Effects of different fertilizers on residues of oxytetracycline and microbial activity in soil

Oxytetracycline (OTC), a type of tetracycline, was used widely as feeding additive to promote animal growth in breeding industry in the world. Its residue has been found in soils. Based on potted maize experiments, the influences of OTC on soil enzyme activity, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and soil fertility were investigated during the growth stages of maize receiving different fertilizers (spent mushroom substrate, worm manure, and biochar, among others, with single applications and combined applications with their cooperating microbial inoculants). The results showed that OTC negatively affected the soil enzyme activity, MBC, MBN, and cation exchange capacity (CEC). Enzyme activity, MBC, and MBN were more sensitive to OTC than soil fertility. The significant negative correlations were found between OTC concentrations and catalase, MBC, and CEC (p < 0.05). This indicated that the effects of OTC on soil can be alleviated by different fertilizers, and the effects of T6 (microbial inoculants), T7 (microbial inoculants + worm manure), T8 (microbial inoculants + SMS), and T9 (microbial inoculants + biochar) were the best among those of all treatments. During the mature stage of maize, the content of OTC in the soil of T7 was the lowest compared with other treatments. The results provide a good basis for the development of methods to remediate OTC-contaminated soils.