Objective The aims were to obtain efficient degrading strains of the herbicide nicosulfuron and to determine their degrading effect on nicosulfuron residual soil and mitigating effect on sorghum drug damage.

Method Enrichment, isolation and screening of efficient nicosulfuron degrading bacteria from soil contaminated by long-term application of nicosulfuron, and monitoring of their inoculation effects using pot and field trials.

Result Two strains, XZ4 and XZ6, were isolated and tentatively identified as Pseudomonas geniculata and Pseudoxanthomonas sp.. The pot results showed that when the concentration of nicosulfuron in soil was 0.05 mg kg^-1, the degradation rates of nicosulfuron were 88.15% and 83.78% treated with microorganism agent XZ4 (10⁸ CFU mL^-1) and microorganism agent XZ6 (10⁹ CFU mL^-1) after 42 d., respectively. This could significantly reduce its inhibition of sorghum plant height, root length and fresh weight; the two strains of bacteria could significantly increase the number of soil bacteria and reduce the number of soil fungi, and the larger the inoculum, the more pronounced the effect. Both of them could increase the activities of soil sucrase, urease and alkaline phosphatase and improve the soil microbiological environment, and the greatest effects on enzyme activities were found at 10⁸ and 10⁹ CFU mL^-1 concentrations, respectively. Compared with strain XZ6, strain XZ4 had a better effect on the indicators. Field trials showed that the microorganism agent XZ4 (450 kg hm^-2) could effectively mitigate 30 and 60 g a.i hm^-2 nicosulfuron damage to sorghum, improve sorghum seedling emergence, chlorophyll content, plant height and yield, reduce disease plant rate. The difference was significant compared with CK, and the growth of sorghum could basically recover to BK level.

Conclusion Pseudomonas geniculata XZ4 has good remediation capacity for nicosulfuron-contaminated soil and reduces the extent of nicosulfuron damage to sorghum.