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Terrestrial soil denitrification is of great importance for closing the nitrogen (N) cycle, yet the current understanding of soil denitrification response to N fertilization remains uncertain. While there has been a focus on factors controlling N 2 O fluxes from agricultural soils because of its global warming effect, much less is known about factors controlling total denitrification losses, yet these can be sufficiently large to affect N use efficiency. Here, we collated 353 observations from 74 papers and conducted a global-scale meta-analysis to explore the effects of N fertilization on agricultural soil denitrification (N 2 O + N 2 ) where the acetylene inhibition technique was used. Relative to the control, N fertilization significantly increased soil denitrification by an average of 174%, although the magnitude of this increase differed significantly across environmental and soil conditions. Soil denitrification was more responsive to N fertilization in grasslands than in croplands. The changes in soil denitrification increased exponentially when the rates of synthetic N fertilizer application ≤ 250 kg N ha − 1 , but above this threshold, there were no further increases. The responses of soil denitrification to N fertilization were negatively correlated with soil clay content, C:N ratio, and bulk density. The comparable responses of soil N 2 O emissions (165%) and denitrification to N fertilization resulted in a small insignificant decrease of the N 2 O:N 2 ratio. Organic fertilizer applied with and without synthetic N fertilizer can contribute to lower N 2 O emissions probably by facilitating the last step of soil denitrification to N 2 production. Taken together, we conclude that these findings can provide important insights on regulating soil denitrification, which might contribute to improvement of N use efficiency and elimination of its negative impacts in agro-ecosystems. [ABSTRACT FROM AUTHOR]

Shifting from conventional tillage to a no-till system can contribute to improving soil carbon sequestration and sustaining crop productivity. However, our understanding of the soil nitrogen (N) process through insights into the no-till effect on soil denitrification remains elusive. Here, we compiled data from 323 observations in 57 studies and quantified the responses of soil denitrification and the size and activity of the denitrifying community to no-till vs. conventional tillage. Across all studies, no-till significantly increased soil denitrification (85%) compared to conventional tillage. The no-till effect on soil denitrification was significantly dependent upon N fertilizer management, with a greater increase with N fertilization than without (101 vs. 46%). The increased soil denitrification under no-till was attributed to increases in the size and activity of the denitrifying community. On average, the potential denitrification activity, the total number of denitrifiers, and the abundance of denitrifying genes were increased by 66, 116, and 14–70%, respectively, in response to no-till. Our results demonstrate that soil denitrification under no-till leads to increased soil nitrous oxide (N 2 O) emission. This is supported by a larger response of soil N 2 O emission compared to the total denitrification, together with a significant increase (33%) in the (nir K + nir S)/ nos Z ratio under no-till conditions. Therefore, the increased soil denitrification under no-till conditions may have negative impacts on soil N cycling and mitigation of N 2 O emission. • The effect of no-till on soil denitrification was meta-analyzed. • No-till significantly increased soil denitrification and N 2 O emissions. • No-till enhanced the activity and abundance of the soil denitrifying community. • An overall positive response of (nir K + nir S)/ nos Z to no-till was found. [ABSTRACT FROM AUTHOR]

Veterinary antibiotics are increasingly used in the livestock industry annually. Sulfonamides introduced into the soil with manure are usually largely degraded in various pathways. However, the influence of the metabolic intermediate of sulfonamides on nitrogen (N) cycling under anaerobic conditions in soils has been overlooked. To this end, we carried out a microcosm experiment to investigate the potential consequences of ADPD (2-amino-4,6-dimethylpyrimidine, a degradation product of sulfonamide) at five concentration gradients (i.e., 0, 0.01, 0.1, 1, and 10 mg kg−1) on nitrous oxide (N 2 O) emissions, associated genes involved in N cycling, antibiotic resistance genes (ARGs), and mobile genetic elements (MGEs) in soils applied with manure or urea. The results showed that ADPD application promoted N 2 O emissions under flooded conditions at environmentally relevant concentrations, and the maximum cumulative N 2 O emissions were observed at 1 mg kg−1 and 0.1 mg kg−1 ADPD for manure and urea applied, respectively. The main reasons were the imbalance of denitrifying bacteria, which affected N 2 O production and reduction, and the increase of antibiotic resistance in soil bacteria. In conclusion, these findings contribute to assessing the eco-environmental risks associated with the prevalence of sulfonamide metabolic intermediates and expand our understanding of the link between antibiotics and N transformation. Further research in the field is warranted to incorporate their recommendations into the greenhouse gas assessment system. [Display omitted] [ABSTRACT FROM AUTHOR]