Dispersion of gaseous nanobubbles (NBs) in water has been demonstrated to improve plant growth and seed germination, which is critical for agricultural production and environmental applications. In this study, we investigated the effects of four types of NBs on seed germination and plant growth first. Air, oxygen, nitrogen, and carbon dioxide NBs were generated and dispersed in tap water. Different plants, including lettuce, carrot, fava bean, and tomato, were used in germination and growth tests. The seeds in water-containing NBs exhibited 6−25% higher germination rates. Especially, nitrogen NBs exhibited considerable effects in the seed germination, whereas air and carbon dioxide NBs did not significantly promote germination. The growth of stem length and diameter, leave number, and leave width were promoted by NBs (except air). Moreover, evaluation of the intriguing interactions between NBs, soil characteristics, and soil microbiome is important to reveal the mechanisms of how NBs enhance crop yield. Therefore, we evaluated the impacts of different gaseous NBs (e.g., oxygen, nitrogen, hydrogen, carbon dioxide and air) on (1) soil chemical properties such as pH, dissolved oxygen (DO) and redox potential in batch experiment, (2) the release of key elements such as NH4+, NO3−and PO43−, K+ and Mg2+ from soil as well as other soil contents such as natural organic matters, and (3) the effects of NBs on the microbiome in soil. Results of the batch leaching experiments showed that different NBs had different effects on different ion released from soil. Particularly, the concentration of NH4+ and PO43- were significantly higher in N2 NBs and CO2 NBs treatment system treatment system than others. With their characteristics of long persistence time and surface negative charges, the NBs acted as a bus for ions; they transfer nutrient ions from soil near to plant roots which may enhance the plant growth or reduce the use of chemical fertilizers. In addition, NBs could adjust soil ambient environment, for example, O2 NBs could increase the DO concentration and redox potential in soil significantly up to 22 mg/L and 280 mV compare to control (DI water) (8.5 mg/L, 220 mV), separately. The rhizosphere bacterial communities before and after irrigation with NB water were also investigated. Overall, this study offers a new insight into the impacts of NB water irrigation on plant growth and reduce the use of chemical fertilizer by a sustainable approach.

Nanobubbles and soil interactions and the effects on soil nutrient release and plant growth

ACS Fall 2021

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