Introduction:

Agricultural production is the mainstay of many emerging nations. Fertilizer is primarily used in agriculture to provide the full range of macro and micronutrients that the soil typically lacks. Fertilizer accounts for 35–40% of crop productivity; nevertheless, some fertilizer directly impacts plant development. The three main nutrients—nitrogen, phosphorous, and potash—are needed in significant amounts by plants in order to survive and grow healthily. Increased productivity levels and agricultural intensification have resulted in a multiplication of nutrient deficits beyond the NPK scenario due to the removal of secondary and micronutrients, which is actually a key barrier to achieving higher production levels. Although the use of chemical fertilizers has been steadily rising over time, the efficiency of how they apply nutrients—N (30–40%), P (15–20%), K (50–55%), and micronutrients (2–5%)—remains low. This is because nutrients are either lost from soils or are converted into slowly cycling or recalcitrant pools within the soils. The efficiency of fertilizer use is decreasing in India over time. Making increased fertilizer use more profitable, appealing, and sustainable for farmers is the main priority. This can be attained by the application of nanotechnology. The art and science of working with matter at the nanoscale (1 nm = 10-9 m, or one billionth of a meter) is known as nanotechnology. Utilizing nanoparticles smaller than 100 nm, nanotechnology may present a hitherto unheard-of chance to create concentrated plant nutrition sources with increased absorption rates, more effective utilization, and lower losses. Richard Feynman introduced the idea of nanotechnology for the first time in 1959. Norio Taniguchi first used the word “nanotechnology” in 1974. Heinrich Rohrer is the father of nanotechnology.

Nano-fertilizers

Nano-Fertilizers are substances that are produced and modified using nanotechnology to boost soil fertility, increase crop quality, and increase agricultural production. A product is referred to as a nano-fertilizer if it increases nutrient efficiency by utilizing nanotechnology or nanoparticles. Nano-fertilizers are designed to regulate the release of nutrients based on crop requirements. They are considered to be more efficient than conventional fertilizers. Nano-fertilizers can be used to reduce nitrogen loss due to leaching, emissions, and long-term uptake by soil microorganisms. Fertilizers with a slow, regulated release help enhance soil by minimizing the negative consequences of excessive fertiliser use.

Three categories of Nano-fertilizers are proposed

1. Nanoscale fertilizer: Nanoparticles which contain nutrients in it. 

2. Nanoscale additives: Traditional fertilizers containing nanoscale additives. 

3. Nanoscale coating: Traditional fertilizers coated or loaded with nanoparticles.

Conventional fertilizers are mostly employed in the current agricultural system to fulfill the nutritional needs of the crop plants. The two main methods used to apply conventional fertilizers in agricultural fields are spraying and broadcasting. Out of the overall concentration or volume applied, the concentration of conventional fertilizers that actually reaches the targeted site in the plants is much lower than the desired concentration.  The primary causes of conventional fertilizer losses include runoff, leaching, evaporation, drift, hydrolysis by soil water, microbiological breakdown, and photolytic destruction. The natural flora of the soil is declining due to increased fertilizer use, and the soil’s capacity to fix nitrogen is also decreasing. Nanotechnology has made it possible to study nano structured materials as fertilizer or controlled vectors for the construction of smart fertilizers as new facilities to improve NUE and reduce the costs. Improved nutrient uptake efficiency, site-directed agrochemical distribution, and decreased environmental toxicity, particularly in water bodies, are the main advantages of nanofertilizer over conventional fertilizers. When compared to traditional fertilizers, the mineral nutrients have a better bioavailability. Compared to conventional fertilizers, the chemicals would be available to plants for a longer period of time. The remaining conventional fertilizers are transformed into insoluble salts in the soil and are only available at the time of delivery.

Synthesis of Nano-fertilizers

According to Arole and Munde’s (2014) report, there are two established approaches for synthesizing nanomaterials: the Top-down approach, which involves breaking down bulk materials into small pieces by applying an external force, and the Bottom-up approach, which involves combining and gathering gas and/or liquid atoms or molecules. In terms of how NPs are made, Satyanarayana and Reddy (2018) highlighted out that physical techniques such as irradiation, mechanical pressure, ultra-sonication, thermal energy, or electrical energy are used to melt, abrade, condense, or evaporate materials. The top-down strategy used in these physical procedures has the advantages of being time- and energy-consuming, solvent-free, and producing homogenous monodisperse nanoparticles; nevertheless, physical processes are less cost-effective due to the large amount of waste generated during this synthesis. Conversely, some of the most often used techniques in the synthesis of nanoparticles are chemical ones, such as the sol-gel method, hydrothermal synthesis, micro-emulsion technique, polymer synthesis, chemical vapour synthesis, or plasma accelerated chemical vapour deposition technique. Green synthesis and biosynthesis, two bioassisted techniques that are efficient, low-toxic, and safe for the environment, are offered as alternatives to chemical and physical approaches in the synthesis and fabrication of nanoparticles. 

Types of Nano-fertilizers

1. Macronutrient Nano-fertilizers: Macronutrient nano-fertilizers are made up of one or more macronutrient elements, such as nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and sulphur (S). But eventually, significant amounts of these fertilizers (N, P, and K) find their way into surface and groundwater, seriously harming aquatic ecosystems. Therefore, in order to achieve sustainable food production based on the preservation of the ecological environment, it is imperative to produce highly effective and environmentally safe macronutrient nano-fertilizers.

Nitrogen nano – fertilizer: Different approaches, such as polyolefin resin-coated urea, neem coated urea, and sulphur coated urea, were taken to regulate the N release in order to address the issues related with nitrogen leaching during fertilisation. However, slow-releasing fertilisers are frequently expensive, and when N levels grow high, N is released slowly. Cation exchangers can be used as fertiliser additives to limit NH4 + release and decrease N loss. Zeolite increases crop productivity by retaining necessary nutrients and releasing them when they are needed. The porous material clinoptilolite zeolite (CZ), which has a high cation exchange capacity (CEC, up to 300 c mol (p+) kg-1) and a strong affinity for NH4+(Ming and Mumpton, 1989), has been utilised to reduce NH3 emission from farm manure (Amon et al., 1997) and to eliminate NH3 toxicity to plants (Gupta et al., 1997). According to Perrin et al. (1998), clinoptilolite not only increases the effectiveness of nitrogen fertilisation, but also lowers nitrate leaching by preventing the nitrification of ammonium to nitrate. Lefcourt and Meisinger (2001) stated that   Zeolite has the capacity to decrease ammonia volatilization by sequestering ammonium-N on exchange sites.  Latifahet al. (2011), reported that the combination of urea with zeolite and sago waste water provided a significant advantage over urea alone,as the mixture promoted the synthesis of ammonium and readily available nitrate ions over ammonia. Additionally, the mixture increased the soil’s ability to retain available nitrate and exchangeable ammonium.

Phosphorus nano-fertilizer: As the zeolite absorbs Ca2+ from the phosphate rock, phosphate and ammonium ions are released. Contrary to the leaching of very soluble phosphate that established equilibrium, the controlled-release phosphate in fertilisers (such as super phosphate) is released as a result of a particular chemical process in soil. By altering the proportion of P rock to zeolite, the rate of phosphate release is regulated.  Allen et al. (1996) conducted an experiment to look at the solubility and cation-exchange in mixtures of rock phosphate and NH4+. K-saturated clinoptilolite showed that mixing phosphate rock and zeolite had the ability for slow-release fertilisation of plants in synthetic soils through dissolution and Ion exchange processes. As the zeolite absorbs Ca2+ from the phosphate rock, phosphate and ammonium ions are released. he controlled-release phosphate in fertilisers (such super phosphate) is released as a result of a specific chemical reaction in soil, unlike the leaching of very soluble phosphate that created equilibrium. The rate of phosphate release is controlled by varying the ratio of P rock to zeolite.  In a percolation reactor, SharmilaRahale (2011) examined the PO4-release patterns of surfaces treated with various nanoclays and zeolite. It has been shown that while conventional fertilizers only release nutrients for a maximum of 10–12 days, nano-formulations release phosphate for 40–50 days.

Potassic nano-fertilizer: Some naturally occurring zeolites have high exchangeable K+ concentrations that can promote plant development in potting soil medium. Zhou and Huang (2007), By supplying more vital cations and anions to plant roots, zeolites can develop into a superior substrate for plant growth. This is because zeolites have the potential to exchange ions with specific nutrient cations.

Secondary nano-fertilizers: Secondary nutrients such as sulphur (S), calcium (Ca), and magnesium (Mg) need to be present in relatively high amounts for crop development to be healthy. Zeolite demonstrated a slowrelease fertilizer for calcium and magnesium, according to Supapronet al. (2007). They said that zeolite improved the magnesium and calcium content of the soil. Fansuriet al. (2008), stated that zeolite may freely exchange nutrient ions like calcium and magnesium.

2. Micronutrient Nano-fertilizers: Compared to macronutrients, micronutrients provide plants with relatively small amounts of essential nutrients. They are key elements to activate enzymes and the synthesize biomolecules involved in plant defence. Therefore, as well as, macronutrient Nano-fertilizers, it is also necessary to apply micronutrient Nano-fertilizers to plants, including boron (B), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), zinc (Zn) and chloride (Cl). The capacity of five naturally occurring zeolites and bentonite minerals to adsorb and release zinc and iron was studied by Shetaet al.(2003). The Langmuir and Freundlich equations were used to determine the potential for sorption of these ions. According to the findings, natural zeolites, particularly minerals like chabazite and bentonite, have a great potential for sorption of Zn and Fe as well as a high capacity for slow-release fertilisers. According to Pandey et al. (2010), zinc-rich ZnO NPs raised the amount of IAA in roots (sprouts), which suggests that plants are growing more quickly because zinc is a necessary nutrient for plants.

 

Advantages of Nano-fertilizers

 A Nano-fertilizer releases nutrients in a slow and steady rate for a longer period thereby reducing the nutrient losses and improving the nutrient use efficiency.

 Increased crop yields: Nanotechnology can be used to improve plant growth and yield, allowing farmers to produce more food with less land and resources.

 Reduced use of pesticides and fertilizers: By using targeted delivery systems for pesticides and fertilizers, farmers can reduce the amount of these chemicals needed and minimize their impact on the environment.

 Enhanced food safety: Nanotechnology can be used to develop sensors and monitoring devices that can detect contaminants and pathogens in food, improving food safety and reducing the risk of foodborne illness.

 Soil remediation: Nanoparticles can be used to remove pollutants and heavy metals from soil, improving soil health and reducing contamination of crops.

 Integration of biosensors to the Nano-fertilizers will help in selective release of nutrients according to soil nutrient status, crop growth period and environmental conditions.

 Nano-biofertilizers: Encapsulation of beneficial microorganisms by nanotechnology can enhance plant health. As this could include bacteria or fungi that can improve nitrogen, phosphorus and potassium availability in the root zone.

 Reduction in the emission of greenhouse gases

 

Limitations of Nano-fertilizers

Environmental risks: The use of nanoparticles in agriculture may pose environmental risks, such as soil contamination or unintended impacts on non-target organisms.

Health risks: There is still limited understanding of the potential health risks associated with exposure to nanoparticles, particularly over the long term.

Regulatory challenges: The regulation of nanotechnology in agriculture is still evolving, and it can be difficult to assess the safety and efficacy of new nanotechnology-based products.

Ethical concerns: There are also ethical concerns related to the use of nanotechnology in agriculture, such as potential impacts on small farmers or the exacerbation of social inequalities.

 

Effect of nano-fertilizers on plant growth:

The development of zeolite-based nano-fertilizer has attracted significant economic interest due to the rising awareness and the availability of low-cost natural zeolites worldwide.   Chuprova et al. (2004) stated that zeolite fertilisers have positive impacts on Chernozem’s mobile humus components and the biological productivity of maize. In a different study, it was discovered that a patented nano-composite of N, P, K, micronutrients, mannose, and amino acids increased the uptake and utilisation of nutrients by grain crops (Jinghua, 2004). Bhattacharya et al. (2004), found that a balanced application of NPK coupled with S, Zn, B, and Mo will be a successful strategy for increasing pulses’ grain yield in red and lateritic soils.  With adequate NPK treatment Green and blackgram yield gets increased by 13% and 38% in comparison to control. Liu et al. (2006) demonstrated that the organic material (polystyrene) intercalated in the layers of kaolinite clay produces a cementing of nano and subnano-composites that can control the release of nutrients from the fertilizer capsule. Nanoparticles could therefore be employed to control the release of nutrients across membranes. The efficacy of natural and artificial nutrient sources can be increased by the use of nanotechnology. The efficiency of crops’ fertilizer use is increased via nano-fertilizer technology. Since the public has become increasingly concerned about the negative effects of chemical fertilizers on the agro-ecosystem, there has been an increase in interest in the usage of nano-porous zeolites in farming (Ramesh et al., 2010). These findings and patented goods strongly imply that there is a huge potential market for the creation of nano-fertilizers (De Rosa et al., 2010). The use of nano-fertilizer could be a tactic to increase crop productivity and nutrient use efficiency.

Effect on crop yield:

Jahnzabet al., (2015) conducted pot experiment to study the effect of silver nano-particles (SNPs) on number of grains/spike, 100-grain weight and yield/pot of the Wheat crop. The treatments were seven graded doses of SNPs (0, 25, 50, 75, 100, 125, 150 ppm) results revealed that the largest number of grains/spikes and grain yield were recorded by silver nanoparticles at a concentration of 25 ppm, but a concentration of 75 ppm led to a decrease in grain yield. Hence, silver nanoparticles affect wheat development and yield in both stimulatory and inhibitory ways. Mehta and Bharat (2019) carried out an experiment in the clay loam soil of Jammu to investigate the impact of combined use of nano and non-nano fertilizers on wheat yield and yield attributes. They discovered that the most effective treatment for increasing wheat crop grain yield was 100 % NPK + Nano NPK (L) sprays at 20, 30 and 45 DAS @ 3 ml/litre of water + 2 Nano-K (L) sprays at grain development stage @ 4 ml/litre of water 115 and 125 DAS). 

Conclusion:

Although nano-fertilizers have significantly lower losses and a higher absorption rate than conventional fertilizers, they have the potential to reduce environmental contamination when applied alone or in combination with organic materials. The physical, chemical, and biological characteristics of soil are enhanced by nano-fertilizers, which also maintain soil productivity. In addition, research on the effects of nano-fertilizers on plant growth, germination rate, height, root development, and leaf chlorophyll were carried out. likewise, slow-release fertilizers with a nanoparticle covering improve absorption of photosynthetically active sunlight and optimize nutrient utilization efficiency. The application of nano-fertilizers is anticipated to boost crop yields and could be cost-effective for farmers.

Ms Jyoti Sharma, Assistant Professor

Ms Jyoti Sharma, Assistant Professor

School of Agricultural Studies, Geeta University, Panipat, Haryana

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