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Elevated atmospheric reactive nitrogen (Nr) emissions and the subsequent nitrogen (N) deposition have negatively impacted the global environment, particularly in China. In order to assess the long-term trends in atmospheric N deposition in the south of China, Taojiang County in Hunan Province was selected as a representative rural area for study. We analyzed interannual variation in atmospheric Nr, including gaseous ammonia (NH3), nitrogen dioxide (NO2), nitrate acid (HNO3) vapor, particulate ammonium (NH4+), and nitrate (NO3−) in air and NH4+-N and NO3−-N in precipitation from 2011 to 2020. The 10-year average atmospheric wet-plus-dry N deposition was 41.9 kg N ha−1 yr−1, which decreased by approximately 24% after 2012, indicating that NH3 and NOx emissions were effectively reduced by emission controls introduced in 2013. Wet deposition accounted for approximately 74% of the total N deposition and was significantly influenced by annual precipitation amount. Reduced N (NH3, pNH4+, and NH4+ in rainwater) was the dominant form, comprising approximately 58% of the total N deposition, while oxidized N (pNO3−, NO2, HNO3, and NO3− in rainwater) accounted for 42% of the total N deposition. Atmospheric HNO3, NO2, and NH3 concentrations and deposition declined by 30–80% over the decade, while particulate NH4+ and NO3− concentrations and deposition remained at relatively stable levels, which suggests that ongoing research and policy should focus on rural particulate pollution. Future strategies must concentrate on the integrated control of NH3 and NOx emissions to mitigate air pollution and protect human health, particularly in rural areas because current abatement efforts are primarily directed toward urban areas and the industrial sector, whereas non-point source NH3 pollution, influenced mainly by agricultural activities, dominates in rural regions. [ABSTRACT FROM AUTHOR]

Tea (Camellia sinensis L.), a perennial leaf-harvested crop, favors warm/humid climate and acidic/well-drained soils, and demands high nitrogen (N) fertilizer inputs which lead to significant emissions of N2O. Potential mitigation options should be adopted to improve N use efficiency (NUE) and reduce environmental pollution in tea field system. A 3-year field experiment was carried out in a tea field in southern China from January 2014 to December 2016 to investigate the effect of controlled-release fertilizer (CRF) application on N2O emissions in tea field system. Three practices, namely conventional treatment (CON, 105 kg N-oilcake ha−1 year−1 + 345 kg N-urea ha−1 year−1), treatment with a half amount of the N fertilizer (CRF50%, 105 kg N-oilcake ha−1 year−1 + 120 kg N CRF ha−1 year−1) and full amount of N fertilizer (CRF100%, 105 kg N-oilcake ha−1 year−1 + 345 kg N CRF ha−1 year−1) were used. Compared with the CON, our results showed that CRF50% reduced the N2O emissions by 26.2% (p > 0.05) and increased the tea yield by 31.3% (p > 0.05), while CRF100% significantly increased the N2O emissions by 96.7% (p < 0.05) and decreased the tea yield by 6.77% (p > 0.05). Overall, yield-scaled N2O emissions of tea were reduced by 44.5% (p > 0.05) under CRF50% and significantly increased by 100% (p < 0.05) under CRF100%, compared with CON. Based on the gross margin analysis, CRF50% obtained the highest net economic profit. Our findings suggest that reducing N input of CRF (CRF50%) is necessary and feasible for adoption in the current tea plantation system. [ABSTRACT FROM AUTHOR]

Cattle feedlots are significant ammonia (NH 3 ) emission sources, and cause high NH 3 deposition. This study was conducted to investigate the responses of soil mineral nitrogen (N), percent cover of plant species, leaf N content, and leaf δ 15 N to NH 3 deposition around a 17,500-head cattle feedlot in Victoria, Australia. Soil samples were collected in May 2015 at 100-m intervals along eight downwind transects, and plant samples were collected in June 2015 from five sites at 50- to 300-m intervals along a grassland transect within 1 km downwind of the feedlot. NH 3 deposition was also monitored at five sites within 1 km downwind of the feedlot. The estimated NH 3 -N deposition rates ranged from 2.9 kg N ha −1 yr −1 at 1 km from the feedlot to 203 kg N ha −1 yr −1 at 100 m from the feedlot. The soil mineral N content was high (22–98 mg kg −1 , mainly nitrate), significantly decreased with increasing distance from the feedlot, and significantly increased with increasing NH 3 -N deposition. With increasing NH 3 -N deposition, the percent cover of the herb species Cymbonotus lawsonianus increased significantly, but that of the grass species Microlaena stipoides decreased significantly. The leaf total N contents of the grass and herb species were high (>4%), and were linearly, positively correlated with the NH 3 -N deposition rate. Leaf δ 15 N values were linearly, negatively correlated with the N deposition rate. These results indicate that the leaf N contents and δ 15 N values of C. lawsonianus and M. stipoides may be bioindicators of N deposition. [ABSTRACT FROM AUTHOR]

A field experiment was conducted to study the effects of combination of straw incorporation and water management on fluxes of CH4, N2O and soil heterotrophic respiration (Rh) in a paddy field in subtropical central China by using a static opaque chamber/gas chromatography method. Four treatments were set up: two rice straw incorporation rates at 0 (S1) and 6 (S2) t ha−1combined with two water managements of intermittent irrigation (W1, with mid-season drainage) and continuous flooding (W2, without mid-season drainage). The cumulative seasonal CH4emissions for the treatments of S1W2, S2W1 and S2W2 increased significantly by 1.84, 5.47 and 6.63 times, respectively, while seasonal N2O emissions decreased by 0.67, 0.29 and 1.21 times, respectively, as compared to S1W1 treatment. The significant increase in the cumulative Rh for the treatments S1W1, S2W1 and S2W2 were 0.54, 1.35 and 0.52 times, respectively, in comparison with S1W2. On a seasonal basis, both the CO2-equivalents (CO2e) and yield-scaled CO2e (GHGI) of CH4and N2O emissions increased with straw incorporation and continuous flooding, following the order: S2W2>S2W1>S1W2>S1W1. Thus, the practices of in season straw incorporation should be discouraged, while mid-season drainage is recommended in paddy rice production from a point view of reducing greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

Abstract: Atmospheric emissions of reactive nitrogen (N) species are at high levels in China in recent years, but few studies have employed N deposition monitoring techniques that measure both dry and wet deposition for comprehensive evaluation of the impacts of N deposition on ecosystems. In this study, to quantify the total N deposition, both dry and wet N depositions were monitored using denuder/filter pack systems, passive samplers and wet-only samplers at three sites with different land use types (forest, paddy field and tea field) in a 135-km2 catchment in subtropical central China from September 2010 to August 2011. At the three sampling sites, the annual mean concentrations of total N (the sum of , and DON) in rainwater were 1.2–1.6 mg N L−1, showing small variation across sites. Annual mean concentrations of total N (the sum of NH3, NO2, HNO3, particulate and ) in the air were 13–18 μg N m−3. High NH3 concentrations in the air were observed at the agricultural sites of tea and paddy fields, indicating significant NH3 emissions from N fertiliser application; and high NO2 concentrations were found at the upland sites of forest and tea field, suggesting high NO emissions from soils due to high N deposition or high N fertiliser input. The annual total N deposition for the three sites of paddy field, tea field and forest was estimated as 22, 34 and 55 kg N ha−1 yr−1, in which the dry N deposition components contributed to 21%, 36% and 63% of the annual total N deposition, respectively. The annual deposition of reduced N species was 1.1–1.8 times of the annual deposition of oxidised N species. To minimise the adverse effects of atmospheric N deposition on natural/semi-natural ecosystems, it is crucial to reduce the reactive N emissions from anthropogenic activities (e.g., N fertiliser application, animal production and fossil fuel combustion) in subtropical central China. [Copyright &y& Elsevier]

China is experiencing intense air pollution caused in large part by anthropogenic emissions of reactive nitrogen. These emissions result in the deposition of atmospheric nitrogen (N) in terrestrial and aquatic ecosystems, with implications for human and ecosystem health, greenhouse gas balances and biological diversity. However, information on the magnitude and environmental impact of N deposition in China is limited. Here we use nationwide data sets on bulk N deposition, plant foliar N and crop N uptake (from long-term unfertilized soils) to evaluate N deposition dynamics and their effect on ecosystems across China between 1980 and 2010. We find that the average annual bulk deposition of N increased by approximately 8 kilograms of nitrogen per hectare (P < 0.001) between the 1980s (13.2 kilograms of nitrogen per hectare) and the 2000s (21.1 kilograms of nitrogen per hectare). Nitrogen deposition rates in the industrialized and agriculturally intensified regions of China are as high as the peak levels of deposition in northwestern Europe in the 1980s, before the introduction of mitigation measures. Nitrogen from ammonium (NH4+) is the dominant form of N in bulk deposition, but the rate of increase is largest for deposition of N from nitrate (NO3−), in agreement with decreased ratios of NH3 to NOx emissions since 1980. We also find that the impact of N deposition on Chinese ecosystems includes significantly increased plant foliar N concentrations in natural and semi-natural (that is, non-agricultural) ecosystems and increased crop N uptake from long-term-unfertilized croplands. China and other economies are facing a continuing challenge to reduce emissions of reactive nitrogen, N deposition and their negative effects on human health and the environment. [ABSTRACT FROM AUTHOR]

Abstract: Atmospheric ammonia (NH3) and particulate ammonium (NH4 +) were measured using passive samplers and particulate samplers at four rural and two suburban sites in the North China Plain (NCP) from August 2006 to September 2009. The annual mean concentrations of NH3 and NH4 + in PM10 across the sites were 15.6 and 12.4 μg m−3, respectively. Higher concentrations of NH3 and NH4 + were found at the rural sites compared with the suburban sites. NH3 concentrations were highest in summer and lowest in winter, showing positive correlations with N fertilizer application rates and temperature in each season. Particulate NH4 + showed significant positive correlations with particulate SO4 2− and NO3 − at the six sites. The annual mean concentrations of secondary inorganic particles (sum of NH4 +, SO4 2− and NO3 −) accounted for 26.1–41.3% of the PM10 concentration across all sites. The formation of inorganic NH4 + particles was limited mainly by the availability of H2SO4 and HNO3 and partly by NH3. The total NHx deposition in the NCP averaged 43.5 kg N ha−1 yr−1, accounting for 84.1% of the mean NH3 emission intensity. The serious particulate NH4 + pollution and high NHx deposition suggest the urgency of reducing NH3 emission from agricultural sources in the NCP. [Copyright &y& Elsevier]