Food security is under serious threat due to a continual increase in the global population. Fertilizers are used in the agricultural field to enhance crop yield; however, it is important to evaluate the amount of harm a synthetic fertilizer is causing to our environment.
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Although synthetic fertilizers initially enhance crop production, they leave behind some chemical components that have detrimental effects on the environment. Nanotechnology has significantly changed the global agriculture canvass. The use of nanomaterials as nanofertilizers enhances crop production and supports a sustainable agriculture system.
Although large quantities of fertilizers are applied directly to the soil or sprayed on the leaves, only a small amount reaches the target site. This happens due to chemical leaching, hydrolysis, drift, runoff, evaporation, photolytic reactions, or even microbial degradation. This results in excessive use of fertilizers, thereby affecting the inherent nutrient equilibrium of the soil. Also, many synthetic fertilizers remain in the soil for a longer period or contaminate the adjacent rivers or underground water.
Nanoparticles as Nanofertilizers
Nanoparticles are small molecules whose sizes range between 1-100nm and possess many dynamic physical, chemical, thermal, optical, magnetic, and biological properties. These particles have a large surface-to-volume ratio, and their physicochemical properties differ from the bulk materials. Scientists have applied nanoparticles in various disciplines of science and technology, including agriculture.
The development of nanofertilizers has played a major role in supporting sustainable agriculture. Nanofertilizers are classified into three categories, i.e., macro, micro, and nanoparticulate fertilizers.
Nanofertilizers come in different forms, such as nanopowder, nanocapsules, and nanoemulsions. These fertilizers provide nutrients to plants in an available form and enhance their productivity and quality. Some of the key features of nanofertilizers that help to resolve nutrient shortages are described below:
- Provide suitable nutrients for increasing plant growth via foliar and soil applications.
- Developed cost-effectively and are regarded as a sustainable source of plant nutrients.
- Help prevent pollution.
These are applied either via the soil or foliar application. Foliar application of nanofertilizers is the most efficient method that balances nutrient deficiencies and improves crop yield and quality, effectively decreasing the quantity of fertilizer used. Researchers have reported that nanoparticles greater than 10 nm can penetrate via stomata. These fertilizers are regarded as smart delivery systems owing to their high absorption capability and greater surface-to-volume ratio. Nanocarriers can deliver important metabolites or nutrients to a specific site at an appropriate time.
Nanofertilizers and Nutrients Flow
As stated above, a large amount of inorganic fertilizers that are added to the soil are lost due to various factors, and, subsequently, more fertilizers are added in the same field.
To reduce this overuse, slow-releasing nanofertilizers are used. This system also allows plants to absorb sufficient nutrients and, thereby, healthy plants are grown. Some of the bioactive compounds have multiple beneficial effects, such as enhancing plant growth and protecting the plants from biotic and abiotic stress. Nanoencapsulation is a system that allows active ingredients to be released from particles in a slow and controlled matter. This system protects the bioactive compounds to lose efficacy that are often susceptible to heat and oxidation.
Polymers-coated nano-fertilizers aid in the slow release of nutrients. Polymeric chitosan nanomaterials (size of 78 nm) have been developed for the controlled release of nano nitrogen-phosphorus-potassium (NPK) fertilizers.
Nanoporous zeolites are silicate materials that possess a high surface-to-volume ratio and cation exchange capacity. The layered structure of zeolites helps the easy loading of nutrients such as potassium and nitrogen. One of the main advantages of using a zeolite-based nanofertilizer is the ability to release nutrients gradually, making them available for the plant throughout the growing season. Urea-hydroxyapatite nanofertilizer are also used for the slow release of nitrogen.
Role of Nanofertilizers in Crop Improvement
Scientists have synthesized many micronutrients, such as silica, copper, zinc, and iron at a nanoscale which helps plant growth management. For instance, nano Fe-chelated plant growth-promoting rhizobacteria nanofertilizer has a tremendous effect on maize growth and grain yield.
Also, foliar application of zinc nanoparticles along with Bradyrhizobium japonicum improved plant growth, yield, and quantity and quality of oil in soybean. Researchers observed an increase in the physiological properties, germination vigor, photosynthesis rate, and production of essential enzymes such as glutamic-pyruvic transaminase, nitrate reductase glutamine synthase, when the seeds of spinach were treated with 0.25–4.0% titanium dioxide nanoparticles.
Nanofertilizers enhance nutrient availability to plants. The application of nano NPK has been seen to increase the yield in wheat crops. Similarly, foliar application of zinc nanofertilizers has substantially increased plant growth and dry biomass of cotton and pearl millet.
An improvement in the plants’ quality and quantity is linked with improvement in physiological processes and biochemical reactions. Zinc nanofertilizer enhances the synthesis of plant growth hormones (e.g., natural auxin) by stimulating an essential enzyme that is associated with biochemical pathways, such as carbohydrate and protein metabolism, growth regulator metabolism, and pollen formation.
Application of titanium dioxide nanofertilizer as a foliar spray in the maize crop showed enhancement of the biomass of the plant by improving nitrogen assimilation and photoreduction activities of photosystem II and electron transport chain. Additionally, chlorophyll, anthocyanin, and carotenoid content of the plant also significantly improved. Researchers have also reported that the yield of chickpea, groundnut, and cotton increased substantially after applying zinc, iron, and NPK nanofertilizers.
Continue reading: Why Nanotoxicology Should be the First Step Towards a Nanotechnology Future.
References and Further Reading
Kaila, M.T. et al. (2021) Nanofertilizers in Agriculture. Acta Scientific Agriculture. 5 (3). pp.35-46. Available at: https://actascientific.com/ASAG/pdf/ASAG-05-0956.pdf
Shang, Y. et al. (2019). Applications of Nanotechnology in Plant Growth and Crop Protection: A Review. Molecules (Basel, Switzerland). 24(14), pp. 2558. Available at: https://doi.org/10.3390/molecules24142558
Zulfiqar, M. et al. (2019) Nanofertilizer use for sustainable agriculture: Advantages and limitations. Plant Scient. 289. 110270. Available at: https://doi.org/10.1016/j.plantsci.2019.110270