Plasma-a fourth state of matter, has been characterized with various properties like temperatures (cold & hot plasma), particle trajectories, fluid flow properties, wave’s formation & propagation etc. due to different components of plasma like particle nature (e.g., electrons, ions, neutral particles) and as a fluid under the influence of external electric and magnetic fields. Plasma initially being searched as a source of fusion energy has come a long way with its exotic spin off applications to mankind like plasma medicine, plasma activated water, plasma agriculture, plasma modification of surfaces, plasma in pollution control, plasma propulsion, plasma electronics, plasma cutting and welding, waste to energy conversion, sterilization, etc. 

Most of these applications of plasma are already meeting the requirements mankind and others are expected to reach to commercial level soon.  Plasma in its different forms i.e., cold and hot plasmas is proposed to be generated by using various techniques, however, each process is still a difficult, costly and highly energy demanding. Moreover, confinement of plasma for longer times has not been very successful due to various instabilities arising by virtue of plasma containment itself. In a simple case, a gas discharge (plasma) is initiated via a plasma power supply in an oxygen and nitrogen containing gas flow. This ionizes the gas flow, creating ions, radicals and reactive species.

Role in agriculture

With the planet’s population projected to reach almost 10 billion by 2050, growing trends of people shunning away from agriculture due to un-reliable agriculture produce outcomes, too much dependence on un-predicted natural climatic conditions, dependence on the un-wanted use of pesticides & fertilizers, innovative approaches to both food production and processing will be required to meet food demands. Increasing agricultural productivity-caused by population growth-and closing the yield gap between real yields and potential yields plus taking into account protection of the environment, must be addressed with novel approaches. Decontamination of foods and minimization of food spoilage are critical issues to ensure food safety and sustainability. While thermal and chemical approaches remain a cornerstone for food processing, there is an ongoing search for non-thermal solutions for the treatment of food. Such approaches should contribute to improved food safety and quality profiles. Use of plasma in agriculture and food will concentrate on each step of this agriculture-food chain from seed germination- plant growth- plant yield-food safety during transportation & storage. Cold plasma technology has brought a new dimension to the concept of decontamination under ambient conditions, in that it truly is an ensemble of both physical and chemical decontamination methods. This innovation stems from the development of methods to generate plasma at atmospheric pressures and temperatures.

Obtaining high yields in agricultural production is essential due to the world’s population growth and increased food demand; but at the same time, adverse effects of agriculture on the environment need to be kept to a minimum. Plasma Technology has many agricultural benefits and some of the notable benefits are: increased farm productivity, enhanced food and fiber production, better soil fertility management, better plant and livestock health management, sustainable food production, and globally increased plant and human health. The recent developments in cold plasma (also known by other names like: rarefied, non-thermal, weekly ionized) sources, the confirmation of strong antimicrobial action and the ability to plasma treat foods with the retention of their quality has led to the emergence of a new subject area within food science. Plasma can be used in the entire life cycle of fresh produce, from soil to fork:

• Sterilize seeds while in storage
• Enhance seed germination
• Air cleaning, sterilization, and removal of volatile organic compounds in greenhouse facilities
• Treatment, sterilization, and cleaning of water used for produce washing after harvest
• Disinfection of produce before packaging
• Air cleaning, sterilization, and removal of volatile organic compounds in the packaged produce storage facility and transportation vehicles
• Control of pests and pathogens at the in-store display case and in-store storage
• Removal of ethylene from air to reduce rate of aging
• Sterilization of cutting boards, knives, and other food processing equipment both at home and in food processing facilities or grocery stores
• Plasma-assisted destruction of hazardous waste and/or waste-to-energy conversion of the nonhazardous food wastes

Plasma technology in agriculture

In agriculture, plasma technology is increasingly transforming people’s understanding of plants and soils, and their diverse magnetic and gravitational fields' interactions with their environments. With this new understanding, plasma scientists and agricultural practitioners are, in turn, revitalizing agricultural development, research, and education and practice across the world. The new plasma technology has potential to completely revolutionize agricultural practices, enhance environmental health and healthy living for both producers and consumers, and virtually eliminate external inputs in agricultural systems across the world.  With full understanding of how plants absorb carbon dioxide from the atmosphere, scientists designed a technology that replicates a plant’s leaf for the effective capture of CO2 and other gases in their Nano states (GANS). A gas in Nano state is a new state of matter, where a gas molecule that becomes Nano of itself appears as a solid state of matter. It is especially this seemingly simple GANS capture technology that will completely transform global agricultural development and practice once and for all. CO2 GANS are increasingly used to transform agriculture practices across the world. Before sowing, for example, seeds are soaked in CO2 GANS liquid plasma to decontaminate any that may be disease infected or adulterated, while irrigation of crops with CO2 liquid plasma virtually eliminates the need for fertilizers and pesticides. The use of CO2 liquid plasma and other such liquid plasmas increasingly provide the much needed agriculture solutions for enhancing plant growth, ensuring plant health, and increasing crop yields at minimum cost to producers. For crop pests, application of CO2 GANS liquid plasma creates conditions under which the pests do not damage crops. In addition, pests also absorb the energy of the applied CO2 GANS liquid plasma. When they absorb enough energy for their bodies' metabolism, such pests do not need to feed on the crops.

The plasma treatment increases the nitrogen content of the water. Nitrogen is one of the main components in many commonly used fertilizers, the other two being potassium and phosphorus. Nitrogen is especially important in the germination phase of a plant’s life. Other benefits of the plasma treated water include the ability to control pH and increased efficiency of water use. The technology is not only beneficial in the stages of growth for the plant but can also be used to sterilize fruits and vegetables for consumption as well as keep fruit fresh when it is in transportation and storage by eliminating ethylene oxide, the chemical responsible for food spoilage. Plasma is emerging as a disinfectant in a variety of applications, including wounds and crops. It is used to sterilize crops after the harvest, where there is little concern about damaging living cells. Diseased rice seeds treated with atmospheric plasma show significant improvement and growth, offering a potential tool to protect rice crops from fungus and blight. A research team found that immersing infected rice seeds in hot water and then irradiating them with plasma reduced infection rates between 60 and 90 percent. The team found the most effective way to reduce disease rates was the hot water bath followed by plasma irradiation. There was no damage to the seeds, which germinated and grew like healthy seedlings. The researchers concluded that the combination of water immersion and plasma irradiation of rice seeds seems to provide an excellent pest integrated management system to reduce risks to human health and the environment by minimizing the use of chemical pesticides.

Recent developments

Low temperature plasmas (LTPs) show promise as efficient green technologies for enhancing productivity while maintaining good food quality and safety in the many steps of the food cycle. As a result, applications of LTPs in agriculture have led to creation of a new, rapidly developing field called “plasma agriculture.”  One such approach is to use LTPs in agriculture whereby plasma can boost yield in a robust way without demanding more water or more chemical 

fertilizer. In other words, Plasma agriculture potentially offers increased production with less impact on ecosystem, by suppressing plant diseases and enhancing crop yields. For a long time the link between plasmas and food processing was limited to the treatment of packaging materials to improve, for examples, wettability, sealability, printability, and barrier properties, or for purposes of decontamination. More recently, the capability of plasma as an antimicrobial agent has been explored for the sanitation of food products. Indeed, the emergence of new pathogens that can contaminate products, change production processes, and consumer lifestyles and needs, are posing unprecedented new challenges. To achieve this goal, collaborations between plasma research scientists, plant biologists, agricultural experts, and food technologists will be needed to understand, control, and scale up these new processes. Agriculture across the globe is moving more and more towards new ways to increase sustainability and environmental responsibility. Water shortage, a growing world population, shortages of land, and increasing government regulations are all reasons behind agriculture’s move towards utilizing new technology to achieve improved and progressive results. By activating air and water with plasma, lab studies have shown that an increased production of crop yield is possible, among several other benefits.

Conclusion

Plasma state of matter offers a unique source of energy with lots of useful and controllable properties towards t\its applications its various forms like plasma activated water or plasma injections or plasma environment in agriculture to food chain is gaining its grounds with lots of benefits to the users. Efforts should be made further towards quantifying and repeatability of the effects of plasma applications in agriculture and food. Less complicated, having low energy requirement, affordable and safe methods to generate plasma have to be developed for best use of plasma spin off applications like in agriculture, food and medicine.