Effects of the novel HPPD-inhibitor herbicide QYM201 on enzyme activity and microorganisms, and its degradation in soil

QYM201 is a 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibiting herbicide recently registered in China for controlling grass and broadleaf weeds in wheat. It is a novel herbicide, and its potential harm to soil ecosystems has not yet been reported. This study investigates the influence of QYM201 on soil enzyme activity and microorganism quantities in two different soils at concentrations of 0.1, 1, and 5 mg kg^-1 soil. Results indicate that QYM201 initially inhibited soil protease, urease, and sucrase activity and this effect increased with concentration. During the later stages of incubation, inhibitory effects gradually weakened and by the end of the experiment (45 days), enzyme activity was restored to control levels. Catalase activity was stimulated by QYM201, with significant differences observed between the QYM201-treated groups and the control at the onset of exposure. This stimulation effect decreased during the later stages of the experiment. However, catalase activity was still significantly higher at the end of the experiment compared to the control. The effects of QYM201 on soil microorganisms differed. Initially, bacteria and actinomycetes quantities were decreased by QYM201 (10 days). As the incubation progressed, microorganism quantities in the lower concentration groups (0.1 and 1 mg kg^-1 soil) were restored to control levels, while those of the high concentration group (5 mg kg^-1 soil) did not fully recover. QYM201 did not significantly impact the quantity of fungi. The half-life and degradation rate constant (k) of QYM201 for the two studied soil types were 23.1 days and 16.1 days, and 0.030 and 0.043 day^-1, respectively.