Effect of Direct Plasma Treatment and the Applicatiion of Plasma Activated Water on Soybean Development

The direct plasma treatment of soybeans and the use of plasma activated water for irrigation are examples of innovative and sustainable plasma-based initiatives with potentially significant socio-economic impacts. Preliminary results have shown that such treatments affect water absorption, germination, and root development, among other physiological traits of plants. Additional biological effects due to the plasma-generated reactive oxygen and nitrogen species (RONS) are also possible. In this work, atmospheric pressure plasmas were used to treat seeds and water. In the direct seed treatment, discharges were sustained in a packed bed reactor (PBR) in which seed aggregate acts as the packing material. The PBR was also set up in two dimensions to allow optical access to study discharge propagation through the matrix of seeds. The discharge was formed using nanosecond, high voltage pulses, and various feedstock gases to assess sensitivity to the production of RONS. Characterization of reactants and their effects were investigated using a fast-camera and spectroscopy setup on the $2\mathrm{d}$ apparatus. Contact angle measurements were also performed on the plasma treated seeds. In the indirect treatment, water was exposed to DBD-type plasmas. Hydrogen peroxide, nitrate and nitrite concentration along with pH of the treated water were measured as a function of operating condition. The associated effects on seeds were quantified as a function of the relative densities of these species. Changes in peak voltage, frequency, feedstock gas, and water chemistry induced by the plasma was related to the soybean plant's physiological development.