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Halving nitrogen pollution is crucial for achieving Sustainable Development Goals (SDGs). However, how to reduce nitrogen pollution from multiple sources remains challenging. Here we show that reactive nitrogen (Nr) pollution could be roughly halved by managed urban development in China by 2050, with NH3, NOx and N2O atmospheric emissions declining by 44%, 30% and 33%, respectively, and Nr to water bodies by 53%. While rural-urban migration increases point-source nitrogen emissions in metropolitan areas, it promotes large-scale farming, reducing rural sewage and agricultural non-point-source pollution, potentially improving national air and water quality. An investment of approximately US$ 61 billion in waste treatment, land consolidation, and livestock relocation yields an overall benefit of US$ 245 billion. This underscores the feasibility and cost-effectiveness of halving Nr pollution through urbanization, contributing significantly to SDG1 (No poverty), SDG2 (Zero hunger), SDG6 (Clean water), SDG12 (Responsible consumption and production), SDG14 (Climate Action), and so on. Here the authors demonstrate how managed urbanization in China could halve reactive nitrogen pollution to both the atmosphere and water resources. Investing 61 billion USD could provide 245 billion USD in benefits, while contributing to multiple SDG goals. [ABSTRACT FROM AUTHOR]

The Chinese government recently proposed ammonia (NH 3) emission reductions (but without a specific national target) as a strategic option to mitigate fine particulate matter (PM 2.5) pollution. We combined a meta-analysis of nationwide measurements and air quality modeling to identify efficiency gains by striking a balance between controlling NH 3 and acid gas (SO 2 and NO x) emissions. We found that PM 2.5 concentrations decreased from 2000 to 2019, but annual mean PM 2.5 concentrations still exceeded 35 µ g m -3 at 74 % of 1498 monitoring sites during 2015–2019. The concentration of PM 2.5 and its components were significantly higher (16 %–195 %) on hazy days than on non-hazy days. Compared with mean values of other components, this difference was more significant for the secondary inorganic ions SO 42- , NO 3- , and NH 4+ (average increase 98 %). While sulfate concentrations significantly decreased over this period, no significant change was observed for nitrate and ammonium concentrations. Model simulations indicate that the effectiveness of a 50 % NH 3 emission reduction for controlling secondary inorganic aerosol (SIA) concentrations decreased from 2010 to 2017 in four megacity clusters of eastern China, simulated for the month of January under fixed meteorological conditions (2010). Although the effectiveness further declined in 2020 for simulations including the natural experiment of substantial reductions in acid gas emissions during the COVID-19 pandemic, the resulting reductions in SIA concentrations were on average 20.8 % lower than those in 2017. In addition, the reduction in SIA concentrations in 2017 was greater for 50 % acid gas reductions than for the 50 % NH 3 emission reductions. Our findings indicate that persistent secondary inorganic aerosol pollution in China is limited by emissions of acid gases, while an additional control of NH 3 emissions would become more important as reductions of SO 2 and NO x emissions progress. [ABSTRACT FROM AUTHOR]

China's agriculture is dominated by smallholder farms, which have become major sources of negative environmental impacts including eutrophication, formation of haze, soil acidification and greenhouse gas emissions. To mitigate these environmental impacts, new farming models including family farming, cooperation farming and industrial farming have emerged in recent years. However, whether these new farming practices would improve the economic and environmental performance as compared to the current smallholder farming has yet to be verified on ground level. In this paper, by using pilot farming cases within the watershed of Tai Lake, we found that alternative farming models produced 7% more crop yield, while using 8% less fertilizer, leading to a 28% decrease in pollutant emission per hectare. These alternative farming models have a 17% higher fertilizer use efficiency and 50% higher profit per hectare. Compared to smallholder farming, these alternative farming practices invest 27% more resources into agricultural facilities, including advanced machinery, and have a younger, better educated labor force as a consequence of a larger farm size and more specialization. These input changes substantially increase fertilizer use efficiency and reduce agricultural pollution. Policy arrangements to support and facilitate the uptake of these farming models will further promote the green development and sustainable intensification of agricultural production. [ABSTRACT FROM AUTHOR]

Cropland ammonia (NH3) 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 NH3 emissions, which may be induced by such policies, are not well evaluated. Here, we quantify the China's cropland‐NH3 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‐NH3 emission in China doubled from 1.93 to 4.02 Tg NH3‐N in period 1980–1996, and then decreased to 3.50 Tg NH3‐N in 2017. The prevalence of four agricultural policies may avoid ~3.0 Tg NH3‐N in 2017, mainly located in highly fertilized areas. Optimization of fertilizer management and food consumption could mitigate three‐quarters of NH3 emission in 2050 and lower NH3 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‐NH3 from crop production in China and suggest the need to achieve cropland‐NH3 mitigation while sustaining crop yields in other developing economies. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract An increasing disconnect between livestock production and croplands has been observed in many world regions, including China, which has the world's largest livestock production sector. Here we propose a cropland-based livestock production system to rebuild the linkage between livestock and cropland from both agriculture production and human consumption perspectives for China. In 2015, the total excretion nitrogen (N) generated by livestock production operations was 14.6 Tg N, and it would grow to 15.0 Tg in 2030 by extrapolating current trends. The optimal demand of total N by crops in China was estimated to be 23.0 Tg N in 2030, suggesting that Chinese livestock would be within the carrying capacity of cropland on national level, but substantial variations were found across provinces. The carrying capacity of cropland with regard to N input from manure would be exceeded in 74% provinces, under the assumption that manure providing half of the N supply for crops. Furthermore, from the perspective of domestic feed supply for livestock production, about 51% of feed N needs to be imported. If following the optimized dietary structure of China to manage livestock sector, livestock production could be reduced by 37% in excretion nitrogen, which would not only benefit the food security and human health, but also mitigate the agricultural pollution. Accordingly, policy regulations on reduction and spatially reallocation of livestock production on a regional scale could substantially reduce manure N loss from 10.5 Tg yr−1 to 1–1.2 Tg yr−1 under different recoupled scenarios. [ABSTRACT FROM AUTHOR]

Reliable detection and attribution of changes in nitrogen (N) runoff from croplands are essential for designing efficient, sustainable N management strategies for future. Despite the recognition that excess N runoff poses a risk of aquatic eutrophication, large-scale, spatially detailed N runoff trends and their drivers remain poorly understood in China. Based on data comprising 535 site-years from 100 sites across China's croplands, we developed a data-driven upscaling model and a new simplified attribution approach to detect and attribute N runoff trends during the period of 1990–2012. Our results show that N runoff has increased by 46% for rice paddy fields and 31% for upland areas since 1990. However, we acknowledge that the upscaling model is subject to large uncertainties (20% and 40% as coefficient of variation of N runoff, respectively). At national scale, increased fertilizer application was identified as the most likely driver of the N runoff trend, while decreased irrigation levels offset to some extent the impact of fertilization increases. In southern China, the increasing trend of upland N runoff can be attributed to the growth in N runoff rates. Our results suggested that increased SOM led to the N runoff rate growth for uplands, but led to a decline for rice paddy fields. In combination, these results imply that improving management approaches for both N fertilizer use and irrigation is urgently required for mitigating agricultural N runoff in China. [ABSTRACT FROM AUTHOR]

The fast economic development of southwest China has resulted in significant increases in the concentrations of reactive nitrogen (Nr) in the atmosphere. In this study, an urban (Chengdu, CD), suburban (Shifang, SF) and agriculture (Yanting, YT) – dominated location in the Sichuan Province, southwest China, were selected to investigate the atmospheric composition of Nr, their concentrations and deposition rates. We measured Nr concentrations in precipitation (NH 4 + , NO 3 − and organic N (DON)), the gas phase (NH 3 and NO 2 ), and the aerosol particles (PM 2.5 ), and calculated their fluxes over a two year period (2014–2016). Total annual N deposition rates were 49.2, 44.7 and 19.8 kg N ha −1 yr −1 at CD, SF and YT, respectively. Ammonia concentrations were larger at the urban and suburban sites than the agricultural site (12.2, 14.9, and 4.9 μg N m −3 at CD, SF and YT, respectively). This is consistent with the multitude of larger sources of NH 3 , including city garbage, livestock and traffic, in the urban and suburban areas. Monthly NO 2 concentrations were lower in warmer compared to the colder months, but seasonal differences were insignificant. Daily PM 2.5 concentrations ranged from 7.7 to 236.0, 5.0–210.4 and 4.2–128.4 μg m −3 at CD, SF and YT, respectively, and showed significant correlations with fine particulate NH 4 + and NO 3 − concentrations. Ratios of reduced to oxidized N were in the range of 1.6–2.7. This implies that the control of reduced Nr especially in urban environments is needed to improve local air quality. [ABSTRACT FROM AUTHOR]

Nitrogen use efficiency (NUE, defined as the fraction of N input harvested as product) is an important indicator to understand nitrogen use and losses in croplands as an element of determining sustainable food production. China, as the country with the largest amount of nitrogen fertilizer use globally, research into NUE consistently finds it to be much lower than that in developed countries. Understanding the driving forces of the underlying causes of this low NUE is thus crucial to improve nitrogen use and reduce losses in China. Here we applied the CHANS model to estimate cropland NUE for over 2800 counties in China for the year 2017. Results showed that in most counties NUE ranged between 20% and 40%, while an NUE >50% was mainly found in Northeastern China, likely as a result of large-scale, modern agriculture operations. The source of N input and crop types significantly affected NUE in our assessment. Nitrogen deposition, straw recycling, and biological nitrogen fixation (BNF) could improve NUE, while chemical nitrogen fertilizer and manure inputs reduce NUE. Grain crops have a much higher NUE compared to vegetables, which are often over-fertilized. Moreover, NUE in Southern China is strongly influenced by natural factors such as temperature and precipitation. Specifically, NUE in the Yangtze River Delta (eastern coastal region of China) is associated with socio-economic factors including GDP and the degree of urbanization, while in North-central China, NUE is mainly determined by nitrogen input sources. These examples illustrate that approaches aiming at improving NUE need to be location-specific with consideration of multiple natural and socioeconomic factors. [Display omitted] • The cropland NUE in China based on county scale was estimated. • Most counties in China have a NUE ranging between 20% and 40%. • Opposite to vegetables, the higher the share of cereals grown the greater the NUE. • NUE effected by multiple driving factors, not only socio-economic, but also natural. [ABSTRACT FROM AUTHOR]

The study of emissions and depositions of atmospheric reactive nitrogen species (N r s) in a region is important to uncover the sources and sinks of atmospheric N r s in the region. In this study, atmospheric total N r s depositions including both wet-only and dry deposition were monitored simultaneously across major land-use types in a 105 km2 catchment called Jinjing River Catchment (JRC) in subtropical central China from 2015 to 2016. Based on activity data and emission factors for the main N r s emission sources, ammonia (NH 3) and nitrogen oxides (NO x) emission inventories for the catchment were also compiled. The estimated total N r s deposition in JRC was 35.9 kg N ha−1 yr−1, with approximately 49.7 % attributed to reduced compounds (NH x), and 40.5 % attributed to oxidized (NO y). The total N r s emission rate in JRC was 80.4 kg N ha−1 yr−1, with 61.5 and 18.9 kg N ha−1 yr−1 from NH 3 and NO x emissions, respectively. Livestock excretion and fertilization were the two main contributing emission sources for NH 3 , while vehicle sources contributed the bulk of NO x emissions. The net atmospheric budgets of N r s in paddy field, forest, and tea field were +3.7, −36.1, and +23.8 kg N ha−1 yr−1, respectively. At the catchment scale, the net atmospheric budget of N r s was +47.7 kg N ha−1 yr−1, with +43.7 kg N ha−1 yr−1 of NH x and +4.0 kg N ha−1 yr−1 of NO y , indicating that the subtropical catchment was net sources of atmospheric N r s. Considering that excessive atmospheric N r emissions and deposition may cause adverse effects on the environment, effects should be conducted to mitigate the N r s emissions from agriculture and transportation, and increasing the area of forest is good for reducing the net positive budget of atmospheric N r s in the subtropical catchments in China. [Display omitted] • Mean atmospheric N r deposition was 36 kg N ha−1 yr−1 in a subtropical catchment in a 2-yr study. • Total N r emissions in catchment were 80 kg N ha−1 yr−1, with 62 kg N ha−1 yr−1 from NH 3 emissions. • The net N r budget showed high emissions due to NH 3 emissions from livestock and fertilization. • Paddy and tea fields were net sources of N r s, while forest was a net strong sink of N r s. Both atmospheric emissions and depositions of Nrs were high, and the net budget showed high emissions in a typical agricultural catchment in subtropical central China. [ABSTRACT FROM AUTHOR]

Ammonia (NH 3) volatilization is one of the main pathways of nitrogen loss from cropland, resulting not only in economic losses, but also environmental and human health impacts. The magnitude and timing of NH 3 emissions from cropland fertilizer application highly depends on agricultural practices, climate and soil factors, which previous studies have typically only considered at coarse spatio-temporal resolution. In this paper, we describe a first highly detailed empirical regression model for ammonia (ERMA) emissions based on 1443 field observations across China. This model is applied at county level by integrating data with unprecedented high spatio-temporal resolution of agricultural practices and climate and soil factors. Results showed that total NH 3 emissions from cropland fertilizer application amount to 4.3 Tg NH 3 yr−1 in 2017 with an overall NH 3 emission factor of 12%. Agricultural production for vegetables, maize and rice are the three largest emitters. Compared to previous studies, more emission hotspots were found in South China and temporally, emission peaks are estimated to occur three months earlier in the year, while the total amount of emissions is estimated to be close to that calculated by previous studies. A second emission peak is identified in October, most likely related to the fertilization of the second crop in autumn. Incorporating these new findings on NH 3 emission patterns will enable a better parametrization of models and hence improve the modelling of air quality and subsequent impacts on ecosystems through reactive N deposition. [Display omitted] • A empirical model of NH 3 emissions from croplands was established. • Two emission peaks are found in April and October following the fertilization. • Total emission was estimated at 4.3 Tg NH 3 yr−1 in 2017 with an emission factor of 12%. • More emission hotspots were found in South China due to warming climate. The highly spatio-temporal resolution NH 3 emission inventory from cropland fertilization was developed by an empirical regression model in 2853 counties of China. [ABSTRACT FROM AUTHOR]

Rapid urbanization in China is leading to substantial adverse air quality issues, particularly for NO2 and particulate matter (PM). Land-use regression (LUR) models are now being applied to simulate pollutant concentrations with high spatial resolution in Chinese urban areas. However, Chinese urban areas differ from those in Europe and North America, for example in respect of population density, urban morphology and pollutant emissions densities, so it is timely to assess current LUR studies in China to highlight current challenges and identify future needs. Details of twenty-four recent LUR models for NO2 and PM2.5/PM10 (particles with aerodynamic diameters <2.5 µm and <10 µm) are tabulated and reviewed as the basis for discussion in this paper. We highlight that LUR modelling in China is currently constrained by a scarcity of input data, especially air pollution monitoring data. There is an urgent need for accessible archives of quality-assured measurement data and for higher spatial resolution proxy data for urban emissions, particularly in respect of traffic-related variables. The rapidly evolving nature of the Chinese urban landscape makes maintaining up-to-date land-use and urban morphology datasets a challenge. We also highlight the importance for Chinese LUR models to be subject to appropriate validation statistics. Integration of LUR with portable monitor data, remote sensing, and dispersion modelling has the potential to enhance derivation of urban pollution maps. [ABSTRACT FROM AUTHOR]

Abstract Farm size plays a critical role in agricultural sustainability. This may have far-reaching consequences for the economic and environmental performance of agricultural production, resulting, for instance, in an excessive use of mineral fertilizers. However, the magnitude of such effects and their main causes are not well understood, while being essential for effective policy development, especially for countries like China where the agricultural sector is still largely dominated by smallholder farms. In this paper, we review the current understanding of how farm size affects agricultural sustainability using China's crop farming as an example from economic, environment and social aspects. We analyze impacts from both a Chinese and a global perspective to identify intervention points to improve agricultural performance. We found that increasing farm size has a positive impact on farmer's net profit, as well as economic, technical and labor efficiency with mean coefficients of 0.005, 0.02 and 2.25, respectively. Nevertheless, the relationships between farm size and overall productivity, total factor productivity and allocative efficiency are still not well understood and therefore require more research. Meanwhile, increase in farm size is associated with statistically significant decrease in fertilizer and pesticide use per hectare, showing clear benefits for environmental protection. In line with the experiences documented for the evolution of agricultural practices in developed countries, the expansion of large-scale farming is a critical path for modernizing agricultural production and ensuring sustainable food production from the social perspective. Measures concerning farm size should be implemented in an interaction between farmers and the government to promote the green development of agriculture. Highlights • Farm size plays an important role in the performance of agriculture. • Increasing farm size shows clear benefits for environmental protection. • Large-scale farming is a critical path for modernizing and sustaining agriculture. • Smallholders prefer to use more non-fixed inputs to increase yields. [ABSTRACT FROM AUTHOR]

Rapid demographic ageing substantially affects socioeconomic development 1-4 and presents considerable challenges for food security and agricultural sustainability 5-8 , which have so far not been well understood. Here, by using data from more than 15,000 rural households with crops but no livestock across China, we show that rural population ageing reduced farm size by 4% through transferring cropland ownership and land abandonment (approximately 4 million hectares) in 2019, taking the population age structure in 1990 as a benchmark. These changes led to a reduction of agricultural inputs, including chemical fertilizers, manure and machinery, which decreased agricultural output and labour productivity by 5% and 4%, respectively, further lowering farmers' income by 15%. Meanwhile, fertilizer loss increased by 3%, resulting in higher pollutant emissions to the environment. In new farming models, such as cooperative farming, farms tend to be larger and operated by younger farmers, who have a higher average education level, hence improving agricultural management. By encouraging the transition to new farming models, the negative consequences of ageing can be reversed. Agricultural input, farm size and farmer's income would grow by approximately 14%, 20% and 26%, respectively, and fertilizer loss would reduce by 4% in 2100 compared with that in 2020. This suggests that management of rural ageing will contribute to a comprehensive transformation of smallholder farming to sustainable agriculture in China., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

Farm size affects nitrogen fertilizer input and agricultural practices, which are key determinants of ammonia (NH 3 ) emissions from croplands. However, the degree to which NH 3 emissions are associated with changes in farm size is not well understood yet despite its crucial role in achieving agricultural sustainability in China, where agricultural production is still dominated by smallholder farms. Here we provide a first analysis of the relationship between farm size and NH 3 emissions based on 863 000 surveys conducted in 2017 across China. Results show that NH 3 emissions (kg ha -1 ) on average decrease by 0.07% for each 1% increase in average farm size. This change occurs mainly due to a reduction in nitrogen fertilizer use and the introduction of more efficient fertilization practices. The largest reduction in NH 3 emissions is found in maize, with less pronounced changes in rice cultivation, and none for wheat production. Overall lower NH 3 emissions factors can be observed in the north of China with increasing farm size, especially in the northeast, the opposite pattern was found in the south. National total NH 3 emissions could be approximately halved (1.5 Tg) in a scenario favoring a conversion to large-scale farming systems. This substantial reduction potential highlights the potential of such a transition to reduce NH 3 emissions, including benefits from a socioeconomic point of view as well as for improving air quality.

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.

Managing reactive nitrogen (N r ) to achieve a sustainable balance between production of food, feed and fiber, and environmental protection is a grand challenge in the context of an increasingly affluent society. Here, we propose a novel framework for national nitrogen (N) assessments enabling a more consistent comparison of the uses, losses and impacts of N r between countries, and improvement of N r management for sustainable development at national and regional scales. This framework includes four key components: national scale N budgets, validation of N fluxes, cost-benefit analysis and N r management strategies. We identify four critical factors for N r management to achieve the sustainable development goals: N use efficiency (NUE), N r recycling ratio (e.g., ratio of livestock excretion applied to cropland), human dietary patterns and food waste ratio. This framework was partly adopted from the European Nitrogen Assessment and now is successfully applied to China, where it contributed to trigger policy interventions toward improvements for future sustainable use of N r . We demonstrate how other countries can also benefit from the application our framework, in order to include sustainable N r management under future challenges of growing population, hence contributing to the achievement of some key sustainable development goals (SDGs).