Abstract:

This research investigated the degradation of carbendazim fungicide residues in white clover （Trifolium repens） silage cut within an orchard and the effect of carbendazim residues on the diversity of the fermentative microbial community， to explore options for the use of cover plants with pesticide residues in orchards. Different carbendazim concentrations （2.0， 2.5， 3.0 g·L^-1，_{with a water spray as Control） were sprayed on white clover prior to ensiling. The silage was harvested after 60 days fermentation at room temperature. Samples were taken before ensiling， on the 3rd day and on the 60th day after ensiling to study the diversity and composition of the microbial fermentative community using Miseq high-throughput sequencing technology. The degradation rate of carbendazim during was found to be up to 59.6%， and the higher the application rate， the higher the degradation rate. Carbendazim treatment significantly increased the content of lactic acid， acetic acid， and propionic acid in white clover silage during fermentation. For days 0， 3 and 60 of ensiling， lactic acid increased by 47.55%， 63.24%， 71.08%， respectively； acetic acid increased by 24.49%， 44.90%， 46.94%， respectively， and propionic acid increased by 66.67%， 187.50%， and 250.00%， respectively. These changes enhanced the retention of nutrients in the clover silage. High-throughput sequencing results showed that spraying carbendazim significantly changed the composition of white clover silage bacterial community and increased the abundance and diversity of the silage flora. After spraying carbendazim， the abundance of Lactococcus， Weissella， Pantoea， Rosenbergiella， Pseudomonas， Stenotrophomonas， Enterobacter， and Bacillus increased and these changes not conducive to good silage fermentation. However， with the passage of time after ensiling， the abundance of Stenotrophomonas， Enterobacter， Bacillus and other flora decreased. In summary， carbendazim pesticide increased the number of microorganisms beneficial to silage fermentation， and altered the abundance of bacteria harmful to silage fermentation. Carbendazim spraying also increased the diversity of carbendazim-degrading bacteria and the silage microorganisms. The residual amounts of carbendazim in silage were higher than the maximum residue of this fungicide stipulated for feed crops by the European Food Safety Agency and hence the silage did not meet the feed standards. These results provide test data on the level of carbendazim residues remaining in herbage after ensiling following spraying and will assist in the development of safe practices for the use of orchard cover plants.}

Key words: carbendazim, carbendazim degradation, microbial fermentative community, white clover, silage quality