Keywords

1 Introduction

Nanotechnology is one of the unique technologies of the twenty-first century. In the last decade, a large variety of nanomaterials (NMs) have been developed and used under the umbrella of nanotechnology in multifaceted sectors (Lien et al. 2017). The basis of nanotechnology was laid by Nobel laureate Richard P. Feynman through his popular lecture “There’s Plenty of Room at the Bottom” (Feynman 1960). Taniguchi (1974) first coined the term nanotechnology and stated that nanotechnology consists of the processing, separation, consolidation, and deformation of materials by one atom or one molecule. The term “nanotechnology” is based on the prefix “nano” which hails from the Greek word meaning “dwarf.” It is usually employed for materials having a size ranging from 1 to 100 nm (NNI 2009). Several researches had been awarded Nobel Prize for the development of nanotechnology (Table 26.1).

Table 26.1 Prizes for elucidating atoms and subatomic particles
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Nanotechnology, according to Joseph and Morrison (2006), is the modification or self-assembly of individual atoms, molecules, or molecular clusters into structures in order to produce materials devices with new or drastically different properties. Nanotechnology is the design, fabrication, and utilization of materials, structures, devices, and systems through control of matter on the nanometer length scale and exploitation of novel phenomena and properties (physical, chemical, biological) at that length scale in at least one dimension. Table 26.2 enlisted the size distribution of various natural and fabricated nanoparticles (NPs). At nanoscale, the chemical and physical properties of material change and surface area of material are large compared to its volume. This makes material more chemically reactive and changes the strength and electrical properties of material compared to the bulk counterpart. The synthesis protocols for diverse nanoparticles (NPs) were established and advanced to the molecular level (Gugliotti et al. 2004).Generally, it works by following the top-down (includes reducing the size of the smallest structures to the nanoscale) or the bottom-up (comprises manipulating individual atoms and molecules into nanostructures with nearly similar chemistry or biology) approach.

Table 26.2 Comparison in size between natural and fabricated nanoscale objects
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Nanotechnology has emerged as a cutting-edge technology, acting as a convergent science that attracts a plethora of disciplines (environmental science, energy, plant science, agriculture, materials physics, and nanomedicine) and sectors closely linked with human welfare (Gruère 2012; Dasgupta et al. 2016). The application of nanotechnology in various fields anticipated to be advantageous for society and the environment, reduce the cost of input and cause inflation, boost the quality of goods, open opportunities for jobs (Hansen et al. 2008). A wide range of applications of nanotechnology have emerged into the “agrifood sector” which include the nanosensors, tracking devices, targeted delivery of required components, food safety, new product developments, precision processing, smart packaging, nanofertilizers, and others (McClements et al. 2009; Huang et al. 2010; Ranjan et al. 2014; Dasgupta et al. 2016). Nanotechnology can also improve the water solubility, thermal stability, and bioavailability of the functional compounds of food (McClements et al. 2009; McClements and Li 2010). The use of NPs imparted tremendous efficiency compared to bulk particles or particulate matter (PM) because of their large specific surface area, diverse functionalities, easy functionalization, the presence of active sites on the surface, extraordinary electrical and optical properties, extremely high stability, and high adsorption capacity (Boparai et al. 2011; Zhao et al. 2014; Choi et al. 2015; Jiang et al. 2015; Kumar et al. 2015).

2 Applications of Nanotechnology in Agriculture

The present day agriculture is facing many challenges, such as changing climate due to the greenhouse effect and global warming; urbanization due to life pattern changes; non-judicious use of resources like petroleum, natural gas, high-quality rock phosphate, etc., that are non-renewable; and environmental issues like run off, eutrophication related with the application of more chemical fertilizers than required. These problems get more intensified by the world population, which is increasing at an alarming rate and is expected to reach 9.6 billion by the year 2050 (Desa 2008).The demand for global food production has increased during the last two decades. An increase by 70% in global grain production is required to feed this increasing world population (FAO 2009). Agriculture has always been the backbone of most of the developing countries to fuel the growth of economy. According to 2014–2015 estimates, India’s population is 1.27. With the concern of providing food to such a big population, there is a need of new technology in agriculture giving more yields in short period.

A significant increase in agricultural production could be achieved through utilization of nanotechnology for efficient nutrient management system, good plant protection practices, efficient photocapturing system in plants, precision agriculture, and many others (Tarafdar et al. 2013; Prasad et al. 2014) (Fig. 26.1). Table 26.3 showed the cosmparison between nanofertilizers and conventional products. Applications of nanotechnology in materials science and biomass conversion technologies applied in agriculture are the basis of providing food, feed, fiber, fire, and fuels. Nanotechnology provides a number of cutting-edge techniques for improving precision agricultural practices and allowing precise monitoring at the nanoscale level. In agriculture two types of nanomaterials are mostly used: (1) carbon based single- and multi-walled carbon nanotubes, (2) metal based aluminum, gold, zinc, and metal oxide based ZnO, TiO2, and Al2O3. Single and multi-walled carbon nanotubes are used as nanosensors and plant regulator to enhance plant growth (Khodakovskaya et al. 2012). Nanosilica is used in filtration of food and beverages and packaging. Metal oxides like ZnO, TiO2, and Al2O3 are used in nanofertilizers to boost the crop growth (Gogos et al. 2012; Sabir et al. 2014).

Fig. 26.1
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Nanotechnological developments in agricultural field

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Table 26.3 Property comparison between nanofertilizers and challenges in their applicability
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Application of nanotechnology has been regarded as an innovative and promising technology for sustainable agriculture, to feed the ever-increasing population of the world. It has revolutionized agriculture with innovative nutrients in the form of nanofertilizers (NFs), nanopesticides, and efficient water management system (Ditta and Arshad 2016). Conventional fertilizers with low use efficiency (20–50%) and cost-intensive increase in application rates have increased to develop and promote the use of NFs (Aziz et al. 2006). Many scientists worldwide have focused on this innovative field and have developed such NPs and NMs that could serve as nutrients for the plants (Liu and Lal 2015).

For agricultural use, it is preferable to have particle having size less than 20 nm, polydispersity index less than 1, zeta potential value apart from +30 mV and −30 mV, and mostly cubed shaped particle to enter through the plant pores (Tarafdar et al. 2012). Nanoparticles can be synthesized by physical, chemical, physicochemical (aerosol), and biological techniques. Grinding, thermal evaporation, sputtering, and pulse laser deposition technique are important physical methods. Chemical synthesis includes the technique like sol gel, co-precipitation, microwave synthesis, micro-encapsulation, hydrothermal methods, polyvinylpyrrolidone (PVP) method, and sonochemistry.

3 Nanofertilizers

Nanofertilizers are modified fertilizers synthesized by chemical, physical, or biological methods using nanotechnology to improve their attributes and composition, which can enhance the productivity of crops (Singh et al. 2017; Mahto et al. 2021). Nanofertilizers are nanomaterials that can supply one or more nutrients to the plants and enhance plant growth and yields or those that can improve the performance of conventional fertilizers but do not directly provide crops with nutrients. There are several advantage of using nanoformulation of fertilizers in agriculture (Table 26.4). Nanofertilizers can be classified as macronutrient nanofertilizers and micronutrient nanofertilizers (Fig. 26.2). Compared with the conventional fertilizers, these nanofertilizers are expected to significantly improve crop growth and yields, enhance the efficiency of fertilizer use and reduce nutrients losses, and/or minimize the adverse environmental impacts. Various benefits of using nanofertilizers are:

  • Higher product quality with minimum remnants.

  • Eco-friendly synthesis.

  • Custom-made products.

  • Lower-cost production, reducing the amount of fertilizers used.

  • Less negative impacts and toxicity.

  • Controlled release of plant nutrients.

Table 26.4 Advantages related to nanotech-modified formulation of conventional fertilizers
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Fig. 26.2
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Different types of nanofertilizers

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Small size of the NFs facilitate its effective absorption by the plants due to the tremendous increase in the surface area (Fig. 26.3). Moreover, these have the ability to enter into the cells directly as these materials are small sized, which reduces/bypasses the energy-intensive mechanisms of their uptake/delivery into the cell. Similar to the conventional fertilizers, NFs are dissolved in the soil solution and the plants can directly take them up. However, their solubility might be more than that of related bulk solids found in the rhizosphere due to their small size. These are more efficient compared to the ordinary fertilizers, as these reduce nutrient loss due to leaching, emissions, and long-term incorporation by soil microorganisms. Moreover, controlled release NFs may also improve fertilizer use efficiency (FUE) and soil deterioration by decreasing the toxic effects associated with over application of traditional chemical fertilizers (Suman et al. 2010). There are also reports about the use of nanoencapsulated slow release fertilizers. Recently, biodegradable, polymeric chitosan NPs (~78 nm) have been used for controlled release of NPK fertilizer sources such as urea, calcium phosphate, and potassium chloride (Corradini et al. 2010). Other NMs like kaolin and polymeric biocompatible NPs could also be utilized for this purpose (DeRosa et al. 2010).

Fig. 26.3
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General mechanisms employed by NFs for better uptake in plants

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3.1 Synthesis of Nanofertilizers

Nanofertilizers are synthesized by top-down (physical) or bottom-up (chemical) approaches. Top-down approach is a commonly used method. In top-down approach, the adsorbent or substrate used for synthesis of nanofertilizers such as zeolite or any other carrier is ball milled for several hours to achieve nanodimension. Usually, natural zeolite measures a range of 1000–3000 nm, and grinding using high-energy ball mill reduced the size of the particles. Manik and Subramanian (2014) reported that the ball milling of zeolite at 1, 2, 4, and 6 h had reduced the dimension 1078, 475, 398, 357, and 203 nm, respectively. The size reduction closely coincided with the increase in the respective surface area of 41, 55, 72, 83, and 110 m2 g−1. This phenomenal increase in the surface area provides extensive surface for nutrient adsorption and desorption. Despite the physical method of nanoparticle synthesis is very simple, the product is heterogeneous and particles often get agglomerated. To prevent agglomeration, stabilizing agents such as polymers or surfactants are used. Synthesis, characteristics, and nutrient release capability of some nanofertilizers are presented in Table 26.5.

Table 26.5 Synthesis, characteristics, and nutrient release from nanofertilizers
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The studies on slow release fertilizers (SRFs) based on zeolites are limited to nutrients, which can be loaded in cationic forms such as NH4+ and K+. However, if the nutrients are in anionic forms such as SO42−, NO3−, and PO43−, the loading is negligible on unmodified zeolites. Therefore, it is imperative that the material should have adequate affinity for anions so that the anionic nutrients can be efficiently loaded for its use as SRFs. Anionic properties can easily be imparted on the zeolitic surface using the concept of surface modification using surfactant. Surface modification facilitates the loading of anion into the zeolite’s surface by the anion exchange process. Haggerty and Bowman (1994) reported that surfactant modified zeolite (SMZ), a type of inexpensive anion exchanger has been shown to remove anionic contaminants from water. Hexadecyltrimethylammonium bromide (HDTMABr), a cationic surfactant, was used for surface modification of zeolite. It has been found that HDTMABr loading with a maximum of 200 mmol kg−1 corresponds to 200% of the zeolite’s effective cation exchange capacity. A surfactant bilayer forms and the surface reversed to positive (Li and Bowman 1997). Li et al. (1998) revealed that SMZ has been studied extensively in the last 15 years due to its high capacity of sorption and retention of oxyanions. The surfactant molecules (HDTMABr) form bilayers on zeolite external surfaces with the lower layer held by electrostatic interaction between the negatively charged zeolite surface and the positively charged surfactant head groups, while the upper layer is bound to the lower layer by hydrophobic forces between the surfactant tail groups in both layers (Bowman 2003). Surface modified zeolite showed positive results on the retention of chromate (Krishna et al. 2001) and phosphate (Bansiwal et al. 2006). Li and Zhang (2010) reported that the loading capacity of sulfate compared to nitrate on SMZ may be attributed to the charge effect of the anions. Each HDTMABr molecule contributes one positive charge, which needs only one negative charge to balance. Sulfate is divalent and thus needs two HDTMABr molecules to neutralize. Meanwhile, the HDTMABr surface configuration is not rigid because of the surfactant tail–tail interaction. Thus, bridging two HDTMABr molecules with one sulfate may be less favored compared to 1:1 neutralization of HDTMABr by nitrate.

3.2 Characterization of Nanofertilizers

Synthesized nanofertilizers are to be characterized using particle size analyzer (PSA), zeta analyzer, Fourier transform infrared spectroscopy (FTI-IR), Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDAX), transmission electron microscope (TEM), and atomic force microscope (AFM) to confirm the size, shape, charge distribution, functional groups, elemental composition, and attachment. The synthesized nanofertilizers have been characterized using the set of equipment (Table 26.6). Extensive studies had been undertaken to characterize nitrogenous (Subramanian and Sharmila Rahale 2013; Mohanraj 2013; Manik and Subramanian 2014), phosphatic (Bansiwal et al. 2006; Adhikari 2011; Behnassi et al. 2011), potassic (Subramanian and Sharmila Rahale 2012), sulfatic (Selva Preetha et al. 2014; Thirunavukkarasu 2014), and zinc (Subramanian and Sharmila Rahale 2012) fertilizers.

Table 26.6 Application of different instruments in characterization of nanoparticles
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4 Micronutrient Nanofertilizers

Micronutrients play an important role in many physiological functions of plants. These are required in a very small amount (≤100 ppm) but have a very critical role in various plant metabolic processes. These include chloride (Cl), iron (Fe), boron (B), manganese (Mn), zinc (Zn), copper (Cu), molybdenum (Mo), and nickel (Ni). These are applied to the plants either as Hoagland solution (Hoagland and Arnon 1950) or as foliar or applied in soil depending on crop species and also on the nutrient to be applied. These are also applied to the crop plants with composite fertilizers containing multiple macronutrients like NPK. Micronutrients present in these composites usually provide enough nutrients and cause little environmental risks. However, their availability is severely affected by small changes in pH, soil texture, and organic matter (Fageria 2009). So, it is most likely that under such circumstances, their optimum availability could be achieved through the application of NFs containing these micronutrients. A summary of the studies conducted regarding the investigation of the efficacy of each micronutrient-containing NPs is given in Table 26.7.

Table 26.7 Nanomicronutrient fertilizers and their effects on plant growth parameters
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4.1 Zinc Nanofertilizer

Many researchers around the world have focused on finding the effect of ZnO-NPs on the growth and productivity of crops. Out of all the micronutrients, it is the most widely studied in plant science worldwide. For example, optimal concentration of ZnO-NPs significantly enhanced the growth and yield parameters of mung bean and chickpea (Mahajan et al. 2011). Optimal concentration of ZnO-NPs to be applied depends on the nature of the crop. With the application of 20 mg L−1 ZnO-NPs to mung bean plants, an increase of 42%, 41%, 98%, and 76% in root length, root biomass, shoot length, and shoot biomass, respectively, was recorded. Moreover, the application of higher doses of ZnO-NPs caused a decrease in the growth rates of mung bean and chickpea. In another greenhouse experiment, the application of ZnO-NPs at the rate of 400 and 800 mg kg−1 caused a significant increase in the growth and yield parameters of cucumber (Cucumis sativus) (Zhao et al. 2014). The results clearly showed an increase of 10% and 60% in plant root dry mass with the application of 400 and 800 mg kg−1, respectively, as compared to control (without ZnO-NPs). However, the same rates caused a slight increase of 0.6% and 6% in the dry fruit weight, respectively, as compared to the control. Similarly, Lin and Xing (2007) reported a significant increase in the root elongation of germinated seeds of radish (Raphanus sativus) and rape (Brassica napus) with the application of ZnO-NPs at 2 mg L−1, in comparison to control (deionized water). The authors also found a significant improvement in the growth parameters of ryegrass (Lolium perenne) with the application rate of 2 mg L−1 metallic Zn-NPs. Seed germination was improved with the application of lower concentrations of ZnO-NPs in peanut (Prasad et al. 2012), soybean (Sedghi et al. 2013), wheat (Ramesh et al. 2014), pearl millet (Tarafdar et al. 2014), tomato (Raliya et al. 2015), and onion (Raskar and Laware 2014). In another experiment, a significant improvement in Cyamopsis tetragonoloba plant biomass, shoot and root growth, root area, chlorophyll and protein synthesis, rhizospheric microbial population, acid phosphatase, alkaline phosphatase, and phytase activity in cluster bean rhizosphere was recorded with the application of ZnO-NPs (Raliya and Tarafdar 2013). Similarly, Helaly et al. (2014) found that ZnO-NPs supplemented with MS-media promoted somatic embryogenesis, shooting, regeneration of plantlets, and also induced proline synthesis, activity of superoxide dismutase, catalase, and peroxidase, thereby improving tolerance to biotic stress. In contrast to these studies, many researchers have reported phytotoxicity of the application of Zn-NPs in various crop plants (Mahajan et al. 2011; Lin and Xing 2007; Lee et al. 2010; López-Moreno et al. 2010). However, phytotoxicity depends on the nature of crop plants. Overall, most of the crop plants usually require merely 0.05 mg L−1 soil solution. The researchers in these studies applied metallic Zn-NPs at a very high rate, ranging from 400 to 2000 mg L−1, which was the main reason for their toxic effects. Even the application of Zn-NPs at 10 mg L−1 to ryegrass proved harmful for normal growth (Lin and Xing 2008). In another study, among cucumber, alfalfa, and tomato, the application of ZnO-NPs only enhanced seed germination of cucumber (de la Rosa et al. 2013).

4.2 Iron Nanofertilizer

In a greenhouse study under a hydroponic system, application of lower concentrations of Fe-NPs (30, 45, and 60 mg L−1) significantly improved the chlorophyll contents of the sub-apical leaves of soybean compared to the regular application of Fe-EDTA (Ghafariyan et al. 2013). The results suggested that Fe-NPs could serve as an efficient source of Fe compared to the regular Fe-EDTA applied at <45 mg L−1 as Fe, thereby reducing the chloratic symptoms caused by its deficiency in soybean. Moreover, the uptake efficiency of Fe-NPs in the plant body was enhanced, which ultimately increased the chlorophyll contents of soybean plants. In another experiment, growth and yield parameters of black-eyed peas were significantly improved when Fe-NPs were applied as foliar at 500 mg L−1 (Delfani et al. 2014). Moreover, the application of Fe-NPs improved the effect of another fertilizer nutrient applied in the form of Mg-NPs. Previously, Hoagland and Arnon (1950) found that most of the plants generally require 1–5 mg L−1 Fe in soil solution.

4.3 Manganese Nanofertilizer

A hydroponic culture experiment was conducted to find out the comparative efficacy of Mn-NPs and commonly used Mn-salt, i.e., MnSO4, on the growth and yield parameters of mung bean (Pradhan et al. 2013). Both were applied at 0.05, 0.1, 0.5, and 1.0 mg L−1. The results showed that application of Mn-NPs at 0.05 mg L−1 significantly improved growth and yield parameters compared to the control with no Mn applied. At higher doses, Mn-NPs did not show toxicity to the bean plants, while MnSO4 applied at 1 mg L−1 showed toxic effects like necrotic leaves, brown roots, and gradual disappearance of the rootlet after 15 days of treatment. Moreover, greater oxygen evolution and photophosphorylation in Mn-NP-treated chloroplasts was noted compared to the control. Greater oxygen evolution was caused by enhanced splitting of water in the oxygen-evolving center located in the chloroplast. The authors concluded that Mn-NPs could serve as a potential modulator of photochemistry in the agriculture sector.

4.4 Copper Nanofertilizer

Previously, it has been clearly found that the application rate of Cu-NPs at Cu 0.02 mg L−1 in Hoagland solution is optimum for normal growth and yield of crops. Scientists around the world have found toxic effects of the application of Cu-NPs, as they have applied them at higher rates than required (Lee et al. 2008; Musante and White 2012). They found that Cu-NPs applied at the rate of 200–1000 mg L−1 caused toxic effects on seedling growth of mung bean, wheat, and yellow squash. Similarly, reduced biomass of zucchini by 90% compared to that of the control (without Cu) after the seedlings were incubated in Hoagland solution for 14 days was recorded with the application of metallic Cu-NPs at 1000 mg L−1. However, researchers like Shah and Belozerova (2009) recorded a significant increase of 40% and 91% in 15-day lettuce seedling growth rate with the application of Cu-NPs at 130 and 600 mg kg−1, respectively. Similarly, a 35% increase in photosynthetic rate of waterweed was recorded in a 3-day incubation study using a low concentration of Cu-NPs applied at ≤0.25 mg L−1 (Nekrasova et al. 2011).

4.5 Molybdenum Nanofertilizer

Molybdenum is essential for legumes as it is involved in biological nitrogen fixation (BNF), being the component part of nitrogenase enzyme. For normal metabolism of crop plants the concentration of soil solution Mo should be ≈0.01 mg L−1. Taran et al. (2014) conducted a pot experiment using different combinations of N-fixing bacteria and Mo-NPs (water, Mo-NPs, microbial inoculation with nitrogen-fixing bacteria, and a combination of the microbes and Mo-NPs). The control was treated with distilled water. Chickpea seeds were soaked in each of the treatments for 1–2 h. The results clearly showed that the combined application of microbes and Mo-NPs significantly improved the microbiological properties of the rhizosphere, including all groups of agronomically important microbes. The same combination significantly improved the root number, nodule number per plant, and nodule mass per plant compared to control.

5 Risk of Nanoparticle Application on Environment

Application of nanomaterials in agriculture is not always beneficial. It has number of negative effects on soil, plant, and aquatic life and most importantly human because of long food chain and easy motion of nanoparticles. Study of behavior of nanoparticles at different sizes with different concentrations in soil, plant, and water is as under:

5.1 Risk of Nanoparticle Application on Soil

Soil is prima facie receiver of fertilizers with nanoparticles. There is harmful chemical reactions and contamination by these nanoparticles to soil ecosystem and change in soil structure due to their large surface area and Brownian motion. Nanoparticles used through fertilizers could be harmful to soil biota and fertility (Ranallo 2013). They affect microbes, microfauna of soil, and digestive system of earthworm. An adverse effect of nanoparticles on soil health is presented in Table 26.8.

Table 26.8 Adverse effects of nanoparticles on soil health
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The potential harmful effects of nanoparticles Ag, TiO2, ZnO, CeO2, Fe3O4 include reduction in growth, fertility, survival, and increased mortality of earthworm and soil bacteria. Size is the main factor for ecotoxicity. To find out the relationship between size and toxicity, Roh et al. (2010) have initiated a study with TiO2 and CeO2 nanoparticle on Caenorhabditis elegans. It is a free-living, transparent nematode, about 1 mm in length that lives in temperate soil environments. They found that smaller size of TiO2 (7 nm) and CeO2 (15 nm) nanoparticles are more toxic compared to larger size (TiO2 of 20 nm and CeO2 of 45 nm). It has been found that higher doses of ZnO nanoparticle become toxic for soil (Hu et al. 2010). Whereas, the amount of ZnO in the soil is increased from 1 g kg−1 to 5 g kg−1, ZnO nanoparticles bioaccumulate within the earthworm and cause DNA damage.

5.2 Risk of Nanoparticle Application on Plant

Toxicity of nanoparticles depends upon various factors like plant species, size, and concentration of nanoparticles in different stages of crop. Toxic effect of nanoparticles also depends upon their composition and size. Small sized nanoparticles are more reactive and toxic compared to large sized and affect the respiration or photosynthesis process (Navarro et al. 2008). Hund-Rinke and Simon (2006) worked on different sizes of photocatalytic active TiO2 nanoparticles and its ecotoxic effect on algae (EC50: 44 mg L−1) and daphnids with maximum concentration of 50 mg L−1 and found that ecotoxicity of nanomaterials depends upon nature of particles. Toxicity found in algae is more than daphnids. Lin and Xing (2007) worked on phytotoxicity of nanomaterials. They used MWCNT, Al, Al2O3, Zn, and ZnO in their experiment on radish, rape, ryegrass, lettuce, corn, and cucumber and found that seed germination of corn and ryegrass is affected by nanoscale ZnO and Zn, respectively. Aluminum oxide (Al2O3) nanoparticles showed phytotoxicity only on corn, which reduced the root elongation by 35%. Aluminum (Al) improved root growth of rape and radish and inhibited root elongation of ryegrass and lettuce but had no effect on cucumber. Some of the toxicological studies on the effect of nanomaterials are presented in Table 26.9.

Table 26.9 Toxicological effect of nanoparticles on plant
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The level of toxicity in plants due to nanoparticles is in direct relation with size and nature of the particles. Zinc oxide (ZnO) nanoparticles easily dissolve in soil and uptake by plant and TiO2 nanoparticles accumulate in soil and retain for long time and stick with the cell wall of wheat plant. Both reduced the biomass of wheat crop (Du et al. 2011). Phytotoxicity was studied by Mazumdar and Ahmed (2011) on rice crop. They found that silver nanoparticle accumulated inside the root cell and damage the cell walls during penetration of particles due to complex mechanism and small size of particles, it damaged the external and internal portion of cell wall. The other factor for plant toxicity is the concentration of nanoparticle because a nanoparticle of same size in different concentration changes its chemical properties. Zinc oxide nanoparticle showed great toxicity in different concentrations (Boonyanitipong et al. 2011). They found that ZnO starts showing adverse effect on rice plant from 100 mg L−1 and fully inhabits root growth and biomass at 500–1000 mg L−1 concentration.

5.3 Risk of Nanoparticle Application on Water

The nanoparticles can easily be released in water body or air and uptake by living organisms, create toxic effect for human, animals, and also for aquatic life. Titanium oxide (TiO2) reduced the light to entrap the algal cell and thus reduce the growth (Sharma 2009). The toxicity study of Ag, Cu, Al, Ni, TiO2, and Co nanomaterials on algal species, zebrafish, and daphnids revealed that Ag and Cu nanoparticles cause toxicity to all organisms (Griffitt et al. 2008) and the metal form is less toxic than soluble form of nanoparticles. Table 26.10 describes the aquatic toxicity of use of nanomaterials release in surface water body. It has been proved from different studies that nanoparticles like Ag, Cu, Al, Ni, and TiO2 cause unrecoverable toxic effect on aquatic ecosystem. Silver, iron oxide, and copper nanoparticle adversely affected health of zebrafish. It enhances mortality, hatching, and reduces heartbeat and survival rate affect normal development (Asharani et al. 2008; Griffitt et al. 2007; Zhu et al. 2012). Therefore, the level of nanotoxicity in soil, plant, and water mainly depends on the composition, size (<20 nm), and concentration (>100 ppm) of the nanoparticle.

Table 26.10 Adverse effects of nanoparticles on aquatic species
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5.4 Risk of Nanoparticle Application on Human Health

The emerging field of nanotechnology has created an interest on human health risk associated with nanoparticles. These particles create new challenge for researchers to understand and find risk associated with human health. Exposure of these materials occurs through inhalation, ingestion, and dermal exposure during synthesis, manufacturing, and application of these nanomaterials. Table 26.11 shows the adverse effects of nanomaterials on human health.

Table 26.11 Adverse effects of nanoparticles on human health
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The most common way of exposure is inhalation of airborne nanoparticles. Greatest emission risk occurs in the manufacturing process with poor filtering and ventilation system (AFSSET 2006). Factors that affect inhaled dose are particle geometry and physiochemical properties, lung morphology, respiration physiology, and environmental condition (Shade and Georgopoulos 2007). Nanoparticles deposit in respiratory traces after inhalation increases the total deposition fraction (TDF) in the lungs with decrease in particle sizes. Nanoparticles can also be taken-up in the brain through the olfactory epithelium (Borm et al. 2006; Jaques and Kim 2000). Ultrafine airborne particles may increase respiratory and cardiovascular morbidity and mortality (Shade and Georgopoulos 2007).

Ingestion is another source of entry of nanoparticles into human body. The nanoparticles entered through gastrointestinal tract directly through intentional ingestion or indirectly via water, food, animal food, and fish (Bergin and Witzmann 2013). Mucociliary escalators may be excreted as inhaled particles or absorbed into the gastrointestinal tract; however, absorption is dependent on particle size and physicochemical characteristics (Hagens et al. 2007). Jani et al. (1990) found that particle size less or equal to 50 nm had more uptake or absorbed across gastrointestinal tract and can be passed to the liver, spleen, blood, and bone marrow by the momentary lymph supply and nodes. Plants have more resistance to prevent translocation of nanoparticles than mammalian barriers (Birbaum et al. 2010).

Dermal exposure is an import route to absorb nanoparticles via the skin. Skin constitutes about 10% of the body’s weight and acts as a buffer against external impurities, as well as shielding, preserving homeostasis, digestion, synthesis, and deposition functions (Crosera et al. 2009). Penetration of nanoparticles depends upon physicochemical characteristics of nanoparticles and medical condition of skin such as eczema, dermatitis, and skin irritation. Absorption between epidermis and dermis or permeability increases in damage skin (Nielsen et al. 2007). Dermal exposure of small size nanoparticles lower than 10 nm is more dangerous. This size of particles may cause erythema, edema, and eschar formation. Further larger size particles cannot penetrate into the skin from transappendageal routes (Gautam et al. 2011).

Thus, it has been established that nanoparticles adversely affect human health and the potential routing could be through inhalation, ingestion, and dermal exposure. It is understood that the nanoparticles show significant health complications in human when exposed to the size of particles less than 50 nm.

5.5 Asian Prospects of Micronutrient Nanofertilizer

Nanotechnology is considered as one of the key technologies in the twenty-first century that promises to advance traditional agricultural practices and offers sustainable development by improving the management and conservation tactics with reduced waste of agricultural inputs (Dubey and Mailapalli 2016; Shang et al. 2019). In 2018, both public and private sectors of worldwide had invested about US $1055.1 million on nanotechnology market which is projected to reach $2231.4 million by 2025. The exponential growth of global investment in nanotechnology research closely coincides with the number of patents relating to nanoproducts. Recent statistics suggests that 88% of the patents are generated from just seven countries comprising US, China, Germany, France, South Korea, Switzerland, and Japan (Subramanian and Tarafdar 2011). The Government of India is currently spending Rs.1000 crores under Nano Science and Technology Mission (Nano Mission) during the Eleventh Five-year Plan period to promote research and development in all flourishing sectors of nanotechnology, and agriculture is one of them. Within the sphere of agricultural sciences, nanotechnology application in relation to soil and crop management is in its nascent stage and over the next few years it is expected to grow exponentially.

Fertilizers play a pivotal role in agricultural production. It has been unequivocally demonstrated that fertilizer contributes to the tune of 35–40% of the productivity of any crops. Without the fertilizer input, it is hardly possible to sustain agricultural productivity of any country. Thus, attempts are being made to synthesize nanofertilizers in order to regulate the release of nutrients demand of crops and overcome the uncertainty of crop production sector with limited natural resources (Godfray et al. 2010). Based on their actions, nanofertilizer could be classified as control or slow release fertilizers, control loss fertilizers, magnetic fertilizers, nanocomposite fertilizers as combined nanodevice to supply wide range of macro- and micronutrients in desirable properties (Panpatte et al. 2016; Lateef et al. 2016). A very few nanofertilizer formulations have been synthesized in China, Taiwan, India, Germany, and the USA and are being tested under laboratory conditions. Liu et al. (2006a, b) an associate from Chinese Academy of Agricultural Sciences (CAAS) have shown that nanocomposites containing organic polymer intercalated in the layers of kaolinite clays can be used as a cementing materials to regulate the release of nutrients from conventional fertilizers. This process increases the nutrient use efficiencies, besides preventing environmental hazard. Bansiwal et al. (2006) reported the use of surface modified zeolite as a carrier of slow release phosphatic fertilizer for the first time in India.

As a promising interdisciplinary research field, nanotechnology has aroused its enormity in agriculture. Micronutrients like zinc (Zn), copper (Cu), iron (Fe), manganese (Mn), boron (B), chlorine (Cl), molybdenum (Mo) also play an integral role in steady increase of crop productivity. However, numerous factors, such as soil pH, cation exchange capacity, soil texture, calcium carbonate content, water content, etc. stimulate their deficiencies in crop production with extensive farming practice (Ghormade et al. 2011). The deficiency of micronutrients decreases not only the productivity of crops, but also affects human health through the consumption of micronutrient-deficient foods (Swaminathan et al. 2013; Monreal et al. 2016). In contrast, the supplementation of nanoformulated or nanoentrapped micronutrients for the slow or controlled release of nutrients would stimulate the uptake process by plants, promote the growth and productivity of crops, and contribute to maintaining soil health as well (Peteu et al. 2010). Although the exact mechanism behind promotion of plant growth and enriched quality is not clear, it may be at least partially explained by the potentialities of nanomaterials to absorb more nutrients and water that in turn helps to enhance the vigor of root systems with increased enzymatic activity (Dubey and Mailapalli 2016; Shojaei et al. 2019). Therefore, the developing countries of Asia come forward to adopt these high potential technologies to ameliorate micronutrient deficiency in crop production and secure the nutritional security to the human being. The government of Myanmar is the first to undertake a program to include micronutrient nanofertilizers in their national fertilizer regimen. Later on, several other Asian countries like, India, Taiwan, Thailand, Malaysia, Iran also approved to commercialize the micronutrient nanofertilizers and Table 26.12 shows some approved micronutrient nanofertilizers currently used in these countries (Dimkpa and Bindraban 2017; Prasad et al. 2017; Elemike et al. 2019).

Table 26.12 List of various micronutrients nanofertilizer products available in market
Full size table

Nanoform of micronutrients improves their bioavailability to the plants and shows a significant improvement in plant growth and nutrition quality and some recent advancement in micronutrient nanofertilizer research in Asian countries is summarized in Table 26.13. Among the various micronutrients, Zn is the most important one, as it requires for structural component or regulatory co-factor for various enzymes and proteins in plants (Noreen et al. 2018). The foliar application of Zn and B nanofertilizers at 636 and 34 mg tree−1, respectively, increased fruit yield by 30% in pomegranate trees (Khot et al. 2012). Similarly, foliar application of nano Zn and B fertilizers was found to increase fruit yield and quality, including 4.4–7.6% increases in total soluble solids (TSS), 9.5–29.1% decreases in titratable acidity (TA), 20.6–46.1% increases in maturity index, and 0.28–0.62 pH unit increases in juice pH on pomegranate without affecting any physical fruit characteristics (Davarpanah et al. 2016). Cucumber seedlings grown in nutrient solution including rubber type nanomaterial as a Zn source increased shoot and fruit yield compared with those grown in commercial ZnSO4 fertilizer (Mattiello et al. 2015). Application of Zn nanoparticles in pearl millet significantly enhanced grain yield by 38%, which was also associated with an improvement of 15% in shoot length, 4% in root length, 24% in root area, 24% in chlorophyll content, 39% in total soluble leaf protein, and 12% in plant dry biomass compared to the control in a period of 6 weeks (Moghaddasi et al. 2017). It was also observed a considerable yield increase using Zn nanoparticles as a nutrient source in rice, maize, wheat, potato, sugarcane, and sunflower (Monreal et al. 2016; Chhipa 2017). Under Zn deficient soil, application of nano ZnO at low doses positively influences the growth and physiological responses, such as shoot and root elongation, the fresh dry weight, and photosynthesis in many plant species compared to the control (Ali et al. 2019; Asl et al. 2019). Kale and Gawade (2016) reported that application of nano ZnO with other fertilizer in Zn deficient soil not only promotes nutrient use efficiency but also increases barley productivity by 91% compared to the control. Nanoparticles of ZnO showed a significant improvement in biomass, shoot length, root, chlorophyll and protein content, and phosphatase enzyme activity in Vigna radiate, Cicer arietinum, Cucumis sativus, Raphanus sativus, Brassica napus, and Cyamopsis tetragonoloba (Lin and Xing 2007; Mahajan et al. 2011; Zhao et al. 2013; Raliya and Tarafdar 2013).

Table 26.13 Indicative list of beneficial effects of micronutrients nanofertilizer application in various agro-climatic zones of the Asia
Full size table

Iron is also an important nutrient required by plants in minute quantities for maintaining proper growth and development (Palmqvist et al. 2017). Delfani et al. (2014) reported that use of nano Fe on blacked eyed pea recorded 10% increment in chlorophyll content in leaves. In Glycine max chlorophyll content was increased significantly by nano Fe application at 30–60 mg kg−1 (Ghafariyan et al. 2013). Disfani et al. (2017) also found that Fe/SiO2 nanomaterials have significant potential to improve seed germination in barley and maize. Application of 50 mg L−1 nano FeO in Citrus maxima plants significantly improved the chlorophyll contents and root activity by 23% and 24%, respectively, compared to controls (Sharma 2006). Yousefzadeh and Sabaghnia (2016) demonstrated that the application of nano Fe fertilizer not only increased the agronomic traits of Dracocephalum moldavica with sowing density, but also improved essential oil contents of plants. Elfeky et al. (2013) found that foliar application of nano Fe3O4 could significantly enhance total chlorophyll, total carbohydrate, essential oil levels, iron content, plant height, branches per plant, leaves per plant, fresh weight, and dry weight of Ocimum basilicum plants compared to that of soil application. Disfani et al. (2017) demonstrated that 15 mg kg−1 of nano Fe and SiO2 increased shoot length of barley and maize seedlings about 8.25% and 20.8%, respectively.

Application of nano Cu improved photosynthesis in Elodea desaplanch by 35% at low concentration (Nekrasova et al. 2011) and seeding growth up to 40% in lettuce (Shah and Belozerova 2009). Spray of nano Mn on Vigna radiata increased 52% root length, 38% shoot length 71% rootlet, and 38% biomass at 0.05 mg kg−1 concentration in comparison with bulk MnSO4 (Pradhan et al. 2013). However, MnO nanoparticles and FeO nanoparticles were not only less toxic than their ionic counterparts but they also stimulated the growth of lettuce seedlings from 12% to 54%, respectively (Lü et al. 2016). Molybdenum nanoparticle also showed improved microbial activity and seed growth in chickpea after combined treatment with nitrogen fixation bacteria (Taran et al. 2014). In addition to germination, nanomaterials, such as ZnO, FeO, and ZnFeCu-oxide, are reported to increase crop growth and development with quality enhancement in many crop species including peanut, soybean, mung bean, wheat, onion, spinach, tomato, potato, and mustard (Dubey and Mailapalli 2016; Shalaby et al. 2016; Shojaei et al. 2019; Zulfiqar et al. 2019).

The basic economic benefits of the use of micronutrient nanofertilizers are reduced leaching and volatilization associated with the use of conventional fertilizers. Simultaneously, the well-known positive impact on yield and product quality has a tremendous potential to increase growers’ profit margin through the utilization of this technology. Biosynthesized nanoparticles-based fertilizers and nanobiofertilizers should be explored further as a promising technology in order to improve yields while achieving sustainability.

6 Conclusion

The opportunity for application of nanotechnology in agriculture is prodigious. Research on the applications of nanotechnology in agriculture needs to be initiated in all sectors of agriculture. Nanotechnology promises a breakthrough in improving nutrient use efficiency through nanoformulation of fertilizers, breaking yield and nutritional quality barriers through bionanotechnology, surveillance and control of pests and diseases, understanding the mechanism of host–parasite interactions at the molecular scale, development of new-generation pesticides and safe carriers, preservation and packaging of food and food additives, strengthening of natural fiber, removal of contaminants from soil and water bodies, improving the shelf-life of vegetables and flowers, and use of clay minerals as receptacles for nanoresources involving nutrient ion receptors, precision water management, regenerating soil fertility, reclamation of salt-affected soils, checking acidification of irrigated lands, and stabilization of erosion-prone surfaces, to name a few. The use of nanomaterials for delivery of pesticides and fertilizers is expected to reduce the dosage and ensure controlled slow delivery. Nanotechnology has the potential to revolutionize the fertilizer use and has the ability to play an important role in crop nutrition. The usefulness and effectiveness of nanofertilizers to enhance the growth and yield has been clearly demonstrated. Nanomaterials could preferably be used for foliar application but can also be used as seed treatment or for soil application. Nanomaterials perform better under lower concentration and can enhance the nutrient use efficiency and improve soil fertility in an eco-friendly manner. However adverse impact of its use has also been reported. There is very limited knowledge about its long-term adverse effect on soil, plants, and ultimately on human. It is required to study about the non-toxic limit of nanoparticles related to its size and concentration. The positive benefit of nanoparticles should be selected on the basis of their risk related to environment and human.