Study on the natural attenuation mechanism of gibberellic acid in soil under different water content conditions

As a micro-toxic pesticide with a wide application range and large dosage, the high solubility of gibberellic acid (GA₃) causes its weak adsorption and strong migration in soil, accompanied by strong natural attenuation, and it is also affected by changing soil water content during intermittent irrigation. Therefore, it is necessary to systematically study the natural attenuation mechanism of GA₃ in soil under different water content conditions. In this study, the natural attenuation mechanism of GA₃ under different soil water content conditions was investigated by setting three soil water contents of 10%, 20% and 30%, the influence of soil microorganisms on the natural attenuation process of GA₃ was analyzed, and the natural attenuation products were qualitatively identified. The results show: (1) at the end of the experiment (34 d), the natural attenuation rates of GA₃ in the soil of the sterilized group and the unsterilized group with initial water content of 10%, 20% and 30% were 87.77%, 89.70%, 90.70% and 87.70%, 94.47%, 95.87%, respectively, and the natural attenuation half-lives were 12.38 d, 12.16 d, 12.60 d and 8.56 d, 6.80 d, 7.07 d, respectively. (2) Soil water content had no significant effect on the natural attenuation rate of GA₃ in the soil of the sterilized group, while the natural attenuation rate of GA₃ in the unsterilized group was different under different soil water content (the largest in the 20% soil water content). (3) On the basis of hydrolysis, biodegradation further promoted the natural degradation of GA₃, with a biodegradation contribution rate of 39.62%±7.58%. (4) The main natural attenuation products of GA₃ were isomerized gibberellic acid (Iso-GA₃) and gibberellenic acid (GEA) (of which Iso-GA₃ accounted for a larger proportion). The more attention should be paid to the biotoxicity and environmental risks of the natural attenuation products of GA₃ in the environment in the future. This study can help to understand the environmental behavior of GA₃ in agricultural soils and provide data support for the assessment and control of its environmental toxicity and potential risk.