[Effects of the Veterinary Antibiotic Sulfamethazine on Ammonia Volatilization from a Paddy Field Treated with Conventional Synthetic Fertilizer and Manure].

Veterinary antibiotics have been widely detected in croplands due to the application of animal excrements as fertilizer. However, their effects on ammonia (NH3) volatilization remain unclear. A field experiment was conducted to evaluate the effect of sulfamethazine on NH3 volatilization from a paddy field when conventional synthetic fertilizer or manure was applied as basal fertilizer. Five different treatments were conducted in this study: without application of fertilizers and antibiotics (CK), compound fertilizer used as basal fertilizer with and without the addition of sulfamethazine (CF+SD and CF respectively), and pig manure used as base fertilizer with and without the addition of sulfamethazine (CM+SD and CM respectively). Urea was used for topdressing in the CF, CF+SD, CM, and CM+SD treatments. The results showed that regardless of the fertilizer type applied, sulfamethazine did not affect the seasonal pattern of NH3volatilization. However, it promoted the NH3 volatilization rate in the topdressing stage significantly (P<0.01). During the observation period, the proportions of applied N lost as NH3-N in the CF+SD and CM+SD treatments were 1.65 and 2.78 times higher than those in the CF and CM treatments, respectively. The promoting effect of sulfamethazine was more obvious in the pig manure treatment than in the compound fertilizer treatment. Sulfamethazine significantly increased the soil urease activity (P<0.05). Furthermore, the NH3 volatilization rate was positively correlated with urease activity and soil ammonia nitrogen content (P<0.05). This indicates that sulfamethazine can increase the NH3 volatilization rate by changing the soil urease activity and inorganic nitrogen content. Controlling the misuse of veterinary antibiotics and environmental and ecological risks posed by the antibiotic residues in farmland excrements are urgent problems in China that need to be solved.

Assessment of reactive nitrogen mitigation potential of different nitrogen treatments under direct-seeded rice and wheat cropping system.

The reactive nitrogen (Nr) pollution is a serious environmental problem. A wise application of nitrogen fertilizer is important for mitigating Nr loss. Field experiments were undertaken during the direct-seeded rice and winter-wheat growing seasons from 2014 to 2015 in Nanjing, one of the typical rice-wheat rotation regions in China, to evaluate the potential of different nitrogen fertilizers for mitigating Nr (N2O, NH3 emissions, and NO3- leaching) losses. Seven different fertilizer treatments were included in this study: a no fertilizer treatment (NF), conventional fertilizer (CF), urea-ammonium mixed nitrogen fertilizer (UA), stabilized urea (UHD; urea + hydroquinone + dicyandiamide), sulfur-coated urea (SCU), urea formaldehyde (UF) and organic fertilizer (OF). In comparison with the CF, all the fertilizer treatments except for UA decreased NH3 volatilization by 14.5-36.0% (p < 0.05), while none of the N fertilizers had an obvious mitigation effect on N2O emissions and NO3- leaching during the rice and wheat seasons. Further analyses showed that the UHD, UF and OF treatments reduced the yield-scaled Nr loss (NLI) by 32.6-42.5% for the rice season and by 15.5-34.5% for the wheat season as compared to the CF; other treatments relative to CF had no obvious effect with regard to lowering the NLI. UHD, UF and OF could be adopted as an effective mitigation alternative to reduce Nr loss and maintain crop yield in future rice/wheat production. Graphical abstract ᅟ.