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We applied the adapted model VSD + to assess cropland acidification in four typical Chinese cropping systems (single Maize (M), Wheat-Maize (W-M), Wheat-Rice (W-R) and Rice-Rice (R-R)) on dominant soils in view of its potential threat to grain production. By considering the current situation and possible improvements in field (nutrient) management, five scenarios were designed: i) Business as usual (BAU); ii) No nitrogen (N) fertilizer increase after 2020 (N2020); iii) 100% crop residues return to cropland (100%RR); iv) manure N was applied to replace 30% of chemical N fertilizer (30%MR) and v) Integrated N2020 and 30%MR with 100%RR after 2020 (INMR). Results illustrated that in the investigated calcareous soils, the calcium carbonate buffering system can keep pH at a high level for > 150 years. In non-calcareous soils, a moderate to strong decline in both base saturation and pH is predicted for the coming decades in the BAU scenario. We predicted that approximately 13% of the considered croplands may suffer from Al toxicity in 2050 following the BAU scenario. The N2020, 100%RR and 30%MR scenarios reduce the acidification rates by 16%, 47% and 99%, respectively, compared to BAU. INMR is the most effective strategy on reducing acidification and leads to no Al toxicity in croplands in 2050. Both improved manure and field management are required to manage acidification in wheat-maize cropping system. [ABSTRACT FROM AUTHOR]

In a recent publication in the journal Science of the Total Environment, Zhu et al. (2015) reported the composition, spatial patterns, and factors influencing atmospheric wet nitrogen (N) deposition based on one year's data from 41-monitoring sites in China. We suspect their results may largely underestimate dissolved organic N (DON) but overestimate total particulate N (TPN) in wet deposition due to the uncertainty resulting from the sampling, storage and analysis methods in their study. Our suspicions are based mainly on our experience from earlier measurements and the literature. We therefore suggest that enhanced data quality control on atmospheric N deposition measurements should be taken into account in future studies. [ABSTRACT FROM AUTHOR]

Significant soil pH decrease has been reported in Chinese croplands in response to enhanced chemical fertilizer application and crop yields. However, the temporal and spatial variation of soil acidification rates across Chinese croplands is still unclear. We therefore assessed trends in soil acidification rates across provincial China for the period 1980–2010 by calculating inputs-outputs of major cations and anions in cropland systems. Nitrogen (N) induced proton production increased from 4.7 keq H + /ha/yr in 1980 to a peak of 11.0 keq H + /ha/yr in 1996 and remained nearly constant after 2000 at a rate of approximately 8.6 keq H + /ha/yr. The proton production induced by crop removal increased from 1.2 to 2.3 keq H + /ha/yr. The total proton production thus increased from 5.9 to 10.9 keq H + /ha/yr in the 30 years. As a result, the actual acidification rate, reflected by (base) cation losses, accelerated from 2.3 to 6.2 keq H + /ha/yr and the potential acidification rate, reflected by phosphorus accumulation accelerated from 0.2 to 1.3 keq H + /ha/yr. The national averaged total acidification rates were thus estimated to increase from 2.6 to 7.6 keq H + /ha/yr in the past 30 years. The highest soil acidification rate occurred in the Jiangsu Province with a rate of 17.9 keq H + /ha/yr, which was due to both high N application rates and high base cation removals by crops and crop residues. The combination of elevated N inputs and decreased N use efficiency (NUE) in response to those N inputs, thus enhancing the nitrate discharge, were the main reasons for the accelerated acidification in Chinese croplands. Considering the expected growth of food demand in the future, and the linkage between grain production and fertilizer N consumption, a further acceleration of soil acidification can thus be expected, unless the N inputs is reduced and/or the NUE is increased substantially. [ABSTRACT FROM AUTHOR]

Nitrogen availability is a key factor that regulates soil priming (the strong short-term changes in microbial decomposition of soil organic carbon after addition of fresh carbon resources); however, how soil priming changes under nitrogen addition is unclear. In this study, we collected soils from a grassland with 11-year history of nitrogen addition (0, 60, 120, and 240 kg N ha−1 yr−1 NH 4 NO 3), and the soils were incubated for 6 weeks to estimate the direction and magnitude of soil priming and the underlying microbial carbon use strategy. We found glucose addition triggered a positive priming effect among all the treatments; however, the magnitude of the positive priming did not change under nitrogen addition. The stable soil organic carbon content under different nitrogen addition levels might support the no significant change in the magnitude of those positive priming. Using DNA stable-isotope probing (DNA-SIP), we found that bacterial and fungal taxa consuming the added glucose were different in different nitrogen addition levels. The relative abundance of the K-strategist Acidobacteria increased with increasing nitrogen addition levels, while the r-strategist Firmicutes decreased with increasing nitrogen addition levels. Our results indicated microbial taxa exhibited carbon use plasticity, with most taxa altering their use of glucose under nitrogen addition. Unlabelled Image • Long-term nitrogen addition changed the quality rather than quantity of soil carbon. • Long-term nitrogen addition didn't change the magnitude of positive soil priming. • Bacterial and fungal taxa exhibited carbon use plasticity under different nitrogen addition levels. [ABSTRACT FROM AUTHOR]

Abstract There has been increasing interest in and use of biochar as a soil amendment. However, the effects of biochar addition on ammonia volatilization (AV) appeared contradictory from the many reported studies and the main influencing factors remain unclear. Here, we conducted a comprehensive meta-analysis of 41 published articles with 144 observations to reveal the effects of biochar addition on AV and used a boosted regression tree modelling approach to further interpret the contribution of biochar characteristics, soil properties and experimental conditions to this process. On average, biochar addition did not impact on AV, but this varied greatly under different soil, biochar and experimental conditions. The pH of soil and biochar were important factors impacting AV. Biochar application to acidic soil could stimulate AV, and addition of biochar with a high pH and at a low application rate also showed the same trend. In contrast, combining biochar with urea or organic fertilizer, or using wood-based or acidified biochar at appropriate rates had benefits in reducing AV. These findings have major implications for biochar management strategies in agricultural systems, where an important consideration is the mitigation of potentially detrimental environmental consequences. Graphical abstract Unlabelled Image Highlights • The pH of soil and biochar were crucial factors impacting ammonia volatilization. • Biochar applied in acidic soil could stimulate ammonia volatilization. • Adding acidic biochar had benefit for reducing ammonia volatilization. • Combining biochar with organic fertilizer could decrease ammonia volatilization. [ABSTRACT FROM AUTHOR]

This study detected the long-term trends in NO 2 concentrations in China from 1997 to 2016 based on the NO 2 columns from GOME, SCIAMACHY, and GOME-2A. Both differences in the time-overlapped NO 2 columns from GOME vs. SCIAMACHAY and SCIAMACHAY vs. GOME-2A showed seasonal variations, and the annual NO 2 columns from GOME were 0.9% higher than those from SCIAMACHY, which exceeded that from GOME-2A by 14%. The long-term trends of the NO 2 columns on a provincial scale could be simulated by cubic models (0.60 < R 2  < 0.96, p < 0.05) and presented three shapes: first decreasing then increasing and decreasing again; first decreasing then increasing; and continuously decreasing. The peak years of NO 2 columns in 17 provinces occurred in 2011 and 2012. These trends in NO 2 columns were determined by the economic developments and enacted air quality policies in nearly all the provinces except for Xizang and Qinghai Provinces, where the trends were determined by natural NO x emission sources. In detail, the panel data analysis showed that the simulated model had fixed effects, and the thermal power generation, consumption of diesel oil in agriculture, passenger traffic by highways, and freight traffic by highways significantly increased NO 2 , while the air quality policies in the 12th five-year plan decreased NO 2 columns from 1997 to 2016. The benefits to decreasing NO 2 columns from the air quality policies issued in the 10th and 11th five-year plans were offset by the quickly increasing economies. [ABSTRACT FROM AUTHOR]

Desert ecosystems are likely to change in response to global climate change and nitrogen (N) deposition. The effects of increased precipitation and N deposition on plant growth and the N cycle largely depend on N allocation and N recovery efficiency in the plant-soil ecosystem, but there is limited research on this in desert ecosystems. Here we report results using double-labeled 15 NH 4 15 NO 3 (30 and 60 kg N ha − 1 yr − 1 ) as a tracer under ambient (no additional water addition) and enhanced precipitation (60 mm water addition) in a Haloxylon ammodendron dominated ecosystem in the Gurbantunggut Desert of Northwest China. Herbaceous plants were a significantly larger sink for added 15 N than the H. ammodendron trees, and N retention varied with water and N addition, relative to growing season precipitation. The retention of added 15 N varied within the components of H. ammodendron , with the stems retaining most, followed by the assimilation branches. Soil was the dominant sink for added 15 N, in which the topsoil and subsoil respond differently to water and N addition over the two-year period. Nitrogen relative recovery percentage in the whole ecosystem ranged from 43% to 61%, lower than average recovery rate in temperate forests; N tracer recovery percentage significantly increased with water addition but decreased with enhanced N deposition. Future N cycling in central Asian deserts will depend on changes in precipitation. [ABSTRACT FROM AUTHOR]

China has been suffering high levels of fine particulate matter (PM 2.5 ). Designing effective PM 2.5 control strategies requires information about the contributions of different sources. In this study, a source-oriented Community Multiscale Air Quality (CMAQ) model was applied to quantitatively estimate the contributions of different source sectors to PM 2.5 in China. Emissions of primary PM 2.5 and gas pollutants of SO 2 , NO x , and NH 3 , which are precursors of particulate sulfate, nitrate, and ammonium (SNA, major PM 2.5 components in China), from eight source categories (power plants, residential sources, industries, transportation, open burning, sea salt, windblown dust and agriculture) were separately tracked to determine their contributions to PM 2.5 in 2013. Industrial sector is the largest source of SNA in Beijing, Xi'an and Chongqing, followed by agriculture and power plants. Residential emissions are also important sources of SNA, especially in winter when severe pollution events often occur. Nationally, the contributions of different source sectors to annual total PM 2.5 from high to low are industries, residential sources, agriculture, power plants, transportation, windblown dust, open burning and sea salt. Provincially, residential sources and industries are the major anthropogenic sources of primary PM 2.5 , while industries, agriculture, power plants and transportation are important for SNA in most provinces. For total PM 2.5 , residential and industrial emissions are the top two sources, with a combined contribution of 40–50% in most provinces. The contributions of power plants and agriculture to total PM 2.5 are about 10%, respectively. Secondary organic aerosol accounts for about 10% of annual PM 2.5 in most provinces, with higher contributions in southern provinces such as Yunnan (26%), Hainan (25%) and Taiwan (21%). Windblown dust is an important source in western provinces such as Xizang (55% of total PM 2.5 ), Qinghai (74%), Xinjiang (59%). The large variation in sources of PM 2.5 across China suggests that PM 2.5 mitigation programs should be designed separately for different regions/provinces. [ABSTRACT FROM AUTHOR]

Ammonia (NH 3), as an alkaline gas, contributes substantially to atmospheric nitrogen deposition, which can cause biodiversity loss, water eutrophication and soil acidification. Advances in the application of satellite observations allow us to gain deeper insights into atmospheric NH 3 concentrations at large spatial scales. A new satellite-based methodology is proposed for estimating dry NH 3 deposition with consideration of bi-directional NH 3 exchange. We estimate the global dry NH 3 deposition for nine years (2008–2016) by using the Infrared Atmospheric Sounding Interferometer Instrument (IASI) NH 3 retrievals. Satellite-based dry NH 3 deposition is in general consistent with measured dry NH 3 deposition over the monitoring sites (R2 = 0.65). Global dry NH 3 deposition over 8 kg N ha−1 is mainly distributed in the Eastern China, Northern and Central Pakistan, and Northern India. An annual increase rate of 0.27 and 0.13 kg N ha−1 y−1 in dry NH 3 deposition during 2008–2016 occurs in Eastern China and Sichuan Basin, which are the major Chinese agricultural regions. The NH 3 compensation point is high during warm months, and can be above 1 μg m−3 such as in Eastern China, implying the importance of considering the NH 3 compensation points for estimating dry NH 3 deposition. We find, if the upward NH 3 flux was ignored, it will cause 11%, 17%, 5% and 3% overestimation in dry NH 3 deposition in Eastern China, Northern India, Eastern United States and Western Europe, respectively. This study presents the potential of using the satellite retrievals to estimate the large-scale dry NH 3 deposition, and the methodology is able to provide temporally continuous and spatially complete fine-resolution datasets. Unlabelled Image • A new satellite-based method is proposed to estimate dry ammonia deposition. • An overestimation in dry ammonia deposition will be caused using unidirectional methods. • Satellite-based estimates capture the general variability of dry ammonia deposition. [ABSTRACT FROM AUTHOR]