Nitrogen and phosphorus use efficiencies and losses in the food chain in China at regional scales in 1980 and 2005

Impact of transition from permanent pasture to new swards on the nitrogen use efficiency, nitrogen and carbon budgets of beef and sheep production

There is currently much debate around the environmental implications of ruminant farming and a need for robust data on nitrogen (N) and carbon (C) fluxes from beef and sheep grazing systems. Here we use data collected from the North Wyke Farm Platform along with the SPACSYS model to examine the N and C budgets and the N use efficiency (NUE) of grassland swards at different stages of establishment. We assessed the transition from permanent pasture (PP) to a high-sugar grass (HSG), and a mixed sward of HSG with white clover (HSGC), identifying data specifically for the reseed (RS) years and the first year following RS (HSG-T and HSGC-T). Dominant fluxes for the N budget were N offtake as cut herbage and via livestock grazing, chemical-N fertiliser and N leaching at 88-280, 15-177, and 36-92 kg N ha^-1 a^-1, respectively. Net primary productivity, soil respiration and C offtake as cut herbage and via livestock grazing at 1.9-15.9, 1.74-12.5, and 0.34-11.7 t C ha^-1 a^-1, respectively, were the major C fluxes. No significant differences were found between the productivity of any of the swards apart from in the RS year of establishment. However, NUE of the livestock production system was significantly greater for the HSGC and HSGC-T swards at 32 and 42% compared to all other swards, associated with the low chemical-N fertiliser inputs to these clover-containing swards. Our findings demonstrate opportunities for improving NUE in grazing systems, but also the importance of setting realistic NUE targets for these systems to provide achievable goals for land-managers.

Multi-scale Modeling of Nutrient Pollution in the Rivers of China

Chinese surface waters are severely polluted by nutrients. This study addresses three challenges in nutrient modeling for rivers in China: (1) difficulties in transferring modeling results across biophysical and administrative scales, (2) poor representation of the locations of point sources, and (3) limited incorporation of the direct discharge of manure to rivers. The objective of this study is, therefore, to quantify inputs of nitrogen (N) and phosphorus (P) to Chinese rivers from different sources at multiple scales. We developed a novel multi-scale modeling approach including a detailed, state-of-the-art representation of point sources of nutrients in rivers. The model results show that the river pollution and source attributions differ among spatial scales. Point sources accounted for 75% of the total dissolved phosphorus (TDP) inputs to rivers in China in 2012, and diffuse sources accounted for 72% of the total dissolved nitrogen (TDN) inputs. One-third of the sub-basins accounted for more than half of the pollution. Downscaling to the smallest scale (polygons) reveals that 14% and 9% of the area contribute to more than half of the calculated TDN and TDP pollution, respectively. Sources of pollution vary considerably among and within counties. Clearly, multi-scale modeling may help to develop effective policies for water pollution.

Animal based diets and environment: Perspective from phosphorus flow quantifications of livestock and poultry raising in China

Identifying the key nodes of the phosphorus flows in animal raising system is fundamental to improve P utilization efficiency and reduce the P contamination. This study established a phosphorus flow analysis model for livestock and poultry raising, depicted P flows for major livestock and poultry under two raising modes, and further analyzed their spatial and temporal distributions. We find that around 15% of P input was transferred into the products, and in P output around 40% lost into the environment in 2015. The P flows have been increasing since 2000, and the main contributor is pigs followed by beef cattle. It should be noticed that P loss from livestock and poultry raising is huge with extensive prospect of recycling in some central provinces of China, and western region where ecological environment is fragile, has a higher P loss rate which need to change the dietary preference and adjust raising structure. As for diets, pork and eggs are better choices than milk or other kinds of meat in terms of reducing the P load, when producing per unit protein or energy. This study contributes to the understanding of P management in husbandry industry, the quantification of environmental loads of animal-based food and the identification of the potential of reducing P loss to realize sustainable utilization of P.

Driving forces of nitrogen flows and nitrogen use efficiency of food systems in seven Chinese cities, 1990 to 2015

The effects of population growth (PG), dietary changes (DC), native rural-to-urban migration (NM), migration from regions distant from the cities (M), and agricultural patterns and practices (AP) on N use in food systems and the food trade, and on apparent and virtual nitrogen (N) and N use efficiencies (NUE), at the city scale, are not well understood. Here we selected seven Chinese cities as the study subjects, analyzed the food trade effects on apparent and virtual N inputs and NUE, and quantified the relative magnitudes of these factors on N inputs to cities' food systems during 1990-2015, by designing several scenarios. Our results show that food-sink cities are relying more and more on external food and feed, but in 2015 they transferred 33.8-74.9% of their N input for food or feed productions to areas outside their boundaries, and the food trade showed different effects on the virtual N cost of food N consumption. Apparent NUEs of food systems were 33.1-74.9% higher than those calculated from virtual N costs in Beijing, Tianjin, Shanghai, Lanzhou and Xiamen in 2015. But in cities that export large amounts of food and feed-for example, Chongqing and Changchun-apparent NUE was underestimated by 4.0-46.4% relative to virtual NUE. Native PG, DC, NM, M, and AP accounted for 1.2-14.1%, -6.6-30.0%, 0.6-8.2%, -7.7-131.0%, and -43.8-12.8%, respectively, of the increase in virtual N inputs associated with cities' food systems in 2015, compared to 1990. Our study concludes that M, DC, and AP changes should be considered for mitigating N input in these Chinese cities, and virtual N exports induced by the food trade should also be included if the city is a net food exporter. Selective food trade could help improve the NUE of cities' food systems, and virtual NUE should be used as an indicator, rather than apparent NUE.

Comprehensive Environmental Assessment of Potato as Staple Food Policy in China

The Chinese government projected 30% of total consumed potatoes as a staple food (PSF) by 2020. We comprehensively assessed the potential impacts of PSF on rice and flour consumption, rice and wheat planting, energy and nutrient supply, irrigation-water, chemical nitrogen (N), phosphorus pentoxide (P₂O₅) and potassium oxide (K₂O) fertilizer inputs and total greenhouse gases (GHG) emission for potatoes, rice and wheat, by assuming different proportions of potato substitutes for rice and flour. The results showed that per capita, 2.9 ± 0.3 and 4.7 ± 0.5 kg more potatoes per year would enter the Chinese staple-food diet, under the government’s target. PSF consumed are expected to reach 5.2 ± 0.7 Tg yr⁻¹, equivalent to substituting potatoes for 4.2 ± 0.8–8.5 ± 0.8 Tg yr⁻¹ wheat and 5.1 ± 0.9–10.1 ± 1.8 Tg yr⁻¹ rice under different scenarios. While this substitution can increase the nutrient supply index by 63% towards nutrient reference values, it may induce no significant effect on staple-food energy supply with lower chemical fertilizer (except for K₂O) and irrigation-water inputs and GHG emissions in different substitution scenarios than the business as usual scenario. The reduction in rice and wheat demands lead to wheat in the North China Plain and early rice decrease by 6.1–11.4% and 12.1–24.1%, respectively. The total GHG reduction is equal to 1.1–9.0% of CO₂ equivalent associated with CH₄ and N₂O emitted from the Chinese agroecosystem in 2005. The saved irrigation water for three crops compared to 2012 reaches the total water use of 17.9 ± 4.9–21.8 ± 5.9 million people in 2015. More N fertilizer, irrigation-water, and GHG can be reduced, if the PSF ratio is increased to 50% together with potato yield improves to the optimal level. Our results implied that the PSF policy is worth doing not only because of the healthier diets, but also to mitigate resource inputs and GHG emissions and it also supports agricultural structure adjustments in the areas of irrigated wheat on the North China Plain and early rice across China, designed to increase the adaptability to climate change.

Excess nutrient loads to Lake Taihu: Opportunities for nutrient reduction

Intensive agriculture and rapid urbanization have increased nutrient inputs to Lake Taihu in recent decades. This resulted in eutrophication. We aim to better understand the sources of river export of total dissolved nitrogen (TDN) and phosphorus (TDP) to Lake Taihu in relation to critical nutrient loads. We implemented the MARINA-Lake (Model to Assess River Inputs of Nutrients to seAs) model for Lake Taihu. The MARINA-Lake model quantifies river export of dissolved inorganic and organic N and P to the lake by source from sub-basins. Results from the PCLake model are used to identify to what extent river export of nutrients exceeds critical loads. We calculate that rivers exported 61 kton of TDN and 2 kton of TDP to Lake Taihu in 2012. More than half of these nutrients were from human activities (e.g., agriculture, urbanization) in Sub-basins I (north) and IV (south). Most of the nutrients were in dissolved inorganic forms. Diffuse sources contributed 90% to river export of TDN with a relatively large share of synthetic fertilizers. Point sources contributed 52% to river export of TDP with a relatively large share of sewage systems. The relative shares of diffuse and point sources varied greatly among nutrient forms and sub-basins. To meet critical loads, river export of TDN and TDP needs to be reduced by 46-92%, depending on the desired level of chlorophyll-a. There are different opportunities to meet the critical loads. Reducing N inputs from synthetic fertilizers and P from sewage systems may be sufficient to meet the least strict critical loads. A combination of reductions in diffuse and point sources is needed to meet the most strict critical loads. Combining improved nutrient use efficiencies and best available technologies in wastewater treatment may be an effective opportunity. Our study can support the formulation of effective solutions for lake restoration.

Estimating soil nitrate leaching of nitrogen fertilizer from global meta-analysis

Global estimates of soil nitrate leaching of applied nitrogen (N) in agricultural production systems are not imprecise; however, the results of some field experiments have suggested that nitrate leaching responds exponentially rather than linearly to increasing N inputs. In this study, we compiled field data on nitrate leaching for 324 site-year combinations extracted from 86 peer-reviewed articles to test the hypothesis that in response to N fertilizer addition, soil nitrate leaching emission factors (EF) do not remain constant, but rather increase rapidly with increasing rates of N application. The averaged overall results showed that the proportional change in the EF response to increasing N input (ΔEF, %) was 0.042. Because this value was positive and significantly different from zero, our results demonstrate that EF is not constant, but rather increases with N addition. We compared our ΔEF response pattern with other constant EF patterns, and found that the 30% EF estimate of the Intergovernmental Panel on Climate Change and the 19% EF used in another published model were too high. A global estimate of soil nitrate leaching in arable uplands calculated with our ΔEF pattern was substantially lower than other estimates calculated with other procedures. In conclusion, our ΔEF pattern provided a globally applicable procedure for more accurate estimation of leaching loss and potential environmental costs incurred by various N application gradients.

Recent patterns of anthropogenic reactive nitrogen emissions with urbanization in China: Dynamics, major problems, and potential solutions

Anthropogenic emissions of reactive nitrogen (Nr) result in adverse impacts on the ecosystems. Nowhere has that threat been more challenging than in rapidly urbanized China, the world's largest anthropogenic Nr producer. The Nanjing Declaration in 2004 called for global reductions in Nr emissions. To assess China's progress, multisource Nr emissions were evaluated with a quantitative method from 2004 to 2014. The results showed that national Nr emissions had increased with fluctuation over this period, 55-59% of the total Nr emissions were emitted to the atmosphere, and that agricultural production still was the biggest contributor (62-69%). The hotspots were mainly located in the developed and coastal regions that also have high population densities. Urbanization was associated with overall decreases in agricultural Nr emission and increases in industrial and residential Nr emissions. The overall increase in residential Nr emission per capita played a large role in driving the growth of national Nr emission. Continuing urbanization poses a significant challenge to future Nr mitigation for ecosystem sustainability and a range of strategies, covering improvement of N-use efficiency, slowdown of Western China's urbanization, and promotion of low N intensive lifestyle, are proposed that can promote Chinese low-nitrogen development.

Response of Nitrogen Losses to Excessive Nitrogen Fertilizer Application in Intensive Greenhouse Vegetable Production

Excessive nitrogen fertilizer application in greenhouse vegetable production (GVP) is of scientific and public concern because of its significance to international environmental sustainability. We conducted a meta-analysis using 1174 paired observations from 69 publications on the effects of nitrogen fertilizer application and reducing nitrogen fertilizer application on the nitrogen losses on a broad scale. We found that the increase in nitrogen loss is much higher than that in production gain caused by excessive application of nitrogen fertilizer: nitrate leaching (+187.5%), ammonium leaching (+28.1%), total nitrogen leaching (+217.0%), nitrous oxide emission (+202.0%), ammonia emission (+176.4%), nitric oxide emission (+543.3%), yield (+35.7%) and nitrogen uptake (+24.5%). Environmental variables respond nonlinearly to nitrogen fertilizer application, with severe nitrate leaching and nitrous oxide emission when the application rate exceeds 570 kg N/ha and 733 kg/N, respectively. The effect of nitrogen fertilizer on yield growth decreases when the application rate exceeds 302 kg N/ha. Appropriate reduction in nitrogen fertilizer application rate substantially mitigates the environmental cost, for example, decreasing nitrate leaching (−32.4%), ammonium leaching (−6.5%), total nitrogen leaching (−37.3%), ammonia emission (−28.4%), nitrous oxide emission (−38.6%) and nitric oxide emission (−8.0%), while it has no significant effect on the nitrogen uptake and yield.

Quantifying the Urban Food-Energy-Water Nexus: The Case of the Detroit Metropolitan Area

The efficient provision of food, energy, and water (FEW) resources to cities is challenging around the world. Because of the complex interdependence of urban FEW systems, changing components of one system may lead to ripple effects on other systems. However, the inputs, intersectoral flows, stocks, and outputs of these FEW resources from the perspective of an integrated urban FEW system have not been synthetically characterized. Therefore, a standardized and specific accounting method to describe this system is needed to sustainably manage these FEW resources. Using the Detroit Metropolitan Area (DMA) as a case, this study developed such an accounting method by using material and energy flow analysis to quantify this urban FEW nexus. Our results help identify key processes for improving FEW resource efficiencies of the DMA. These include (1) optimizing the dietary habits of households to improve phosphorus use efficiency, (2) improving effluent-disposal standards for nitrogen removal to reduce nitrogen emission levels, (3) promoting adequate fertilization, and (4) enhancing the maintenance of wastewater collection pipelines. With respect to water use, better efficiency of thermoelectric power plants can help reduce water withdrawals. The method used in this study lays the ground for future urban FEW analyses and modeling.

Nutrient use efficiencies, losses, and abatement strategies for peri-urban dairy production systems

Manure management is an important aspect of urban livestock production that has a profound impact on metropolitan living. Data were collected from 28 dairy farms in peri-urban Beijing and analysed to determine farm nitrogen and phosphorus flows and costs associated with various manure management options to reduce nutrient losses. Dairy production in peri-urban Beijing was characterized by its use of high protein diets (16.3-17.0% crude protein), high reliance on imported feeds (92-98%), and low manure recycling (3.0-10.8%). Farms of 900-2000 cattle showed lower use efficiencies than farms of <900 cattle. Costs of manure handling ranged from 0.1 to 1.0 Yuan kg^-1 milk. Among various manure treatment options, biogas digesters with aerobic lagoons had the lowest N losses and costs, justifying their investments. In conclusion, peri-urban dairy production systems were contrasting with traditional systems and within their own systems in nutrient use efficiency and losses, which was mainly decided by their farm size. To improve the nutrient use efficiencies and reduce losses, farmers and managers of peri-urban dairy production system should have a full awareness of different feed intake and manure management.

Structural Change and Its Impact on the Energy Intensity of Agricultural Sector in China

China’s agricultural structure has undergone significant changes for the past four decades, mainly presenting as the fall of sown proportion of grain crops and the rise of vegetables, as has its energy consumption. Employing the panel data on 30 provinces during 1991–2016, this paper empirically explores the impact of agricultural structure changes (ASC) on the energy intensity of agricultural production (EIAP), direct energy intensity of agricultural production (DEIAP) and indirect energy intensity of agricultural production (IEIAP) in China. Besides, the regional heterogeneity of such impact is examined. The results show that: (1) ASC increases EIAP and IEIAP significantly, while ASC decreases DEIAP, which is explained by the structural effect and different planting modes of different crops; (2) the impact in the three administrative regions is similar to national situation, except the impact of ASC on DEIAP in the West Region, which is explained by regional differences of vegetable mechanization; (3) the result of the six vegetable production regions reveals greater regional heterogeneity, and this is attributed to the scale economy effect and the incremental effect of vegetable mechanization; and (4) fuel price, income, agricultural labor, old dependency ratio, and fiscal expenditure have different but significant impacts on EIAP, DEIAP, and IEIAP. Finally, some policy implications are given.

Nutrient-derived environmental impacts in Chinese agriculture during 1978-2015

Nitrogen (N) and phosphorus (P) play a critical role in agricultural production and cause many environmental disturbances. By combing life cycle assessment (LCA) method with the mass balance principle of substance flow analysis (SFA), this study establishes a nutrient-derived environmental impact assessment (NEIA) model to analyze the environmental impacts caused by nutrient-containing substances of agricultural production in China during 1978-2015. The agricultural production system is composed of crop farming and livestock breeding, and the environmental impacts include energy consumption, global warming, acidification, and eutrophication. The results show all these environmental impacts had increased to 8.22*10⁹ GJ, 5.01*10⁸ t CO₂-eq, 2.41*10⁷ t SO₂-eq, and 7.18*10⁷ t PO₄^3--eq, respectively. It is noted the energy consumption and the climate change caused by the crop farming were always higher than those from livestock breeding, which were average 60 and two times, respectively. While the acidification and the eutrophication were opposite after 1995 and 2000, even they were similar. This was mainly due to the high N application including synthetic N fertilizer (from 1.33*10⁹ GJ to 2.08*10⁹ GJ), applied manure (from 4.94*10⁸ GJ to 5.65*10⁸ GJ) and applied crop residue (from 2.94*10⁸ GJ to 5.30*10⁹ GJ), while the synthetic N fertilizer was controlled and the livestock expanded rapidly after 1995. Among the sub-categories, the three staple crops (rice, wheat, and maize) contributed greater environmental impacts, which were about two to 10 times as other crops and livestock, due to their high fertilizer uses, sown areas and harvests. While the oil crops and fruit consumed the least energies because of their much lower fertilizer-use intensities. Pig and poultry especially pig also caused obvious effects on environment (even 20 times as other livestock) because of their large quantities and excretions, which emitted much higher N₂O and P loss resulting in much higher climate change, acidification and eutrophication than other livestock. Then the study proposes the nutrient management in agricultural production by considering crop production, livestock breeding and dietary adjustment, so that some valuable experiences can be shared by the stakeholders in other Chinese regions.

Environmental impacts and resource use of milk production on the North China Plain, based on life cycle assessment

Life cycle assessment methodology was used to quantify the environmental impacts and resource use of milk production on the North China Plain, the largest milk production area in China. Variation in environmental burden caused by cow productivity was evaluated, as well as scenario analysis of the effects of improvement practices. The results indicated that the average environmental impact potential and resource use for producing 1kg of fat and protein corrected milk was 1.34kgCO₂eq., 9.27gPO₄^3-eq., 19.5gSO₂eq., 4.91MJ, 1.83m² and 266L for global warming potential (GWP), eutrophication potential (EP), acidification potential (AP), non-renewable energy use (NREU), land use (LU) and blue water use (BWU; i.e. water withdrawal), respectively. Feed production was a significant determinant of GWP, NREU, LU and BWU, while AP and EP were mainly affected by manure management. Scenario analysis showed that reducing use of concentrates and substituting with alfalfa hay decreased GWP, EP, AP, NREU and LU (by 1.0%-5.5%), but caused a significant increase of BWU (by 17.2%). Using imported soybean instead of locally-grown soybean decreased LU by 2.6%, but significantly increased GWP and NREU by 20% and 6.9%, respectively. There was no single perfect manure management system, with variable effects from different management practices. The environmental burden shifting observed in this study illustrates the importance of assessing a wide range of impact categories instead of single or limited indicators for formulating environmental policies, and the necessity of combining multiple measures to decrease the environmental burden. For the North China Plain, improving milking cow productivity and herd structure (i.e. increased proportion of milking cows), combining various manure management systems, and encouraging dairy farmers to return manure to nearby crop lands are promising measures to decrease multiple environmental impacts.

Hotspots for Nitrogen and Phosphorus Losses from Food Production in China: A County-Scale Analysis

Food production in China results in large losses of nitrogen (N) and phosphorus (P) to the environment. Our objective is to identify hotspots for N and P losses to the environment from food production in China at the county scale. To do this, we used the NUFER (Nutrient flows in Food chains, Environment and Resources use) model. Between 1990 and 2012, the hotspot area expanded by a factor of 3 for N, and 24 for P. In 2012 most hotspots were found in the North China Plain. Hotspots covered less than 10% of the Chinese land area, but contributed by more than half to N and P losses to the environment. Direct discharge of animal manure to rivers was an important cause of N and P losses. Food production was found to be more intensive in hotspots than in other counties. Synthetic fertilizer use and animal numbers in hotspots were a factor of 4-5 higher than in other counties in 2012. Also the number of people working in food production and the incomes of farmers are higher in hotspots than in other counties. This study concludes with suggestions for region-specific pollution control technologies for food production in China.

Human Perturbation of the Global Phosphorus Cycle: Changes and Consequences

The phosphorus (P) cycle is an important Earth system process. While natural P mobilization is slow, humans have been altering P cycle by intensifying P releases from lithosphere to ecosystems. Here, we examined magnitudes of which humans have altered the P cycles by integrating the estimates from recent literatures, and furthermore illustrated the consequences. Based on our synthesis, human alterations have tripled the global P mobilization in land-water continuum and increased P accumulation in soil with 6.9 ± 3.3 Tg-P yr^-1. Around 30% of atmospheric P transfer is caused by human activities, which plays a significant role than previously thought. Pathways involving with human alterations include phosphate extraction, fertilizers application, wastes generation, and P losses from cropland. This study highlights the importance of sustainable P supply as a control on future food security because of regional P scarcity, food demand increase and continuously P intensive food production. Besides, accelerated P loads are responsible for enhanced eutrophication worldwide, resulting in water quality impairment and aquatic biodiversity losses. Moreover, the P enrichment can definitely stimulate the cycling of carbon and nitrogen, implying the great need for incorporating P in models predicting the response of carbon and nitrogen cycles to global changes.

The Contrasting Effects of Alum-Treated Chicken Manures and KH2PO4 on Phosphorus Behavior in Soils

Alum [KAl(SO)⋅12HO] is often added to chicken manure to limit P solubility after land application. This is generally ascribed to the formation of Al-PO complexes. However, Al-PO complex formation could be affected by the matrix of chicken manure, which varies with animal diet. Alum was added to KHPO (as a reference material) and two manures from typical chicken farms in China, one from an intensive farm (CMIF) and another from free-ranging chickens (CMFR). These were subsequently incubated with soils for 100 d to investigate P transformations. Alum reduced water-soluble colorimetrically reactive phosphorus (RP) from soils amended with manure more effectively than in soils amended with KHPO. Alum addition lowered Mehlich-3 RP in soils with CMFR but had no influence on Mehlich-3 RP in CMIF- or KHPO-amended soils. A comparison of P in digested Mehlich-3 extracts with RP in undigested samples showed significantly increased P in digests of alum-treated CMFR only. Fractionation data indicated that alum treatment increased P in the NHF-RP (Al-P) fraction only in soils with KHPO, but not in soils with manure treatments. Furthermore, NaOH-extracted nonreactive P was markedly higher in soil with alum-treated CMFR relative to normal CMFR. The CMFR manure was assumed to contain higher concentrations of organic P because these chickens were fed grains only. These results suggest that the formation of alum-organic P complexes may reduce P solubility. By comparing alum-treated KHPO and manures, it appears that organic matter in manure could interfere with the formation of Al-PO complexes.

Driving forces and impacts of food system nitrogen flows in China, 1990 to 2012

Food nitrogen (N), which includes animal-food (AN) and plant-food N (PN), has been driven by population growth (PG), dietary changes associated with income growth (DC) and rural-urban migration (M) over the past three decades, and these changes combined with their N cost, have caused some effect on N use in China's food system. Although there is an increasing literature on food N and its environmental impacts in China, the relative magnitude of these driving forces are not well understood. Here we first quantify the differences in per capita AN and PN consumption in urban and rural areas and their impacts on N input to the food system during 1990-2012, and then quantify the relative contributions of DC, PG and M in the overall N change during this period. Our results show that a resident registered as living in city required 0.5kg more ANyr^-1 and 0.5kg less PNyr^-1 than one living in a rural area, in 2012. DC, PG and M accounted for 52%, 31% and 17% of the total AN increase, respectively. These three factors caused 46% of the increased N use for food production over the past two decades. Another 54% was mainly caused by the declining in N use efficiencies of the food system. Food-sourced N loss intensity in urban and rural areas were 502 and 162kgNhm^-2 in 2012, a three-fold difference due to the increasing amount and a linear rural-urban flow of N input, and inadequate N recovery via solid waste and wastewater treatment in cities. Our study highlights China is facing higher risks of environmental N pollution with urbanization, because of the high demand for AN and higher food-sourced N loss intensity in urban than in rural areas.

Reactive nitrogen losses from China's food system for the shared socioeconomic pathways (SSPs)

Food production in China has been changing fast as a result of socio-economic development. This resulted in an increased use of nitrogen (N) in food production, and also to increased reactive nitrogen (Nr) losses to the environment, causing nitrogen pollution. Our study is the first to quantify future Nr losses from China's food system for the Shared Socio-economic Pathways (SSPs). We show that Nr losses differ largely among SSPs. We first qualitatively described the five SSP storylines for China with a focus on food production and consumption. Next, we interpreted these SSP scenarios quantitatively for 2030 and 2050, using the NUFER (NUtrient Flows in Food chains, Environment and Resources use) model to project the Nr losses from China's food system. The results indicate that Nr losses from future food system in China are relatively low for SSP1 and SSP2, and relatively high for SSP3 and SSP4. In SSP5 Nr losses from China's food system are projected to be slightly lower than the level of today.

Life cycle energy efficiency and environmental impact assessment of bioethanol production from sweet potato based on different production modes

The bioethanol is playing an increasingly important role in renewable energy in China. Based on the theory of circular economy, integration of different resources by polygeneration is one of the solutions to improve energy efficiency and to reduce environmental impact. In this study, three modes of bioethanol production were selected to evaluate the life cycle energy efficiency and environmental impact of sweet potato-based bioethanol. The results showed that, the net energy ratio was greater than 1 and the value of net energy gain was positive in the three production modes, in which the maximum value appeared in the circular economy mode (CEM). The environment emission mainly occurred to bioethanol conversion unit in the conventional production mode (CPM) and the cogeneration mode (CGM), and eutrophication potential (EP) and global warming potential (GWP) were the most significant environmental impact category. While compared with CPM and CGM, the environmental impact of CEM significantly declined due to increasing recycling, and plant cultivation unit mainly contributed to EP and GWP. And the comprehensive evaluation score of environmental impact decreased by 73.46% and 23.36%. This study showed that CEM was effective in improving energy efficiency, especially in reducing the environmental impact, and it provides a new method for bioethanol production.

Reducing future river export of nutrients to coastal waters of China in optimistic scenarios

Coastal waters of China are rich in nitrogen (N) and phosphorus (P) and thus often eutrophied. This is because rivers export increasing amounts of nutrients to coastal seas. Animal production and urbanization are important sources of nutrients in Chinese rivers. In this study we explored the future from an optimistic perspective. We present two optimistic scenarios for 2050 (OPT-1 and OPT-2) for China. Maximized recycling of manure on land in OPT-1 and OPT-2, and strict sewage control in OPT-2 (e.g., all sewage is collected and treated efficiently) are essential nutrient strategies in these scenarios. We also analyzed the effect of the current policy plans aiming at "Zero Growth in Synthetic Fertilizers after 2020" (the CP scenario). We used the MARINA (a Model to Assess River Inputs of Nutrients to seAs) model to quantify dissolved N and P export by Chinese rivers to the Bohai Gulf, Yellow Sea and South China Sea and the associated coastal eutrophication potential (ICEP). The Global Orchestration (GO) scenario of the Millennium Ecosystem Assessment was used as a basis. GO projects increases in river export of dissolved N and P (up to 90%) between 2000 and 2050 and thus a high potential for coastal eutrophication (ICEP>0). In contrast, the potential for coastal eutrophication is low in optimistic scenarios (ICEP<0). This is because in 2050 loads of most dissolved N and P in Chinese seas are around their levels of 1970. Maximizing manure recycling can reduce nutrient pollution of Chinese seas considerably. Sewage control is effective in reducing P export by rivers from urbanized areas. The CP scenario, on the other hand, shows that current policy plans may not be sufficient to avoid coastal eutrophication in the future. Our study may help policy makers in formulating strategies to ensure clean coastal waters in China in the future.

A Network Flow Analysis of the Nitrogen Metabolism in Beijing, China

Rapid urbanization results in high nitrogen flows and subsequent environmental consequences. In this study, we identified the main metabolic components (nitrogen inputs, flows, and outputs) and used ecological network analysis to track the direct and integral (direct + indirect) metabolic flows of nitrogen in Beijing, China, from 1996 to 2012 and to quantify the structure of Beijing's nitrogen metabolic processes. We found that Beijing's input of new reactive nitrogen (Q, which represents nitrogen obtained from the atmosphere or nitrogen-containing materials used in production and consumption to support human activities) increased from 431 Gg in 1996 to 507 Gg in 2012. Flows to the industry, atmosphere, and household, and components of the system were clearly largest, with total integrated inputs plus outputs from these nodes accounting for 31, 29, and 15%, respectively, of the total integral flows for all paths. The flows through the sewage treatment and transportation components showed marked growth, with total integrated inputs plus outputs increasing to 3.7 and 5.2 times their 1996 values, respectively. Our results can help policymakers to locate the key nodes and pathways in an urban nitrogen metabolic system so they can monitor and manage these components of the system.

The MARINA model (Model to Assess River Inputs of Nutrients to seAs): Model description and results for China

Chinese agriculture has been developing fast towards industrial food production systems that discharge nutrient-rich wastewater into rivers. As a result, nutrient export by rivers has been increasing, resulting in coastal water pollution. We developed a Model to Assess River Inputs of Nutrients to seAs (MARINA) for China. The MARINA Nutrient Model quantifies river export of nutrients by source at the sub-basin scale as a function of human activities on land. MARINA is a downscaled version for China of the Global NEWS-2 (Nutrient Export from WaterSheds) model with an improved approach for nutrient losses from animal production and population. We use the model to quantify dissolved inorganic and organic nitrogen (N) and phosphorus (P) export by six large rivers draining into the Bohai Gulf (Yellow, Hai, Liao), Yellow Sea (Yangtze, Huai) and South China Sea (Pearl) in 1970, 2000 and 2050. We addressed uncertainties in the MARINA Nutrient model. Between 1970 and 2000 river export of dissolved N and P increased by a factor of 2-8 depending on sea and nutrient form. Thus, the risk for coastal eutrophication increased. Direct losses of manure to rivers contribute to 60-78% of nutrient inputs to the Bohai Gulf and 20-74% of nutrient inputs to the other seas in 2000. Sewage is an important source of dissolved inorganic P, and synthetic fertilizers of dissolved inorganic N. Over half of the nutrients exported by the Yangtze and Pearl rivers originated from human activities in downstream and middlestream sub-basins. The Yellow River exported up to 70% of dissolved inorganic N and P from downstream sub-basins and of dissolved organic N and P from middlestream sub-basins. Rivers draining into the Bohai Gulf are drier, and thus transport fewer nutrients. For the future we calculate further increases in river export of nutrients. The MARINA Nutrient model quantifies the main sources of coastal water pollution for sub-basins. This information can contribute to formulation of effective management options to reduce nutrient pollution of Chinese seas in the future.

Nutrient Loads Flowing into Coastal Waters from the Main Rivers of China (2006-2012)

Based on monthly monitoring data of unfiltered water, the nutrient discharges of the eight main rivers flowing into the coastal waters of China were calculated from 2006 to 2012. In 2012, the total load of NH3-N (calculated in nitrogen), total nitrogen (TN, calculated in nitrogen) and total phosphorus (TP, calculated in phosphorus) was 5.1 × 10(5), 3.1 × 10(6) and 2.8 × 10(5) tons, respectively, while in 2006, the nutrient load was 7.4 × 10(5), 2.2 × 10(6) and 1.6 × 10(5) tons, respectively. The nutrient loading from the eight major rivers into the coastal waters peaked in summer and autumn, probably due to the large water discharge in the wet season. The Yangtze River was the largest riverine nutrient source for the coastal waters, contributing 48% of the NH3-N discharges, 66% of the TN discharges and 84% of the TP discharges of the eight major rivers in 2012. The East China Sea received the majority of the nutrient discharges, i.e. 50% of NH3-N (2.7 × 10(5) tons), 70% of TN (2.2 × 10(6) tons) and 87% of TP (2.5 × 10(5) tons) in 2012. The riverine discharge of TN into the Yellow Sea and Bohai Sea was lower than that from the direct atmospheric deposition, while for the East China Sea, the riverine TN input was larger.

Environmental sustainability of bioethanol produced from sweet sorghum stem on saline-alkali land

Life cycle assessment was conducted to evaluate the energy efficiency and environmental impacts of a bioethanol production system that uses sweet sorghum stem on saline-alkali land as feedstock. The system comprises a plant cultivation unit, a feedstock transport unit, and a bioethanol conversion unit, with 1000L of bioethanol as a functional unit. The net energy ratio is 3.84, and the net energy gain is 17.21MJ/L. Agrochemical production consumes 76.58% of the life cycle fossil energy. The category with the most significant impact on the environment is eutrophication, followed by acidification, fresh water aquatic ecotoxicity, human toxicity, and global warming. Allocation method, waste recycling approach, and soil salinity significantly influence the results. Using vinasse to produce pellet fuel for steam generation significantly improves energy efficiency and decreases negative environmental impacts. Promoting reasonable management practices to alleviate saline stress and increasing agrochemical utilization efficiency can further improve environmental sustainability.

Life-cycle phosphorus management of the crop production-consumption system in China, 1980-2012

Phosphorus (P) is an essential resource for agriculture and also a pollutant capable of causing eutrophication. The possibility of a future P scarcity and the requirement to improve the environment quality necessitate P management to increase the efficiency of P use. This study applied a substance flow analysis (SFA) to implement a P management procedure in a crop production-consumption (PMCPC) system model. This model determined the life-cycle P use efficiency (PUE) of the crop production-consumption system in China during 1980-2012. The system includes six subsystems: fertilizer manufacturing, crop cultivation, crop processing, livestock breeding, rural consumption, and urban consumption. Based on this model, the P flows and PUEs of the subsystems were identified and quantified using data from official statistical databases, published literature, questionnaires, and interviews. The results showed that the total PUE of the crop production-consumption system in China was low, notably from 1980 to 2005, and increased from 7.23% in 1980 to 20.13% in 2012. Except for fertilizer manufacturing, the PUEs of the six subsystems were also low. The PUEs in the urban consumption subsystem and the crop cultivation subsystem were less than 40%. The PUEs of other subsystems, such as the rural consumption subsystem and the livestock breeding subsystem, were also low and even decreased during these years. Measures aimed to improve P management practices in China have been proposed such as balancing fertilization, disposing livestock excrement, adjusting livestock feed, changing the diet of residents, and raising the waste disposal level, etc. This study also discussed several limitations related with the model and data. Conducting additional related studies on other regions and combining the analysis of risks with opportunities may be necessary to develop effective management strategies.

Increasing eutrophication in the coastal seas of China from 1970 to 2050

We analyzed the potential for eutrophication in major seas around China: the Bohai Gulf, Yellow Sea and South China Sea. We model the riverine inputs of nitrogen (N), phosphorus (P) and silica (Si) to coastal seas from 1970 to 2050. Between 1970 and 2000 dissolved N and P inputs to the three seas increased by a factor of 2-5. In contrast, inputs of particulate N and P and dissolved Si, decreased due to damming of rivers. Between 2000 and 2050, the total N and P inputs increase further by 30-200%. Sewage is the dominant source of dissolved N and P in the Bohai Gulf, while agriculture is the primary source in the other seas. In the future, the ratios of Si to N and P decrease, which increases the risk of harmful algal blooms. Sewage treatment may reduce this risk in the Bohai Gulf, and agricultural management in the other seas.

Energy efficiency and environmental performance of bioethanol production from sweet sorghum stem based on life cycle analysis

Life cycle analysis method was used to evaluate the energy efficiency and environmental performance of bioethanol production from sweet sorghum stem in China. The scope covers three units, including plant cultivation, feedstock transport, and bioethanol conversion. Results show that the net energy ratio was 1.56 and the net energy gain was 8.37 MJ/L. Human toxicity was identified as the most significant negative environmental impact, followed by eutrophication and acidification. Steam generation in the bioethanol conversion unit contributed 82.28% and 48.26% to total human toxicity and acidification potential, respectively. Fertilizers loss from farmland represented 67.23% of total eutrophication potential. The results were significantly affected by the inventory allocation methods, vinasse reusing approaches, and feedstock yields. Reusing vinasse as fuel for steam generation and better cultivation practice to control fertilizer loss could significantly contribute to enhance the energy efficiency and environmental performance of bioethanol production from sweet sorghum stem.

Environmental assessment of management options for nutrient flows in the food chain in China

The nitrogen (N) and phosphorus (P) costs of food production have increased greatly in China during the last 30 years, leading to eutrophication of surface waters, nitrate leaching to groundwater, and greenhouse gas emissions. Here, we present the results of scenario analyses in which possible changes in food production-consumption in China for the year 2030 were explored. Changes in food chain structure, improvements in technology and management, and combinations of these on food supply and environmental quality were analyzed with the NUFER model. In the business as usual scenario, N and P fertilizer consumption in 2030 will be driven by population growth and diet changes and will both increase by 25%. N and P losses will increase by 44 and 73%, respectively, relative to the reference year 2005. Scenarios with increased imports of animal products and feed instead of domestic production, and with changes in the human diet, indicate reductions in fertilizer consumption and N and P losses relative to the business as usual scenario. Implementation of a package of integrated nutrient management measures may roughly nullify the increases in losses in the business as usual scenario and may greatly increase the efficiency of N and P throughout the whole food chain.

Nitrogen and phosphorus use efficiencies in dairy production in china

Milk production has greatly increased in China recently, with significant impacts on the cycling of nitrogen (N) and phosphorus (P). However, nutrient flows within the changing dairy production system are not well quantified. The aim of this study was to increase the quantitative understanding of N and P cycling and utilization in dairy production through database development and simulation modeling. In 2010, of the entire 1987 and 346 thousand tons (Gg) of N and P input, only 188 Gg N and 31 Gg P ended up in milk. The average N and P use efficiencies were 24 and 25%, respectively, at the whole system level. Efficiencies differed significantly between the four dairy systems. Losses of N from these systems occurred via NH volatilization (33%), discharge (27%), denitrification (24%), NO leaching and runoff (16%), and NO emission (1%). Industrial feedlots use less feed per kg milk produced than traditional systems, and rely more on high-quality feed from fertilized cropland; they have very poor recycling of manure nutrients to cropland. As industrial feedlot systems are booming, overall mean N and P use efficiencies will increase at herd level but will decrease at the whole dairy production system level unless manure N and P are used more efficiently through reconnecting China's feed and dairy production sectors.

The driving forces for nitrogen and phosphorus flows in the food chain of china, 1980 to 2010

Nitrogen (N) and phosphorus (P) use and losses in China's food chain have accelerated in the past three decades, driven by population growth, rapid urbanization, dietary transition, and changing nutrient management practice. There has been little detailed quantitative analysis of the relative magnitude of these driving forces throughout this period. Therefore, we analyzed changes in N and P flows and key drivers behind changes in the food (production and consumption) chain at the national scale from 1980 to 2010. Food (N and P) consumption increased by about fivefold in urban settings over this period but has decreased in rural settings since the 1990s. For urban settings, the integrated driving forces for increased food consumption were population growth, which accounted for ∼60%, and changing urban diets toward a greater emphasis on the consumption of animal products. Nutrient inputs and losses in crop and animal productions have continuously increased from 1980 to 2010, but the rates of decadal increase were greatly different. Increased total inputs and losses in crop production were primarily driven by increased crop production for food demand (68-96%) in the 1980s but were likely offset in the 2000s by improved nutrient management practices, as evidenced by decreased total inputs to and losses from cropland for harvesting per nutrient in crop. The contributions of animal production to total N and P losses to waters from the food chain increased by 34 and 60% from 1980 to 2010. These increases were caused mainly by decreased ratios of manure returned to cropland. Our study highlights a larger impact of changing nutrient management practice than population growth on elevated nutrient flows in China's food chain.

An analysis of developments and challenges in nutrient management in china

During the past 50 years, China has successfully realized food self-sufficiency for its rapidly growing population. Currently, it feeds 22% of the global population with 9% of the global area of arable land. However, these achievements were made at high external resource use and environmental costs. The challenge facing China is to further increase food production while drastically decreasing the environmental costs of food production. Here we review the major developments in nutrient management in China over the last 50 years. We briefly analyze the current organizational structure of the "advisory system" in agriculture, the developments in nutrient management for crop production, and the developments in nutrient management in animal production. We then discuss the nutrient management challenges for the next decades, considering nutrient management in the whole chain of crop production-animal production-food processing-food consumption by households. We argue that more coherent national policies and institutional structures are required for research extension education to be able to address the immense challenges ahead. Key actions include nutrient management in the whole food chain concomitant with a shift in objectives from food security only to food security, resource use efficiency, and environmental sustainability; improved animal waste management based on coupled animal production and crop production systems; and much greater emphasis on technology transfer from science to practice through education, training, demonstration, and extension services.

The mixotrophic nature of photosynthetic plants

Plants typically have photosynthetically competent green shoots. To complement resources derived from the atmospheric environment, plants also acquire essential elements from soil. Inorganic ions and molecules are generally considered to be the sources of soil-derived nutrients, and plants tested in this respect can grow with only inorganic nutrients and so can live as autotrophs. However, mycorrhizal symbionts are known to access nutrients from organic matter. Furthermore, specialist lineages of terrestrial photosynthetically competent plants are mixotrophic, including species that obtain organic nutrition from animal prey (carnivores), fungal partners (mycoheterotrophs) or plant hosts (hemi-parasites). Although mixotrophy is deemed the exception in terrestrial plants, it is a common mode of nutrition in aquatic algae. There is mounting evidence that non-specialist plants acquire organic compounds as sources of nutrients, taking up and metabolising a range of organic monomers, oligomers, polymers and even microbes as sources of nitrogen and phosphorus. Plasma-membrane located transporter proteins facilitate the uptake of low-molecular mass organic compounds, endo- and phagocytosis may enable the acquisition of larger compounds, although this has not been confirmed. Identifying the mechanisms involved in the acquisition of organic nutrients will provide understanding of the ecological significance of mixotrophy. Here, we discuss mixotrophy in the context of nitrogen and phosphorus nutrition drawing parallels between algae and plants.

Long-term soil nutrient dynamics comparison under smallholding land and farmland policy in northeast of China

There are two kinds of land policies, the smallholding land policy (SLP) and the farmland policy (FLP) in China. The farmland nutrient dynamics under the two land policies were analysed with the soil system budget method. The averaged nitrogen (N) input of the SLP and the FLP over sixteen years increased about 23.9% and 33.3%, respectively and the phosphorus (P) input climbed about 39.1% and 42.3%, respectively. The statistical analysis showed that the land policies had significant impacts on N and P input from fertilizer and manure, but did not obviously affect the N input from seeds and biological N fixation. The efficiency percentage of N of the SLP and the FLP climbed about 54.5% and 59.4%, respectively, and the P efficiency improved by 52.7% and 82.6%, respectively. About the nutrient output, the F-test analysis indicated that the land polices had remarkable impacts on N output by crop uptake, ammonia volatilisation, denitrification, leaching and runoff, and P output by uptake, runoff, and leach. The balance showed that the absolute loss of N from land deceased about 43.6% and 46.0%, respectively, in the SLP and the FLP, and P discharge reduced about 34.2% and 75.2%, respectively. The F-test analysis of N and P efficiency and balance of between two polices both indicated that the FLP had significant impact on nutrient dynamic. With the Mitscherlich model, the correlations between nutrient input and crop uptake, usage efficiency and loss were analysed and showed that was a threshold value for the optimal nutrient input with the highest efficiency rate. For the optimal nutrient efficiency, the space for extra P addition was bigger than the N input. The FLP have more advantage than the SLP on the crop yield, nutrient efficiency and environmental discharge.

Climate change and coupling of macronutrient cycles along the atmospheric, terrestrial, freshwater and estuarine continuum

This paper provides an introduction to the Special Issue on "Climate Change and Coupling of Macronutrient Cycles along the Atmospheric, Terrestrial, Freshwater and Estuarine Continuum", dedicated to Colin Neal on his retirement. It is not intended to be a review of this vast subject, but an attempt to synthesize some of the major findings from the 22 contributions to the Special Issue in the context of what is already known. The major research challenges involved in understanding coupled macronutrient cycles in these environmental media are highlighted, and the difficulties of making credible predictions of the effects of climate change are discussed. Of particular concern is the possibility of interactions which will enhance greenhouse gas concentrations and provide positive feedback to global warming.