The Innovation Team of Soil Health Care of the Institute of Agricultural Resources and Regional Planning (IARRP) of the Chinese Academy of Agricultural Sciences (CAAS), in collaboration with the CAAS-CIAT Joint Laboratory in Advanced Technologies for Sustainable Agriculture, hasconducted a study on the impacts and mechanisms of cherbicide mixtures on the soil microbial communities. The findings were published in the prestigious academic journal "Environmental Pollution".

Figure 1: Response mechanisms of soil microbial community in the maize rhizosphere to the herbicide mixtures application

Chemical herbicides have historically played an important role in weed management, with China's annual herbicide usage exceeding 100,000 tons. This has been a crucial guarantee for high and stable agricultural production. However, the prolonged and exclusive use of single herbicide has led to a series ofissues , such as the rapid succession of weed population, the emergence of herbicide-resistant weeds, soil contamination from the residual herbicides, and crop damage, which have affected the sustainable development of Chinese agriculture. The application of herbicide mixtures with diverse spectra is believed to be a more scientific and efficient approach, and the registration and utilization of herbicide mixture products have been on the rise.However, the potential impact of mixed herbicide residues on soil ecosystem health and safety remains unclear, which hampers the healthy management and sustainable utilization of cultivated land.

This study focused on the most widely used herbicide mixtures  (nicosulfuron + mesotrione + atrazine) in maize cultivation.The investigation scrutinized  the effects of different dosesof single herbicides and mixed herbicides on key soil enzyme activities, microbial community structure, microbial functions, and changes in microbial interactions under the influence of mixed herbicide residues.

The results showed that when herbicides were used in combination, the persistence of each active ingredient was extended when used individually. The microbial community structure in the rhizosphere-a zone around crops roots demostrated more sensitive to herbicide mixtures application. The activities of vital soil enzyes, including dehydrogenase, urease, and invertase, were temporarily inhibited. Additionaly, the key functional groups associated with  crop growth (e.g., Pseudomonadaceae, Enterobacteriaceae) exhibited significant decrease in abundance and struggled to recover. The complexity and stability of soil bacterial networks were both reduced, while the interactions between rhizosphere fungal communities were amplified, potentially increasing the risk of disease occurrence. Furthermore, the excessive application of herbicides led to an enrichment of microbial communities within the rhizosphere with more pathways related to pollutant degradation, enabling them to cope with the stronger disturbance caused by excessive herbicide application.

This study offers a comprehensive understanding of the response mechanisms of soil microbial communities in the maize rhizosphere to the application of herbicide mixtures, which is of great significance for guiding more accurate herbicide application, facilitating risk assessment of herbicide residues, and promoting the technology development of microbial remediation.

The first author of this study is MA Qingyun, a graduate with master's degree from IARRP, and Associate Professor RUAN Zhiyong serves as the corresponding author. This research was supported by the National Natural Science Foundation, the Scientific and Technological Innovation Project of the Chinese Academy of Agricultural Sciences, and the Fundamental Research Funds for Central Non-profit Scientific Institution.

Paper Link: https://doi.org/10.1016/j.envpol.2023.122393