# Applications of Plasma Produced with Electrical Discharges in Gases for Agriculture and Biomedicine
## 3 Review of Plasma Applications in Agriculture and Medicine
### Plasma Applications in Agriculture
#### 3.1.2 Agricultural Soil Treatment and Pest Control
The ozone remediation process can be divided into two phases [136]:  
* Instantaneous ozone demand phase, when rapid interactions with soil organic matter and metal oxides occur and most of the pollutant-removing processes take place. * Relatively slow decay stage. AOTs result in ring cleavage of poorly soluble aromatic compounds and insertion of oxygen, which increases their water solubility, thereby facilitating their degradation in the natural environment (www.H2O2.com accessed on 23 April 2022). Remediation was positively tested for such pollutants as diesel range organics, trichloroethylene, and PAHs (polycyclic aromatic hydrocarbons) [137; 138]. In highly cultivated areas, soil and groundwater contamination with herbicides and pesticides causes severe health problems (bioaccumulation) and significantly reduces the amount of crop yield. Non-thermal plasma with ozone and oxidative species can inactivate pathogens via:  
* Direct destruction, volatisation, and etching of cells. * Decreasing of biofilm adhesivity by decomposition of the polymer matrix. * Oxidative stress due to the formation of radicals of various active agents (O\({}_{3}\), OH, and O) and the influence of hydrogen peroxide, H\({}_{2}\)O\({}_{2}\), or UV radiation during the electrical discharges. * Nitrogen stress (research results suggest cell damage from reactive nitrogen intermediates, such as nitric oxide, peroxynitrite, nitrous acid, and nitrogen trioxide) [139]. Japanese researchers [134; 132; 133; 134; 135; 136; 137; 138; 139; 14; 13] developed a portable back-pack ozone--mist spray system that is environmentally friendly and intended for use in non-chemical agricultural management. The system, depicted in Figure 3, consists of an ozone generator, a water-mist spray, and a specific nozzle, which is used to kill harmful insects, bacteria and viruses on the surface of plants and in agricultural soil. The results of insect inactivation with the ozone-mist spray are presented in Table 3. Sterilisationefficiency is expressed as a percentage of the inactivation of all tested insects in a given sample. The plasma inactivation conditions are expressed by the following parameters: mist-spray ozone concentration in g/m\({}^{3}\); oxygen flow rate in litres per minute; spray time in seconds and ozone solubility in ppm. Inactivation studies were carried out on leaves of four different plants (i.e., tobacco, Canada goldenrod, orange, and green tea) and on five insects feeding on these plant's leaves: green-peach aphid and green caterpillar--on tobacco; goldenrod aphid--on Canada goldenrod; black citrus aphid--on orange; plant lice--on green tea. Treatment parameters for the ozone-mist spray system were the same for all cases, with the exception of green caterpillar and plant lice (No. 2 and No. 5 in Table 3, respectively), for which the spraying time was not 10, but 20 s. As can be seen from Table 3, the sterilisation rate was relatively high in all cases of insect treatment by ozone-mist spray; the lowest for the green caterpillar insect on tobacco was equal to 50% at 20 s of treatment time; the biggest one was equal to 100% for black citrus aphid at 10 s of spraying time, while it was 90% for plant lice over a treatment time equal to 20 s. Using the ozone gas instead of the ozone-mist spray for 20 s allows for 100% inactivation of green tea plant lice insects [84; 134]. The same authors [140] proposed and conducted preliminary studies of a mobile soil purification system, which was a project for the practical use of surface barrier discharge and ozone diffusion into the soil, and which was used to treat the soil in a greenhouse. Soil treatment with ozone increased soil acidity, which improved sprouting for some plants (radish) and worsened it for others (spinach). The acidity of the soil returned to the values from before the plasma treatment, which in actual cultivation requires optimisation of the sowing time of the grain, depending on the type of plants.