Perspective Chapter: Recent Advances in Nanotechnology, Nanomaterials, Nanofertilizers and Smart Farming

Abstract

From survey of literature showing a traditional farm practicing which leads to loses in all field crops, it was thought of interest to study novel and new nanotechnologies in farming of field crops to increase yield quantity and quality, to reduce the use of chemical fertilizers, to reduce water irrigation, to exclude the use of pesticides for control of plant diseases, to produce a biosafety crops and finally to produce a safe crops. All these can easily take place by introducing smart farming, the nanofertilizer and nanodrug delivery systems for treatment and control of all plant diseases.

1. Introduction

1.1 NPK-nanofertilizers

Nanotechnology has evolved over the last few decades to occupy everyday life, and agriculture is one of the areas where nano-applications have recently reached.

The massive increase in human populations all over the globe means that we need to provide more food from the same area of cultivated lands. This means that we need to produce better crops and increase supplies with the same resources present. For this reason, new methods to increase crop productivity and lower fertilizer consumption are now being researched.

Artificial fertilizers are identified as inorganic fertilizers which are formed in appropriate concentrations to supply three chief elements: nitrogen, phosphorus and potassium (N, P and K) for different crops and growing conditions. NPK-inorganic fertilizers are vital for plant growth and development. N (nitrogen) stimulates leaf growth and is found in proteins and chlorophyll, P (phosphorus) improves root, flower and fruit development, and K (potassium) enhances stem and root growth and the production of proteins. However, plants utilized only about 30–60%, 10–20% and 30–50% the applied dose of N, P and K, respectively, and the rest is lost to the environment causing serious contamination to soil and water as well as substantial economic and resource losses. To minimize these conventional fertilizer demerits and utilize the major proportion of the applied dose of the chemical, nanotechnology can be applied by encapsulating the nutrients in nanomaterials, coated with a thin protective film or delivered as emulsions or nanoparticles.

1.2 What is a nanofertilizer?

Nanofertilizers are nutrient carriers in the dimension of 1–100 nm. “Nano” refers to one-billionth of a meter or one-millionth of a millimeter. When the size gets reduced, the surface area has tremendously increased. Nanofertilizers are a nano-structured formulation of fertilizers that release nutrients into the soil gradually and in a controlled way. The nutrient uptake efficiency can be increased by using nano-based slow-release or controlled release fertilizers which can lead to significantly reduce the wastage of nutrients. The nanomaterials may be applied either in the soil nutrition or by foliar application by developing the formulations, i.e., coated, encapsulated or buried in the nanomaterials.

1.3 NPK-fertilizers coated or encapsulated with nanoparticles

In our research work, we used chitosan nanoparticles loaded with NPK as foliar fertilizer for wheat plants. We used three concentrations of the nanofertilizer which are 10, 25 and 100%. During foliar application, all pots were covered to prevent the entry of nanofertilizers to the soil. The results showed that nanofertilizers induced significant increases in all growth and yield variables determined when compared with the control (water) or normal-fertilized wheat plants. To our surprise, nanofertilizers decreased the life span of the crop from 170 days for control and normal fertilized plants to just 130 days (a decrease of 23.5%). In addition, these results enabled wheat plants to grow in pure sandy soil with efficient crop productivity. When we studied the uptake of the nanoparticles by the plant through transmission electron microscopy, nanoparticles were found to accumulate in sieve tubes of phloem tissue, while xylem vessels appeared with zero nanoparticles. The lowest concentration (10%) produced the best results as a nanofertilizer for wheat plants. Foliar application of nanofertilizers showed a significant increase in total saccharide content of wheat grains. The magnitude of increase was most pronounced in the nanofertilized wheat plants grains, particularly at 10% nanofertilizer than in normal fertilized ones. Significant decrease in each protein and nitrogen content of the wheat grains was induced when wheat plants were with increasing levels of either normal or nanofertilizer as compared with the control ones. On the other hand, the element content of wheat grains especially potassium and phosphorus contents was significantly increased in nanofertilized wheat plants.

1.4 Foliar application

In another trial, we used carbon nanotubes loaded with NPK and compared them with chitosan nanoparticles loaded with NPK and used both of these types as fertilizers for French bean. In this trial, we tried three different application methods of the nanofertilizers used: soil incorporation, seed priming and foliar application. For soil incorporation, nanoparticles were mixed with the soil. For seed priming, the seeds were soaked in nanosolutions for 30 minutes prior to planting. For foliar application, nanofertilizers were foliary sprayed on the sixteenth day after planting. The results showed that foliar application gave the best results for growth and yield of the plants. Also, foliar application of both nanofertilizers reduced the life span of the plant to 80 days when compared with 110 days for soil and seed priming treatments. For uptake and translocation studies, chitosan nanoparticles appeared in the phloem tissue only and were absent from the xylem vessels. However, carbon nanotubes appeared in both xylem and phloem tissues. Foliar application of nanofertilizers resulted in progressive significant increases in total carbohydrate, protein and vitamin C contents of the yielded French bean seeds, when compared with the control seeds and with the seeds of French bean plants treated by seed priming and soil incorporation. The best nanofertilizer in this trial appeared to be chitosan nanoparticles loaded with NPK (10%), compared with carbon nanotubes NPK (20 μg/L) (Figure 1).

Figure 1.

A: Effects of normal NPK fertilizer and nanoengineered chitosan NPK fertilizer on the life span of wheat plants grown in sandy soil. B: Effects of different methods of application of NPK nanofertilizers on the life span of French bean plants grown in clay-sandy soil.

1.5 Pros and cons

NPK-nanofertilizers promise to be a revolution in the fertilizer industry. The high efficiency of crop production, better seed quality, better yield attributes and productivity are key elements when we consider the application of NPK-nanofertilizers. But, until now, few studies have dealt with the possible phytotoxic effects of nanofertilizers to plants. The major threat here is that plants, especially food crops, enter the food chain and the bioaccumulation of nanoparticles may reach animals or humans or may reside in the environment. Possible ways to study the phytotoxic effects of nanofertilizers are now under research. Also, the safety of long-term nanofertilizer consumption is yet to be confirmed. Possible measures and safety levels must be defined for each nanofertilizer used.

1.6 Current research

Up-to-date studies have found that either negative, insignificant or positive effects of nanoparticles on plant may depend on the type of nanoparticles, plant and soil. Depending on their physical and chemical properties, nanoparticle bioaccumulation in plants is specific. While some studies report beneficial effects on some plant species, the overall negative effect of the accumulation of these nanoparticles in the soil and plants might exceed the minor beneficial temporary effects. The main negative effects may involve the inhibition of growth, oxidative stress and genetic alteration due to the interactions between the plants and nanoparticles. For plant morphology, nanoparticles were found to alter morphological features of plants in vital organs such as the roots and leaves in addition to their effect on seed germination. Many nanoparticles can be translocated within plants and enter the food chain, be available for trophic transfer and become available in food for humans and animals. Many nanoparticles are shown to be toxic to humans, and uptake of nanoparticles in plants poses major safety concerns. Nanomaterials can become an environmental pollutant that might be conducive to irreversible or undesirable modifications with potentially harmful consequences on plants, animals and humans alike (Figure 2).

Figure 2.

Effects of different methods of application of NPK nanofertilizers on total carbohydrates (mg glucose equivalent/g dry weight), total protein (mg/g dry weight) and vitamin C (mmole/g dry weight) contents of French bean yielded seeds. (Data from experiments in 2016 in the plant physiology laboratory, Faculty of Science, Mansoura University, Egypt).

2. Experimental methodologies

2.1 Preparation of nanomaterials

2.1.1 Preparation of chitosan nanoparticles (Cs)

Chitosan nanoparticles (CS-nanoparticles or CS-PMAA nanoparticles) were prepared according to DeMoura et al. [1] and Hasaneen et al. [2] method by polymerization of methacrylic acid (MAA) in chitosan (CS) solution.

For 12 hours, about 0.2 g of chitosan powder was dissolved in a (0.5 v/v) methacrylic acid aqueous solution under magnetic stirring. Then, about 5 mg of K₂S₂O₈was added to the solution with continued stirring till the solution became clear. After that, the mixture was heated up at 70°C for one hour under magnetic stirring to ensure the formation of chitosan nanoparticles. Finally, to stop the reaction, the solution was cooled in an ice bath.

2.1.2 Preparation of carbon nanotubes (CNTs)

In the present study, CNTs were prepared by using the method of Lee and Seo [3]. To a mixture of sulfuric acid and nitric acid (2:1 v/v), five grams of graphite powder was added slowly and stirred for 30 minutes, then cooled at 4°C. After that, about 25 g of potassium chlorate was slowly added to the solution and stirred for 30 minutes, and then, the mixture was heated for 24 hours at 70°C. The mixture then was left for 3 days, and the floating solution was collected and rinsed with distilled water to 1000 cm³, stirred for l hour and filtered, and finally, the sample was dried.

2.1.3 Preparation of solid lipid nanoparticles (SLN)

Solid lipid nanoparticles were prepared via hot homogenization method at a temperature above the melting point of lipid using the solid lipid, Tween 80 as the hydrophilic surfactant and soya lecithin as the lipophilic surfactant [4].

2.1.4 Loading of fertilizers NPK on sequences of nanoparticles

According to Corradini et al. [2, 5], the loading of CS-nanoparticles surface with NPK fertilizers was obtained by dissolving about 0.1 g of urea, 0.02 g of calcium phosphate and 0.06 g of potassium chloride as sources of N, P and K fertilizers into 100 cm³ of CS-nanoparticle solution for 6 hours under magnetic stirring at room temperature. The pH of resulting solution was between 4.2 and 4.7. Meanwhile, the loading carbon nanotubes surface with NPK fertilizers was achieved by adding about 0.4 g of N, 0.1 g of P and 0.4 g of K into 100 cm³ of CNTs solution and stirring at 25°C for 6 hours.

2.1.5 Impact of engineered nanomaterials either alone or loaded with NPK on growth and productivity of plants

Abdel-Aziz et al. [6] reported that nanotechnology has become a solution to several problems facing humans nowadays. In agriculture, nanofertilizers play a vital role to minimize environmental pollution problems and enrich crop productivity. In this paper, we study the possible effects of using two different nanoengineered materials chitosan nanoparticles (nano-Cs) and carbon nanotubes (CNTs) either alone or loaded with NPK as fertilizers on French bean plants using two different methods of application, namely foliar application and seed priming. It is apparent from the obtained results that foliar application is the better method for application than seed priming. This is obvious from the improvement of growth, yield, antioxidant system and biochemical content of the yielded seeds of foliary applied plants than in plants treated with seed priming technique as compared with control ones. In addition, foliar treatment shortened the days to harvest without reducing yield by 37.5% (80 days) as compared with control and seed priming treatment (110 days). Of interest, nanochitosan either alone or loaded with NPK improved the growth and yield of the foliary treated plants more than CNTs. In conclusion, nanofertilizers foliar application holds tremendous potential to improve crop productivity.

The key focus areas for nanotechnology agricultural research are drug delivery, nano-biofarming, nanopesticides and nanoherbicides and controlled release of nanofertilizers [7]. Nanofertilizers are nutrient carriers on which nutrient ions can be able to be loaded due to their high surface area and able to release these ions in a minimal dose to the soil according to the needs of the cultivated plant which can reduce environmental pollution problems related with excess release of ions which is apparent such in the case of incorporation of essential elements (NPK) on the surface of chitosan nanoparticles as described by Golbashy et al. [8] and AbdelAziz et al. [9]. There are slow-release and super sorbent nitrogenous and phosphatic fertilizers [10, 11].

Nanofertilizers increase the absorption capacity of plant roots which leads to increased photosynthesis and improved crop production [12]. Benzon et al. [13] showed that the application of nanofertilizer to rice plants led to an increment in both total phenolics content and antioxidants which increased plant nutrition and enhanced crop productivity.

Chitosan nanoparticles (nanochitosan or Cs nanoparticles) are engineered nanomaterials produced from chitosan (a linear hydrophilic polysaccharide) which has been used as a functional biopolymer in pharmaceutics and food [14]. Due to physicochemical properties such as size, surface area and cationic nature, the new form of Cs-nanoparticles provides a variety of possible biological activities [15]. Furthermore, Cs and its derivatives have the ability to stimulate both physiological and biochemical activities in plants from single cells and tissues to molecular level changes at gene expression [16], also play a main role in seed germination and plant growth enhancement [17], increase nutrient uptake by plants [18], increase the content of chlorophyll and chloroplast development which enhances photosynthetic activity and increase crop productivity [19, 20].

Carbon nanotubes (CNTs) are defined as cylinders of carbon atoms at nanoscale diameters and microscale lengths [21] and may be categorized to either single-walled CNTs (SWCNTs) or multi-walled CNTs (MWCNTs) depending on the carbon shells number present in the nanotube [22]. The nanoscale of CNTs provide them with unique properties different from carbon and graphite such as physicochemical characteristics like diameter, length and functionality which gives them varied chemical reactivity [23, 24]. Mondal et al. [25] reported positive effects of low CNTs doses in seed germination, water transport and root development in mustard plants, but negative effects were recorded at high concentrations due to the production of reactive oxygen species (ROS) in cells which caused membrane and cell injury which might lead to cell death [26].

Zheng et al. [27] and Klaine et al. [28] reported that nano-TiO₂ at low doses were able to increase nitrogen metabolism and improve photosynthesis which improves plant growth of spinach plants. Farnia and Ghorbani [29] reported that foliary application of K-nanofertilizer to red bean plants increased the 1000 grain weight, number of grains per pod, biomass yield and grain yield as compared to control ones.

In seed priming technique, seeds are soaked in a specific solution for a period of time (no radicle emergence or breaks in seed coat) and then are used for germination [30]. Priming the seeds with nanoparticles solutions can produce highly resistant seeds and improve its germination and consequently improve seedling growth especially under stressful conditions [31]. Zayed et al. [32] reported that priming of bean seeds with (0.1%, 0.2% and 0.3%) nanochitosan for three hours and germinated under salt stress (100 mM NaCl) enhanced seed germination and radicle length. Also, the content of both proline and chlorophyll a as well as antioxidant enzyme activities of bean seedlings treated with 0.1% nanochitosan showed significant improvement as compared with salt-stressed untreated bean seedlings.

2.1.6 Carbon nanotubes NPK and chitosan nanoparticles NPK fertilizer on productivity of plants

Froggett [33] and Hasaneen et al. [34] stated that nanotechnology has proved its place in agriculture and related industries and the using of nanomaterial has the potential to revolutionize the agriculture with novel tools to enhancing the plant ability to absorb nutrients. The ability of plants to uptake nanomaterials has shown a very recent field of nanoagriculture. Several studies reported that nanomaterials were able to penetrate the plant cell by endocytosis. As mentioned above, we designed this work to investigate the effects of different concentrations of two different types of engineered nanofertilizer specifically carbon nanotubes (CNTs) and chitosan nanoparticles (nano-Cs) coated with NPK on the different growth criteria French bean plants. Herein, the results of the both morphological and anatomical analysis indicate that after about 30 days from the date of planting our experimental conditions, nanofertilizers either alone or in combination with conventional fertilizers significantly improved the growth and biomass of plant compared to unfertilized plants. Transmission electron microscopy images (TEM) of the plant leaves indicated the presence of engineered nanomaterials in vascular bundles specifically in sieve tubes of phloem elements in case of nanochitosan-NPK and in both xylem vessels and sieve tubes in case of CNTs- NPK. Overall, after investigation, we conclude that low nanofertilizers doses have seen to be beneficial, improving water absorption and nutrients uptake, found to enhance the plant growth.

Chitosan is a linear hydrophilic polysaccharide that is biocompatible, biodegradable, non-toxic nature biopolymer and reacts with bioactive molecules [14, 35, 36]. Chitosan nanoparticles with a size about 78 nm can be used for controlled release of NPK fertilizer sources such as urea, calcium phosphate and potassium chloride [5]. Carbon nanotubes have an important position due to their unique physicochemical properties such as length, diameter, atomic configuration, defects, impurities and functionality, which allow them to have wide-ranging conductivity, flexibility, tension strength and chemical reactivity properties [23]. CNTs have positive effects on seed germination, root development and water transport within the plant or no evidence of phytotoxicity when plants treated with low doses. On the other hand, the negative effects can be produced at high concentrations due to the generation of harmful reactive oxygen species (ROS) [25]. The uptake of nanofertilizers into plant cell can occur via various ways such as binding to carrier proteins through aquaporin, ion channels or endocytosis [37], and also, they may diffuse apoplectically in the space between the cell wall and plasma membrane and can merge into the simplest then penetrate into vascular system [38]. Engineered nanofertilizers can be transported through the phloem elements when applied foliary. For foliar uptake of nanoparticles, there are two possible pathways, namely cuticular and stomatal pathways [39]. In cuticular pathway, nanoparticles with sizes below 5 nm can be uptaken due to extremely small sizes of cuticular pores [40]. While, in stomatal pathways, larger nanoparticles can be penetrated since the typical stomatal size is in micrometer size range [39].

2.1.7 Nano-drug delivery systems and plant diseases

Hasaneen et al. [41] stated that due to the development of antibiotic resistant strains in pathogenic microbes, there is an increasing in microbial diseases yearly which represents a great challenge to the public health, and this considered as an alarming issue worldwide [42]. It is well known that the current medicinal regime delivers drugs to the site of action or inflammation with unavoidable side effects [43]. With nanodrug delivery system, antimicrobial compounds can be accessed to the targeting site of the microbial pathogens [41]. We concluded from our study that antimicrobial compounds extracted from the local isolate namely Streptomyces rimosus and loaded on either chitosan nanoparticles or calcium phosphate nanoparticles were found to be facilitate drug delivery to some bacterial species (Escherichia coli ATCC25922, Staphylococcus aureus ATCC25923 and Bacillus cereus ATCC66331 and the yeast Candida albicans ATCC10231. The best incubation period for the production of antifungal and antibacterial compounds, pH, temperature, carbon sources and nitrogen sources was around the third day, 70, 30°C, starch and potassium nitrate, respectively. Gas chromatography–mass spectrometry (GC–MS) analysis was used for the identification of the extracted compounds which revealed to the identification of nine antimicrobial organic acids. The prepared NPs were characterized using transmission electron microscopy (TEM) and Zeta potential analyzer. The tested strains were resistant to solo nanoparticles, but the extracted antimicrobial compounds, especially CaP-NPs, improved the isolated antimicrobial compounds potency causing differential antimicrobial activity. The activity of nanoparticles loaded with antimicrobial compounds was more obvious against bacteria than fungi, against, Gram-positive than Gram-negative bacteria and against B. cereus than S. aureus.

Nanotechnology offers an effective mean of sustained drug delivery and release with avoidance of the problems of the current delivery systems. For proper manipulation, drugs must have a size such that they can be injected without blocking needles and capillaries [44]. This can be achieved by using either nano-liposomes, nano-gels or micelles. By the aid of nanotechnology, drugs can be either loaded on the surface of nanoparticles or encapsulated and cared within then to the drug destination. By this way, the effective dose of the drug can be lowered several orders of magnitude, which led to the minimization of the drug side effects [45].

Chitosan (CS) itself and its derivatives or in the form of nanoparticles have attracted great attention due to their antifungal and antibacterial activity [46, 47]. The safe CS can interact with polyanions to form complexes and gels [48, 49]. While, CaP are the most important component of human teeth, bone and the biological hard tissues in the form of carbonated hydroxyapatite, which afford stability, hardness and proper function [50, 51]. CaP-NPs were manipulated as successful adjuvant with DNA vaccines [52]. New and aggressive antibiotic-resistant bacteria and parasites call for the development of new therapeutic strategies to overcome the inefficiency of conventional antibiotics and to bypass treatment imitations related to these pathologies. Therefore, the present work focuses on the development and combination of CSNPs and CaPNPs with potent antimicrobial compounds that can aid in delivery of antibiotics to the target sites of drug-resistant microorganisms.

3. Conclusion

In smart farming, summarizing the obtained results, using nanochitosan and carbon nanotubes either singly or loaded with NPK as nanofertilizers, throughout the entire period of the cultivation led to:

1. The best technique used for application of nanofertilizers to plant was foliar application [53, 54].

2. The best nanofertilizer used to field crops was nanochitosan-NPK followed by CNTs-NPK.

3. Giving a percent improvement in the quantity and quality of the yielded crops seeds treated foliary with Cs-NPK and CNTs-NPK was 82% and 84%, respectively.

4. A novel technique, treatment and control of plant disease by nanodrug delivery strategies showed a high percent of recovery from disease with 100% in case of using solid lipid nanoparticles loaded with antibiotic and 80% recovery from disease in case of using chitosan nanoparticles loaded with antibiotic and finally 60% recovery from disease in case of using carbon nanotubes loaded with antibiotic [41, 55].