The herbicides saflufenacil and indaziflam have recently been registered in Brazil for weed control in sugarcane crops; however, little information exists regarding their residual effects or influences on soil microorganisms. Therefore, the present study aimed: (a) to determine the effects of saflufenacil and indaziflam on soil microorganisms and (b) to evaluate the residual and dose effects of these herbicides on soybean, sunflower, sunn hemp and peanut crops. The herbicides indaziflam (100 g a.i. ha-1) and saflufenacil (120 g a.i. ha-1) were applied to dark red latosol samples, and the CO2-C released by soil basal respiration was measured at 7, 14, 21, 28, 35, 42, 49 and 56 days after treatment (DAT), in an experiment with a completely randomized design (CRD) and five replicates. The microorganisms were quantified via the use of different culture media, each replicated three times at 0, 15, 30 and 60 DAT. No significant difference occurred among the treatments for the carbon content of the microbial biomass. Regarding the basal respiration, the soils treated with saflufenacil showed a decrease in the carbon released by the soil at 49 DAT, whereas the carbon released by the soils treated with indaziflam increased until the last day of evaluation. The responses of the fungal and bacterial populations and the amylolytic and cellulolytic microorganisms differed among the treatments. The residual effect of the herbicides on the crops was evaluated via a CRD, in a 6 (doses) × 5 (sowing times) factorial arrangement with four replicates. The different indaziflam and saflufenacil doses were sprayed separately at pre-emergence. At 0, 10, 20, 40 and 60 days after the herbicide applications, soybean, sunn hemp, sunflower and peanut were sown. The phytotoxicity of saflufenacil to the crops declined throughout the evaluations for all the doses and species. Indaziflam was highly phytotoxic to all the crop species until 60 days after application, preventing the field sowing of the crops during that period.
Key words: Phytotoxicity, sugarcane, carryover, microbial degradation.