P. KARTHIK REDDY*, N.C. MAMATHA, PRASHANTH NAIK, V. SRILATHA AND PAVAN KUMAR P.
Department of Horticulture, S. V. Agricultural College, ANGRAU, Tirupati – 517 502, Andhra Pradesh
Nanotechnology has great potential as it can enhance the quality of life through its applications in various fields like agriculture and the food system. In a world where the human population is growing rapidly, and agriculture industry is facing challenges such as stagnation in crop yields, low nutrient use efficiency, declining soil organic matter, multi-nutrient deficiencies, climate change, shrinking arable land and water availability, post harvest losses and shortage of labour and thereby food security is a very important problem in near future. Now, increasing agricultural production efficiency and decreasing post harvest wastage using novel scientific researches such as nanotechnology in products could be counted as the best solution to this problem. Nanotechnology using of particular characteristics of nanoparticles can be a very useful technology in all science and industry branches. So now a lot of usage of nanotechnology in agricultural science has been founded. In relation with crop production, crop protection, storage, post harvest shelf life and marketing, nanotechnology can help us in some grounds like balanced crop nutrition, effective pest, disease and weed control, water management, product quality maintenance, product tracking and labeling, precision agriculture and agricultural waste management.
Nanotechnology was first introduced in 1960’s by Dr. Richard Feynman. Since then scientists are working on it and have developed many technologies and applications of nano science. Nanotechnology, which deals with the matter at nanoscale (1-100 nm), is commonly referred to as a generic technology that offers better-built, safer, long -lasting, cost-effective and smart products that will find wide applications in household, communications, medicine, agriculture and food industry, amongst others. Nanotechnology- based products and its applications in agriculture include nano-fertilizers, nano-herbicides, nano-pesticides, recalcitrant contaminants from water, nano-scale carriers, nanosensors, detection of nutrient deficiencies, preservation, photocatalysis, nanobarcode, quantum dots etc. This fast growing technology is already having a significant commercial impact, which will certainly increase in the future. While nanotechnologies offer many opportunities for innovation, the use of nanomaterials in food and agriculture has also raised a number of safety, environmental, ethical, policy and regulatory issues.
Agricultural scientists are facing a wide spectrum of challenges such as stagnation in crop yields, low nutrient use efficiency, declining soil organic matter, multi-nutrient deficiencies, climate change, shrinking arable land andwater availability and shortage of labour besides exodus of people from farming. In spite of immense constraints faced, we need to attain a sustainable growth in agriculture at the rate of 4% to meet the food security challenges. To address these problems, there is a need to explore one of the frontier technologies such as ‘Nanotechnology’ to precisely detect and deliver the correct quantity of nutrients and pesticides that promote productivity while ensuring environmental safety and higher use efficiency. The nanotechnology can be exploited in the value chain of entire agriculture production system (Subramanian and Tarafdar, 2011). The nanotechnology aided applications have the potential to change agricultural production by allowing better management and conservation of inputs of crop production. A survey by Salamanca–Buentella et al. (2008) predicted several nanotechnology applications for agricultural production for developing countries within next 10 years. These included – (i) Nano forms zeolites for slow release and efficient dosage of water and fertilizers for plants; nanocapsules and herbicide delivery
(ii) Nanosensors for soil quality and for plant health monitoring; nanosensors for pests detection (iii) Nanomagnets for removal of soil contaminants and (iv) Nanoparticles for new pesticides, insecticides, and insect repellents.
The Indian Council of Agricultural Research (ICAR) has opened up an exclusive platform to target Nanotechnology Applications in Agriculture. The ICAR
– Nanotechnology Platform encompasses major themes such as synthesis of nano-particles for agricultural use, quick diagnostic kits for early detection of pests and diseases, nano-pheromones for effective pest control, nano agri-inputs for enhanced use efficiencies, precision water management, stabilization of organic matter in soil, nano food systems and bio safety besides establishing the policy frame work. Green-synthesis and microbial synthesis of nanomaterials for their agricultural use may be very important as they are naturally encapsulated with mother protein, therefore, more stable and safer to biological system. At present in India research is mainly concentrated on nano particle synthesis, smart release of nutrients from nano-fertilizers, nano-induced polysaccharide powder for moisture retention/soil aggregation and C build up, regulated release of active ingredients from nano-encapsulated herbicides, nano-seed invigoration, and slow and steady release of pesticides, nano-film for extended shelf-life of perishables and nano-remediation of soil and aquatic pollutants. These are cutting-edge researchable areas which are expected to expand in the years to come. However, if the nano products and the processes for creating them are not managed judiciously, there could be serious health and environmental risks.
Investigation confirms that application of nanotechnology in the horticulture was first in the fruit packaging and later in other areas such as tracking, tracing, storage and distribution. Currently, most nanotechnology applications in the horticultural supply chain are concentrated in packaging, mainly in the improvement of packaging materials for product security, quality and safety. The FAO put the global food losses and wastages during 2012 at 30– 40% and in developing countries more than 40% of the food losses occur at post-harvest and processing levels. In horticultural commodities, there are five stages at which post-harvest losses occur – production/harvest, post-harvest handling and storage, processing, distribution and consumption. Post-harvest losses represent a waste of resources used in production such as land, water, energy and inputs. Nanotechnology offers great scope not only to reduce the post harvest wastage but also aids in increasing the production
efficiency. Nanotechnology has already associated with supply chain management, food quality, processing, preservation, vase life, handling, packaging and food safety. Nanocomposite polymers, antimicrobial packaging and nano packaging products are already in the market (Table 1). Using electro-spinning methodology, strong and naturally antimicrobial nanofibers were produced for developing the “green” food packaging (Neethirajan and Jayas, 2011). The novel edible films can be value-added by addition of functional ingredients as encapsulated nutraceuticals like vitamins, water-insoluble flavonoids, and other flavor/color enhancing phytochemicals, antioxidants like anthocyanins, carotenoids for avoiding discoloration of the cut surface and antimicrobial agents like bacteriocins (natural), biogenic nanoparticles of silver, titanium, or zinc (inorganic synthesized) to curb the growth of spoilage causing microbes (Rojas-Grau et al., 2009; Janjarasskul and Krochta, 2010; Oms-Oilu et al., 2010). Postharvest treatments with nano-silver significantly improve water relations and therefore prolong the vase life of several cut flowers. Nano silver and Nano copper ions in combination adapted from Miller and Senjen (2008) with biocides have been helpful in extending the vase life and quality of cut flowers like rose (Barbaz et al., 2013), gerbera (Mousa et al., 2009), lilium (Maryam et al., 2013) and tuberose (Asgari et al., 2013). Fruit ethylene efflux can be measured with great accuracy in a short period of time using nanotechnology in fruits like apple, avocado pear and kiwi which helps to open new avenues for the researchers which is otherwise could not be possible due to lack of real-time measurement equipments. Green tea with nano-packing, had better maintenance of vitamin C, chlorophyll, polyphenols and aminoacids than with normal packing (Hu and Fu, 2003).
Seed is most important input determining productivity of any crop. Conventionally, seeds are tested for germination and distributed to farmers for sowing. In spite of the fact that seed testing is done in well equipped laboratories, it is hardly reproduced in the field due to the inadequate moisture under rainfed conditions. In India, more than 60% of the net area sown is rainfed; hence, it is quite appropriate to develop technologies for rainfed agriculture. A group of research workers is currently working on metal oxide nano-particles and carbon nanotube to improve the germination of rainfed crops. Khodakovskaya et al. (2009) have reported the use of
carbon nanotube for improving the germination of tomato seeds through better permeation of moisture. Their data show that carbon nanotubes (CNTs) serve as new pores for water permeation by penetration of seed coat and act as a passage to channelize the water from the substrate into the seeds. These processes facilitate germination which can be exploited in rainfed agricultural system. Biosensors help in seed storage as seeds during storage emit several volatile aldehydes that determine the degree of ageing. These gases are harmful to even other seeds. Such volatile aldehydes can be detected and seeds showing signs of deterioration can be separated and invigorated prior to their use. Hence this technique can be employed in storage decision making.
In India, fertilizers, along with quality seed and irrigation, are mainly responsible for enhanced food grain production (55 mt) in 1960s to (254 mt) in 2011 coinciding with the spectacular increase in fertilizer consumptions from 0.5 mt to 23 mt, respectively. It has been conclusively demonstrated that fertilizer contributes to the tune of 35-40 per cent of the productivity of any crop. Considering its importance, the Government of India is heavily subsidising the cost of fertilizers particularly urea. This has resulted in imbalanced fertilization and occurrence in some areas, nitrate pollution of ground waters due to excessive nitrogen application. In the past few decades, use efficiencies of N, P and K fertilizers have remained constant as 30-35%, 18-20% and 35-40%, respectively, leaving a major portion of added fertilizers to accumulate in the soil or enter into aquatic system causing eutrophication. In order to address issues of low fertilizer use efficiency, imbalanced fertilization, multi-nutrient deficiencies and decline of soil organic matter, it is important to evolve a nano-based fertilizer formulation with multiple functions. Nano-fertilizer technology is very innovative but scantily reported in the literature. However, some of the reports and patents strongly suggest that there is a vast scope for the formulation of nano-fertilizers. Significant increase in yields has been observed due to foliar application of nano particles as fertilizer (Tarafdar, 2012; Tarafdar et al. 2012a). It was shown that 640 mg/ ha foliar application of nanophosphorus gave 80 kg/ ha P equivalent yield of cluster bean and pearl millet under arid environment. Similarly, nano-based ZnO application in peanut (Prasad et al. 2012) and maize (Venkatasubbaiah et al. 2016) has enhanced the yield. It was also reported
for the first time that nano-based Ca had greater mobility in the phloem tissues, as bulk Ca is immobile (Deepa et al., 2015) Currently, research is underway to develop nano-composites to supply all the required essential nutrients in suitable proportion through smart delivery system. Preliminary results suggest that balanced fertilization may be achieved through nanotechnology (Tarafdar et al., 2012b). Indeed the metabolic assimilation within the plant biomass of the metals, e.g., micronutrients, applied as Nano-formulations through soil-borne and foliar application or otherwise needs to be ascertained. Further, the Nano-composites being contemplated to supply all the nutrients in right proportions through the “Smart” delivery systems also needs to be examined closely. Currently, the nitrogen use efficiency is low due to the loss of 50-70% of the nitrogen supplied in conventional fertilizers. New nutrient delivery systems that exploit the porous nanoscale parts of plants could reduce nitrogen loss by increasing plant uptake. Fertilizers encapsulated in nanoparticles will increase the uptake of nutrients (Tarafdar et al., 2012c). In the next generation of nanofertilizers, the release of the nutrients can be triggered by an environmental condition or simply released at desired specific time.
Weeds are menace in agriculture. Since two-third of Indian agriculture is rainfed farming where usage of herbicide is very limited, weeds have the potential to jeopardize the total harvest in the delicate agro-ecosystems. Herbicides available in the market are designed to control or kill the above ground part of the weed plants. None of the herbicides inhibits activity of viable belowground plant parts like rhizomes or tubers, which act as a source for new weeds in the ensuing season. Soils infested with weeds and weed seeds are likely to produce lower yields than soils where weeds are controlled. Improvements in the efficacy of herbicides through the use of nanotechnology could result in greater production of crops. The encapsulated nano-herbicides are relevant, keeping in view the need to design and produce a nano-herbicide that is protected under natural environment and acts only when there is a spell of rainfall, which truly mimics the rainfed system. Developing a target specific herbicide molecule encapsulated with nanoparticle is aimed for specific receptor in the roots of target weeds, which enter into roots system and translocated to parts that inhibit glycolysis of food reserve
in the root system. This will make the specific weed plant to starve for food and gets killed (Chinnamuthu and Kokiladevi, 2007). Adjuvants for herbicide application are currently available that claim to include nanomaterials. One nanosurfactant based on soybean micelles has been reported to make glyphosate-resistant crops susceptible to glyphosate when it is applied with the ‘nanotechnology-derived surfactant’.
Persistence of pesticides in the initial stage of crop growth helps in bringing down the pest population below the economic threshold level and to have an effective control for a longer period. Hence, the use of active ingredients in the applied surface remains one of the most cost-effective and versatile means of controlling insect pests. In order to protect the active ingredient from the adverse environmental conditions and to promote persistence, a nanotechnology approach, namely “nano-encapsulation” can be used to improve the insecticidal value. Nano-encapsulation comprises nano-sized particles of the active ingredients being sealed by a thin-walled sac or shell (protective coating). Previously pheromones were combined with water-based gels (hydrogels), but this proved to be ineffective as the hydrogels either got evaporated due to exposure to heat and air or were washed away during monsoon. Recently, a pheromone-based nanogel to attract and trap the fruit flies in guava was developed. (Bhagat et al., 2013 and Ipsita, 2014).
Nano-encapsulation of insecticides, fungicides or nematicides will help in producing a formulation which offers effective control of pests while preventing accumulation of residues in soil. In order to protect the active ingredient from degradation and to increase persistence, a nanotechnology approach of “controlled release of the active ingredient” may be used to improve effectiveness of the formulation that may greatly decrease amount of pesticide input and associated environmental hazards. Nano-pesticides will reduce the rate of application because the quantity of product actually being effective is at least 10-15 times smaller than that applied with classical formulations, hence a much smaller than the normal amount could be required to have much better and prolonged management. Several pesticide manufacturers are developing pesticides encapsulated in nanoparticles (OECD and Allianz, 2008). These pesticides may be time released or released upon the occurrence of an environmental trigger (for example, temperature, humidity and light). It is unclear whether these pesticide products will be commercially available in the short-term.
Plant diseases are major factors limiting crop yields. The problem with the disease management lies with the detection of the exact stage of prevention. Most of the time appropriate plant protection chemicals are applied to the crop as a precautionary measure leading to avoidable environmental hazards, or else applications are made after the appearance of the disease symptoms, thereby causing some amount of crop losses. Among the different diseases, the viral diseases are the most difficult to control, as one has to stop the spread of the disease by the vectors. But once it starts showing its symptoms, pesticide application would not be of much use. Therefore, detection of the exact stage such as stage of viral DNA replication or the production of initial viral protein is the key to the success of control of viral diseases. Nano-based viral diagnostics, including multiplexed diagnostics kits development, have taken momentum in order to detect the exact strain of virus and the stage of application of some therapeutic to stop the disease. Detection and utilization of biomarkers, that accurately indicate disease stages, is also an emerging area of research in bio-Nanotechnology. Measuring differential protein production in both healthy and diseased states leads to the identification of the development of several proteins during the infection cycle. Clay nanotubes (halloysite) have been developed as carriers of pesticides at low cost, for extended release and better contact with plants, and they will reduce the amount of pesticides by 70-80%, thereby reducing the cost of pesticide with minimum impact on water streams.
Nanotechology, offers the potential of novel nanomaterials for the treatment of surface water, groundwater and wastewater contaminated by toxic metal ions, organic and inorganic solutes and microorganisms. Due to their unique activity towards recalcitrant contaminants many nanomaterials are under research and development for use for water purification. To maintain public health, pathogens in water need to be identified rapidly and reliably. Unfortunately, traditional laboratory tests are time consuming. Faster methods involving enzymes, immunological or genetic tests are under development. Water filtration may be improved with the use of nanofiber membranes and the use of nanobiocides, which appear promisingly effective. Biofilms contaminating potable water are mats of bacteria wrapped in natural polymers which are difficult to treat with antimicrobials or other chemicals. They can be cleaned up only mechanically, which cost substantial down-time and labour. Work is in progress to develop enzyme treatments that may be able to break down such biofilms.
Nanoscale carriers can be utilized for the efficient delivery of fertilizers, pesticides, herbicides, plant growth regulators, etc. The mechanisms involved in the efficient delivery, better storage and controlled release include: encapsulation and entrapment, polymers and dendrimers, surface ionic and weak bond attachments among others. These help to improve stability against degradation in the environment and ultimately reduce the amount to be applied, which reduces chemical runoff and alleviates environmental problems. These carriers can be designed in such a way that they can anchor plant roots to the surrounding soil constituents and organic matter. This can only be possible if we unravel the molecular and conformational mechanisms between the nanoscale delivery and targeted structures, and soil fractions. Such advances as and when they happen will help in slowing the uptake of active ingredients, thereby reducing the amount of inputs to be used and also the waste produced.
Protection of the soil health and the environment requires the rapid, sensitive detection of pollutants and pathogens with molecular precision. Soil fertility evaluation is being carried out for the past sixty years with the same set of protocols which may be obsolete for the current production systems and in the context of precision farming approaches. Accurate sensors are needed for in situ detection, as miniaturized portable devices, and as remote sensors, for the real-time monitoring of large areas in the field. These instruments are able to reduce the time required for lengthy microbial testing and immunoassays. Application of these instruments includes detection of contaminants in different bodies such as water supplies, raw food materials and food products. Enzymes can act as a sensing element as these are very specific in attachment to certain biomolecules. Electronic nose (E-nose) is used to identify different types of odours; it uses a pattern of response across an array of gas sensors. It can identify the odorant, estimate the concentration of the odorant and find characteristic properties of the odour in the same way as might be perceived by the human nose. It mainly consists of gas sensors which are composed of nanoparticles e.g. ZnO nanowires. Their resistance changes with the passage of a certain gas and generates a change in electrical signal that forms the fingerprint pattern for gas detection.
Nanoscale devices are envisioned that would have the capability to detect and treat diseases, nutrient deficiencies or any other maladies in crops long before symptoms were visually exhibited. “Smart Delivery Systems” for agriculture can possess timely controlled, spatially targeted, self-regulated, remotely regulated, pre-programmed, or multi-functional characteristics to avoid biological barriers to successful targeting. Smart delivery systems can monitor the effects of delivery of nutrients or bioactive molecules or any pesticide molecules. This is widely used in health sciences wherein nanoparticles are exploited to deliver required quantities of medicine to the place of need in human system. In the smart delivery system, a small sealed package carries the drug which opens up only when the desirable location or infection site of the human or animal system is reached. This would allow judicious use of antibiotics than otherwise would be possible.
Nanodevices for Identity Preservation (IP) and Tracking: One of the major constraints in Indian agriculture is the quality maintenance of agricultural produce. Proper monitoring of production system through nanotechnology will be appropriate to promote quality and make a clear distinction with organic products. Identity Preservation (IP) is a system that creates increased value by providing customers with information about practices and activities used to produce a particular crop or other agricultural products. Certifying inspectors can take advantage of IP as a better way of recording, verifying, and certifying agricultural practices.
Through IP, it is possible to provide stakeholders and consumers with access to information, records and supplier protocols. Quality assurance of agricultural products safety and security could be significantly improved through IP at the nano-scale. Nano-scale IP holds the possibility of continuous tracking and recording of the history which a particular agricultural product experiences. The nano-scale monitors may be linked to the recording and the tracking devices to improve identity preservation of food and agricultural products. The IP system is highly useful to discriminate organic versus conventional agricultural products.
Nanolignocellulosic materials: Recently, nanosized lignocellulosic materials have been obtained from crops and trees which had opened up a new market for innovative and value-added nano-sized materials and products, e.g. nano-sized cellulosic crystals have been used as lightweight reinforcement in polymeric matrix (Mathew et al., 2010). These can be applied in food and other packaging, construction, and transportation vehicle body structures. Cellulosic nano-whisker production technology from wheat straw has been developed by the Michigan Biotechnology Incorporate (MBI) International, and is expected to make biocomposites that could substitute for fiber glass and plastics in many applications, including automative parts (Liestritz, et al., 2007). For the commercialization of this technology, North Dakota State University (NDSU), USA is currently engaged in a project.
Photocatalysis: One of the processes using nanoparticles is photocatalysis. The mechanism of this reaction is that when nanoparticles of specific compounds are subjected to UV light, the electrons in the outermost shell (valence electrons) are excited resulting in the formation of electron hole pairs, i.e. negative electrons and positive holes. Due to their large surface-to-volume ratio, these have very efficient rates of degradation and disinfection. As the size of the particles decrease, surface atoms are increased, which results in tremendous increase in chemical reactivity and other physico-chemical properties related to some specific conditions such as photocatalysis, photoluminescence, etc. So this process can be used for the decomposition of many toxic compounds such as pesticides, which take a long time to degrade under normal conditions. Nanoparticles can be used for the bioremediation of resistant or slowly degradable compounds like pesticides. The removal of toxins from wastewater is an emerging issue due to its effects on living organisms. Many strategies have been applied for wastewater treatment with little success. Photocatalysis can be used for purification, decontamination and deodorization of air. It has been found that semiconductor sensitized photosynthetic and photocatalytic processes can be used for the removal of organics, destruction of cancer cells, bacteria and viruses. Application of photocatalytic degradation has gained popularity in the area of wastewater treatment.
Nanobarcode technology: In our daily life, identification tags have been applied in wholesale agriculture and livestock products. Due to their small size, nanoparticles have been applied in many fields ranging from advanced biotechnology to agricultural encoding. Nanobarcodes (> 1 million) have been applied in multiplexed bioassays and general encoding because of their possibility of formation of a large number of combinations that render them attractive for this purpose. The UV lamp and optical microscope are used for the identification of micrometer-sized glass barcodes which are formed by doping with rare earth containing a specific type of pattern of different fluorescent materials. The particles to be utilized in nanobarcodes should be easily encodable, machine readable, durable, sub-micron sized taggant particles. For the manufacture of these nanobarcode particles, the process is semi-automated and highly scalable, involving the electro plating of inert metals (gold, silver, etc.) into templates defining particle diameter, and then the resulting striped nanorods from the templates are released. Nanobarcodes have been used as ID tags for multiplexed analysis of gene expression and intracellular histopathology. In the near future, more effective identification and utilization of plant gene trait resources is expected to introduce rapid and cost effective capability through advances in nanotechnology-based gene sequencing. Nanobarcodes serve as uniquely identifiable nanoscale tags and have been applied for non-biological applications such as for authentication or tracking in agricultural food and husbandry products. Such nanobarcode technology will enable one to develop new auto-ID technologies for the tagging of items previously not practical to tag with conventional barcodes. With the enhanced importance of traceability in food trade, such technologies will be helpful in promoting biosafe international food trade.
Wireless nanosensors for precision agriculture: Crop growth and field conditions like moisture level, soil fertility, temperature, crop nutrient status, insects, plant diseases, weeds, etc. can be monitored through advancement in nanotechnology. Such real-time monitoring is done by employing networks of wireless nano-sensors across the cultivated fields, providing essential data for agronomic processes like optimal time of planting and harvesting of the crops. It is also helpful for monitoring the time and amount of water application, fertilizers, pesticides, herbicides and other treatments. This has moved precision agriculture to a much higher level
of control, for instance, in water usage, leading eventually to conservation of water. More precise water delivery systems are likely to be developed in the near future. The factors critical for such development include water storage, in situ water holding capacity, water distribution near roots, water absorption efficiency of plants, encapsulated water released on demand, and interaction with field intelligence through nano-sensor systems.
Nanotechnology is also applied to prevent waste in agriculture, particularly in the cotton industry. When cotton is processed into fabric or garment, some of the cellulose or the fibers are discarded as waste or used for low-value products such as cotton balls, yarns and cotton batting. With the use of newly-developed solvents and a technique called electrospinning, scientists produce 100 nanometer diameter fibers that can be used as a fertilizer or pesticide absorbent. These high-performance absorbents allow targeted application at desired time and location. Ethanol production from maize feedstocks has increased the global price of maize in the past two years. Cellulosic feedstocks are now regarded as a viable option for biofuels production and nanotechnology can also enhance the performance of enzymes used in the conversion of cellulose into ethanol. Scientists are working on nano-engineered enzymes that will allow simple and cost-effective conversion of cellulose from waste plant parts into ethanol. Rice husk, a rice-milling byproduct can be used as a source of renewable energy. When rice husk is burned into thermal energy or biofuel,
a large amount of high-quality nano-silica is produced which can be further utilized in making other materials such as glass and concrete. Since there is a continuous source of rice husk, mass production of nano-silica through nanotechnology can alleviate the growing rice husk disposal concern.
Nanotechnology is a new science promising great potential in agriculture. The changing climate, sustainable use of natural resources, environmental factors, urbanization, agricultural waste disposal, accumulation of pesticides and over use fertilizers are the most important problems of modern agriculture. New techniques and methods have been used in order to avoid the detrimental effects of these factors. Nanotechnology clearly has the potential to dramatically impact and improve agriculture with new tools for the enhancing the ability of plants to absorb nutrients, molecular treatment of diseases, rapid
disease detection, etc. Smart sensors and smart delivery systems will help the agricultural industry combat viruses and other crop pathogens. In the near future nano structured catalysts will be available which will increase the efficiency of pesticides and herbicides, allowing lower doses to be used. Nanotechnology will also protect the environment indirectly through the use of alternative (renewable) energy supplies, and filters or catalysts to reduce pollution and clean-up existing pollutants.