Nano fertilizers may be considered as new frontiers of modern agro inputs and can revolutionize the field of soil fertility and fertilizer management in Bangladesh. It is well recognized that fertilizer plays a key role and its contribution compared to other inputs such as seed, variety, plant protection chemicals and irrigation is about 50-60% in increasing the yield. Unfortunately, the price of fertilizer is increasing at an alarming rate. This is due to the shrinking of natural resources being used since long. Moreover, the increasing use of chemical fertilizers, especially nitrogen fertilizers, causes irreparable damage to soil structure, environment, and health, and kills many beneficial microbes. Therefore, there is an urgent need to develop environment–friendly fertilizers with high nutrient values.
Nano fertilizers offer an excellent alternative enabling plants’ capability to increase nutrient usage, mitigate excessive harmful effects of chemical fertilizers, reduce soil toxicity and decrease application frequency. Moreover, nano biofertilizers are excellent materials which, when applied to soils, foliage or seeds colonize the rhizosphere and enhance growth by increasing the availability of nutrients to the host plants. Biofertilizers, through natural processes of nitrogen fixation, solubilizing phosphorus and stimulating plant growth through the synthesis of growth-promoting substances, restore the soil’s natural nutrient recycle and build soil organic matter.
Due to the growing population the country is facing challenges of increasing food production within limited land resources which is also shrinking every year due to infrastructure development and unplanned rural housing. Besides, impacts of climate change like low rainfall, drought, flooding, and heavy stormy rain coupled with the recent increase in oils and fertilizer prices have made the agro environment more unfavorable to obtaining the desired yield.
Nano fertilizers are broadly classified into three groups:
- Nano formulation of macronutrients,
- Nano formulation of micronutrients and
- Nutrients–loaded nanomaterials. Among the three groups, nanomaterials of nutrients are more popular compared to nanomaterials made of nutrients. The nutrient-loaded nanomaterials are environment-friendly and safe for workers. These fertilizers may be called slow-release fertilizers which release nutrients according to the needs of the crops. The coating includes polymeric nanomaterials, carbon-based nanoparticles, nanoclays, mesoporus silica etc. Porous nanomaterials significantly reduce nitrogen loss by regulating demand-based release, and by enhancing the plant uptake process.
Nano fertilizers can also be classified based on their actions:
- slow-release fertilizers,
- control loss fertilizers,
- nanocomposite fertilizers using a nanodevice to supply a wide range of macro and micronutrients in desirable concentrations.
Different types of nano fertilizers
The nano fertilizer is a full combination of organic materials, macro and micronutrient elements and humic substances that increase the fertility of the soil. The unique properties of nanoparticles, such as high sorption capacity, the increased surface-to-volume ratio, and controlled-release kinetics make them a potential plant growth stimulator.
Among the macronutrient fertilizers nano chelated mixed NPK 20-20-20 & 12-12-36 fertilizer, single nutrient based nano chelated nitrogen (17 %), phosphorus (17%), potassium (27%), calcium (7%), magnesium (6%) and sulphur (12%) are worth mentioning. Among the micronutrient fertilizers nano complete micro fertilizers as well as single nutrient-based chelated zinc (12%), boron (9%), and iron (9% &7%), manganese (12%), molybdenum (5%) and copper (8%) are the prominent ones. The beauty of these products is that they are available in powder form, completely soluble in water and absorbable through both soil and foliar application.
Formulation of nano fertilizers
Nano-formulations can be prepared through different methods:
- physical (top-down),
- chemical (bottom-up) and
- biological (biosynthetic). The raw materials used include ammonium humate, ammonia, urea, peat, plant wastes, and other synthetic fertilizers. An example of nano-formulation is nano-sized nitrogen fertilizer which is produced as a result of the deposition of urea on calcium cyanamid. Nano-nitrogen fertilizers are instrumental in enhancing the productivity of rice. This may be regarded as an excellent alternative to chemical fertilizers as it accelerates the growth of plants and reduces environmental pollution. Excessive use of conventional fertilizers causes environmental pollution by leaching, denitrification, and volatilization. Another effective nano fertilizer has been prepared by grinding urea and mixing it with different biofertilizers. This kind of nano fertilizer offers a slow and gradual release of nitrogen for an extended period meeting up to the ripening stage.
The recent methods in nano fertilizer formulation use targeted nutrients to be 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 Rhizobium, blue-green algae, mycorrhizae, azotobactor, asospirillum, phosphate-solubizing bacteria such as Pseudonomas and Bacillus spp, has shown promise as it can enhance the availability of nitrogen, phosphorus and potassium in the rhizosphere thereby promoting plant growth.
Mechanism of uptake
Nano fertilizers enter into plant issues either through roots or foliage. Although specific uptake and translocation of nano particles are yet to be known, several reports suggest that uptake and translocation of nano particles are mainly dependent on the size, shape and interaction behavior of nanoparticles with cell wall. Nano particles may enter through stomatal openings or cuticle into the vascular system via apoplastic and sympathetic pathway. The large particle with a size range of 50-200 nm prefers sympathetic pathway, while the smaller one with a size range of 10-50 nm prefers the apoplastic pathway.
Opportunities and Constraints
Nano fertilizers are excellent fertilizing materials that can fulfill the requirements of crops to produce desired yields and at the same time maintain soil health. Because of teeming millions, there is no alternative but to increase crop productivity. Due to recent price hikes and shortfalls in the supply of fertilizers, the vast majority of farmers in the country are growing crops under low fertility. It is afraid that the production target could not be achieved. Food security will be at stake.
Under such situations, the policymakers must encourage the scientists to take up initiative for appropriate research and standardize the materials as soon as possible. The government is facing a big burden to pay heavy subsidies on chemical fertilizers every year. The subsidy will increase as the prices of fertilizers in the international market is rising.
Despite of beneficial effects of nano fertilizers in increasing nutrient use efficiency, improving crop quality, controlling nutrient release, reducing loss and demand of fertilizer, reducing pest infestation, and improving soil health, some demerits of nano fertilizers are observed. These include creating toxicity by interacting with soil components, accumulating in plant tissue, and causing the death of some cells. Nanoparticles may also accumulate in food parts, which when consumed, may cause human health problems. These problems draw urgent attention, research, and solution.
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