| In recent years, Global climate warming and increasing organic pollution have become the most important environmental problems of threating to human survival, and been paid much attention at home and abroad. Croplands ecosystem is an important source of CH4 and N2O emissions. Herbicides have been widely used for controlling weeds in croplands; however, their effect on N2O and CH4 emissions remains unclear.To investigate the effects of commonly used herbicides on CH4 and N2O emissions and related soil and microbial parameters from the winter-wheat and rice field, a series of field experiments were conducted in this study. Five treatments in the winter-wheat field experiment included a control without herbicide(N) and four commercial herbicides such as acetochlor(AC), tribenuron-methyl(TBM), fenoxaprop-p-ethyl (FE), and the mixture of fenoxaprop-p-ethyl plus tribenuron-methyl (FE+TBM). In the rice field experiment, no herbicide and no fertilizer treatment (CK) was added as background emission, and no herbicide with nitrogen fertilizer (N) still employed as a control. Three commercial herbicides including butachlor (BC), bensulfuron-methyl (BSM) and the mixture of butachlor plus bensulfuron-methyl (BC+BSM) were used. All the herbicides were applied at field rate (namely manufacturer’s recommended dose).The wheat field experiment showed that both AC and TBM+FE significantly decreased N2O emissions by approximately 50%in the first ten days following herbicides application (P<0.05), while alone application of FE or TBM had no significant effect on N2O emissions (P>0.05), only with the reduction of N2O flux of 28.6% and 26.0%, respectively. For the remaining sampling days, AC, TBM, FE and TBM+ FE had no significant effect on N2O emissions (P>0.05), the average N2O flux being 95.3%,101.8%, 92.5% and 88.7% of the N treatment, respectively. The soil urease activity was always enhanced by AC during the measuring periods (P<0.05), and was initially inhibited but stimulated afterwards by FE or TBM+FE, while was not influenced by TBM (P>0.05). During the first ten days after herbicides application, N2O fluxes were positively correlated with soil water-filled porespace (WFPS), DNB (P<0.01) and AOB (P<0.05), but negatively correlated with DOC (P<0.05), and had no relationship with NOB, NH4+-N, NO3-N and soil urease activity (P>0.05). Due to less abundance of DNB in AC and TBM+FE plots and less abundance of AOB in TBM+FE plots, AC and TBM+FE significantly inhibited N2O emissions. TBM or FE had no significant effect on N2O emissions from the wheat field, which was mainly ascribed to the shift in the effect of promotion and inhibition on AOB and DNB.The rice field experiment results showed that the effects of different herbicides on CH4 and N2O emissions were different under the same climate and soil condition, and the effects on related biochemical parameters of soil were also different. The application of BC reduced CH4 emissions by 58%(P<0.05), while application of BSM or BC+BSM had no significant effect on CH4 emissions (P>0.05). BSM significantly decreased N2O emissions by 27%(P<0.05), while application of BC or BC+BSM had no obvious effect on N2O emissions (P>0.05). No significant difference was found with regard to an integrated global warming potential of N2O and CH4 emissions among treatments. Relative to the N treatment, a combined application of herbicides BC and BSM reduced GHGI by 22%, though the reduction is not statistical significant (p=0.596). CH4 fluxes were negatively correlated with correlated with the soil urease activity (P<0.01) during the measuring periods. Significantly positively relationships were found between N2O emissions and NOB (P<0.05), while there was no correlation with others soil factors (P>0.05). A further investigation suggested that the inhibitory effect of BSM on N2O emissions associated with low soil nitrate nitrogen and less abundance of denitrifying bacteria, and that BC depressed CH4 emissions was linked to high soil nitrate nitrogen and urease activity. |
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