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Global food security is under serious threat across the world because of the limited availability of natural resources such as fertile land, quality seeds, and water. It has been estimated that the world population (currently 7.8 billion people) will increase to approximately nine billion by 2050. Global agricultural systems are facing numerous unprecedented challenges, including rapid climatic changes.
Fertilizers play a vital role in increasing agricultural production, but excessive use of chemical fertilizers irreversibly damages the chemical ecology of soil and reduces the available area for crop production.
Sustainable agriculture demands minimal use of agrochemicals. Advanced nanoengineering techniques are being used to overcome an agricultural crisis by developing an improved crop production system that assures sustainability.
Nanotechnology in the Production of Fertilizers
Nanomaterials improve the productivity of crops and efficiently regulate the delivery of nutrients to plants and targeted sites, guaranteeing the minimal usage of agrochemicals.
In conventional agriculture, an excess of fertilizer is applied directly into the soil or sprayed on the leaves, which surpass the nutritional need of the plant. This is because a very low percentage of fertilizer reaches its target site, due to leaching of chemicals, evaporation, drift, hydrolysis, run-off, and photolytic or microbial degradation.
This excess of chemical fertilizer negatively affects the nutrient equilibrium of the soil, and causes contamination of local water supplies, due to the leaching of toxic materials into water bodies.
Nanomaterials can increase crop yield by increasing fertilizer nutrient availability in soil and nutrient uptake by plants.
These materials can suppress crop diseases by acting directly on phytopathogens through a variety of mechanisms, including the production of reactive oxygen species. These materials also enhance crop production indirectly by improving crop nutrition and boosting plant defense pathways.
The efficient use of nanomaterials may reduce the negative environmental impact of conventional agricultural practices. In recent laboratory analyses, it has been reported that nano fertilizers can improve crop productivity by enhancing the rate of seed germination, seedling growth and photosynthetic activity.
Nanomaterials incite the plant root and leaf surface, which are the main nutrient gateways of plant systems and highly porous at the nanoscale. The application of nano fertilizers can enhance the nutrient uptake of the plant through these pores, or the process can facilitate complexation with molecular transporters or root exudates through the creation of new pores, or by the exploitation of endocytosis or ion channels.
Additionally, several researchers have reported that a decrease in the size of nanomaterials facilitates an increase in the surface mass ratio of particles. This enables the absorption of abundant nutrient ions that is later desorbed slowly and steadily for an extended period. Therefore, formulations of nano fertilizers can provide balanced nutrition for crops throughout the growth cycle, which in turn improves agricultural production.
Nanobiosensors that react with specific root exudates are also being explored. These techniques are relatively new and have numerous ethical and safety issues that must be carefully studied before implementation.
The global agricultural landscape has radically changed since the revolution of green nanotechnology. Nano fertilizers are now being used in specific concentrations, in accordance with the nutritional requirements of the crops, ensuring minimal differential losses.
There are three types of nano fertilizers: nanoscale fertilizers, nanoscale additive fertilizers, and nanoscale coating fertilizers.
Nanoscale fertilizers are made of nanoparticles that contain nutrients. Nanoscale additive fertilizers are traditional fertilizers with nanoscale additives. Nanoscale coating fertilizers are traditional fertilizers coated or loaded with nanoparticles.
The encapsulation of nutrients most commonly produces nano fertilizers with nanomaterials. Preliminary nanomaterials are produced by using both physical (top-down) and chemical (bottom-up) approaches.
More recently, the targeted nutrients are either encapsulated inside nanoporous materials, coated with a thin polymer film particle, or coated with emulsions of nanoscale dimension.
Encapsulation of beneficial microorganisms, such as bacteria or fungi, has shown promise as it can enhance the availability of nitrogen, phosphorus, and potassium in the root zone, thereby improving plant growth.
Nanofertilizers can also be classified based on their actions: control or slow-release fertilizers; control loss fertilizers; magnetic fertilizers or nanocomposite fertilizers (which use a nanodevice to supply a wide range of macronutrient and micronutrients in desirable concentration).
Porous nanomaterials significantly reduce nitrogen loss by regulating demand-based release, and by enhancing the plant uptake process. Examples of porous nanomaterials include:
- Ammonium charged zeolites, which can enhance the solubility of phosphate minerals, showing an improvement in phosphorus availability and uptake by crops.
- Graphene oxide films, a carbon-based nanomaterial, can prolong potassium nitrate release, extending the time of function and minimizing losses by leaching.
- Nanocalcite (CaCO3-40%) with nano SiO2 (4%), MgO (1%), and Fe2O3 (1%) which not only improve the uptake of calcium, magnesium and iron, but also notably enhance the intake of phosphorous with micronutrients zinc and manganese.
References and Further Reading
Shang, Y., Hasan, K., Ahammed, G.J., Li, M., Yin H., and Zhou, J. (2019). Applications of Nanotechnology in Plant Growth and Crop Protection: A Review. Molecules, 24, 2558.
Adisa, I. O., Reddy, V. L., Peralta-Videa, J. R. et al., (2019). Recent advances in nano-enabled fertilizers and pesticides: a critical review of mechanisms of action. Environmental Science: Nano, vol. 6, no. 7, pp. 2002–2030.