Effect of Tank Mix Post-emergence Herbicides on Soil Dehydrogenase Activity and Its Phytotoxicity on Wheat

Aims: The study was conducted to assess the efficacy of tank mix post emergence herbicides on soil dehydrogenase activity and its phytotoxic effect on wheat.

Study Design: The experiment consists of ten treatments and was laid out in randomised complete block design with three replications.

Place and Duration of Study: The present investigation was conducted at Main Agricultural Research Station, University of Agricultural Sciences, Dharwad, Karnataka, during rabi 2020-21.

Methodology: Weed control and phyto-toxicity ratings at 7, 14 and 21 days after herbicide application were recorded in each treatment on 0-10 scale on the basis of visual observations. Dehydrogenase activity in the soil samples was determined and expressed as μg TPF formed per g soil for 24 hrs.

Results: Post emergent application of metsulfuron-methyl + carfentrazone-ethyl (8.00) recorded good weed control being on par with post-emergence herbicide tank mixture of metsulfuron-methyl + sulfosulfuron (7.83) at 14 DAHA. At 7 DAHA, slight phytotoxic injury to crop was noticed IN T2 (0.5), T3 (0.5), T7 (0.5), T4 (1.00) and T1 (1.00). There was no phytotoxic injury to the crop with any of the post-emergence herbicides at 14 and at 21 DAHA. Soil dehydrogenase activity was found to be higher (41.02 µg TPF g-1 day-1) before herbicide application, whereas the activity was reduced upon herbicide application. Among the herbicide treatments, higher dehydrogenase activity of soil was found with the application of metsulfuron-methyl + pinoxaden (34.07 µg TPF g-1 day-1).

Conclusion: T4 was found to be better in controlling weeds and recorded higher weed control rating. The herbicides and their mixtures used in the present study did not cause any injury, hence it has no phytotoxic effect on wheat crop. However, soil dehydrogenase activity was higher before the application of herbicides, whereas herbicide application resulted in reduced dehydrogenase activity.