Soybean ( Glycine max (L.) Merrill) is a globally important crop, providing oil and protein. Diaporthe/Phomopsis complex includes seed-borne pathogens that affect this legume. Non-thermal plasma treatment is a fast, cost-effective and environmental-friendly technology. Soybean seeds were exposed to a quasi-stationary (50 Hz) dielectric barrier discharge plasma operating at atmospheric pressure air. Different carrying gases (O 2 and N 2 ) and barrier insulating materials were used. This work was performed to test if the effects of non-thermal plasma treatment applied to healthy and infected seeds persist throughout the entire cycle of plants. To this aim, lipid peroxidation, activity of catalase, superoxide dismutase and guaiacol peroxidase, vegetative growth and agronomic traits were analysed. The results here reported showed that plants grown from infected seeds did not trigger oxidative stress due to the reduction of pathogen incidence in seeds treated with cold plasma. Vegetative growth revealed a similar pattern for plants grown from treated seeds than that found for the healthy control. Infected control, by contrast, showed clear signs of damage. Moreover, plasma treatment itself increased plant growth, promoted a normal and healthy physiological performance and incremented the yield of plants. The implementation of this technology for seeds treatment before sowing could help reducing the use of agrochemicals during the crop cycle.

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The nozzle current-voltage characteristic for a cutting arc is presented in this work. The measurements are reported using a high energy density cutting arc torch with a nozzle bore radius of 0.5 mm. The arc current was fixed at 30 A while the plenum pressure and the oxygen gas mass flow rate were varied in the range of 0.55-0.65 MPa and 0.32-0.54 g s −1 , respectively. The results show a very low electron density and the lack of electron attachment at the plasma boundary layer. No ion saturation current was found. For the smallest mass flow rate value gas breakdown was found for a biasing nozzle potential close to that of the cathode, but no evidence of such breakdown was found for the larger mass flow rate values. Using an expression for the ion speed at the entry of the collisional sheath formed between the nonequilibrium plasma and the negatively biased nozzle wall together with a generalized Saha equation coupled to the ion branch of the characteristic, the radial profile of the electron temperature, the spatial distribution of the plasma density at the plasma boundary, and the sheath thickness were obtained. In particular, the obtained thickness value at the breakdown condition was in good agreement with that obtained from the oxygen Paschen's curve. An electron temperature of about 4700-5700 K and a corresponding plasma density of the order of 10 19-10 20 m −3 were found close to the nozzle wall. A physical interpretation on the origin of the double-arcing phenomenon is presented, that explains why the double-arcing ͑that it is established when the sheath breaks down͒ appears at low values of the gas mass flow.

Soybean (Glycine max (L.) Merrill) is one of the most important crops worldwide providing dietary protein and vegetable oil. Most of the nitrogen required by the crop is supplied through biological n 2 fixation. Non-thermal plasma is a fast, economical, and environmental-friendly technology that can improve seed quality, plant growth, and crop yield. Soybean seeds were exposed to a dielectric barrier discharge plasma operating at atmospheric pressure air with superimposed flows of O 2 or n 2 as carrying gases. An arrangement of a thin phenolic sheet covered by polyester films was employed as an insulating barrier. We focused on the ability of plasma to improve soybean nodulation and biological nitrogen fixation. The total number of nodules and their weight were significantly higher in plants grown from treated seeds than in control. Plasma treatments incremented 1.6 fold the nitrogenase activity in nodules, while leghaemoglobin content was increased two times, indicating that nodules were fixing nitrogen more actively than control. Accordingly, the nitrogen content in nodules and the aerial part of plants increased by 64% and 23%, respectively. Our results were supported by biometrical parameters. The results suggested that different mechanisms are involved in soybean nodulation improvement. Therefore, the root contents of isoflavonoids, glutathione, auxin and cytokinin, and expansin (GmEXP1) gene expression were determined. We consider this emerging technology is a suitable pre-sowing seed treatment. Soybean (Glycine max (L.) Merrill) crop is considered a highly valuable source of protein, oil, and biofuel. With a worldwide sown area of 130 million hectares, soybean production achieved 370 million metric tons (68% of global production) in 2018-2019, up 9 percent from the previous year. Approximately 45% of this production corresponds to South American countries: Argentina, Brazil, and Paraguay 1. Growers in the main agricultural areas of the world employ chemical fertilizers as the only reliable tool for facing the increasing demand for food that accompanies the ever-growing world population 2. There is a substantial concern around the world for the optimization of alternative nitrogen sources that may help to avoid the intensification of chemical fertilizer usage. The contribution of biological nitrogen fixation (BNF) to the stock of N available for the crop results essential. The symbiotic associations between legumes and rhizobia represent the most important N 2-fixing agents in agricultural systems. Soybean is considered among the most efficient legume species regarding the ability to fix N: 58-68% of soybean plant N derives from N 2 fixation 3. Only bacteria contain the nitrogenase enzyme that can reduce N 2 to ammonium, and the major problem in maintaining a high rate of N 2 fixation is that this enzyme is oxygen-labile 4. Leghaemoglobin accumulated in the cytoplasm of infected plant cells binds to free oxygen avoiding the inactivation of nitrogenase 5. Many scientific efforts have been made in the last de...

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Low-frequency (100 Hz), intermediate-current (50 to 200 mA) glow discharges were experimentally investigated in atmospheric pressure air between blunt copper electrodes. Voltage-current characteristics and images of the discharge for different inter-electrode distances are reported. A cathode-fall voltage close to 360 V and a current density at the cathode surface of about 11 A/cm 2 , both independent of the discharge current, were found. The visible emissive structure of the discharge resembles to that of a typical low-pressure glow, thus suggesting a glow-like electric field distribution in the discharge. A kinetic model for the discharge ionization processes is also presented with the aim of identifying the main physical processes ruling the discharge behavior. The numerical results indicate the presence of a non-equilibrium plasma with rather high gas temperature (above 4000 K) leading to the production of components such as NO, O, and N which are usually absent in low-current glows. Hence, the ionization by electron-impact is replaced by associative ionization, which is independent of the reduced electric field. This leads to a negative current-voltage characteristic curve, in spite of the glow-like features of the discharge. On the other hand, several estimations show that the discharge seems to be stabilized by heat conduction; being thermally stable due to its reduced size. All the quoted results indicate that although this discharge regime might be considered to be close to an arc, it is still a glow discharge as demonstrated by its overall properties, supported also by the presence of thermal non-equilibrium.

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Departures from local thermodynamic equilibrium in cutting arc plasmas derived from electron and gas density measurements using a two-wavelength quantitative Schlieren technique J. Appl. Phys. 109, 063302 (2011) Plasma temperature and radial density profiles of the plasma species in a high energy density cutting arc have been obtained by using a quantitative schlieren technique. A Z-type two-mirror schlieren system was used in this research. Due to its great sensibility such technique allows measuring plasma composition and temperature from the arc axis to the surrounding medium by processing the gray-level contrast values of digital schlieren images recorded at the observation plane for a given position of a transverse knife located at the exit focal plane of the system. The technique has provided a good visualization of the plasma flow emerging from the nozzle and its interactions with the surrounding medium and the anode. The obtained temperature values are in good agreement with those values previously obtained by the authors on the same torch using Langmuir probes.