Ultrafine bubble water irrigation promotes soil particle fragmentation and reduces soil hardness in paddy fields.

Irrigation with water containing ultrafine bubbles (UFB) promotes crop growth under environmental stress conditions. This study evaluated the changes in soil physical properties when using low-cost UFB for paddy field irrigation. An experimental paddy field was divided into eight sections, with regular agricultural (control) and UFB irrigation, and rice cultivation was conducted over three seasons. The findings indicate that the sand content, linked to the fragmentation of gravel, increased 2.6% due to UFB irrigation over two years. A one-week stirring experiment was conducted in the laboratory to observe the accelerated fragmentation of the soil particles. A UFB containing distilled water significantly decreased the sand content by 3.5-7.1% and increased the clay content by 5.3-5.6% compared to the control distilled water. The thickness of the viscous colloidal layer on the soil surface increased by a maximum of 29 mm, and the penetrometer resistance decreased with UFB irrigation under submerged paddy conditions. These results indicated that continuous irrigation with low-cost UFB water from air and agricultural water promotes soil particle fragmentation and reduces soil penetrometer resistance. This study provides valuable insights into the potential benefits and limitations of UFB irrigation in sustainable agricultural practices.