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Producing enough food to simultaneously address food shortage and agro-environmental pollution problems attracts attention globally. To quantify the risks of nutrition crisis to food security and the agro-environment under current agricultural policies in China, this study evaluates and predict the spatiotemporal patterns of nitrogen (N) flows during 1949–2050 through material flow analysis (MFA) and spatial analysis methods. The results show that (1) the crop harvest (including grains, fruits and vegetables) in China increased by a factor of 8.12 from 1949 to 2019, accompanied by a large amount of N loss to the environment. Compared to 1949, N runoff increased 1.23 times in 1979 and 3.43 times in 1999 after which time agricultural pollution control policy achieved initial results, and the crop harvest increased steadily. (2) At the national average level, crop production will increase by 58.60% in 2050, which is higher than the food security threshold while N loss to the environment will be lower than the agro-environmental risk threshold. Under the current agricultural policy, the win-win goals of crop production increase and pollution control can be realized in China. (3) China has obvious temporal and spatial differences in N flows, for which four regions has been divided. Region II, mainly located in Yangtze River Economic Belt, is a high-risk area for N loss. By 2050, environmental pollution can be controlled under the current agricultural policies. However, crop production will only increase by 10% compared with its historical high value, lower than food security threshold. It is necessary to implement more targeted management of high-risk areas by adopting methods such as fallowing or construction of pollution buffer zones while improving N fertilizer use efficiency. For region III, the impact of N loss on the environment has always been at a low level, so there is still great room for increasing future crop production in this region. On average, China will be able to achieve green and sustainable development for agriculture nationally, but there are remaining food security risks in high N loss areas. More targeted N management strategies should be applied to achieve better goals in the future. [Display omitted] • Crop harvest increased by 8.12 times, accompanied by a large amount of N losses. • Compare to 2014, N runoff in 2019 reduced by 15% for the environmental policies. • Win-win goals for food security and pollution control can be reached in 2050. • To achieve better goals, 4 regions are divided to apply more targeted N management strategies. [ABSTRACT FROM AUTHOR]

The nitrogen balance can serve as an indicator of the risk to the environment of nitrogen loss from agricultural land. To investigate the temporal and spatial changes in agricultural nitrogen application and its potential threat to the environment of the Haihe Basin in China, we used a database of county-level agricultural statistics to calculate agricultural nitrogen input, output, surplus intensity, and use efficiency. Chemical fertilizer nitrogen input increased by 51.7% from 1990 to 2000 and by 37.2% from 2000 to 2010, concomitant with increasing crop yields. Simultaneously, the nitrogen surplus intensity increased by 53.5% from 1990 to 2000 and by 16.5% from 2000 to 2010, presenting a continuously increased environmental risk. Nitrogen use efficiency decreased from 0.46 in 1990 to 0.42 in 2000 and remained constant at 0.42 in 2010, partly due to fertilizer composition and type improvement. This level indicates that more than half of nitrogen inputs are lost in agroecosystems. Our results suggest that although the improvement in fertilizer composition and types has partially offset the decrease in nitrogen use efficiency, the environmental risk has still increased gradually over the past 20 years, along with the increase in crop yields and nitrogen application. It is important to achieve a better nitrogen balance through more effective management to significantly reduce the environmental risk, decrease nitrogen surplus intensity, and increase nitrogen use efficiency without sacrificing crop yields. [ABSTRACT FROM AUTHOR]

In order to analyze the distribution pattern of the sediment nitrogen and phosphorus of the Three Gorges Reservoir (TGR), the mainstream of TGR and five tributary bays in Hubei province were observed from October 2005 to July 2006. The spatial and seasonal dynamics of the sediment total nitrogen (TN sed ) and total phosphorus (TP sed ), the relationship between the mainstream and tributary, and the sediment nutrients’ effect to the surface water were analyzed. The results showed that, concentrations of TN sed ranged from 0.27 to 2.04 mg/g, and TP sed fluctuated between 0.17 and 1.21 mg/g. Both of the maximum of TN sed and TP sed appeared in the Xiangxi Bay (the longest bays studied), 1.09 and 0.90 mg/g respectively. No significant spatial differences were found among different sites in other bays ( p > 0.05). For seasonal dynamics of TP sed , only the difference in the Yuanshui Bay between spring and summer was significant ( p < 0.05). For TN sed , significant differences existed among different seasons in most bays, especially between autumn and other seasons. Cluster analysis based on the surface water nutrients and sediment nutrients indicated that the influence range of the mainstream to the surface water ranged from 10.7 to 15.1 km, while the length of the influence range to the sediment was about 5.34 km. Results of the correlation analysis showed that the internal loading in Hubei province of TGR has not caused a significant effect on the surface water in a large spatial scale, although the influence was significant in some shallow regions. [ABSTRACT FROM AUTHOR]

Critical nitrogen (N c) dilution curves have been widely used for the plant N status diagnosis, N management, crop modeling, and remote sensing. Wheat is a major crop worldwide whose N c dilution curves developed under different conditions (genotype × environment × management) show large parameter variations. Herein, a dataset of 19 nitrogen fertilizer experiments (n = 656) from five wheat planting sites in China was used to evaluate the uncertainty in these curves and explain the sources of differences using the Bayesian theory method. The uncertainty of the fitted curve decreased with the increase in plant biomass. The parameter A 2 of fitted curves of genotype × environment × management combinations showed a greater variation than A 1 , with slight parameter differences among different genotypes and planting sites. The variables related to genotype and growth environment, i.e., maximum N concentration, maximum biomass, and accumulated growing degree days during the vegetative growth period, were the sources of differences in curve parameters. Though the N c curve differences between genotype × environment × management were statistically significant, the nitrogen nutrition index (NNI) differences remained relatively small. This study provides insights for developing a more diverse N c dilution curve to aid in optimal nitrogen fertilization management in wheat. [ABSTRACT FROM AUTHOR]

• δ15N bulk of mudstones from the Chang-7 3 Member is higher than that of Chang-7 1,2. • Nitrogen isotopic composition of mudstone is related to depositional redox condition. • Nitrogen isotopic composition can be used to evaluate depositional redox condition. In this study, we report new analyses of stable nitrogen isotopic compositions (δ15N) of the black mudstones from the Chang-7 Member of the Upper Triassic Yanchang Formation in the Ordos Basin, China, to examine the possible linkage of such isotopic compositions with the depositional environment. These mudstones were deposited mainly under suboxic bottom water column conditions. The core descriptions and trace element concentrations differ between samples obtained from the Chang-7 3 and Chang-7 1,2 members, situated at the bottom and top of the Chang-7 Member, respectively, such that the depositional condition of the former implies a more reduced water regime. The bulk rock nitrogen isotope (δ15N bulk) values of the samples obtained from the Chang-7 3 Member are higher than those of the Chang-7 1,2 Member. No significant differences were identified in the organic carbon isotopes (δ13C org), total organic carbon (TOC), or total nitrogen (TN) values between the two units. The results of δ15N bulk cross-plotting with the TOC, TN, and carbon to nitrogen atomic ratio (C/N) show an absence of significant modification of the primary nitrogen isotopic compositions from post-depositional processes. Given the depositional history of these units, we suggest that the sedimentary redox environment can have a significant influence on δ15N bulk. Denitrification, which occurs mainly in suboxic conditions, plays an important role in such an environment, resulting in 15N enrichment during the original deposition. Thus, owing to its sensitivity to sedimentary redox environments, the δ15N bulk index can be an effective tool for evaluating depositional redox conditions, particularly for further subdivision of suboxic environments. [ABSTRACT FROM AUTHOR]

• Nitrogen use efficiency (NUE) varies considerably in space and time in China. • Partial factor productivity of nitrogen was large in north- and south-east China. • Partial nutrient balance of nitrogen was low in south China. • Multiple linear regression explained 74 % of the NUE variation. • Crop type, soil properties and climate are major explanatory variables of NUE. Nitrogen use efficiency (NUE) is crucial to establish efficient fertilizer application guidelines that balance crop yield, economic return and environmental sustainability. Although there are quite a few researches about the spatial and temporal variation of NUE, little work has been done on modelling NUE through deriving empirical relationships with explanatory environmental variables and exploring their relative importance quantitatively. The space-time patterns of NUE indicators (i.e., the Partial Factor Productivity of nitrogen, PFP N , and the Partial Nutrient Balance of nitrogen, PNB N) at provincial scale in China were derived and related to environmental covariates using stepwise multiple linear regression. PFP N was higher in east and south China than in central and west China and was smaller than 30 kg kg−1 yr−1 in most provinces, while PNB N was moderate in most provinces (0.41–0.50 kg kg−1 yr−1) and low (< 0.40 kg kg−1 yr−1) in south China. The national PFP N declined slightly from 32 kg kg−1 in 1978 to 27 kg kg−1 in 1995 and went up gradually to reach 38 kg kg−1 in 2015. The national PNB N decreased from 0.53 to 0.36 kg kg−1 from 1978 to 2003, thereafter stabilizing at around 0.40 kg kg−1 yr−1 between 2004 and 2015. The multiple linear regression models explained 74 % of the variance of PFP N and PNB N. The main explanatory variables of PFP N were planting area index of sugar crop (32 % of the R-square), followed by Arenosols (12 %), planting area index of oil crop (8 %), planting area index of vegetables (5 %), silt content (5 %) and total potassium (5 %). For PNB N , the variation was mainly attributed to mean annual daytime surface temperature (28 % of the R-square), planting area index of crops (beans 20 %, orchards 10 % and vegetables 9 %) and wet day frequency (5 %). The results of this study indicate that crop types, temperature and soil properties are important variables that determine NUE. These should be considered by policy makers when agricultural land development decisions are made in order to balance NUE and productivity (i.e., agronomy and environment). [ABSTRACT FROM AUTHOR]