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Agricultural soils are the largest anthropogenic emission source of nitrous oxide (N 2 O). National agricultural policies have been implemented to increase crop yield and reduce nitrogen (N) losses to the environment. However, it is difficult to effectively quantify crop-specific and regional N 2 O mitigation priorities driven by policies, due to lack of long-term, high-resolution crop-specific activity data, and oversimplified models. Here, we quantify the spatiotemporal changes and key drivers of crop-specific cropland-N 2 O emissions from China between 1980 and 2017, and future N 2 O mitigation potentials, using a linear mixed-effect model and survey-based data set of agricultural management measures. Cropland-N 2 O emissions from China tripled from 102.5 to 315.0 Gg N yr -1 between 1980 and 2017, and decelerated since 1998 mainly driven by country-wide deceleration and decrease in N rate and the changes in sowing structure. About 63% of N 2 O emissions could be reduced in 2050, primarily in the North China Plain and Northeast China Plain; 83% of which is from the production of maize (33%), vegetables (27%), and fruits (23%). The deceleration of N 2 O emissions highlights that policy interventions and agronomy practices (i.e., optimizing N rate and sowing structure) are potential pathways for further ambitious N 2 O mitigation in China and other developing countries.

Cropland ammonia (NH 3 ) emission is a critical driver triggering haze pollution. Many agricultural policies were enforced in past four decades to improve nitrogen (N) use efficiency while maintaining crop yield. Inadvertent reductions of NH 3 emissions, which may be induced by such policies, are not well evaluated. Here, we quantify the China's cropland-NH 3 emission change from 1980 to 2050 and its response to policy interventions, using a data-driven model and a survey-based dataset of the fertilization scheme. Cropland-NH 3 emission in China doubled from 1.93 to 4.02 Tg NH 3 -N in period 1980-1996, and then decreased to 3.50 Tg NH 3 -N in 2017. The prevalence of four agricultural policies may avoid ~3.0 Tg NH 3 -N in 2017, mainly located in highly fertilized areas. Optimization of fertilizer management and food consumption could mitigate three-quarters of NH 3 emission in 2050 and lower NH 3 emission intensity (emission divided by crop production) close to the European Union and the United States. Our findings provide an evidence on the decoupling of cropland-NH 3 from crop production in China and suggest the need to achieve cropland-NH 3  mitigation while sustaining crop yields in other developing economies., (© 2021 John Wiley & Sons Ltd.)

Reducing ammonia (NH 3 ) volatilization from croplands while satisfying the food demand is strategically required to mitigate haze pollution. However, the global pattern of NH 3 volatilization remains uncertain, primarily because of the episodic nature of NH 3 volatilization rates and the high variation of fertilization practices. Here, we improve a global estimate of crop-specific NH 3 emissions at a high spatial resolution using an updated data-driven model with a survey-based dataset of the fertilization scheme. Our estimate of the globally averaged volatilization rate (12.6% ± 2.1%) is in line with previous data-driven studies (13.7 ± 3.1%) but results in one-quarter lower emissions than process-based models (16.5 ± 3.1%). The associated global emissions are estimated at 14.4 ± 2.3 Tg N, with more than 50% of the total stemming from three stable crops or 12.2% of global harvested areas. Nearly three-quarters of global cropland-NH 3 emissions could be reduced by improving fertilization schemes (right rate, right type, and right placement). A small proportion (20%) of global harvested areas, primarily located in China, India, and Pakistan, accounts for 64% of abatement potentials. Our findings provide a critical reference guide for the future abatement strategy design when considering locations and crop types.