Transient Effects of Air and Oxygen Nanobubbles on Soil Moisture Retention and Soil–Substance Interactions in Compost-Amended Soil

This study examined the impact of watering with air and oxygen nanobubble-saturated water (NBSW) on soil moisture retention, electrical conductivity (EC), nutrient leaching, and CO2 emissions in sandy loam (SL) and silty clay loam (SCL) soils amended with composted sludge (CS). The results revealed that air nanobubbles (air NBs) had greater stability, while oxygen nanobubbles (ONBs) showed lower stability but higher oxygen diffusion potential. Soil moisture under NBSW treatment was more sensitive to changes in ambient conditions and tended to decrease due to higher evaporation compared to conventional water. NBSW was more effective in enhancing moisture in SL soil than in SCL soil. Overall, the results revealed that the application of NBSW tended to increase soil compaction due to stimulation of microbial activity; however, air NBs may temporarily reduce compaction and enhance soil–water interactions. Additionally, NBSW increased soil EC due to increased dissolved ion concentration, with effects more apparent in SL soil than in SCL. This may indicate increased nutrient availability for plant uptake. Notably, NBSW, particularly ONB, showed quick but short-lived changes in soil physical and microbial properties, and soil texture played a significant role in treatment results. Furthermore, the leaching of nutrients and heavy metals remained negligible across all treatments. The study confirms that using NB in controlled environments is more practical for boosting short-term plant growth than improving long-term soil water retention to support more sustainable agriculture systems.