Efficiency of Soil Extracellular Enzymes in Soils Treated by Organic and Mineral Conditioners Against Mostly Applied Veterinary Antibiotics (Gentamicin, Oxytetracycline and Penicillin)

Veterinary antibiotics enter into agricultural soils through application in animal husbandry and manures where these soils could be the source of dissemination of antibiotics in soil and water habitats. Owing to increasing antibiotic applications in our country, the aim of present study was to understanding and evaluating the consequences of mostly applied antibiotics in soil (with and without organic and mineral conditioners) on extracellular enzymes activity, alkaline phosphatase and urease, and their resistance and resilience indices as well as mean soil enzyme activity, in a 90-day incubation period.

In the present study, the impact of releasing mostly applied antibiotics in soil (control (without antibiotic), gentamicin, oxytetracycline and penicillin) at different concentrations (50, 100 and 200 mg/kg dry soil) with and without organic and mineral conditioners (manure, biochar and nano-zeolite) on efficiency of soil alkaline phosphatase and urease enzymes and their resistance and resilience indices as well as enzymes efficiency index at 1-7, 7-30 and 30-90 days of a 90-day incubation as split-factorial design in which soil conditioners were as main plots and antibiotics and their concentrations were secondary plots.

In treatments without conditioner application, gentamicin at 200 mg/kg concentration caused 68.9 percent decrease in alkaline phosphatase efficiency compared to control (without antibiotic), however, decreasing enzyme activity in soil treated by 200 mg/kg oxytetracycline at control (without conditioner), application of manure, biochar and nano-zeolite compared to control (without antibiotic) was 17.5, 13.8, 17.5 and 16 percent, respectively. Urease enzyme efficiency at 30-90 days had an increasing trend and the highest enzyme activity recorded at this time period. Based on the results, measured enzymes had different responses, so that penicillin and oxytetracycline had not such a considerable impact of soil alkaline phosphatase activity. While, gentamicin and oxytetracycline at all applied concentrations, had significantly negative impact on soil urease activity. Considering the great responsivene of alkaline phosphatase to gentamicin antibiotic, application of soil conditioners had no significant efficiency in improving resistance of this enzyme in gentamicin treated soils. also, application of soil conditioners had no significant impact on increasing resistance index of urease enzyme in oxytetracycline applied soils. results show that increasing application amout of antibiotics caused decrease in soil enzymes activity and highest enzymes resilience observed in 50 mg/kg antibiotic concentration. Also results showed that urease enzyme had the highest resilience indec in penicillin application treatments followed by gentamicin and then oxytetracycline treatments.

Present study showed that application of conditioners, especially manure and its biochar improved soil properties and increased soil microorganisms’ resistance against antibiotics, even at higher concentrations. There was difference among responsiveness of studied enzymes, so that oxytetracycline had no significant impact on soil alkaline phosphatase activity, penicillin had no considerable effect on soil urease activity. Totally, the present study showed that application of soil conditioners could alleviate toxic impacts of antibiotics and result in increase in resistance and resilience indices of soil enzymes and improved enzymes activity and efficiency in antibiotic-treated soils.