Search

This paper presents a review of the trends and geographic variation of impacts of reactive nitrogen (N) inputs on in Europe through impacts on air, soil and water quality. It illustrates those impacts, by assessing temporal and spatial variation in air, soil and water quality indicators and their exceedances of critical thresholds in view of impacts on human health, terrestrial and aquatic ecosystems, during 1990-2019. Trends are derived from regular inventory and monitoring data and from simulated trends in air quality using the EMEP model. Well quantified adverse impacts of increased N use are: (i) the effects on human health due to increased tropospheric concentrations of NO x and ozone, and N-induced increases in fine particulate matter, (ii) the contribution of N 2 O to climate change and stratospheric ozone depletion, (iii) the loss of plant and faunal diversity both in terrestrial and aquatic ecosystems via direct and soil mediated impacts, (iv) the acidification of forest soils, with impacts on tree forest nutrition, tree growth and tree vitality, and (v) the eutrophication of marine ecosystems, and associated biodiversity loss and occurrence of harmful algae blooms. Over the period 1990-2019, N inputs to agriculture stayed relatively constant, but the emissions of ammonia (NH 3) decreased by 27%, while emissions of nitrogen oxides (NO x) decreased by 57%. In response to those reductions, concentrations of NO x , and of N in particulate matter also declined, although less than 50%. In contrast, the reduction in NO x -induced ozone concentrations and ozone related indicators (AOT40, SOMO35 and POD) was much less (ca 15-20%). Exceedances of critical ozone concentrations for human health and of critical AOT40 and POD vales for vegetation reduced in a similar order of magnitude. Despite decreasing NH 3 emissions, NH 3 concentrations showed a slight and steady increase from 1995 onwards, due to the large reduction in SO x emissions. Nitrogen deposition and exceedances of critical N loads for terrestrial ecosystems decreased by ca 60%, but the area exceeding critical N loads only reduced by ca 10%. Unlike N, the area exceeding critical acid loads has declined by more than 90% due to high reduction in SO x and NO x emissions. Trends in nitrate (NO 3) concentrations in groundwater varied across Europe, but showed overall limited changes over the last two decades. However, N concentrations in surface water and the area exceeding critical levels in view of aquatic biodiversity has decreased and the same holds for N concentrations in coastal regions. Nevertheless, the eutrophication condition of coastal waters has overall not improved due to adverse impacts of elevated phosphorus inputs. Finally the negative impacts of N induced N 2 O emissions on climate are estimated to be outweighed by the positive effects of N induced CO 2 sequestration, mainly in forests, and this holds for the whole period 1990-2019. Nitrogen hotspots, being areas with high exceedances in critical levels and loads of N compounds in air and water, are concentrated in intensive agricultural areas with high livestock densities and in urban region with strong industrial and traffic activities. Cost-benefit analysis shows that environmental costs of reactive N release to the environment are substantial and tend to exceed the direct economic benefits for agriculture. Given the relevance of N for safeguarding food production it is key to develop integrated and targeted plant nutrition strategies following a food system approach and practices that minimize trade-offs between productivity and the environment. In addition, targeted strategies to further reduce NO x emissions are needed to reduce air quality related health and biodiversity impacts. • Adverse impacts of reactive nitrogen are most evident for human health and for aquatic and terrestrial ecosystems. • Effects of nitrous oxide emissions on climate are largely counteracted by N induced carbon sequestration. • Ecosystem restoration in response to declined N inputs in Europe since 1995 shows a time lag. • There is large spatial variation across Europe in N impacts, requiring regional policies. • Environmental costs of reactive nitrogen varied from 0.4 to 6.8 euro per kg N. [ABSTRACT FROM AUTHOR]

Base cations, such as potassium (K + ), calcium (Ca 2+ ) and magnesium (Mg 2+ ), are essential nutrients for plant growth and their atmospheric inputs can buffer the effect of acid deposition by nitrogen (N) and sulphur (S) compounds. However, the spatial variation in atmospheric deposition of these base cationic nutrients is less understood compared with N and S deposition. By synthesizing bulk deposition data for K + , Ca 2+ and Mg 2+ , we assessed their annual rates and spatial characteristics at 34 forested sites across China. Our synthesis showed relatively high levels of bulk deposition of base cationic nutrients in China's forests, being an order of magnitude higher than in the USA and Europe. On average, K + , Ca 2+ and Mg 2+ accounted for 13%, 72% and 15% of the bulk deposition of base cationic nutrients, respectively. Surprisingly, base cation deposition was lower at sites near semi-arid regions compared with sites in eastern and southern China, which were far from semi-arid regions. Moreover, elevated base cation deposition was associated with urban hotspots, exhibiting a significant power-law increase with closer distance to the nearest large cities. We estimated that on average base cationic nutrients neutralized a significant proportion (76%) of the potential acid load due to acid deposition. Our findings suggest that in China there is considerable anthropogenic alteration of the regional cycling of base cationic nutrients, which plays an important role in counteracting the risk of soil acidification and base cation depletion in forest ecosystems, especially in the southern regions. [ABSTRACT FROM AUTHOR]

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

Abstract: Elevated nitrogen (N) deposition may increase net primary productivity in N‐limited terrestrial ecosystems and thus enhance the terrestrial carbon (C) sink. To assess the magnitude of this N‐induced C sink, we performed a meta‐analysis on data from forest fertilization experiments to estimate N‐induced C sequestration in aboveground tree woody biomass, a stable C pool with long turnover times. Our results show that boreal and temperate forests responded strongly to N addition and sequestered on average an additional 14 and 13 kg C per kg N in aboveground woody biomass, respectively. Tropical forests, however, did not respond significantly to N addition. The common hypothesis that tropical forests do not respond to N because they are phosphorus‐limited could not be confirmed, as we found no significant response to phosphorus addition in tropical forests. Across climate zones, we found that young forests responded more strongly to N addition, which is important as many previous meta‐analyses of N addition experiments rely heavily on data from experiments on seedlings and young trees. Furthermore, the C–N response (defined as additional mass unit of C sequestered per additional mass unit of N addition) was affected by forest productivity, experimental N addition rate, and rate of ambient N deposition. The estimated C–N responses from our meta‐analysis were generally lower that those derived with stoichiometric scaling, dynamic global vegetation models, and forest growth inventories along N deposition gradients. We estimated N‐induced global C sequestration in tree aboveground woody biomass by multiplying the C–N responses obtained from the meta‐analysis with N deposition estimates per biome. We thus derived an N‐induced global C sink of about 177 (112–243) Tg C/year in aboveground and belowground woody biomass, which would account for about 12% of the forest biomass C sink (1,400 Tg C/year). [ABSTRACT FROM AUTHOR]

We modelled the effects of past and expected future changes in climate (temperature, precipitation), CO 2 concentration, nitrogen deposition (N) and ozone (O 3 ) exposure (phytotoxic ozone dose, POD) on carbon (C) sequestration by European forest ecosystems for the period 1900–2050. Tree C sequestration was assessed by using empirical response functions, while soil C sequestration was simulated with the process-based model VSD, combined with the RothC model. We evaluated two empirical growth responses to N deposition (linear and non-linear) and two O 3 exposure relationships (linear function with total biomass or net annual increment). We further investigated an ‘interactive model’ with interactions between drivers and a ‘multiplicative model’, in which the combined effect is the product of individual drivers. A single deposition and climate scenario was used for the period 1900–2050. Contrary to expectations, growth observations at European level for the period 1950–2010 compared better with predictions by the multiplicative model than with the interactive model. This coincides with the fact that carbon responses in kg C ha − 1 yr − 1 per unit change in drivers, i.e. per °C, ppm CO 2 , kg N ha − 1 yr − 1 and mmol m − 2 yr − 1 POD, are more in line with literature data when using the multiplicative model. Compared to 1900, the estimated European average total C sequestration in both forests and forest soils between 1950 and 2000 increased by 21% in the interactive model and by 41% in the multiplicative model, but observed changes were even higher. This growth increase is expected to decline between 2000 and 2050. The simulated changes between 1950 and 2000 were mainly due to the increase in both N deposition and CO 2 , while the predicted increases between 2000 and 2050 were mainly caused by the increase in CO 2 and temperature, and to lesser extent a decrease in POD, counteracted by reduced N deposition. [ABSTRACT FROM AUTHOR]

Acidification of cropland soils is a serious problem in China that may cause long term pH decline, which threatens the sustainability of soil fertility and crop yields. The objective of this research was to investigate those rates and mechanisms for a slightly calcareous soil. The field data were based on selected treatments from a long-term (1991–2015) N fertilization experiment at a rice-wheat rotation on a slightly calcareous (pH 7.7), young and hardly weathered clay soil (Regosol), including two plots with urea and NH 4 Cl fertilization and a control plot (no N fertilization). Urea and NH 4 Cl were applied at annual rates of 300 kg (1991–1996) and 285 kg (1997–2015) N ha − 1 . Soil pH and exchangeable Ca 2 + and Mg 2 + declined in the first 12 years for the urea treatments, but remained constant thereafter. For the NH 4 Cl and control treatment, the exchangeable base cations showed an oscillating decrease over the 25 years. Soil pH and exchangeable Ca 2 + , and Mg 2 + levels were significantly ( P < 0.05) lower in the NH 4 Cl treatment plot than the control. After 25 years, soil pH in the plots receiving urea and NH 4 Cl were 0.9 and 2.0 units lower than the control, respectively, while the total exchangeable base cations were about 10% and 16% lower, respectively. Carbonate dissolution, base cation exchange and mineral weathering were the main H + buffer pathways of the Regosol. Long-term N fertilization favored the formation of smectite and vermiculite and accelerated the weathering of mica, potassium feldspar, and illite. This was more evident in the NH 4 Cl treatment than in the urea treatment. Consequently, the soil acid-buffering capacity was slightly enhanced after year 13 in the order of urea > control > NH 4 Cl. The increased weathering of soil primary minerals and clay minerals was the main reason that soil pH and exchangeable base cations stayed constant after about 12 years. [ABSTRACT FROM AUTHOR]

Agricultural soil acidification in China is known to be caused by the over-application of nitrogen (N) fertilizers, but the long-term impacts of different fertilization practices on intensive cropland soil acidification are largely unknown. Here, we further developed the soil acidification model VSD+ for intensive agricultural systems and validated it against observed data from three long-term fertilization experiments in China. The model simulated well the changes in soil pH and base saturation over the last 20 years. The validated model was adopted to quantify the contribution of N and base cation (BC) fluxes to soil acidification. The net NO3 - leaching and NO4 +input accounted for 80% of the proton production under N application, whereas one-third of acid was produced by BC uptake when N was not applied. The simulated long-term (1990-2050) effects of different fertilizations on soil acidification showed that balanced N application combined with manure application avoids reduction of both soil pH and base saturation, while application of calcium nitrate and liming increases these two soil properties. Reducing NH4 + input and NO3 leaching by optimizing N management and increasing BC inputs by manure application thus already seem to be effective approaches to mitigating soil acidification in intensive cropland systems. [ABSTRACT FROM AUTHOR]

Soils below croplands and grasslands have acidified significantly in China since the 1980s in terms of pH decline in response to acid inputs caused by intensified fertilizer application and/or acid deposition. However, it is unclear what the rate is of pH decline of forest soils in China in response to enhanced acid deposition and wood production over the same period. We therefore gathered soil pH data from the Second National Soil Inventory of China and publications from the China National Knowledge Infrastructure (CNKI) database in 1981–1985 and 2006–2010, respectively, to evaluate the long-term change of pH values in forest soils. We found that soil pH decreased on average by 0.36 units in the period 1981–1985 to 2006–2010., with most serious pH decline occurring in southwest China (0.63 pH units). The soil type with the strongest pH decline was the semi-Luvisol (0.44 pH units). The decrease in pH was significantly correlated with the acid input induced by atmospheric deposition and forest harvesting. On average, the contribution of atmospheric deposition to the total acid input was estimated at 84% whereas element uptake (due to forest wood growth and harvest) contributed 16% only. Atmospheric deposition is thus the major driver for the significant forest soil acidification across China. [ABSTRACT FROM AUTHOR]

Organic amendments (OAs) can improve the hydro‐physical properties of a soil and thereby potentially enhance the resilience of agricultural systems to droughts and floods. An OA's contribution to this resilience, however, depends on the timeliness of its impacts, as soil improvements should be achieved when droughts are most frequent or flood risks are greatest. Yet little is known regarding the temporal variability of OA impacts or the influence of OA quantity and quality thereupon. In this research, therefore, we investigated at two agricultural sites the temporal variability of improvements in soil bulk density, aggregate stability, infiltration capacity and water retention after the application of compost, farmyard manure, bokashi, a selection of organic residues from landscape maintenance, and a combination of these residues with manure. Results showed that, depending on management practices and soil type, OAs decrease bulk density by up to 9.8%, increase infiltration capacity by up to 108.1%, aggregate stability by up to 60.0%, and water retention by up to 77.8% relative to unamended controls within 3 years of repeated application. However, the magnitude of these improvements varies up to 96% between seasons, depending on the soil property and OA treatment. On average, for all treatments, impacts relative to the control varied between different seasons by 5% for bulk density, 47.1% for infiltration capacity, 22.6% for aggregate stability, and 26.3% for water retention. When offsetting OA nutrient differences with mineral fertilizers, this variability showed a stronger correlation to differences in OA application quantity than quality (i.e., chemical composition). Results suggest that disregarding temporal variability in OA impacts can result in an inaccurate valuation of OAs as either effective or ineffective in improving soil resilience, given that impacts may, instead of their frequently presumed persistency, actually be highly transient or lagged. Our findings highlight the importance of considering the potential intra‐annual variability of OA impacts on soil hydro‐physical properties when designing OA application strategies to ameliorate the effects of specific seasonal climatic challenges. Core Ideas: Hydro‐physical properties improved within 3 years of repeated organic amendment (OA) application.Improvements were more closely related to OA application rates than to OA composition.The impact of OAs on hydro‐physical properties showed significant temporal variability.Temporal variability in OA impacts was influenced by soil type and land management practices.No single OA quantity or qualitative property could consistently explain the observed temporal variability. [ABSTRACT FROM AUTHOR]

Various model approaches have been developed for assessing emissions of different forms of reactive nitrogen in various parts of Europe at various geographic resolutions and for various time periods. The modeling approaches include emission factor approaches, empirical models, simple process-based models, and detailed ecosystem models. In this study, we compared three relatively simple process-based models, developed for the national scale (Integrated NITrogen Impact AssessmenT model On a Regional Scale (INITIATOR2)), European scale (MITERRA) and global scale (integrated model to assess the global environment (IMAGE)), with respect to their response to structural and technological changes in the agricultural systems based on the IPCC B2 baseline scenario for the period 2000-2030. Changes are predicted by the IMAGE model and relate to crop yield, crop area, animal numbers, and N fertilizer inputs. The predicted relative changes by IMAGE are used in INITIATOR2 and MITERRA while relating the animal categories and crop categories in IMAGE to those in the latter models. A comparison was made of NH3, N2O and NOx emissions and N leaching to ground water. We compared predictions for the years 2000 and 2030 for: (i) the Netherlands between INITIATOR2 and MITERRA and (ii) Europe (EU-27 countries) between MITERRA and IMAGE. The results of the comparison are presented and evaluated in view of differences in model structure and the effect of aggregating input data at larger spatial scales. [ABSTRACT FROM AUTHOR]

A European Union (EU-27) wide N2O emission estimate for the agricultural sector is presented, using the INTEGRATOR model, combined with detailed GIS-based environmental data and farming data. INTEGRATOR links various modules, calculating NH3, NOx, N2O, CO2, and CH4 emissions from housing and manure storage systems, agricultural and non-agricultural soils and surface waters, while accounting for the interaction between agricultural and non-agricultural systems through an emission-deposition model for NH3 and NOx. This study is limited to N2O emissions from housing and manure storage systems and agricultural soils. All emissions are based on N2O emission factors which depend on environment (weather and soil conditions), land use (grassland, arable land, crop residues), and management (type of manure and fertilizer, etc). We assessed the plausibility by a comparison of calculated present nitrous oxide emissions at country level with those derived by more simple emission factor approaches and detailed ecosystem models. The model was used to assess the impact of various farming practice packages to mitigate N2O emissions. For the agricultural sector of the EU-27, a total N2O emission of 347 kton N2O-N is calculated for the year 2000, which is comparable to other estimates. The overall achievable reduction in N2O emissions with the evaluated mitigation measures is about 25%. For the EU-27, the most effective measures are balanced fertilization and maximum manure application, but this is highly variable per country. [ABSTRACT FROM AUTHOR]

Abstract: An analysis of the uncertainties in critical loads and target loads of sulphur (S) and nitrogen (N) for 182 European forest soils was carried out using the Very Simple Dynamic (VSD) model. The VSD model was calibrated with a Bayesian approach using prior probability functions for model parameters based on literature data, data from 200 Dutch forest sites and from simulated denitrification rates from a detailed ecosystem model. The calibration strongly improved the fit of the model to observed soil and soil solution concentrations, especially for pH and base saturation. Calibration also narrowed down the ranges in input parameters. The uncertainty analysis showed which parameters contribute most to the uncertainty in the critical loads and target loads. Base cation weathering and deposition and the parameters describing the H–Al equilibrium in the soil solution determine the uncertainty in the maximum critical loads for S, CLmax(S), when based on the aluminium to base cation (Al/Bc) criterion. Uncertainty in CLmax(S) based on an acid neutralizing capacity (ANC) criterion is completely determined by base cation inputs alone. The denitrification fraction is the most important source of uncertainty for the maximum critical loads of N, CLmax(N). N uptake and N immobilisation determine the uncertainties in the critical load for N as a nutrient, CLnut(N). Calibration of VSD reduced the uncertainty: the coefficient of variation (CV) was reduced for all critical loads and criteria. After calibration, the CV for CLmax(S) was below 0.4 for almost all plots; however for CLmax(N) high values occurred for plots with high denitrification rates. Model calibration also improved the robustness of target load estimates: after calibration, no target loads were needed in any of the simulations for 40% of the plots, with the uncalibrated model there was a positive probability for the need of a target load for almost all plots. [Copyright &y& Elsevier]

Abstract: Over the past decade steady-state methods have been developed to assess critical loads of metals avoiding long-term risks in view of food quality and eco-toxicological effects on organisms in soils and surface waters. However, dynamic models are needed to estimate the times involved in attaining a certain chemical state in response to input (deposition, fertilizers or manure) scenarios. Starting from a mass balance, a universal dynamic model was developed by defining appropriate dimensionless quantities, which depend only on the metal under consideration. For any given metal, the model (differential equation) is characterised by the interplay of four (dimensionless) variables: the initial condition, i.e. the concentration at the start of the simulation, the input (driving force), time, and the concentration of the metal at any given point in time. Depending on the question asked, one of these quantities is fixed and the functional relationship between the other three provides the answer. The model allows to investigate the time development of the soil chemical status under a constant future input of the metal to predict (i) the future metal concentration as a function of time (scenario analysis), (ii) the time when a prescribed chemical state (e.g., a critical concentration or steady state) is reached (delay times), and (iii) which future input (reduction) is needed to reach a prescribed chemical state within a prescribed time period (target loads). The general solutions are illustrated with concrete examples, using (average) data from the Netherlands for four metals: cadmium, lead, copper and zinc. The modelling approach set out in this paper illustrates the potential use of dynamic models in the support of policies aimed at reducing emissions of metals by providing an understanding of the structural properties of the model, independent of site-specific parameters. It thus allows assessing temporal behaviour and time scales before embarking on detailed modelling for individual sites. [Copyright &y& Elsevier]

An estimate of net carbon (C) pool changes and long-term C sequestration in trees and soils was made at more than 100 intensively monitored forest plots (level II plots) and scaled up to Europe based on data for more than 6000 forested plots in a systematic 16 km × 16 km grid (level I plots). C pool changes in trees at the level II plots were based on repeated forest growth surveys At the level I plots, an estimate of the mean annual C pool changes was derived from stand age and available site quality characteristics. C sequestration, being equal to the long-term C pool changes accounting for CO2 emissions because of harvest and forest fires, was assumed 33% of the overall C pool changes by growth. C sequestration in the soil were based on calculated nitrogen (N) retention (N deposition minus net N uptake minus N leaching) rates in soils, multiplied by the C/N ratio of the forest soils, using measured data only (level II plots) or a combination of measurements and model calculations (level I plots). Net C sequestration by forests in Europe (both trees and soil) was estimated at 0.117 Gton yr−1, with the C sequestration in stem wood being approximately four times as high (0.094 Gton yr−1) as the C sequestration in the soil (0.023 Gton yr−1). The European average impact of an additional N input on the net C sequestration was estimated at approximately 25 kg C kg−1 N for both tree wood and soil. The contribution of an average additional N deposition on European forests of 2.8 kg ha−1 yr−1 in the period 1960–2000 was estimated at 0.0118 Gton yr−1, being equal to 10% of the net C sequestration in both trees and soil in that period (0.117 Gton yr−1). The C sequestration in trees increased from Northern to Central Europe, whereas the C sequestration in soil was high in Central Europe and low in Northern and Southern Europe. The result of this study implies that the impact of forest management on tree growth is most important in explaining the C pool changes in European forests. [ABSTRACT FROM AUTHOR]

Human activities have drastically increased nitrogen (N) deposition onto forests globally. This may have alleviated N limitation and thus stimulated productivity and carbon (C) sequestration in aboveground woody biomass (AGWB), a stable C pool with long turnover times. This 'carbon bonus' of human N use partly offsets the climate impact of human‐induced N2O emissions, but its magnitude and spatial variation are uncertain. Here we used a meta‐regression approach to identify sources of heterogeneity in tree biomass C‐N response (additional C stored per unit of N) based on data from fertilization experiments in global forests. We identified important drivers of spatial variation in forest biomass C‐N response related to climate (potential evapotranspiration), soil fertility (N content) and tree characteristics (stand age), and used these relationships to quantify global spatial variation in N‐induced forest biomass C sequestration. Results show that N deposition enhances biomass C sequestration in only one‐third of global forests, mainly in the boreal region, while N reduces C sequestration in 5% of forests, mainly in the tropics. In the remaining 59% of global forests, N addition has no impact on biomass C sequestration. Average C‐N responses were 11 (4–21) kg C per kg N for boreal forests, 4 (0–8) kg C per kg N for temperate forests and 0 (−4 to 5) kg C per kg N for tropical forests. Our global estimate of the N‐induced forest biomass C sink of 41 (−53 to 159) Tg C yr−1 is substantially lower than previous estimates, mainly due to the absence of any response in most tropical forests (accounting for 58% of the global forest area). Overall, the N‐induced C sink in AGWB only offsets ~5% of the climate impact of N2O emissions (in terms of 100‐year global warming potential), and contributes ~1% to the gross forest C sink. [ABSTRACT FROM AUTHOR]

Arising from: F. Magnani et al. 447, 849–850 (2007); Magnani et al. replyMagnani et al. present a very strong correlation between mean lifetime net ecosystem production (NEP, defined as the net rate of carbon (C) accumulation in ecosystems) and wet nitrogen (N) deposition. For their data in the range 4.9–9.8 kg N ha-1 yr-1, on which the correlation largely depends, the response is approximately 725 kg C per kg N in wet deposition. According to the authors, the maximum N wet deposition level of 9.8 kg N ha-1 yr-1 is equivalent to a total deposition of 15 kg N ha-1 yr-1, implying a net sequestration near 470 kg C per kg N of total deposition. We question the ecological plausibility of the relationship and show, from a multi-factor analysis of European forest measurements, how interactions with site productivity and environment imply a much smaller NEP response to N deposition. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is an essential nutrient for crops and is applied to agricultural soil to bring or keep the soil at a certain target soil P status in view of an optimal crop yield. Environmental objectives, however, are rarely considered in current P fertilizer recommendations. In this review paper, we argue that current P fertilizer recommendations must be revised in order to balance crop yield, water quality and the use of finite P resources. This revision requires insights into the total pool of reversibly bound P and the capacity of the soil to bind P. Current soil P tests (SPTs) used in routine agronomic soil testing do not provide these insights. We identify the oxalate extraction method as a high-potential agri-environmental SPT as it measures the total pool of reversibly bound P acting as a reserve for plant-available P while it also quantifies the maximum soil P sorption capacity from the simultaneous measurement of amorphous iron- and aluminium-(hydr)oxides. From these results, the Phosphorus Saturation Degree (PSD) can be calculated. We show that those insights are pivotal for the combined assessment of crop response, the risk of P losses to the water system and the judicious use of finite P reserves. In practice, agronomic target P levels should be lowered in soils with a low P sorption capacity to decrease the risk of P leaching. Agronomic target levels should also be lowered in soils with a high P sorption capacity to ensure a judicious use of finite P reserves. [ABSTRACT FROM AUTHOR]

Fertilizer recommendations (FR) to improve yields and increase profitability are based on relationships between crop yields and soil nutrient levels measured via soil extraction methods. Within these FR, critical soil nutrient (CSN) levels are used to distinguish nutrient deficient from non-deficient soils. The variation in CSN levels is large, implying a risk of over- or under-fertilization. Here, we review and assess the factors influencing the derivation of CSN levels in order to increase both their reliability and applicability within FR systems. The evaluated factors included site conditions, i.e., crop type and location as a surrogate for climate and soil properties, and methodological factors, i.e., the experimental approach (field or pot experiments), and statistical methods and cut-off point. Results showed that the range of values used to define the medium soil fertility classes coincided with the range of CSN levels derived from experimental data. We show that harmonizing methodological aspects can substantially reduce the uncertainty in the CSN levels (> 50%), implying a substantial enhancement of the reliability of FR systems. Inclusion of site conditions might further improve the reliability. To enable reduction in CSN levels requires well-documented field experiments and standardization of data collection and analysis. We foresee the potential for generic FR systems that make use of reliable data, more process-based interpretation of nutrient pools and accounting for the interactions among nutrients. [ABSTRACT FROM AUTHOR]

Soil amendments, including lime, biochar, industrial by-products, manure, and straw are used to alleviate soil acidification and improve crop productivity. Quantitative insight in the effect of these amendments on soil pH is limited, hampering their appropriate use. Until now, there is no comprehensive evaluation of the effects of soil amendments on soil acidity and yield, accounting for differences in soil properties. We synthesized 832 observations from 142 papers to explore the impact of these amendments on crop yield, soil pH and soil properties, focusing on acidic soils with a pH value below 6.5. Application of lime, biochar, by-products, manure, straw and combinations of them significantly increased soil pH by 15%, 12%, 15%, 13%, 5% and 17%, and increased crop yield by 29%, 57%, 50%, 55%, 9%, and 52%, respectively. The increase of soil pH was positively correlated with the increase in crop yield, but the relationship varied among crop types. The most substantial increases in soil pH and yield in response to soil amendments were found under long-term applications (>6 year) in strongly acidic (pH < 5.0) sandy soils with a low cation exchange capacity (CEC, <100 mmol c kg−1) and low soil organic matter content (SOM, <12 g kg−1). Most amendments increased soil CEC, SOM and base saturation (BS) and decreased soil bulk density (BD), but lime application increased soil BD (1%) induced by soil compaction. Soil pH and yield were positively correlated with CEC, SOM and BS, while yield declined when soils became compacted. Considering the impact of the amendments on soil pH, soil properties and crop yield as well as their costs, the addition of lime, manure and straw seem most appropriate in acidic soils with an initial pH range from <5.0, 5.0–6.0 and 6.0–6.5, respectively. [Display omitted] • Soil amendments increased soil pH and crop yield by ca. 13% and 36%, respectively. • Amendments increased soil CEC, OM and base saturation and decreased bulk density. • Lime is the most economical while biochar is the most expensive for raising pH. • Lime, manure and straw are recommended at pH < 5.0, 5.0–6.0 and 6.0–6.5, respectively. [ABSTRACT FROM AUTHOR]

Stellar occultation observations from space can probe the stratosphere and mesosphere at a fine vertical scale around the globe. Unlike other measurement techniques like radiosondes and aircraft, stellar occultation has the potential to observe the atmosphere above 30 km, and unlike radio occultation, stellar occultation probes fine-scale phenomena with potential to observe atmospheric turbulence. We imaged the refractive bending angle of a star centroid for a series of occultations by the atmosphere. Atmospheric refractivity, density, and then temperature are retrieved from the bending observations with the Abel transformation and Edlén's law, the hydrostatic equation, and the ideal gas law. The retrieval technique is applied to data collected by two nanosatellites operated by Terran Orbital. Measurements were primarily taken by the GEOStare SV2 mission, with a dedicated imaging telescope, supplemented with images captured by spacecraft bus sensors, namely the star trackers on other Terran Orbital missions. The bending angle noise floor is 10 and 30 arcsec for the star tracker and GEOStare SV2 data, respectively. The most significant sources of uncertainty are due to centroiding errors due to the fairly low-resolution stellar images and telescope pointing knowledge derived from noisy satellite attitude sensors. The former mainly affects the star tracker data, while the latter limits the GEOStare SV2 accuracy, with both providing low vertical resolution. This translates to a temperature profile retrieval up to roughly 20 km for both star tracker and GEOStare SV2 datasets. In preparation of an upcoming 2023 mission designed to correct these deficiencies, SOHIP, we simulated bending angle measurements with varying magnitudes of error. The expected maximum altitude of retrieved temperature is 41 km on average for these simulated measurements with a noise floor of 0.39 arcsec. Our work highlights the capabilities of stellar occultation observations from nanosatellites for atmospheric sounding. Future work will investigate high-frequency observations of atmospheric gravity waves and turbulence, mitigating the major uncertainties observed in these datasets. [ABSTRACT FROM AUTHOR]

Phosphorus is an essential element to enhance the needed increase in crop production in the forthcoming century. On the other hand environmental losses of phosphorus cause eutrophication of surface waters. Both problems call for reliable models to predict the behaviour of phosphorus in agricultural soils. In this study the performances of five different sorption approaches were evaluated. The ultimate aim was to identify the most suitable concept for large scale predictions of P dynamics in soils, in terms of a high comparability between observations and predictions with a minimum amount of input data. The model results were compared with unique data from long term (10–15 years) experimental field studies of grassland including situations with P mining, equilibrium P fertilization and P surpluses and a pot experiment with P mining. The model performance was evaluated while using site specific constants and generic constants for adsorption and desorption. Three rate limited models (DPPS, INITIATOR and ANIMO) showed good performance when site specific constants were used but the performance of the equilibrium model (NEWS-Dynamic) was reasonably comparable. Model performance was better for experiments with a P surplus than for P mining and was also better for sandy soils as compared to clay and peat soils. However, long term desorption rates had to be calibrated for each application rate. The performance of all models declined when generic data were used. We conclude that none of the included models properly describe what happens when the soil changes its P status, considering that parameterization needs to be treatment-specific to obtain reliable predictions. Considering this flaw, models of intermediate complexity, including both equilibrium and rate limited sorption, and a limited data demand, like DPPS and INITIATOR, seem most suited for regional model application. [ABSTRACT FROM AUTHOR]

Stellar occultation observations from space can probe the stratosphere and mesosphere at a fine vertical scale around the globe unlike other measurement techniques like radiosondes, aircraft, and radio occultation. We imaged the refractive bending angle of a star centroid for a series of occultations by the atmosphere. Atmospheric refractivity, density, and then temperature are retrieved from the bending observations with the Abel transformation and Edlén's law, the hydrostatic equation, and the ideal gas law. 5 The retrieval technique is applied to data collected by two nanosatellites operated by Terran Orbital. Measurements were primarily taken by the GEOStare SV2 mission, with a dedicated imaging telescope, supplemented with images captured by spacecraft bus sensors, namely the star trackers on other Terran Orbital missions. The bending angle noise floor is arcseconds and 30 arcseconds for the star tracker and GEOStare SV2 data, respectively. The most significant sources of uncertainty are due to centroiding errors due to the fairly low-resolution stellar images and telescope pointing knowledge de10 rived from noisy satellite attitude sensors. The former mainly affects the star tracker data, while the latter limits the GEOStare SV2 accuracy with both providing low vertical resolution. This translates to a temperature profile retrieval up to roughly km for both star tracker and GEOStare SV2 datasets. In preparation of an upcoming 2023 mission designed to correct these deficiencies, SOHIP, we simulated bending angle measurements with varying magnitudes of error. The expected maximum altitude of retrieved temperature is 41 km on average for these simulated measurements with a noise floor of 0.39 arcseconds. Our work highlights the capabilities of stellar occultation observations from nanosatellites for atmospheric sounding. Future work will investigate high frequency observations of atmospheric gravity waves and turbulence, mitigating the major uncertainties observed in these datasets. [ABSTRACT FROM AUTHOR]

An erratum is presented concerning the article "Ecologically implausible carbon response?" which was published in the volume 451 (2008) issue, pages E1 - E3.

Since the 1980s, the widespread use of N fertilizer has not only resulted in a strong increase in agricultural productivity but also caused a number of environmental problems, induced by excess reactive N emissions. A range of approaches to improve N management for increased agricultural production together with reduced environmental impacts has been proposed. The 4R principles (right product, right amount, right time and right place) for N fertilizer application have been essential for improving crop productivity and N use efficiency while reducing N losses. For example, site-specific N management (as part of 4R practice) reduced N fertilizer use by 32% and increased yield by 5% in China. However, it has not been enough to overcome the challenge of producing more food with reduced impact on the environment and health. This paper proposes a new framework of food-chainnitrogen-management (FCNM). This involves good N management including the recycling of organic manures, optimized crop and animal production and improved human diets, with the aim of maximizing resource use efficiency and minimizing environmental emissions. FCNM could meet future challenges for food demand, resource sustainability and environmental safety, key issues for green agricultural transformation in China and other countries. [ABSTRACT FROM AUTHOR]

The global urban area is expanding continuously, resulting in unprecedented emissions and deposition of reactive nitrogen (N) in urban environments. However, large knowledge gaps remain in the ecological effects of N deposition on urban forests that provide key ecosystem services for an increasing majority of city dwellers. The current understanding of the spatial patterns and ecological effects of N deposition in urban forests was synthesized based on a literature review of observational and experimental studies. Nitrogen deposition generally increases closer to cities, resulting in an urban hotspot phenomenon. Chemical components of N deposition also shift across urban-suburban-rural gradients, showing higher ratios of ammonium to nitrate in and around urban areas. The ecological effects of N deposition on urban forest ecosystems are overviewed with a special focus on ecosystem N cycling, soil acidification, nutrient imbalances, soil greenhouse gas emissions, tree growth and forest productivity, and plant and soil microbial diversity. The distinct effects of unprecedented N deposition on urban forests are discussed in comparison with the common effects in natural forests. Despite the existing research efforts, several key research needs are highlighted to fill the knowledge gaps in the ecological effects of N deposition on urban forests. [ABSTRACT FROM AUTHOR]

To represent the sustainability of nitrogen management in the Sustainable Development Goals indicator framework, this paper proposes a sustainable nitrogen management index (SNMI). This index combines the performance in N crop yield and N use efficiency (NUE), thereby accounting for the need for both food production and environmental protection. Applying SNMI to countries around the world, the results showed improvement in the overall sustainability of crop N management over the past four decades, but this improvement has been mainly achieved by crop yield increase, while global NUE has improved only slightly. SNMI values vary largely among countries, and this variation has increased since the 1970s, implying different levels of success, even failure, in improving N management for countries around the world. In the standard SNMI assessment, the reference NUE was defined as 1.0 (considered an ideal NUE) and the reference yield was defined as 90 kg·ha-1·yr-1 N (considering a globally averaged yield target for meeting food demand in 2050). A sensitivity test that replaced the reference NUE of 1.0 with more realistic NUE targets of 0.8 or 0.9 showed overall reduction in SNMI values (i.e., improved performance), but little change in the ranking among countries. In another test that replaced the universal reference yield with region-specific attainable yield, SNMI values declined (i.e., improved performance) for most countries in Africa and West Asia, whereas they increased for many countries in Europe and South America. The index can be improved by further investigation of approaches for setting region-specific yield targets and high-quality data on crop yield potentials. Overall, SNMI offers promise for a simple and transparent approach to assess progress of countries toward sustainable N management with a single indicator. [ABSTRACT FROM AUTHOR]

Purpose: Rapid urbanization has altered regional nutrient cycles and consequently affected soil nutrient availability for plant growth. This study aims to explore the way in which urbanization shapes the spatial patterns of soil phosphorus (P) concentrations as well as the imprint on tree leaf P concentrations across gradients of urban-rural forests. Methods: We collected soil samples of the surface (0-10 cm) and subsurface (10-20 cm) layers and leaf samples of three common tree species (Chinese pine, Pinus tabuliformis; Chinese scholar tree, Sophora japonica; golden rain tree, Koelreuteria paniculata) from forest patches in twenty parks across urban-rural transects in the Beijing metropolitan region, China. By measuring soil total P, soil available P, and leaf P concentrations, we tested the urban soil P hotspot hypothesis and assessed the consequent imprint on tree leaf P concentrations. Results: Soil total P and available P concentrations in the surface and subsurface layers both increased significantly with closer distance to the urban core. Spatially, leaf P concentrations showed an increase with soil available P concentrations only for the legume Chinese scholar tree, while leaf P concentrations of Chinese pine and broadleaf golden rain tree both increased significantly with the diameter at breast height. Conclusion: Our results confirmed the occurrence of an urban soil P hotspot and identified its significant imprint on leaf P nutrition of legume trees across transects of urban-rural forests. The findings improve the understanding of the way that urbanization alters regional P cycles and consequent P availability for plant growth. [ABSTRACT FROM AUTHOR]

Widespread adoption of improved cropland management measures is advocated to increase soil organic carbon (SOC) levels, thereby improving soil fertility and mitigating climate change. However, spatially explicit insight on management impacts is limited, which is crucial for region‐specific and climate‐smart practices. To overcome these limitations, we combined global meta‐analytical results on improved management practices on SOC sequestration with spatially explicit data on current management practices and potential areas for the adoption of these measures. We included (a) fertilization practices, i.e., use of organic fertilizer compared to inorganic fertilizer or no fertilizer, (b) soil tillage practices, i.e., no‐tillage relative to high or intermediate intensity tillage, and (c) crop management practices, i.e., use of cover crops and enhanced crop residue incorporation. We show that the estimated global C sequestration potential varies between 0.44 and 0.68 Gt C yr−1, assuming maximum complementarity among all measures taken. A more realistic estimate, not assuming maximum complementarity, is from 0.28 to 0.43 Gt C yr−1, being on the lower end of the current range of 0.1–2 Gt C yr−1 found in the literature. One reason for the lower estimate is the limited availability of manure that has not yet been recycled. Another reason is the limited area for the adoption of improved measures, considering their current application and application limitations. We found large regional differences in carbon sequestration potential due to differences in yield gaps, SOC levels, and current practices applied. The highest potential is found in regions with low crop production, low initial SOC levels, and in regions where livestock manure and crop residues are only partially recycled. Supporting previous findings, we highlight that to encourage both soil fertility and SOC sequestration, it is best to focus on agricultural soils with large yield gaps and/or where SOC values are below levels that may limit crop production. [ABSTRACT FROM AUTHOR]

Background and aims: Phosphorus (P) availability in calcareous soils is limited. Acidifying the soil by adding sulfur (S) or enhancing microbial activity by adding carbon (C) can increase P bioavailability. However, understanding of the impact of the combined application of P, S and C on P availability in calcareous soils is lacking. In this study, we investigated the effects of heterogeneous (co-localized) supply of different combinations of P, S and C on the maize (Zea mays L.) shoot and root growth and soil P availability in calcareous soil with low available P.A rhizo-box experiment with heterogeneous supply of P, S and C was conducted to assess the responses of maize growth, root morphology and physiology, as well as soil P availability.Heterogeneous low P (P1) with S supply significantly increased shoot and root biomass, shoot P content and P-use efficiency (PUE) compared to homogenous or heterogeneous P1 supply alone. Application of S decreased the rhizosphere soil pH and stimulated the proliferation of maize roots. By contrast, heterogeneous P1 and C supply did not change shoot biomass, P uptake or PUE but decreased root biomass. The addition of C, however, enhanced acid phosphatase activity and carboxylates concentration in the rhizosphere, and increased NaHCO3-extractable P, implying enhanced P availability.Adding S combined with P is an effective approach to engineer the rhizosphere by increasing maize growth and PUE in calcareous soil, whereas adding C increased NaHCO3-extractable soil P but did not influence maize shoot growth.Methods: Phosphorus (P) availability in calcareous soils is limited. Acidifying the soil by adding sulfur (S) or enhancing microbial activity by adding carbon (C) can increase P bioavailability. However, understanding of the impact of the combined application of P, S and C on P availability in calcareous soils is lacking. In this study, we investigated the effects of heterogeneous (co-localized) supply of different combinations of P, S and C on the maize (Zea mays L.) shoot and root growth and soil P availability in calcareous soil with low available P.A rhizo-box experiment with heterogeneous supply of P, S and C was conducted to assess the responses of maize growth, root morphology and physiology, as well as soil P availability.Heterogeneous low P (P1) with S supply significantly increased shoot and root biomass, shoot P content and P-use efficiency (PUE) compared to homogenous or heterogeneous P1 supply alone. Application of S decreased the rhizosphere soil pH and stimulated the proliferation of maize roots. By contrast, heterogeneous P1 and C supply did not change shoot biomass, P uptake or PUE but decreased root biomass. The addition of C, however, enhanced acid phosphatase activity and carboxylates concentration in the rhizosphere, and increased NaHCO3-extractable P, implying enhanced P availability.Adding S combined with P is an effective approach to engineer the rhizosphere by increasing maize growth and PUE in calcareous soil, whereas adding C increased NaHCO3-extractable soil P but did not influence maize shoot growth.Results: Phosphorus (P) availability in calcareous soils is limited. Acidifying the soil by adding sulfur (S) or enhancing microbial activity by adding carbon (C) can increase P bioavailability. However, understanding of the impact of the combined application of P, S and C on P availability in calcareous soils is lacking. In this study, we investigated the effects of heterogeneous (co-localized) supply of different combinations of P, S and C on the maize (Zea mays L.) shoot and root growth and soil P availability in calcareous soil with low available P.A rhizo-box experiment with heterogeneous supply of P, S and C was conducted to assess the responses of maize growth, root morphology and physiology, as well as soil P availability.Heterogeneous low P (P1) with S supply significantly increased shoot and root biomass, shoot P content and P-use efficiency (PUE) compared to homogenous or heterogeneous P1 supply alone. Application of S decreased the rhizosphere soil pH and stimulated the proliferation of maize roots. By contrast, heterogeneous P1 and C supply did not change shoot biomass, P uptake or PUE but decreased root biomass. The addition of C, however, enhanced acid phosphatase activity and carboxylates concentration in the rhizosphere, and increased NaHCO3-extractable P, implying enhanced P availability.Adding S combined with P is an effective approach to engineer the rhizosphere by increasing maize growth and PUE in calcareous soil, whereas adding C increased NaHCO3-extractable soil P but did not influence maize shoot growth.Conclusion: Phosphorus (P) availability in calcareous soils is limited. Acidifying the soil by adding sulfur (S) or enhancing microbial activity by adding carbon (C) can increase P bioavailability. However, understanding of the impact of the combined application of P, S and C on P availability in calcareous soils is lacking. In this study, we investigated the effects of heterogeneous (co-localized) supply of different combinations of P, S and C on the maize (Zea mays L.) shoot and root growth and soil P availability in calcareous soil with low available P.A rhizo-box experiment with heterogeneous supply of P, S and C was conducted to assess the responses of maize growth, root morphology and physiology, as well as soil P availability.Heterogeneous low P (P1) with S supply significantly increased shoot and root biomass, shoot P content and P-use efficiency (PUE) compared to homogenous or heterogeneous P1 supply alone. Application of S decreased the rhizosphere soil pH and stimulated the proliferation of maize roots. By contrast, heterogeneous P1 and C supply did not change shoot biomass, P uptake or PUE but decreased root biomass. The addition of C, however, enhanced acid phosphatase activity and carboxylates concentration in the rhizosphere, and increased NaHCO3-extractable P, implying enhanced P availability.Adding S combined with P is an effective approach to engineer the rhizosphere by increasing maize growth and PUE in calcareous soil, whereas adding C increased NaHCO3-extractable soil P but did not influence maize shoot growth. [ABSTRACT FROM AUTHOR]

• Digital Soil Mapping of oxalate-extractable iron and aluminium contents. • Predictions at 25 m spatial resolution across six soil depth intervals. • Prediction uncertainty using a quantile regression forest algorithm. • Map quality assessed with design-based statistical inference. • Maps aid in balancing crop production, water quality and carbon sequestration. Amorphous iron- and aluminium-(hydr)oxides are key soil properties in controlling the dynamics of phosphorus availability and carbon storage. These oxides affect the potential of soils to retain phosphorus and carbon, thus affecting ecosystem services such as crop production, water quality and carbon sequestration. In this study, we spatially predicted oxalate-extractable Fe and Al (Fe OX , Al OX) contents in the Netherlands at 25 m resolution across six soil depth layers between 0 and 200 cm and quantified the associated prediction uncertainty using quantile regression forest. For model training and validation, geo-referenced data of Fe OX and Al OX contents were used including 12,110 wet-chemical observations and 102,393 NIR spectroscopy observations. Over 150 spatial covariates were selected that provide information about soil typology, climate, soil organisms, land use, relief, parent material and space (sampling depth and oblique coordinates). Map quality was assessed by comparing predictions with observations using an independent data set of 4841 soil samples from agricultural fields. Soil sample locations were selected by stratified random sampling, allowing us to assess map quality using design-based statistical inference. Map quality was evaluated using the metrics Model Efficiency Coefficient (MEC), Root Mean Square Error (RMSE) and Mean Error (ME). Map quality differed, depending on the target variable and soil depth, with MEC ranging from 0.19 to 0.80, RMSE from 13.5 to 56.9 mmol kg−1 and ME from −6.8 to 6.8 mmol kg−1. Overall, map quality was better for topsoil than for subsoil and better for Al OX contents than for Fe OX contents. Prediction uncertainty quality was evaluated by calculating the Prediction Interval Coverage Probability of the 90 per cent Prediction Interval, which were close to 0.90 in all cases and slightly below 0.90 for Al OX. Thus, prediction uncertainties were generally reliable, though for Al OX contents uncertainty was slightly underpredicted. The maps are a valuable tool for site-specific manure and fertiliser management strategies aiming to balance crop production, water quality and carbon sequestration in agriculture. [ABSTRACT FROM AUTHOR]

Nitrogen (N) deposition is known to increase carbon (C) sequestration in N‐limited boreal forests. However, the long‐term effects of N deposition on ecosystem carbon fluxes have been rarely investigated in old‐growth boreal forests. Here we show that decade‐long experimental N additions significantly stimulated net primary production (NPP) but the effect decreased with increasing N loads. The effect on soil heterotrophic respiration (Rh) shifted from a stimulation at low‐level N additions to an inhibition at higher levels of N additions. Consequently, low‐level N additions resulted in a neutral effect on net ecosystem productivity (NEP), due to a comparable stimulating effect on NPP and Rh, while NEP was increased by high‐level N additions. Moreover, we found nonlinear temporal responses of NPP, Rh and NEP to low‐level N additions. Our findings imply that actual N deposition in boreal forests likely exerts a minor contribution to their soil C storage. [ABSTRACT FROM AUTHOR]

Sustainable agricultural management implies optimization of resources for crop production while minimizing adverse impacts on the environment. This requires a better understanding of the synergies and trade-offs of agronomic management while accounting for the controlling effects of site-specific factors (covariates). We systematically evaluated 113 meta-analytical studies assessing impacts of crop management measures (rotation, cover cropping, residue retention), soil and water measures (irrigation, tillage), soil amendments (enhanced efficiency, biochar), fertilizer use (organic, mineral, combined organic-mineral) and "4R'" fertilizer strategies (right source, rate, timing, placement) on sustainability indicators. These indicators include crop yield, crop N and P (content, uptake, and use efficiency), soil quality indicators (soil organic C, N and P contents, compaction), soil emissions of ammonia (NH 3) and greenhouse gases (CO 2 , N 2 O), and nutrient losses to water (N and P surplus or leaching). Nutrient management, including 4R practices as well as enhanced efficiency amendments, had the largest impact, increasing crop yields and N uptake while reducing N 2 O and NH 3 emissions as well as N surplus, whereas effects on CO 2 emissions were variable. Although all measures positively impacted soil C, the largest effect was due to biochar, followed by organic fertilizer input. Biochar positively impacted crop yield, diminished N 2 O and NH 3 emissions as well as N surplus, and increased CO 2 emissions. Within crop management, only cover cropping had a significant positive effect on crop yield, while both cover crops and rotation slightly enhanced N uptake and the sequestration of C and N in soil, thus reducing N 2 O emissions and N surplus. Minimal tillage practices generally increased SOC, while results for crop yield, N surplus and N 2 O emissions were variable. Site-specific factors had substantial impacts on the evaluated impacts of measures, most importantly climate, crop type, soil texture, soil pH, soil organic C, N dose, and experimental duration. Considering the variation among meta-analytical protocols followed, we recommend that field studies and meta-analytical work adhere to harmonized guidelines with respect to the reporting of site-level data, experimental design, and the statistical procedures used. This will ensure data comparability between studies, improve the quality of meta-analysis results, and give better insights into currently uncertain or unknown impacts of agronomic measures. [Display omitted] • We synthesized 113 meta-analyses assessing impacts of improved agronomic measures. • Nutrient management enhanced crop yield, N uptake, and SOC and reduced N losses. • Crop management measures had variable effects on crop yield, but reduced N losses. • Minimum tillage had small and/or variable impacts on crop yield, SOC and N losses. • Significant covariates included climate, crop, soil and experimental factors. [ABSTRACT FROM AUTHOR]

We present a sample of 40 ultrasteep spectrum (USS; ) radio sources selected from the Westerbork in the Southern Hemisphere (WISH) catalogue. The USS sources have been imaged in K band at the Cerro Tololo Inter-American Observatory (CTIO) and with the Very Large Telescope (VLT) at Cerro Paranal. We also present VLT, Keck and William Herschel Telescope (WHT) optical spectroscopy of 14 targets selection from four different USS samples. For 12 sources, we have been able to determine the redshifts, including four new radio galaxies at . We find that most of our USS sources have predominantly small (<6 arcsec) radio sizes and faint magnitudes . The mean K-band counterpart magnitude is . The expected redshift distribution estimated using the Hubble K– z diagram has a mean of , which is higher than the predicted redshift obtained for the Sydney University Molonglo Sky Survey–NRAO VLA Sky Survey (SUMSS–NVSS) sample and the expected redshift obtained in the 6C** survey. The compact USS sample analysed here may contain a higher fraction of galaxies which are high redshift and/or are heavily obscured by dust. Using the 74, 352 and 1400 MHz flux densities of a subsample, we construct a radio colour–colour diagram. We find that all but one of our USS sources have a strong tendency to flatten below 352 MHz. We also find that the highest redshift source from this paper (at ) does not show evidence for spectral flattening down to 151 MHz. This suggests that very low frequency selected USS samples will likely be more efficient to find high redshift galaxies. [ABSTRACT FROM AUTHOR]

Maize production in Zambia is characterized by significant yield gaps attributed to nutrient management and climate change threatens to widen these gaps unless agronomic management is optimized. Insights in the impacts of climate change on maize yields and the potential to mitigate negative impacts by crop management are currently lacking for Zambia. Using five Global Circulation models and the WOFOST crop model, we assessed climate change impacts on maize yields at a 0.5° × 0.5° spatial resolution for RCP 4.5 and RCP 8.5 scenarios. Impacts were assessed for the near future (2035-2066) and far future (2065-2096) in comparison with a reference period (1971-2001). The surface temperature and warm days (above 30 °C) are projected to increase strongly in the southern and western regions. Precipitation is expected to decline, except in the northern regions, whereas the number of wet days declines everywhere, shortening the growing season. The risk of crop failure in western and southern regions increases due to dry spells and heat stress, while crops in the northern regions will be threatened by flooding or waterlogging due to heavy precipitation. The simulated decline in the water-limited and water- and nutrient-limited maize yields varied from 15 to 20% in the near future and from 20 to 40% in the far future, mainly due to the expected temperature increases. Optimizing management by adjusting planting dates and maize variety selection can counteract these impacts by 6-29%. The existing gaps between water-limited and nutrient-limited maize yields are substantially larger than the expected yield decline due to climate change. Improved nutrient management is therefore crucial to boost maize production in Zambia. [ABSTRACT FROM AUTHOR]

Nutrient budgets of agroecosystems are constructed either (i) to increase the understanding of nutrient cycling, (ii) as performance indicator and awareness raiser in nutrient management and environmental policy, or (iii) as regulating policy instrument to enforce a certain nutrient management policy in practice. This paper explores nutrient budgeting approaches and summarizes sources of uncertainty associated with these approaches. Possible implications of uncertainties associated with the different methodologies and approaches for nutrient management and environmental policy are discussed. Three types of nutrient budgets have been distinguished, i.e. farm-gate, soil surface and soil systems budgets. A farm-gate budget is the most integrative measure of environmental pressure, and seems most suitable as environmental performance indicator. A soil surface budget is appropriate for estimating the net loading of the soil with nutrients. Soil system budgets account for nutrient inputs and outputs, recycling of nutrients within the system, nutrient loss pathways and changes in soil nutrient pools; it is the most detailed budget and provides detailed information for nutrient management. Case studies for the dairy farm De Marke indicate that the three budgeting approaches supplement each other. The accuracy and precision of the nutrient budget depend on budgeting approach, data acquisition strategy and type of agroecosystem. There is often a considerable amount of uncertainty in the nutrient budget, due to various possible biases and errors, notably in the partitioning of nutrient losses. Possible sources of biases are personal bias, sampling bias, measurement bias, data manipulation bias and fraud. Sources of errors are sampling and measurement errors. Both biases and errors in nutrient budget estimates may lead to confusion and wrong conclusions. Yet, there is little published evidence that uncertainties are taken into account in decision making. Uncertainties are usually smaller for a farm-gate budget than for a soil surface budget. Therefore, farm-gate budgets are preferred over soil surface budgets as policy instrument. Quantifying uncertainties requires: (a) system identification and analysis, (b) classification of uncertainties, (c) specification of distributions of probabilities of the various sources using Monte Carlo simulation, and (d) monitoring of the nutrient pools, inputs and outputs over time. Analyses of uncertainties in nutrient budgets may provide information about the weakest chain in establishing agri-environmental cause–effect relationships and, therefore, may assist to better focus research efforts. Data for the nitrogen budget of The Netherlands indicate relatively large uncertainties for the items denitrification and leaching, with coefficients of variation >30%. In conclusion, there is a need for standard procedures and guidelines in nutrient budgeting and uncertainty analyses, to improve the confidence in and applicability of nutrient budgets. [Copyright &y& Elsevier]

Maintaining an appropriate soil phosphorus level is key to ensure sustainable phosphorus management for crop production and to minimise phosphorus losses to water bodies. However, the effects of long-term fertilization on different soil phosphorus pools, crop yields and phosphorus loss risk remain unclear. This requires insights into the responses of soil phosphorus pools, crop phosphorus uptake with related crop yields and phosphorus loss to long-term phosphorus inputs. Changes in four soil phosphorus pools (P CACL2 , P OLSEN , P OX and P TOTAL , respectively) and crop yield responses to various fertilization rates were examined in a 29-year long-term phosphorus fertilization experiment in China. Results showed that the increase in the four soil phosphorus pools was proportional to the accumulated phosphorus surplus, i.e., the input minus uptake. P OLSEN and P OX increased linearly with continuous phosphorus application and peaked at a phosphorus accumulation near 3200 kg P ha−1. Beyond this threshold, continuous phosphorus application caused a gradual increase in P TOTAL and a linear increase in P CACL2 , which implies an increasing risk for leaching. The P OX pool accounted for 87% of the accumulated phosphorus surplus until soil phosphorus saturation occurred. The crop yields of wheat and maize responded clearly to changes in P TOTAL , P OX , P OLSEN and P CACL2 , with P OX explaining most of the yield variation. Furthermore, P OX was highly correlated with P CACL2 , being a risk indicator for phosphorus leaching. Given that P OX explains best how much of phosphorus surplus accumulates in soil, the variation in crop yield, and the risk for P leaching, it can be used as a valuable and reliable indicator to manage phosphorus sustainably. • A 29-year experiment was used to assess impacts of fertilization on soil phosphorus pools and crop yields. • 87% of the phosphorus surplus accumulated in the oxalate extractable pool. • P OX and P OLSEN pools were saturated at an accumulated phosphorus surplus near 3200 kg P ha−1. • P OX explained most variation in crop yield, but P CACL2 was a more sensitive indicator. • Use of P OX can guide management to optimize crop production and minimize phosphorus loss. [ABSTRACT FROM AUTHOR]

Increasing use of manure nutrients in crop production and decreasing the input of chemical fertilizers, is a promising way to achieve a more circular economy and more sustainable food systems. The integrated effects of amended composting manure with additives and a 50% substitution of chemical fertilizer nitrogen (N) input by amended manure N input to cropland were proved to halve ammonia (NH 3) emissions from an integrate manure-cropland system. However, the accompanied impacts of these measures on greenhouse gas (GHG) emissions from the integrate manure-cropland system have not been well quantified. Here, we examined the effects of improved manure storage and treatment and its usage at field on GHG emissions from a system perspective, based on a two-year experiment in the North China Plain (NCP). Manure storage and treatment included natural storage (NS) and composting with straw, with or without amendment by zeolite (Z) and superphosphate (SP). Manure products were applied as basal fertilizer for both crops. Results showed that CH4 was the dominant GHG source in the natural storage treatment, whereas N2O dominated in the manure composting treatments. Amending manure with straw, Z and SP stimulated 15–48 times N2O emission and decreased CH4 emissions by 82%–91% during storage and treatment. Replacement of 50% synthetic fertilizer N by manure N decreased total system GHG emissions by 25%–34%. Differences between composted manure treatments in total system GHG emissions were relatively small, although comparatively higher in amended manure treatments; however, they promoted greater soil organic carbon sink activity, resulting in no significant difference in net global warming potential (GWP) and greenhouse gas emission intensity (GHGI). Application of amended manure produced high nitrogen use efficiency (NUE) in the integrated crop–manure system. The NH3 mitigation approach of replacing 50% of synthetic fertilizer N by amended manure N synergistically decreased total GHG emissions, increased system NUE and also increased the net economic benefit by 5%–11% over the 2 years of the experiment. [Display omitted] • The impacts of NH 3 mitigation measures on GHG emissions were quantified to explore a more sustainable food systems. • Manure composting with straw and/or additives increased N 2 O emissions but depressed CH 4 emissions. • The NH 3 mitigation measures reduced GWP in the manure-cropland system by 25%–34% compared to the traditional treatment. • Compared to the traditional treatment, introducing NH 3 mitigation measures increased economic benefit by 5%–11%. [ABSTRACT FROM AUTHOR]

Rapid urbanization has profoundly altered the spatial patterns of multiple element cycles. Whether and how urbanization shapes the spatial patterns of atmospheric trace element deposition remains, however, poorly understood. Using a newly compiled database on bulk deposition of eight trace elements (i.e., Cu, Ni, Zn, As, Cd, Cr, Hg and Pb) in China, we assessed the urban imprints on the spatial patterns of trace element deposition. Bulk deposition of the eight trace elements all showed a significant increase with closer distance to the nearest large cities, while the urban effect was also mediated by point emission sources and precipitation. We further compiled a database of urban topsoil (0–10 cm) concentrations of the eight trace elements and found that urban soil quality standards were exceeded in 80% of the studied cities for Cr, 49% for As, and less than 25% for other trace elements, respectively. The urban topsoil concentrations of six trace elements (except As and Hg) showed no significant correlations with their background values for natural soils, while we found a significant correlation between bulk deposition and urban topsoil concentrations of trace elements corrected by background values. We also demonstrated that current levels of trace element deposition would substantially increase urban soil pollution over the coming decades. Our findings confirm the occurrence of urban hotspots of trace element deposition and their impact on soil pollution and highlight a need of emission control of trace elements for safety urban soil quality. [Display omitted] • Spatial patterns of trace element deposition and the imprints on urban soil quality were evaluated in China. • Bulk deposition of trace elements increased significantly with closer distance to the nearest large cities. • Urban soil quality standards were exceeded in a large proportion of the studied cities for Cr and As. • Bulk deposition of trace elements can make a significant contribution to urban soil pollution. [ABSTRACT FROM AUTHOR]

Aim: Experimental nitrogen (N) addition (fertilization) studies are commonly used to quantify the impacts of increased N inputs on plant biodiversity. However, given that plant community responses can vary considerably among individual studies, there is a clear need to synthesize and generalize findings with meta‐analytical approaches. Our goal was to quantify changes in species richness and abundance in plant communities in response to N addition across different environmental contexts, while controlling for different experimental designs. Location: Global. Time period: Data range: 1985–2016; Publication years: 1990–2018. Major taxa studied: Plants. Methods: We performed a meta‐analysis of 115 experiments reported in 85 studies assessing the effects of N addition on terrestrial natural and semi‐natural plant communities. We quantified local‐scale changes in plant biodiversity in relationship to N addition using four metrics: species richness (SR), individual species abundance (IA), mean species abundance (MSA) and geometric mean abundance (GMA). Results: For all metrics, greater amounts of annual N addition resulted in larger declines in plant diversity. Additionally, MSA decreased more steeply with N that was applied in reduced (NH4+) rather than oxidized (NO3-) form. Loss of SR with increasing amounts of N was found to be larger in warmer sites. Furthermore, greater losses of SR were found in sites with longer experimental durations, smaller plot sizes and lower soil cation exchange capacity. Finally, reductions in the abundance of individual species were larger for N‐sensitive plant life‐form types (legumes and non‐vascular plants). Main conclusions: N enrichment decreases both SR and abundance of plants in N‐addition experiments, but the magnitude of the response differs among biodiversity metrics and with the environmental and experimental context. This underlines the importance of integrating multiple dimensions of biodiversity and relevant modifying factors into assessments of biodiversity responses to global environmental change. [ABSTRACT FROM AUTHOR]