Persistence of the herbicides florasulam and halauxifen-methyl in alluvial and saline alluvial soils, and their effects on microbial indicators of soil quality

• Florasulam and halauxifen-methyl degraded rapidly in soil with a half-life of less than 18 days.
• Recommended doses of the herbicides did not ultimately impair, respiration or the degradation of or β-glucosidase.
• qCO2 and qFDHA, indicated that the soil microbial biomass could overcome the stress imposed upon them at the recommended doses.

The persistence of florasulam and halauxifen-methyl in combination was investigated in an alluvial (AL) and saline alluvial (SAL) soils under laboratory condition at field recommended (FR) dose (i.e. 12.76 g a.i. ha−1), 10 FR and 0FR (control) throughout the experiment. Effect of these herbicides on soil microbial biomass carbon (MBC), basal soil respiration (BSR), substrate induced soil respiration (SIR), hydrolysis of fluorescein diacetate (FDHA) and β-glucosidase activities was also measured under same conditions. The residues of florasulam and haluaxifen-methyl were extracted with acetonitrile using modified QuChERS method, followed by quantification using liquid chromatography-mass spectrometry (LC-MS/MS). Half-lives of florasulam and halauxifen-methyl were in the range of 12.65–16.82 days and 7.13–10.24 days in AL respectively and the same for SAL was 15.28–17.60 days and 7.25–8.88 days. Herbicide treatment inhibited MBC, BSR, SIR, and microbial metabolic quotient (qCO2) up to 30 days of incubation at the applied doses in both the soils. At the end of incubation, FR treated soils became statistically at par with control. However, the FDHA and β-glucosidase activities were affected in both the soils at the applied doses of the herbicide up to 15 days. Thereafter, the FR treated soils were statistically at par with control. Data revealed that, recommended dose of this herbicide formulation did not ultimately impair microbial components of the studied soils.