIR spectroscopy was utilized for agricultural analysis, one of which involved the detection of grass mixtures in fields. By understanding the quantities of different grass mixtures present within fields, farmers are able to better understand the fiber and other nutritional content being ingested by cattle. In the Cherny et al. study, a group of researchers collected grass samples from 91 different sites around New York in 2011, 2012 and 20143. The NIR spectrum was measured for each grass sample following drying and ensiling processes. The model was again validated in 2015 when 98 samples were separated, dried and recombined in random unknown mixtures to assess whether the NIR signals continued to accurately reflect the known compositions. The researchers therefore determined that NIR spectroscopy is a useful tool that can be used to predict the grass composition present in cattle fields at a rapid and affordable rate.
- Pradhan, S., & Pokhrel, M. R. (2013). Spectrophotometric determination of phosphate in sugarcane uice, fertilizer, detergent and water samples by molybdenum blue method. Scientific World 11(11).
- Burns, D. A., & Ciurczak, E. W. (2001). Handbook of Near-Infared Analysis, Second Edition.
- Karayilanli, E., Cherny, J. H., Sirois, P., Kubinec, D., & Cherney, D. J. R. (2016). Botanical composition prediction of alfafa-grass mixtures using NIRS: Developing a robust calibration. Alliance of Crop, Soil and Environmental Science Societies. DOI: 10.2135/cropsci2016.04.0232.