Effect of plasma-generated gaseous nitrogen on plant growth*

Nitrogen (N) content in the soil is a determinant for crop yield. Therefore, the demand for use of N fertilizer is increasing. Currently, most of N fertilizer production relies on the non-eco-friendly Haber-Bosch process. To develop the eco-friendly N fertilizer, nitrogen fixation by plasma is considered to be as one of promising way. Here, we developed a device to selectively produce dinitrogen pentoxide (N₂O₅) from air by plasma. N₂O₅ could be used as a nitrogen source for plant growth owing to high water solubility of N₂O₅ and rapid conversion to nitrate ions in water. We observed that plasma-generated N₂O₅ gas dissolved in a hydroponic medium successfully recovered the growth of N-deficient plants. We supplied the plasma-generated N₂O₅ gas to plants in two ways; 1. direct exposure and 2. indirect exposure to plants. The method 1 impaired leaves and reduced the fresh weight, but prevented anthocyanin accumulation caused by N deficiency. The method 2 showed that plants with N₂O₅ gas allowed the plants to have six leaves, whereas the mock treatment stopped growing. Based on the results, the second method is better because it minimized injuries and maximized benefits. In summary, this study proved that the plasma-generated N₂O₅ gas can be applied as N fertilizer for plant growth.