Individual and combined effects of tebuconazole and carbendazim on soil microbial activity

• The concentration of tebuconazole and carbendazim affects their dissipation in soil.
• Tebuconazole and carbendazim have additive effects on soil basal respiration.
• At 100 mg kg-1, tebuconazole and carbendazim are potentially toxic to soil health.

Tebuconazole and carbendazim are the main fungicides in agricultural practice, and their potential toxicological effects have received considerable attention. However, very little is known about the combined effect of both the fungicides on soil microbial activity. Therefore, a mesocosm experiment was performed to ascertain the dissipation and effects of tebuconazole and carbendazim individual and combined applications on microbial properties (i.e., basal respiration, urease, alkaline phosphatase, invertase, and dehydrogenase) in soil. The results indicated that the dissipation of tebuconazole and carbendazim was affected by concentration applied when the two fungicides were applied individually. However, the degradation of both fungicides accelerated at low concentrations (1 mg kg−1) and slowed down at moderate (10 mg kg−1) to high (100 mg kg−1) concentrations. Whether applied individually or in combination, low doses of both fungicides did not impart negative effects on soil respiration and enzymatic activities after seven days. However, increasing concentrations of moderate and high doses of tebuconazole significantly inhibited soil respiration and enzymatic activities. Apart from moderate doses of carbendazim which stimulated urease and invertase activities, other soil microbial activities were significantly inhibited by the moderate and high doses of carbendazim after seven days. The combined effects of the two fungicides at moderate and high concentrations were additive throughout the entire incubation time.