The quality of fertilizers used in crop production is critical in ensuring that the right amount of nutrients is available to plants throughout the growth cycle. Excess or low levels of some nutrients can be harmful to plant health; therefore, it is critical to keep track of the nutrients in fertilizers.
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Importance of Fertilizers
Fertilizers replenish the nutrients lost by crops in the soil, and agricultural productivity would suffer if fertilizers were not used. Since minerals are readily absorbed and utilized by plants, mineral fertilizers are commonly employed to supplement the soil's nutrition pool. In addition, the fertilizers provide critical elements that improve the soil's ability to retain water while also increasing its fertility.
Why is Analysis of Fertilizers Needed?
The macronutrients, phosphorus, nitrogen, and potassium in fertilizer determine its quality. At the same time, certain secondary elements such as magnesium, calcium, sulfur, and trace amounts of boron, copper, cobalt, iron, molybdenum, manganese, and zinc are present in small amounts but are essential for plant growth.
The elemental analysis of fertilizer ensures that the nutrients are present in sufficient quantity. Therefore, it protects the crops by preventing deficiency or excess nutrients in the fertilizer. Furthermore, the analysis also ensures that the quality and content of the fertilizer meet legal criteria.
Methods of Elemental Analysis
The elemental analysis of fertilizers can be done using inductively coupled plasma atomic emission spectroscopy (ICP-AES), flame atomic absorption spectroscopy (FAAS), and Microwave Plasma Atomic Emission Spectroscopy (MP-AES).
Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES)
ICP-AES is an analytical technique that can identify the trace quantities of nutrients in the fertilizer. In this technique, high-temperature plasma controlled by an electromagnetic field is used to excite atoms.
The emission technique is based on the ability of stimulated atoms to emit light. Whenever electrons in atoms that have acquired enough energy migrate to higher energy levels, they release energy in electromagnetic radiation. An atom of each element emits at a certain wavelength that is unique to that element's spectrum.
Element-specific maximum intensity bands correspond to the most likely electronic transitions in atoms. Because various elements have maxima at different wavelengths, determining whether light with the relevant wavelength is present in the spectrum is sufficient to identify an element in a sample.
The nutrient concentration in the fertilizer can be determined by measuring the intensity of light at the appropriate wavelength and using the calibration curve.
Flame Atomic Absorption Spectroscopy (FAAS)
Flame atomic absorption spectroscopy was first experimented with in 1952 and commercialized in the 1960s. Due to its simplicity and durability, the method has continued in use ever since. The method is based on determining the selective absorption of distinctive radiation by the atomic vapors of the sample (fertilizer). It can determine how much of the required nutrients are present in the fertilizer.
It is based on the notion that atoms and ions may absorb particular wavelengths of light. The atom absorbs the energy (light) when this precise wavelength of light is delivered, and electrons migrate from the ground to the excited state. The concentration of any ingredient in the fertilizer is then calculated by measuring the light absorbed by it.
Microwave Plasma Atomic Emission Spectroscopy (MP-AES)
Recently, elemental analysis has been performed using Microwave Plasma Atomic Emission Spectroscopy (MP-AES). MP-AES is a multi-element analytical approach based on fast sequential emission that utilizes magnetically linked microwave radiation to build a robust and stable plasma from nitrogen gas.
The gas can be supplied via a cryogenic cylinder (Dewar), a tank, or a gas generator powered by compressed air. Nitrogen removes the need for more expensive and hazardous gases such as acetylene, hence boosting laboratory safety and enabling unsupervised operation.
Additionally, the nitrogen plasma achieves a temperature of around 5000 K, which eliminates many chemical interferences prevalent in flame atomic absorption spectroscopy. Atomic emission is strong at these temperatures, resulting in excellent detection limits and linear dynamic range for most components.
Importance of the Elemental Analysis and Future Developments
The current focus of agriculture is on high-quality output while also protecting the environment and natural resources, such as soil fertility. To do this, the nutrients used to feed plants or improve fertilizer qualities must follow strict standards. An in-depth understanding of fertilizer quality can be gained through elemental analysis techniques. This information helps calculate the optimum amount of fertilizer to meet the crop's needs to maximize the yield output.
However, the wide spectrum of nutrients in fertilizer samples makes elemental analysis difficult. In addition, it can be challenging to get accurate results when there are high levels and low levels of trace elements in the same sample. As a result, analytical laboratories are frequently necessary to produce repeated dilutions to achieve analysis for all elements, depending on the technique utilized and the analytical working range of the technique.
References and Further Reading
Chauhan, P., & Chauhan, R. P. (2014). Measurement of fertilizers induced radioactivity in tobacco plants and elemental analysis using ICAP–AES. Radiation Measurements, 63, 6-11. https://doi.org/10.1039/C8JA00077H
Liberato, C. G., Juan, A. V. A., Barros, A. V., Raquel, C., Machado, A. R. A., Nóbrega, J. A., & Schiavo, D. (2020). Determination of macro and micronutrients in plants using the Agilent 4200 MP AES. Available at https://www.perlan.com.pl/uploaded/AppBundleEntityProductApplication/fileKey/260/4200mp-aes-5991-7856en-plant-nutrients.pdf
Morari, Francesco & Vellidis, George & Gay, P.. (2011). Fertilizers. Encyclopedia of Environmental Health. pp 727-737 https://doi.org/10.1016/B978-0-444-52272-6.00464-5
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