Comparison of land nitrogen budgets for European agriculture by various modeling approaches

Regional nitrogen budgets of agricultural production systems in Austria constrained by natural boundary conditions

Nitrogen (N) budgets are valuable tools to increase the understanding of causalities between agricultural production and N emissions to support agri-environmental policy instruments. However, regional agricultural N budgets for an entire country covering all major N flows across sectors and environmental compartments, which also distinguish between different N forms, are largely lacking. This study comprehensively analyses regional differences in N budgets pertainting to agricultural production and consumption in the largely alpine and spatially heterogeneous country of Austria. A special focus is on the interconnections between regional agricultural production systems, N emissions, nitrogen use efficiencies (NUE), and natural boundary conditions. Seven regional and one national balance are undertaken via material flow analysis and are analysed with regards to losses into soils, water bodies and atmosphere. Further, NUE is calculated for two conceptual systems of plant and plant-livestock production. The results reveal major differences among regions, with significant implications for agri-environmental management. The high-alpine region, characterized by alpine pastures with a low livestock density, shows consequent low N inputs, the lowest area-specific N outputs and the most inefficient NUE. In contrast, the highest NUE is achieved in a lowland region specialized in arable farming with a low livestock density and a predominance of mineral fertilizer over manure application. In this region, the N surplus is almost as low as in the high-alpine region due to both significantly higher N inputs and outputs compared to the high-alpine region. Nevertheless, due to low precipitation levels, widespread exceedances of the nitrate target level concentration take place in the groundwater. The same issue arises in another non-alpine region characterized by arable farming and high livestock densities. Here, the highest N inputs, primarily via manure, result in the highest N surplus and related nitrate groundwater exceedances despite an acceptable NUE. These examples show that NUE alone is an insufficient target and that adapted criteria are needed for different regions to consider natural constraints and specific framework conditions. In a geographically heterogeneous country like Austria, the regional circumstances strongly define and limit the scope and the potential effectiveness of agricultural N management strategies. These aspects should be integrated into the design, assessment and implementation of agri-environmental programmes.

Mitigating environmental impacts using net energy system in feed formulation in China's pig production

As the world's largest pork producer, China is facing substantial environmental pressures caused by pig production and the relevant feed production. The net energy (NE) system is promoted as a new evaluation method to evaluate energy content in feed and energy requirements of pigs, but its application lacks of comprehensive and comparative evaluation from the environmental perspective. To identify influence factors and to develop mitigation strategies, the carbon and nitrogen footprints and land use (LU) of pigs (25-120 kg) in China were explored through scenario analysis and cradle-to-farm gate life cycle assessment (LCA). Functional unit (FU) was defined as 1 kg of live weight increase in pig. Among all the procedures of pig production, feed crop production and manure management were the principal contributors to the greenhouse gas (GHG) and nitrogen emissions. As for the carbon footprint, the GHG emissions ranged from 2.37 to 2.55 kg CO₂-eq. FU^-1 for scenarios using the NE system, 2 % lower than that of the metabolizable energy (ME) system. Cottonseed meal-based scenario generated the lowest GHG emissions, and anaerobic digestion achieved the same effects as other manure management methods. As for the nitrogen footprint, reactive nitrogen (Nr) emissions ranged from 53.4 to 66.2 g Nr FU^-1 for scenarios using the NE system, 4 % lower than that of the ME system. Peanut-based scenario won the lowest Nr losses. Moreover, arable LU ranged from 4.63 to 5.85 m² FU^-1 for scenarios using the NE system, 4 % lower than that of the ME system, and economic advantage by using the NE system was also proved. Sensitivity analysis and data quality assessment were conducted to quantify the uncertainties of the above models. In conclusion, the application of the NE system in feed formulation was an effective strategy to improve the environmental sustainability of China's pig production.

Micro-fractionation shows microbial community changes in soil particles below 20 μm

Introduction

Micro-scale analysis of microbes in soil is essential to the overall understanding of microbial organization, interactions, and ecosystem functioning. Soil fractionation according to its aggregated structure has been used to access microbial habitats. While bacterial communities have been extensively described, little is known about the fungal communities at scales relevant to microbial interactions.

Methods

We applied a gentle soil fractionation method to preserve stable aggregated structures within the range of micro-aggregates and studied fungal and bacterial communities as well as nitrogen cycling potentials in the pristine Rothamsted Park Grass soil (bulk soil) as well as in its particle size fractions (PSFs; >250 μm, 250–63 μm, 63–20 μm, 20–2 μm, <2 μm, and supernatant).

Results

Overall bacterial and fungal community structures changed in PSFs below 20 μm. The relative abundance of Basidiomycota decreased with decreasing particle size over the entire measure range, while Ascomycota showed an increase and Mucoromycota became more prominent in particles below 20 μm. Bacterial diversity was found highest in the < 2 μm fraction, but only a few taxa were washed-off during the procedure and found in supernatant samples. These taxa have been associated with exopolysaccharide production and biofilm formation (e.g., Pseudomonas, Massilia, Mucilaginibacter, Edaphobaculum, Duganella, Janthinobacterium, and Variovorax). The potential for nitrogen reduction was found elevated in bigger aggregates.

Discussion

The observed changes below 20 μm particle are in line with scales where microbes operate and interact, highlighting the potential to focus on little researched sub-fractions of micro-aggregates. The applied method shows potential for use in studies focusing on the role of microbial biofilms in soil and might also be adapted to research various other soil microbial functions. Technical advances in combination with micro-sampling methods in soil promise valuable output in soil studies when particles below 20 μm are included.

From planetary to regional boundaries for agricultural nitrogen pollution

Excessive agricultural nitrogen use causes environmental problems globally¹, to an extent that it has been suggested that a safe planetary boundary has been exceeded². Earlier estimates for the planetary nitrogen boundary^3,4, however, did not account for the spatial variability in both ecosystems' sensitivity to nitrogen pollution and agricultural nitrogen losses. Here we use a spatially explicit model to establish regional boundaries for agricultural nitrogen surplus from thresholds for eutrophication of terrestrial and aquatic ecosystems and nitrate in groundwater. We estimate regional boundaries for agricultural nitrogen pollution and find both overuse and room for intensification of agricultural nitrogen. The aggregated global surplus boundary with respect to all thresholds is 43 megatonnes of nitrogen per year, which is 64 per cent lower than the current (2010) nitrogen surplus (119 megatonnes of nitrogen per year). Allowing the nitrogen surplus to increase to close yield gaps in regions where environmental thresholds are not exceeded lifts the planetary nitrogen boundary to 57 megatonnes of nitrogen per year. Feeding the world without trespassing regional and planetary nitrogen boundaries requires large increases in nitrogen use efficiencies accompanied by mitigation of non-agricultural nitrogen sources such as sewage water. This asks for coordinated action that recognizes the heterogeneity of agricultural systems, non-agricultural nitrogen losses and environmental vulnerabilities.

A broad-scale spatial analysis of the environmental benefits of fertiliser closed periods implemented under the Nitrates Directive in Europe

Nutrient pollution from agriculture has been an ongoing challenge for decades, contributing to numerous negative environmental impacts. In the European Union policies have been developed to address nutrient pollution, including Nitrate Action Programmes under Council Directive 91/676/EEC. Although Member States report on progress on implementation, there have been few studies that explore how measures have been implemented; the environmental implications of any differences; and how they vary spatially on a European scale. This study aims to address this gap with respect to fertiliser closed periods (1155 different closed periods across 69 Nitrate Action Programmes). This included the development of an approach that can be applied using readily available spatial data. Each closed period was scored for its coverage of risk periods for losses of nitrate; organic material; nitrous oxide and ammonia. Closed periods were then matched to relevant combinations of spatial data for each environmental zone and fertiliser type. The scores for each combination were used to create maps and calculate spatial statistics. The results show that in addition to nitrate, closed periods also reduce the risk of organic material run-off, emissions of nitrous oxide and to a lesser extent ammonia. However, risk reduction is spatially variable across all the impacts and the scope for synergy is also variable (e.g. nitrate loss does not always correlate with nitrous oxide or ammonia risk reduction). Regions in the Atlantic, Lustanian and some areas within the Mediterranean zones appear to provide the greatest combined risk reduction, with other zones, especially in eastern Europe, having a lower combined risk reduction (due to a combination of different risk periods coupled with lower coverage of individual risks). The spatial analysis within this study is relatively simple; is based on a snapshot of closed periods during 2019-2020; and only explores one measure. However, it does provide some useful data and insights that could support policy development in the future. This includes scope for Member States and regions to learn from others where greater coverage of risk periods has been achieved; and highlighting how a more holistic perspective can be taken to the environmental management of nutrients. As we strive towards developing sustainable production systems, farmers and policy makers need to take a more integrated approach to incorporate additional environmental objectives; which increases the complexity of the challenge. Consequently, the demand for pragmatic approaches that take a more holistic approach is likely to increase in the future.

Spatially explicit boundaries for agricultural nitrogen inputs in the European Union to meet air and water quality targets

Agricultural production in the EU has increased strongly since the 1940s, partly driven by increased nitrogen (N) fertiliser and manure inputs. Increased N inputs and associated losses, however, adversely affect air and water quality, with widespread impacts on terrestrial and aquatic ecosystems and human health. Managing these impacts requires knowledge on 'safe boundaries' for N inputs, i.e., N flows that do not exceed environmental thresholds. We used a spatially explicit N balance model for the EU to derive boundaries for N losses and associated N inputs for three environmental thresholds: (i) N deposition onto natural areas to protect terrestrial biodiversity (critical N loads), (ii) N concentration in runoff to surface water (2.5 mg N l^-1) to protect aquatic ecosystems and (iii) nitrate (NO₃^-) concentration in leachate to groundwater (50 mg NO l^-1) to meet the EU drinking water standard. Critical N losses and inputs were calculated for ~40,000 unique soil-slope-climate combinations and then aggregated at country- and EU-level. To respect thresholds for N deposition, N inputs in the EU need to be reduced by 31% on average, ranging from 0% in several countries to 59% in Ireland and Denmark. The strongest reductions are required in intensive livestock regions, such as Benelux, Brittany and the Po valley. To respect thresholds for N concentration in runoff to surface water, N inputs need to be reduced by 43% on average, ranging from 2% in Estonia to 74% in the Netherlands. Average critical N inputs in view of the threshold for NO₃^- concentration in leachate to groundwater are close to actual (year 2010) inputs, even though leaching thresholds are exceeded in 18% of agricultural land. Critical N inputs and their exceedances presented in this paper can inform more targeted mitigation policies than flat-rate targets for N loss reductions currently mentioned in EU policies.

Reconciling regional nitrogen boundaries with global food security

While nitrogen inputs are crucial to agricultural production, excess nitrogen contributes to serious ecosystem damage and water pollution. Here, we investigate this trade-off using an integrated modelling framework. We quantify how different nitrogen mitigation options contribute to reconciling food security and compliance with regional nitrogen surplus boundaries. We find that even when respecting regional nitrogen surplus boundaries, hunger could be substantially alleviated with 590 million fewer people at risk of hunger from 2010 to 2050, if all nitrogen mitigation options were mobilized simultaneously. Our scenario experiments indicate that when introducing regional N targets, supply-side measures such as the nitrogen use efficiency improvement are more important than demand-side efforts for food security. International trade plays a key role in sustaining global food security under nitrogen boundary constraints if only a limited set of mitigation options is deployed. Policies that respect regional nitrogen surplus boundaries would yield a substantial reduction in non-CO₂ GHG emissions of 2.3 GtCO₂e yr^-1 in 2050, which indicates a necessity for policy coordination.

Development of a groundwater contamination index based on the agricultural hazard and aquifer vulnerability: Application to Portugal

Reducing nitrate leaching may not result in a significant improvement of groundwater quality. The amount of nitrate reaching groundwater depends not only on the hazard related to agricultural activities but also on-site specific groundwater vulnerability. Using national databases and other compiled datasets, the agricultural hazard was calculated as the ratio of (i) the nitrate leached estimated from the N surplus, and (ii) the water surplus, a proxy of the percolating water below the root zone. By combining the hazard with a multi-parameter groundwater vulnerability, a spatially explicit groundwater contamination risk, developed for mainland Portugal, was computed for 1999 and 2009. Results show an increase from 8,800 to 82,679 ha of the territory rated with a very high contamination risk. The priority areas were successfully screened by the Index, coinciding with the current Vulnerable Zones, although additional hotspots were detected in southern Portugal. Percolation, including both irrigation activity and precipitation, was found to be a key driver for the groundwater contamination risk due to its opposite effects in the hazard and in the vulnerability. Reducing nitrogen leaching may be insufficient to reduce the risk of nitrate contamination if there is a relatively larger reduction in precipitation. This index is particularly useful when applied to contrasting situations of vulnerability and hazard, which require distinct mitigation measures to mitigate groundwater contamination.

Bioenergy Potential and Greenhouse Gas Emissions from Intensifying European Temporary Grasslands

Agricultural intensification is considered essential for meeting growing demand for food and biomass for energy purposes. Intensifying grasslands is under-represented, although it is a promising option given their large land area and relatively low management levels. This study quantifies the bioenergy potential from intensifying temporary grasslands in Europe and the integral greenhouse gas emission effects in 2030. We first conducted a literature review of intensification options for European grasslands and then applied the environmental impact assessment model MITERRA-Europe to implement the key intensification option of using multi-species grass mixtures. The results showed that 853 kha (or 8%) of temporary grassland could be made sustainably available for additional biomass production. This can be translated into a bioethanol potential of 23 PJ yr−1 and an emission mitigation potential of 5.8 Mt CO2-eq yr−1 (if conventional grass mixture from surplus temporary grassland is used for energy) or 72 PJ yr−1 and 4.0 Mt CO2-eq yr−1 (if surplus temporary grassland is used for grassy energy crops). Although the bioenergy potential is limited, the key advantage of intensification measure is that it results in a better environmental performance of temporary grasslands. This makes it a key option for sustainably producing bioenergy in areas with high shares of temporary grasslands.

Soil N2O emissions, N leaching and marine eutrophication in life cycle assessment - A comparison of modelling approaches

Nitrogen fertilisation is an essential part of modern agriculture, providing food for a growing human population, but also causing environmental impacts when reactive nitrogen (N) is released to the environment. The amount and impact of these emissions are difficult to quantify in life cycle assessment (LCA), due to their site-dependent nature. This study compared seven models for direct soil nitrous oxide (N₂O) emissions, seven models for N leaching and five characterisation models for marine eutrophication impact assessment, selected to represent medium-effort options for accounting for spatial variation in emissions and impact assessment. In a case study, the models were applied to wheat cultivation at two Swedish sites to estimate climate and marine eutrophication impact. Direct N₂O emissions estimated by the models varied by up to five-fold at one of the sites and contributed 21-56% of the total climate impact. Site-dependent models gave both lower and higher N₂O emissions estimates than the site-generic Tier 1 model from the Intergovernmental Panel on Climate Change (IPCC). Estimated N leaching also varied by up to fivefold at one of the sites and contributed 47-93% of the total eutrophication potential, depending on model choice. All site-dependent models estimated lower N leaching than the site-generic IPCC Tier 1 model. Marine eutrophication impact estimates varied by almost an order of magnitude depending on characterisation model choice. The large variation between models found in this study highlights the importance of model choice for N emissions and marine eutrophication impact assessment in LCA of crop cultivation. Due to the divergence of model outcomes and different limitations of some of the models, no general recommendations on choosing soil N₂O emissions model, N leaching model or characterisation model for marine eutrophication could be given.

In Search for the Missing Nitrogen: Closing the Budget to Assess the Role of Denitrification in Agricultural Watersheds

Although representing a paramount mechanism against nitrogen excess in agricultural landscapes, soil denitrification is still a largely unknown term in nitrogen balances at the watershed scale. In the present work, a comprehensive investigation of nitrogen sources and sinks in agricultural soils and waters was performed with the aim of gaining insights into the relevance of soil denitrification in a highly farmed sub-basin of the Po River delta (Northern Italy). Agricultural statistics, water quality datasets, and results of laboratory experiments targeting nitrogen fluxes in soils were combined to set up a detailed nitrogen budget along the terrestrial–freshwater continuum. The soil nitrogen budget was not closed, with inputs exceeding outputs by 72 kg N·ha−1·year−1, highlighting a potential high risk of nitrate contamination. However, extensive monitoring showed a general scarcity of mineral nitrogen forms in both shallow aquifers and soils. The present study confirmed the importance of denitrification, representing ~37% of the total nitrogen inputs, as the leading process of nitrate removal in heavily fertilized fine-texture soils prone to waterlogged conditions.

Is Flood Irrigation a Potential Driver of River-Groundwater Interactions and Diffuse Nitrate Pollution in Agricultural Watersheds?

In the Po plain, northern Italy, rivers within agricultural basins display steep summer increases in nitrate (NO3−) concentrations. Flood irrigation in overfertilized, permeable soils may drive such diffuse pollution, facilitating interactions between NO3−-rich groundwater and surface waters. We discuss multiple, indirect evidence of this mechanism in the Adda, Oglio, and Mincio rivers. These rivers drain agricultural soils with elevated nitrogen (N) surpluses, averaging 139, 193, and 136 kg ha−1 in the Adda, Oglio, and Mincio watersheds, respectively. The three rivers cross a transitional area between highly permeable and impermeable soils, where summer NO3− concentrations may increase by one order of magnitude over short distances (8–20 km). Upstream of this transitional area, a major fraction of the river flow is diverted for flood irrigation, a traditional and widespread irrigation technique for permeable soils. We speculate that diverted water solubilizes soil N excess, recharges the aquifer, and transfers soil N surplus into groundwater, resulting in NO3− pollution. Groundwater–river interactions were estimated experimentally, via water and NO3− budgets in 0.3 to 1 m3 s−1 km−1 and in 1500 to 5400 kg NO3−–N day−1. The data suggest a pronounced east–west gradient of groundwater to river diffuse water inputs among the three adjacent basins, reflecting the soil permeability and the width of the river–groundwater interaction zone. Given the large stock of NO3− in groundwater, management interventions performed at the basin scale and aimed at decreasing N excess will not produce an immediate decrease in river NO3− pollution.

Multidisciplinary approaches for studying rhizobium–legume symbioses

The rhizobium–legume symbiosis is a major source of fixed nitrogen (ammonia) in the biosphere. The potential for this process to increase agricultural yield while reducing the reliance on nitrogen-based fertilizers has generated interest in understanding and manipulating this process. For decades, rhizobium research has benefited from the use of leading techniques from a very broad set of fields, including population genetics, molecular genetics, genomics, and systems biology. In this review, we summarize many of the research strategies that have been employed in the study of rhizobia and the unique knowledge gained from these diverse tools, with a focus on genome- and systems-level approaches. We then describe ongoing synthetic biology approaches aimed at improving existing symbioses or engineering completely new symbiotic interactions. The review concludes with our perspective of the future directions and challenges of the field, with an emphasis on how the application of a multidisciplinary approach and the development of new methods will be necessary to ensure successful biotechnological manipulation of the symbiosis.

A comparison of disaggregated nitrogen budgets for Danish agriculture using Europe-wide and national approaches

Spatially detailed information on agricultural nitrogen (N) budgets is relevant to identify regions where there is a need for a reduction in inputs in view of various forms of N pollution. However, at the scale of the European Union, there is a lack of consistent, reliable, high spatial resolution data necessary for the calculation of regional N losses. To gain insight in the reduction in uncertainty achieved by using higher spatial resolution input data. This was done by comparing spatially disaggregated agricultural N budgets for Denmark for the period 2000-2010, generated by two versions of the European scale model Integrator, a version using high spatial resolution national data for Denmark (Integrator-DK) and a version using available data at the EU scale (Integrator-EU). Results showed that the national N fluxes in the N budgets calculated by the two versions of the model were within 1-5% for N inputs by fertilizer and manure excretion, but inputs by N fixation and N mineralisation differed by 50-100% and N uptake also differed by ca 25%, causing a difference in N leaching and runoff of nearly 50%. Comparison with an independently derived Danish national budget appeared generally to be better with Integrator-EU results in 2000 but with Integrator-DK results in 2010. However, the spatial distribution of manure distribution and N losses from Integrator-DK were closer to observed distributions than those from Integrator-EU. We conclude that close attention to local agronomic practices is needed when using a leaching fraction approach and that for effective support of environmental policymaking, Member States need to collect or submit high spatial resolution agricultural data to Eurostat.

Size Fractionation of Dissolved Organic Nitrogen in Peatland Fluvial Systems

Understanding the nature and fate of nitrogen (N) in freshwater systems is crucial for assessing the risk of eutrophication. However, there is a paucity of information on the characterization of fluvial N in upland peat-dominated environments. Here, we employ a combination of field sampling and tangential flow ultrafiltration (TFU) to investigate the concentrations and fluxes of low molecular weight (LMW) and high molecular weight (HMW) dissolved organic N (DON) in a peatland stream-reservoir system in the south Pennines (UK). Our TFU results show that ∼26% of DON concentration is LMW DON and represents an estimated fluvial flux of 3.07 ± 22 kg N ha^-1 during the study period. Our mass balance results reveal that the reservoir retains 71% of LMW DON input, which accounts for ∼25% retention of bioavailable (dissolved inorganic N + LMW DON) N. Our study suggests that current understanding of inorganic N as the sole source of bioavailable N with eutrophic significance in upland freshwaters requires a reappraisal. Evaluation of ecosystem response to increased loading of N needs to include a consideration of LMW DON.

Organic market gardening around the Paris agglomeration: agro-environmental performance and capacity to meet urban requirements

Organic market gardening is often promoted by urban municipalities as a way to resource part of the food supply, creating new social links and protecting groundwater resources. The agronomical and environmental performance of six commercial organic market gardening farms supplying vegetables in Paris were evaluated and compared with other vegetable production systems. When expressed in terms of protein production, the yield of these systems appears rather low compared with the productive capacity of open-field organic cropping systems where vegetable production is inserted into rotation with other crops. Moreover, the requirement of producing infiltrated water meeting the drinking water standards seriously limits the allowable rate of fertilisation, thus limiting production. The data reported herein show that to supply the amount of vegetables required by the Paris agglomeration (12 million inhabitants) only by organic market gardening, 160,000-205,000 ha, i.e. 28-36 % of the agricultural area of the surrounding Ile-de-France region, would be required. We conclude that organic market gardening is only one of several other farming systems which can contribute to a re-localised supply of vegetables to large cities.

Precrop Functional Group Identity Affects Yield of Winter Barley but Less so High Carbon Amendments in a Mesocosm Experiment

Nitrate leaching is a pressing environmental problem in intensive agriculture. Especially after the crop harvest, leaching risk is greatest due to decomposing plant residues, and low plant nutrient uptake and evapotranspiration. The specific crop also matters: grain legumes and canola commonly result in more leftover N than the following winter crop can take up before spring. Addition of a high carbon amendment (HCA) could potentially immobilize N after harvest. We set up a 2-year mesocosm experiment to test the effects of N fertilization (40 or 160 kg N/ha), HCA addition (no HCA, wheat straw, or sawdust), and precrop plant functional group identity on winter barley yield and soil C/N ratio. Four spring precrops were sown before winter barley (white lupine, faba bean, spring canola, spring barley), which were selected based on a functional group approach (colonization by arbuscular mycorrhizal fungi [AMF] and/or N2-fixing bacteria). We also measured a subset of faba bean and spring barley for leaching over winter after harvest. As expected, N fertilization had the largest effect on winter barley yield, but precrop functional identity also significantly affected the outcome. The non-AMF precrops white lupine and canola had on average a positive effect on yield compared to the AMF precrops spring barley and faba bean under high N (23% increase). Under low N, we found only a small precrop effect. Sawdust significantly reduced the yield compared to the control or wheat straw under either N level. HCAs reduced nitrate leaching over winter, but only when faba bean was sown as a precrop. In our setup, short-term immobilization of N by HCA addition after harvest seems difficult to achieve. However, other effects such as an increase in SOM or nutrient retention could play a positive role in the long term. Contrary to the commonly found positive effect of AMF colonization, winter barley showed a greater yield when it followed a non-AMF precrop under high fertilization. This could be due to shifts of the agricultural AMF community toward parasitism.

Complementing the topsoil information of the Land Use/Land Cover Area Frame Survey (LUCAS) with modelled N2O emissions

Two objectives of the Common Agricultural Policy post-2013 (CAP, 2014-2020) in the European Union (EU) are the sustainable management of natural resources and climate smart agriculture. To understand the CAP impact on these priorities, the Land Use/Cover statistical Area frame Survey (LUCAS) employs direct field observations and soil sub-sampling across the EU. While a huge amount of information can be retrieved from LUCAS points for monitoring the environmental status of agroecosystems and assessing soil carbon sequestration, a fundamental aspect relating to climate change action is missing, namely nitrous oxide (N2O) soil emissions. To fill this gap, we ran the DayCent biogeochemistry model for more than 11'000 LUCAS sampling points under agricultural use, assessing also the model uncertainty. The results showed that current annual N2O emissions followed a skewed distribution with a mean and median values of 2.27 and 1.71 kg N ha-1 yr-1, respectively. Using a Random Forest regression for upscaling the modelled results to the EU level, we estimated direct soil emissions of N2O in the range of 171-195 Tg yr-1 of CO2eq. Moreover, the direct regional upscaling using modelled N2O emissions in LUCAS points was on average 0.95 Mg yr-1 of CO2eq. per hectare, which was within the range of the meta-model upscaling (0.92-1.05 Mg ha-1 yr-1 of CO2eq). We concluded that, if information on management practices would be made available and model bias further reduced by N2O flux measurement at representative LUCAS points, the combination of the land use/soil survey with a well calibrated biogeochemistry model may become a reference tool to support agricultural, environmental and climate policies.

Precipitation Dominates Interannual Variability of Riverine Nitrogen Loading across the Continental United States

Excessive nitrogen loading to waterways leads to increased eutrophication and associated water quality impacts. An understanding of the regional and interannual variability in nitrogen loading and associated drivers is necessary for the design of effective management strategies. Here we develop a parsimonious empirical model based on net anthropogenic nitrogen input, precipitation, and land use that explains 68% of the observed variability in annual total nitrogen flux (Q_TN) (76% of ln(Q_TN)) across 242 catchment years. We use this model to present the first spatially and temporally resolved estimates of Q_TN for all eight-digit hydrologic unit (HUC8) watersheds within the continental United States (CONUS), focusing on the period 1987-2007. Results reveal high spatial and temporal variability in loading, with spatial variability primarily driven by nitrogen inputs, but with interannual variability and the occurrence of extremes dominated by precipitation across over three-quarters of the CONUS. High interannual variability and its correlation with precipitation persist at large aggregated scales. These findings point to a fundamental challenge in managing regions with high nutrient loading, because these regions also exhibit the strongest interannual variability and because the impact of changes in management practices will be modulated by meteorological variability and climatic trends.

Used water and nutrients: Recovery perspectives in a 'panta rhei' context

There is an urgent need to secure global supplies in safe water and proteinaceous food in an eco-sustainable manner, as manifested from tensions in the nexus Nutrients-Energy-Water-Environment-Land. This paper is concept based and provides solutions based on resource recovery from municipal and industrial wastewater and from manure. A set of decisive factors is reviewed facilitating an attractive business case. Our key message is that a robust barrier must clear the recovered product from its original status. Besides refined inorganic fertilizers, a central role for five types of microbial protein is proposed. A resource cycling solution for the extremely confined environment of space habitation should serve as an incentive to assimilate a new user mindset. To achieve the ambitious goal of sustainable food security, the solutions suggested here need a broad implementation, hand in hand with minimizing losses along the entire fertilizer-feed-food-fork chain.

Budgeting of major nutrients and the mitigation options for nutrient mining in semi-arid tropical agro-ecosystem of Tamil Nadu, India using NUTMON model

Mining of nutrients from soil is a major problem in developing countries causing soil degradation and threaten long-term food production. The present study attempts to apply NUTrient MONitoring (NUTMON) model for carrying out nutrient budgeting to assess the stocks and flows of nitrogen (N), phosphorus (P), and potassium (K) in defined geographical unit based on the inputs, viz., mineral fertilizers, manures, atmospheric deposition, and sedimentation, and outputs, viz., harvested crop produces, residues, leaching, denitrification, and erosion losses. The study area covers Coimbatore and Erode Districts, which are potential agricultural areas in western agro-ecological zone of Tamil Nadu, India. The calculated nutrient balances for both the districts at district scale, using NUTMON methodology, were negative for nitrogen (N -3.3 and -10.1 kg ha(-1)) and potassium (K -58.6 and -9.8 kg ha(-1)) and positive for phosphorus (P +14.5 and 20.5 kg ha(-1)). Soil nutrient pool has to adjust the negative balance of N and K; there will be an expected mining of nutrient from the soil reserve. A strategy was attempted for deriving the fertilizer recommendation using Decision Support System for Integrated Fertilizer Recommendation (DSSIFER) to offset the mining in selected farms. The results showed that when DSSIFER recommended fertilizers are applied to crops, the nutrient balance was positive. NUTMON-Toolbox with DSSIFER would serve the purpose on enhancing soil fertility, productivity, and sustainability. The management options to mitigate nutrient mining with an integrated system approach are also discussed.

Lichens as a useful mapping tool?--an approach to assess atmospheric N loads in Germany by total N content and stable isotope signature

To assess whether nitrogen (N) content and δ(15)N ratios in nitrophytic lichen species (Xanthoria parietina (L.) Th. Fr. (1860) and Physcia spp. (Schreb.) Michaux (1803)) reflect the quantity and quality of atmospheric N loads, 348 lichen samples from 174 sampling grid cells were investigated in the western part of Germany. The analysed lichen N content ranged between 0.98 and 4.28 % and δ(15)N ratios between -15.2 and -1.3 ‰. Based on the N concentrations and the δ(15)N ratios of lichens, different landscape categories and coupled N deposition rates could be inferred for different regions of Germany. By analysing environmental variables like altitude, ammonia emission density, livestock unit and different defined deposition types, a direct relationship was found between lichen chemistry and N compounds produced from agricultural activity. The results support the development of a monitoring method which could be used nationally or even internationally to support current N deposition measurements, by providing reliable information on the quantity and quality of N deposition in high N environments.

Influence of the temporal and spatial variation of nitrate reductase, glutamine synthetase and soil composition in the N species content in lettuce (Lactuca sativa)

The variation of nitrate reductase (NR), glutamine synthetase (GS) and N content in lettuce was evaluated at 5 stages of lettuce growth. Soil physicochemical properties and its N content were also assessed to elucidate the soil-to-plant transfer of inorganic N and potential leaching to groundwater. A decrease of NR activity and an increase of NO3(-) and N-Kjeldahl content in lettuces were observed during plant growth, whereas GS activity and NH4(+) increased during the first few weeks of lettuce growth and then decreased. Although the temporal variation was similar in lettuces grown in different soils, quantitative differences were observed, indicating that high NO3(-) content in soil caused a higher NO3(-) accumulation in lettuce despite the higher NR activity during the initial stage of plant growth. Higher levels of NO3(-) and NH4(+) were correlated with higher levels of N-Kjeldahl in lettuce suggesting a positive effect of these N species in the biosynthesis of organic forms of N. Soil physicochemical properties influenced the mobility of inorganic N within the groundwater-soil-plant system. Sandy soils with low OM content allowed NO3(-) leaching, which was confirmed by higher NO3(-) levels in groundwater. Therefore, lettuces grown in those soils presented lower N content and the inputs of N to the environment were higher.

Towards a climate-dependent paradigm of ammonia emission and deposition

Existing descriptions of bi-directional ammonia (NH3) land-atmosphere exchange incorporate temperature and moisture controls, and are beginning to be used in regional chemical transport models. However, such models have typically applied simpler emission factors to upscale the main NH3 emission terms. While this approach has successfully simulated the main spatial patterns on local to global scales, it fails to address the environment- and climate-dependence of emissions. To handle these issues, we outline the basis for a new modelling paradigm where both NH3 emissions and deposition are calculated online according to diurnal, seasonal and spatial differences in meteorology. We show how measurements reveal a strong, but complex pattern of climatic dependence, which is increasingly being characterized using ground-based NH3 monitoring and satellite observations, while advances in process-based modelling are illustrated for agricultural and natural sources, including a global application for seabird colonies. A future architecture for NH3 emission-deposition modelling is proposed that integrates the spatio-temporal interactions, and provides the necessary foundation to assess the consequences of climate change. Based on available measurements, a first empirical estimate suggests that 5°C warming would increase emissions by 42 per cent (28-67%). Together with increased anthropogenic activity, global NH3 emissions may increase from 65 (45-85) Tg N in 2008 to reach 132 (89-179) Tg by 2100.

Spatial and temporal trend of Chinese manure nutrient pollution and assimilation capacity of cropland and grassland

Dynamics of livestock and poultry manure nutrient was analyzed at a provincial scale from 2002 to 2008. The nutrient capacity of 18 kinds of croplands and grasslands to assimilate nutrients was assessed in the same temporal-spatial scale. Manure nitrogen (N) had increased from 5.111 to 6.228 million tons (MT), while manure phosphorus (P) increased from 1.382 to 1.607 MT. Manure N and P share similar spatial patterns of yields, but proportion of specialized livestock husbandry and contribution of leading livestock categories (swine, cattle, cow, sheep, layer chicken, broiler chicken) were different. The nutrients generated from dominant seven provinces took more than about half of total manure N in China. After subtracting the chemical fertilizers, there were some manure nutrient capacities in western part of China. Risk analysis of manure nutrient pollution overload in eastern and southern parts of China was serious, which should restrict livestock's developments. Amount of chemical fertilizers applied should be reduced to make room for manure nutrients. For the sake of greenhouse effects, the emission of methane (CH4) and nitrous oxide (NO x ) emissions in China is serious for the global change, thus merits further statistics and studies. The spatial and temporal pattern of Chinese manure nutrient pollution from livestock and the assimilation capacity of cropland and grassland can provide useful information for policy development on Chinese soil environment and livestock.

The long-term impact of urbanization on nitrogen patterns and dynamics in Shanghai, China

Urbanization is an important process that alters the regional and global nitrogen biogeochemistry. In this study, we test how long-term urbanization (1952-2004) affects the nitrogen flows, emissions and drivers in the Greater Shanghai Area (GSA) based on the coupled human and natural systems (CHANS) approach. Results show that: (1) total nitrogen input to the GSA increased from 57.7 to 587.9 Gg N yr(-1) during the period 1952-2004, mainly attributing to fossil fuel combustion (43%), Haber-Bosch nitrogen fixation (31%), and food/feed import (26%); (2) per capita nitrogen input increased from 13.5 to 45.7 kg N yr(-1), while per gross domestic product (GDP) nitrogen input reduced from 22.2 to 0.9 g N per Chinese Yuan, decoupling of nitrogen with GDP; (3) emissions of reactive nitrogen to the environment transformed from agriculture dominated to industry and human living dominated, especially for air pollution. This study provides decision-makers a novel view of nitrogen management.

Integrated analysis of the effects of agricultural management on nitrogen fluxes at landscape scale

The integrated modelling system INITIATOR was applied to a landscape in the northern part of the Netherlands to assess current nitrogen fluxes to air and water and the impact of various agricultural measures on these fluxes, using spatially explicit input data on animal numbers, land use, agricultural management, meteorology and soil. Average model results on NH(3) deposition and N concentrations in surface water appear to be comparable to observations, but the deviation can be large at local scale, despite the use of high resolution data. Evaluated measures include: air scrubbers reducing NH(3) emissions from poultry and pig housing systems, low protein feeding, reduced fertilizer amounts and low-emission stables for cattle. Low protein feeding and restrictive fertilizer application had the largest effect on both N inputs and N losses, resulting in N deposition reductions on Natura 2000 sites of 10% and 12%, respectively.

Farm, land, and soil nitrogen budgets for agriculture in Europe calculated with CAPRI

We calculated farm, land, and soil N-budgets for countries in Europe and the EU27 as a whole using the agro-economic model CAPRI. For EU27, N-surplus is 55 kg N ha(-1) yr(-1) in a soil budget and 65 kg N(2)O-N ha(-1) yr(-1) and 67 kg N ha(-1) yr(-1) in land and farm budgets, respectively. NUE is 31% for the farm budget, 60% for the land budget and 63% for the soil budget. NS values are mainly related to the excretion (farm budget) and application (soil and land budget) of manure per hectare of total agricultural land. On the other hand, NUE is best explained by the specialization of the agricultural system toward animal production (farm NUE) or the share of imported feedstuff (soil NUE). Total N input, intensive farming, and the specialization to animal production are found to be the main drivers for a high NS and low NUE.