Inhibitors are widely considered an efficient tool for reducing nitrogen (N) loss and improving N use efficiency, but their effectiveness is highly variable across agroecosystems. In this study, we synthesized 182 studies (222 sites) worldwide to evaluate the impacts of inhibitors (urease inhibitors [UI], nitrification inhibitors [NI] and combined inhibitors) on crop yields and gaseous N loss (ammonia [NH₃] and nitrous oxide [N₂O] emissions) and explored their responses to different management and environmental factors including inhibitor application timing, fertilization regime, cropping system, water management, soil properties and climatic conditions using subgroup meta‐analysis, meta‐regression and multivariate analyses. The UI were most effective in enhancing crop yields (by 5%) and reducing NH₃ volatilization (by 51%), whereas NI were most effective at reducing N₂O emissions (by 49%). The application of UI mitigates NH₃ loss and increases crop yields especially in high NH₃‐N loss scenarios, whereas NI application would minimize the net N₂O emissions and the resultant environmental impacts especially in low NH₃‐N loss scenarios. Alternatively, the combined application of UI and NI enables producers to balance crop production and environmental conservation goals without pollution tradeoffs. The inhibitor efficacy for decreasing gaseous N loss was dependent upon soil and climatic conditions and management practices. Notably, both meta‐regression and multivariate analyses suggest that inhibitors provide a greater opportunity for reducing fertilizer N inputs in high‐N‐surplus systems and presumably favor crop yield enhancement under soil N deficiency situations. The pursuit of an improved understanding of the interactions between plant‐soil‐climate‐management systems and different types of inhibitors should continue to optimize the effectiveness of inhibitors for reducing environmental losses while increasing productivity.

Assessment of the nitrogen (N) inputs and outputs in croplands would help effectively manage the distribution of N to improve crop growth and environmental sustainability. To better understand the N flow of the main cereal systems in China, soil N balance, N use efficiency (NUE), N losses and the potential environmental impacts of maize, wheat and rice cropping systems were estimated at the regional and national scales from 2004 to 2018. Nationally, the soil N balance (N inputs—N outputs) of maize, wheat, single rice and double rice decreased by 28.8%,13.3%, 30.8% and 34.1% from 2004–2008 to 2014–2018, equivalent to an average of 33.3 to 23.7 kg N ha⁻¹, 82.4 to 71.4 kg N ha⁻¹, 93.6 to 64.8 kg N ha⁻¹ and 51.8 to 34.1 kg N ha⁻¹, respectively. The highest soil N balance were observed in Southeast (SE) region for maize and double rice, North central (NC) region for wheat single rice and Northwest region for wheat, whereas Northeast (NE) region had the lowest N balance for all crops. The NUE increased from 49.8%, 41.2%, 49.7% and 53.7% in 2004–2008 to 54.8%, 45.9%, 55.5% and 56.5% in 2014–2018 for maize, wheat, single rice and double rice, respectively. The fertilizer N losses (i.e., N₂O emission, NO emission, N₂ emission, NH₃ volatilization, N leaching and N runoff) were estimated as 43.7%, 38.3%, 40.2% and 36.6% of the total N inputs for maize, wheat, single rice and double rice, respectively in 2014–2018. Additionally, the highest global warming potential and acidification effects were found in NE and NC regions for maize, NC region for wheat, the middle and lower reaches of Yangtze River for single rice and SE region for double rice, respectively. The highest risk of water contamination by N leaching and surface runoff was observed in NC region for all crops mainly due to high N fertilizer input. Furthermore, the dynamics of N balance for all crops were closely tied with grain yields, except for single rice, the N balance of which was mainly correlated with N fertilizer input. Our results could help researchers and policy makers effectively establish optimized fertilization strategies and adjust the regional allocation of grain cropping areas in response to environmental risks and climate change caused by food crop cultivation in China.

Open vegetable fields in China are a major anthropogenic source of nitrous oxide (N₂O) emissions due to excessive nitrogen (N) fertilization. A 4 yr lettuce experiment was conducted to determine the impacts of controlled-release fertilizers (CRFs) and nitrification inhibitors (NIs) on lettuce yield, N₂O emissions and net economic benefits. Five treatments included (i) no N fertilizer (CK), (ii) conventional urea at 255 kg N ha^–1 based on farmers’ practice (FP), (iii) conventional urea at 204 kg N ha^–1 (OPT), (iv) CRF at 204 kg N ha^–1 (CU) and (v) CRF (204 kg N ha^–1) added with NI (CUNI). No significant differences were found in the lettuce yields among different N fertilization treatments. Compared with FP, the cumulative N₂O emissions were significantly decreased by 8.1%, 38.0% and 42.6% under OPT, CU and CUNI, respectively. Meanwhile, the net benefits of OPT, CU and CUNI were improved by USD 281, USD 871 and USD 1024 ha^–1 compared to CN, respectively. This study recommends the combined application of CRF and NI at a reduced N rate as the optimal N fertilizer management for the sustainable production of vegetables in China with the lowest environmental risks and the greatest economic benefits.

Purpose Nitrogen (N) fertilizer application in agricultural soil is a primary anthropogenic nitrous oxide (N₂O) source. Currently, the effect of the N fertilizer type on N₂O emissions from upland soil has been rarely reported. To this end, impacts of various types of N fertilizer on N₂O emissions in purple caitai (Brassica campestris L. ssp. chinensis var. purpurea) fields are investigated in this work. The field experiment was carried out with four treatments, including inorganic N fertilization (I), organic N fertilization (O), integrated organic-inorganic N fertilization (I+O) and no fertilization (CK). The nitrifier/denitrifier abundance was determined using absolute real-time quantitative PCR. Compared with I and O, I+O significantly increased dissolved organic C content, microbial biomass C and microbial biomass N by 24–63%, 12–38% and 13–36% on average, respectively. Moreover, the seasonal cumulative N₂O-N emissions and fertilizer-induced N₂O emission factor under I+O were significantly lower than those under I and O by 17–29% and 23–39%, respectively. The results indicate that N fertilizer type significantly affects the N₂O emissions, and the integrated organic-inorganic N fertilization can mitigate the N₂O emissions primarily by inhibiting the nitrification mediated by ammonia-oxidizing bacteria in purple caitai fields. Integrated organic-inorganic N fertilization is an ideal N fertilization regime to enhance soil fertility and yield and reduce N₂O emissions in the upland fields.