Effects of Ultrafine Bubble Water Irrigation on Dry Weight Allocation and Nitrogen Absorption of Young Southern Highbush Blueberry

Abstract

To clarify the effects of ultrafine bubble (UFB) water irrigation on dry weight (DW) allocation and nitrogen uptake efficiency of pot grown two-year-old ‘O’Neal’ southern highbush blueberry (Vaccinium corymbosum L.), a destructive investigation and ¹⁵N-tracer method were carried out. The trees were irrigated with UFB water or tap water daily by hand irrigation. ¹⁵N-labeled ammonium sulfate was applied on April 19, May 25, and July 24 during the 2018 growing season, and the labeled trees were destructively harvested 2 weeks later for DW measurements, atom% of ¹⁵N, and N content of each of the plant organs. The first destructive investigation showed no difference in DW of each organ between treatments; however, the ¹⁵N content of fine roots was significantly higher with UFB treatment. The second and third destructive investigations showed the significant promotion on not only underground but also aboveground organ DW allocation with UFB treatment. The ¹⁵N content of the third destructive investigation showed a consistent result with an increase of DW with UFB treatment. In July, DW and ¹⁵N content of underground organs and summer shoot were significantly higher, resulting in a significant elongation of the total shoot length per tree. These results suggest that UFB treatment promoted nitrogen absorption and further supports the growth of aboveground organs. We have demonstrated for the first time that UFB water irrigation can enhance the physiological activity of roots, thus improving nitrogen absorption, in blueberry.