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There is substantial interest in mitigating N SB 2 sb O emissions from agricultural activities as a part of the strategy to combat global climate change, yet N SB 2 sb O emission and N budget estimates remain highly uncertain for the majority of terrestrial ecosystems. Here, Yao et al. show that the annual integrated sum of soil inorganic N concentrations can predict annual N SB 2 sb O and NO emissions across a wide variety of ecosystems. In their contribution Leitner et al. ask if closing yield gaps in Africa, through adequate N fertilizer applications, will increase soil N SB 2 sb O emissions. [Extracted from the article]

Abstract Vegetable production in solar greenhouses in northern China results in the excessive use of nitrogen (N) fertilizers and water via flooding irrigation. Both factors result in low N use efficiency and high environmental costs because groundwater becomes contaminated with nitrate (NO 3 −). Four consecutive tomato (Lycopersicum esculentum Mill.) cropping seasons were tested whether drip fertigation and/or the incorporation of maize straw (S) may significantly reduce NO 3 − and dissolved organic N (DON) leaching while increasing the water-use efficiency (WUE) and partial factor productivity of applied N (PFP N) of the tomatoes. The following treatments were used: ① conventional flooding irrigation with overfertilization (CIF, 900 kg N ha−1 season−1), ② CIF + S, ③ drip irrigation with optimized fertilization (DIF, 400 kg N ha−1 season−1), ④ DIF + S. We found that (1) DIF significantly increases the PFP N and WUE by 262% and 73% without compromising the yield compared with CIF, respectively. (2) For CIF, approximately 50% of the total N input was leached at a NO 3 −/DON ratio of approximately 2:1. (3) Compared with CIF, DIF reduced NO 3 − and DON leaching by 88% and 90%, respectively. Water percolation was positively correlated with N leaching (p < 0.001). (4) Straw application only reduced NO 3 − leaching losses in the first year and did not affect DON leaching overall, although DON leaching was increased in DIF in the first growing season. In conclusion, DIF significantly reduces NO 3 − and DON leaching losses by approximately 90% compared with the current farmer practice (CIF). Considering the significant DON leaching losses, which have been overlooked because previous measurements focused on NO 3 −, DON should be considered as a primary factor of environmental pollution in conventional solar greenhouse vegetable production systems. Graphical abstract Image 1 Highlights • Drip fertigation increases water and nitrogen use efficiency without yield jeopardy. • For conventional flooding irrigation, 50% of total N input was leached. • Dissolved organic nitrogen (DON) accounted for 1/3 of total N leaching. • Drip fertigation reduced dissolved inorganic and organic N leaching by 90%. • Straw addition reduced nitrate leaching in the first year, less affect DON leaching. For CIF, 50% of total N input was leached and DON accounted for 33% of the total leached N. Drip fertigation reduced the dissolved inorganic and organic N leaching by 90% compared with CIF. [ABSTRACT FROM AUTHOR]

The conversion of agricultural residues into biochar produces a material with agronomic and environmental benefits. Biochars have been found to positively or negatively affect soil greenhouse gas (GHG) emissions, with the variability being explained by differences in biochar properties and environmental conditions. This study evaluated the effect of soil moisture conditions on the emissions of GHGs from soils amended with different types of biochar. For that, we added biochars to a sandy soil and incubated the samples at 23 °C for 90 days under two moisture conditions. While CH 4 fluxes remained not significantly different from zero in all treatments, CO 2 effluxes were stimulated at higher soil moisture contents, though the stimulating effect varied with biochar type. Soils amended with biochars with a narrow C:N ratio showed a higher CO 2 efflux than soils amended with biochars with a wide C:N ratio. There were significant main effects of pyrolysis temperature and soil moisture conditions on the N 2 O fluxes from the treatments, however total N 2 O fluxes from biochar amended soils were overall not significantly different from the control due to treatment interactions. Our study indicates that the main effect of biochars on the GHG balances of soils is related to an increase in soil C stocks, with little short-term changes in soil CH 4 and N 2 O fluxes. Nevertheless, short-term increases in GHG emissions due to biochar addition to soils can be easily mitigated by use of biochars with high C:N ratios produced under high temperatures and by avoiding application to moist soils. [ABSTRACT FROM AUTHOR]

High nitrogen (N) inputs in Chinese vegetable and cereal productions played key roles in increasing crop yields. However, emissions of the potent greenhouse gas nitrous oxide (N 2 O) and atmospheric pollutant nitric oxide (NO) increased too. For lowering the environmental costs of crop production, it is essential to optimize N strategies to maintain high crop productivity, while reducing the associated N losses. We performed a 2 year-round field study regarding the effect of different combinations of poultry manure and chemical N fertilizers on crop yields, N use efficiency (NUE) and N 2 O and NO fluxes from a Welsh onion-winter wheat system in the North China Plain. Annual N 2 O and NO emissions averaged 1.14–3.82 kg N ha −1 yr −1 (or 5.54–13.06 g N kg −1 N uptake) and 0.57–1.87 kg N ha −1 yr −1 (or 2.78–6.38 g N kg −1 N uptake) over all treatments, respectively. Both N 2 O and NO emissions increased linearly with increasing total N inputs, and the mean annual direct emission factors (EF d ) were 0.39% for N 2 O and 0.19% for NO. Interestingly, the EF d for chemical N fertilizers (N 2 O: 0.42–0.48%; NO: 0.07–0.11%) was significantly lower than for manure N (N 2 O: 1.35%; NO: 0.76%). Besides, a negative power relationship between yield-scaled N 2 O, NO or N 2 O + NO emissions and NUE was observed, suggesting that improving NUE in crop production is crucial for increasing crop yields while decreasing nitrogenous gas release. Compared to the current farmers’ fertilization rate, alternative practices with reduced chemical N fertilizers increased NUE and decreased annual N 2 O + NO emissions substantially, while crop yields remained unaffected. As a result, annual yield-scaled N 2 O + NO emissions were reduced by > 20%. Our study shows that a reduction of current application rates of chemical N fertilizers by 30–50% does not affect crop productivity, while at the same time N 2 O and NO emissions would be reduced significantly. [ABSTRACT FROM AUTHOR]

In this study water balance components as well as nitrogen and dissolved organic carbon leaching were quantified by means of large weighable grassland lysimeters at three sites (860, 770 and 600 m a.s.l.) for both intensive and extensive management. Our results show that at E600, the site with highest air temperature (8.6 °C) and lowest precipitation (981.9 mm), evapotranspiration losses were 100.7 mm higher as at the site (E860) with lowest mean annual air temperature (6.5 °C) and highest precipitation (1359.3 mm). Seepage water formation was substantially lower at E600 (−440.9 mm) as compared to E860. Compared to climate, impacts of management on water balance components were negligible. However, intensive management significantly increased total nitrogen leaching rates across sites as compared to extensive management from 2.6 kg N ha −1 year −1 (range: 0.5–6.0 kg N ha −1 year −1 ) to 4.8 kg N ha −1 year −1 (range: 0.9–12.9 kg N ha −1 year −1 ). N leaching losses were dominated by nitrate (64.7%) and less by ammonium (14.6%) and DON (20.7%). The low rates of N leaching (0.8–6.9% of total applied N) suggest a highly efficient nitrogen uptake by plants as measured by plant total N content at harvest. Moreover, plant uptake was often exceeding slurry application rates, suggesting further supply of N due to soil organic matter decomposition. The low risk of nitrate losses via leaching and surface runoff of cut grassland on non-sandy soils with vigorous grass growth may call for a careful site and region specific re-evaluation of fixed limits of N fertilization rates as defined by e.g. the German Fertilizer Ordinance following requirements set by the European Water Framework and Nitrates Directive. [ABSTRACT FROM AUTHOR]

The Loess Plateau in China constitutes an area short of soil nitrogen and organic carbon due to local land degradation induced by various factors (i.e. long term changes of land use, climate conditions, and soil properties). The present study aimed to examine the effects of species and land management by afforestation on tree N acquisition capacity and soil N and C availability in degraded soils of the Loess Plateau area. We quantified root N uptake of inorganic and organic N sources as well as soil N and C availability, both at the tree species (i.e. Robinia pseudoacacia L., Juglans regia L. and Pinus tabulaeformis Carr.) and the land management (i.e. arable vs. monoculture vs. mixed afforested stands) levels. Our results indicated that afforestation improved soil N and organic C availabilities compared to abandoned arable land ( p < 0.05). In particular, the presence of N 2 -fixing R. pseudoacacia enhanced root N concentrations (ca. 3.0 times) and soil NO 3 - (ca. 5.4 times), soil total N (ca. 1.9 times) and organic C (ca. 3.4 times) availabilities, but decreased soil NH 4 + (ca. −33%), microbial biomass carbon (ca. −74%) and nitrogen (ca. −54%) in the mixed stand compared to J. regia monoculture. Under the experimental conditions applied, the afforested trees preferred organic over inorganic N compounds as well as NO 3 − over NH 4 + ; J. regia in monoculture had a highest root amino acids N uptake capacities (i.e. 76.6 ± 7.7 nmol N (g fw) − 1 h −1 for glutamine, 90.3 ± 8.9 nmol N (g fw) − 1 h −1 for arginine) compared to other tree species whereas such high uptake capacities were largely repressed in the mixed stand with R. pseudoacacia . Thus, in the Loess Plateau area, the inter-planting system of J. regia with N 2 -fixing R. pseudoacacia could improve the total soil N and organic C pools as well as plant N cycling compared to traditional arable land use and J. regia monoculture system. This study shows that inter-planting R. pseudoacacia with economic fruit trees can be considered a successful strategy for soil regeneration by afforestation in future land management projects. [ABSTRACT FROM AUTHOR]

The nitrogen (N) cycle involves a set of N compounds transformed by plants and microbes. Some of these N compounds, such as nitrous oxide (N 2 O) or nitrate (NO 3 − ), are environmental pollutants jeopardizing biodiversity, human health or the global climate. The natural abundances of the common ( 14 N) and rare ( 15 N) stable N isotopes in a given compound, i.e. the isotopic composition, depend on individual production and consumption processes. As each process has an individual preference for the common or rare isotope (isotope effect) the measurement of the isotopic composition has been identified as a powerful tool for improved process understanding and source process identification. Both are key requirements for the development of strategies aiming at mitigating the release of environmental harmful N compounds. However, up to now, no comprehensive compilation of N cycle isotope effects is available. A compilation of isotope effects is also in high demand for testing biogeochemical models as such models are increasingly used to study N cycling in ecosystems and across landscapes and regions. Biogeochemical models are usually calibrated and validated only with single, easily accessible quantities. The isotopic composition of N compounds has a high potential to be used as additional, integrative parameter for a more thorough assessment of simulation results. For instance, the isotopic composition of soil N is determined by fractionation of the most relevant processes and, thus, integrates several N cycle processes, some of which cannot be accessed easily by direct measurement. To implement isotopic fractionation in ecosystem models and to utilize those for model validation, the magnitude of the isotope effects associated with individual transformations in the N cycle need to be assessed. This review summarizes the available methods to determine N isotope effects of various key ecosystem processes, thereby systematically comparing isotope effects for different experimental conditions and processes, exploring the accuracy of theoretical calculations of isotope effects and finally, addressing concepts to implement isotope effects into biogeochemical modeling. Our review shows that published isotope effects for N processes in soil incubations seem to be stronger as compared to those in water saturated systems. In addition to the choice of isotope effects adequate for the respective ecosystem, the challenge for modeling approaches is the sequential calculation of isotopic compositions. Associated numerical inaccuracies can be minimized by controlling the share of reacted substrates, i.e. the time step. The criterion to determine the time step needs to consider the strongest isotope effect, required accuracy of the calculations and the share of substrate consumed from or provided to the compound pool. The combination of biogeochemical models with δ 15 N methods and novel measures like site preference (SP) of N 2 O is a promising approach for improving process understanding at various spatial and temporal scales. Nevertheless, the compilation of isotope effects in this review may not only be of benefit for modelers, but also for experimentalists, as measurement and modeling of isotope effects may eventually help to test and validate our current process understanding of the N cycle. [ABSTRACT FROM AUTHOR]

Although greenhouse vegetable production in China is rapidly changing, consumers are concerned about food quality and safety. Studies have shown that greenhouse soils are highly eutrophicated and potentially contaminated by heavy metals. However, to date, no regional study has assessed whether greenhouse soils differ significantly in their heavy metal and nutrient loads compared to adjacent arable land. Our study was conducted in Shouguang County, a key region of greenhouse vegetable production in China. Soil samples down to soil depths of 3 m were taken from 60 greenhouse vegetable fields of three different ages (5, 10, and 20 years) and from 20 adjacent arable fields to analyze the concentrations of heavy metals, nutrients, and soil physio-chemical parameters. A comparison of greenhouse soils with adjacent arable fields revealed that for greenhouses, (a) micro (heavy metals: Cu, Zn, and Mn) and macronutrients (Nmin, Olsen-P, available K) were significantly higher by a factor of about five, (b) N:P:K ratios were significantly imbalanced towards P and K, and (c) topsoil (0–30 cm) concentrations of the above-mentioned micro- and macronutrients increased with years of vegetable cultivation. In contrast, the soil concentrations of the heavy metals Cr and Pb were lower in greenhouse soils. Heavy metal concentrations did not vary significantly with soil depth, except for the micronutrients Cu and Zn, which were between 1- and 3-fold higher in the topsoil (0–30 cm) than in the subsoil (30–300 cm). The Nemerow pollution index (P N) was 0.37, which was below the recommended environmental threshold value (P N < 1). Structural equation model analysis revealed that soil nutrient concentrations in greenhouse soils are directly related to the input of fertilizers and agrochemicals. Lower values of soil Pb and Cr concentrations in greenhouses were due to the sheltering effect of the greenhouse roof, which protected soils from atmospheric deposition due to emissions from nearby industrial complexes. [Display omitted] • Soil concentrations of Fe, Mn, Cu, and Zn in greenhouses increase with time. • Micro-nutrients Cu and Zn highly elevated in greenhouse soils due to fertilization. • Soil concentrations of Cr and Pb in greenhouses decrease with time. • Greenhouse soils show major nutrient imbalances regarding N:P:K ratios. • Heavy metal pollution of greenhouse soils below critical threshold in study area. [ABSTRACT FROM AUTHOR]

Abstract: The development and testing of (ecological) models require continuous control and adaptation of the simulator to measured data. Optimisation techniques, sensitivity and uncertainty analysis are important tools to automate these validation steps and support modellers to understand and interpret simulation results in terms of their reliability. Since ecological models simulate complex environmental processes, the models developed exhibit a high degree of detail. As a result, the required CPU time is substantial whilst at the same time these models can no longer be analytically analysed and optimised. Therefore representative sampling techniques are often used requiring a high number of model runs. Hence, the model run time and the number of samples needed to create a representative range are the driving factors that determine the total required time for validation. As a consequence, it is therefore indispensable to parallelise parts of the code and run them on more than one processing unit. Therefore, the aim of this study is to show the ease of parallelisation within the statistical software R using the package Rmpi. We present the parallelisation of three different applications (optimisation, Bayesian calibration, sampling from distributions), using our complex ecosystem model LandscapeDNDC. We were able to run the Bayesian Calibration at a computing cluster using 24 CPU's in 11.8days opposed to 236.7days when using only one CPU. This is an acceleration of the evaluation process by a factor of approximately 20. [Copyright &y& Elsevier]

This study provides a combined dataset on N loss pathways and fluxes from sloping cropland in the purple soil area, southwestern China. A lysimeter experiment was conducted to quantify nitrate leaching (May 2004–May 2010) and N2O emission (May 2009–May 2010) losses. Nitrate leaching was the dominant N loss pathway and annual leaching fluxes ranged from 19.2 to 53.4 kg N ha−1, with significant differences between individual observation years (P < 0.05). Direct N2O emissions due to N fertilizer use were 1.72 ± 0.34 kg N ha−1 yr−1, which corresponds to an emission factor of 0.58 ± 0.12%. However, indirect N2O emissions caused by nitrate leaching and surface runoff N losses, may contribute another 0.15–0.42 kg N ha−1 yr−1. Our study shows that nitrate leaching lowered direct N2O emissions, highlighting the importance for a better understanding of the tradeoff between direct and indirect N2O emissions for the development of meaningful N2O emission strategies. [Copyright &y& Elsevier]

Abstract: Assessing the parameter uncertainty of complex ecosystem models is a key challenge for improving our understanding of real world abstractions, such as those for explaining carbon and nitrogen cycle at ecosystem scale and associated biosphere-atmosphere-hydrosphere exchange processes. The lack of data about the variance of measurements forces scientists to revisit assumptions used in estimating the parameter distribution of complex ecosystem models. An increasingly used tool for assessing parameter uncertainty of complex ecosystem models is Bayesian calibration. In this paper, we generate two data sets which may represent a seasonal temperature curve or the seasonality of soil carbon dioxide flux and a single high peak put on a low background signal as is e.g. typical for soil nitrous oxide emission. Based on these examples we illustrate that commonly used assumptions for measurement uncertainty can lead to a sampling of wrong areas in the parameter space, incorrect parameter dependencies, and an underestimation of parameter uncertainties. This step needs particular attention by modelers as these issues lead to erroneous model simulations a) in present and future domains, b) misinterpretations of process feedback and functioning of the model, and c) to an underestimation of model uncertainty (e.g. for soil greenhouse gas fluxes). We also test the extension of the Bayesian framework with a model error term to compensate the effects caused by the false assumption of a perfect model and show that this approach can alleviate the observed problems in estimating the model parameter distribution. [Copyright &y& Elsevier]

Simulations with the process oriented Forest-DNDC model showed reasonable to good agreement with observations of soil water contents of different soil layers, annual amounts of seepage water and approximated rates of nitrate leaching at 79 sites across Germany. Following site evaluation, Forest-DNDC was coupled to a GIS to assess nitrate leaching from German forest ecosystems for the year 2000. At national scale leaching rates varied in a range of 0–>80 kg NO3–N ha−1 yr−1 (mean 5.5 kg NO3–N ha−1 yr−1). A comparison of regional simulations with the results of a nitrate inventory study for Bavaria showed that measured and simulated percentages for different nitrate leaching classes (0–5 kg N ha−1 yr−1:66% vs. 74%, 5–15 kg N ha−1 yr−1:20% vs. 20%, >15 kg N ha−1 yr−1:14% vs. 6%) were in good agreement. Mean nitrate concentrations in seepage water ranged between 0 and 23 mg NO3–N l−1. [Copyright &y& Elsevier]

Human activities have accelerated global nitrogen cycling by approx. a factor of two. Also under future environmental conditions, agricultural nitrogen use is expected to remain the leading cause of reactive nitrogen (Nr) release to the environment. The main process to remove Nr from the environment is microbial denitrification. Here we summarize potential mechanisms that may affect denitrification and associated nitrous oxide (N2O) emissions in/from agricultural systems under future environmental conditions. Though changes in climate, specifically in temperature and precipitation, are likely to directly affect denitrification rates and N2O emissions, we identified several indirect mechanisms of global change that may potentially override direct effects. Among these are a) landscape scale changes of hotspots of denitrification: while the importance of non-hydromorphic upland soils for denitrification may decrease owing to limitations in soil moisture the importance of riparian areas as denitrification hotspots may further increase owing to the increased likeliness of flooding events leading to more frequent occurrences of aerobic–anaerobic cycles in riparian areas and, thus, increased denitrification, b) increased provision of labile carbon substrates via plant root exudation in the rhizosphere under elevated atmospheric carbon dioxide (CO2) concentrations, leading to increased microbial activity and higher denitrification rates in agricultural subsoils, thereby potentially reducing rates of nitrate leaching from agricultural soils and c) increased ammonia (NH3) volatilization from agricultural systems leading to increased denitrification rates and N2O emissions downwind from NH3 emission sources. Obviously, under future environmental conditions the mentioned mechanisms would further strengthen the regional disjunction of areas of Nr application from those of Nr removal by denitrification, thereby calling for a reappraisal of the importance of indirect emissions of N2O from agricultural Nr use. It remains unclear, to which extent climate change mitigation options such as the introduction of no-till systems or the increasing use of slow release fertilizers in conjunction with nitrification inhibitors or the adaptations of agricultural management practices to climate change such as altered timing of cultivation, choice of crop varieties and adaptation of water saving production systems may finally override direct and indirect climate change effects on denitrification and N2O emissions from agricultural systems. [Copyright &y& Elsevier]

Based on multi-year measurements of CH4 exchange in sub-daily resolution we show that clear-cutting of a forest in Southern Germany increased soil temperature and moisture and decreased CH4 uptake. CH4 uptake in the first year after clear-cutting (−4.5 ± 0.2 μg C m−2 h−1) was three times lower than during the pre-harvest period (−14.2 ± 1.3 μg C m−2 h−1). In contrast, selective cutting did not significantly reduce CH4 uptake. Annual mean uptake rates were −1.18 kg C ha−1 yr−1 (spruce control), −1.16 kg C ha−1 yr−1 (selective cut site) and −0.44 kg C ha−1 yr−1 (clear-cut site), respectively. Substantial seasonal and inter-annual variations in CH4 fluxes were observed as a result of significant variability of weather conditions, demonstrating the need for long-term measurements. Our findings imply that a stepwise selective cutting instead of clear-cutting may contribute to mitigating global warming by maintaining a high CH4 uptake capacity of the soil. [Copyright &y& Elsevier]

Livestock excreta on pastures is an important source of nitrous oxide (N 2 O) emissions, however studies measuring these emissions in tropical regions, particularly Africa, remain limited. Therefore we measured N 2 O emissions from different quantities of dung patches during three observation periods (dry, wet and transition from dry to wet season) and different volumes of urine patches during wet and dry seasons. Dung patches did not stimulate soil N 2 O emissions in any of the three observation periods, while urine application stimulated soil N 2 O emissions during both seasons, with higher emissions observed during the wet season. The dung EFs (0.00–0.03%) and the urine EFs (0.04–0.40%) showed no detectable effects of dung quantity or urine volume. We further synthesized observations from other studies in wet and dry tropical regions, which indicated that the excreta N 2 O EFs were similar to the default values provided in the IPCC 2019 refinement (0.11% vs 0.07% for dung and 0.41% vs 0.32% for urine in dry climates, and 0.13% vs 0.13% for dung and 0.65% vs 0.77% for urine in wet climates). However, sub-Saharan African (SSA) studies had consistently lower EFs, possibly due to the lower urine-N: dung-N ratio in SSA compared with the other tropical regions, suggesting that the refinement may still overestimate excreta emissions in SSA. Moreover, considering the large variations in the summarized tropical excreta N 2 O EFs, from -0.01 to 1.77% for dung and 0.00 to 4.90% for urine, more studies under diverse conditions across tropical regions are recommended. • Excreta N 2 O emission factors not influenced by mass or volume. • Soil type and N partitioning are overlooked factors in national N 2 O inventories. • IPCC 2019 refinement may still overestimate excreta N 2 O emissions in SSA. [ABSTRACT FROM AUTHOR]

Abstract: Reduction of nitrous oxide (N2O) to dinitrogen (N2) by denitrification in soils is of outstanding ecological significance since it is the prevailing natural process converting reactive nitrogen back into inert molecular dinitrogen. Furthermore, the extent to which N2O is reduced to N2 via denitrification is a major regulating factor affecting the magnitude of N2O emission from soils. However, due to methodological problems in the past, extremely little information is available on N2 emission and the N2:N2O emission ratio for soils of terrestrial ecosystems. In this study, we simultaneously determined N2 and N2O emissions from intact soil cores taken from a mountainous beech forest ecosystem. The soil cores were taken from plots with distinct differences in microclimate (warm-dry versus cool-moist) and silvicultural treatment (untreated control versus heavy thinning). Due to different microclimates, the plots showed pronounced differences in pH values (range: 6.3–7.3). N2O emission from the soil cores was generally very low (2.0±0.5–6.3±3.8μgNm−2 h−1 at the warm-dry site and 7.1±3.1–57.4±28.5μgNm−2 h−1 at the cool-moist site), thus confirming results from field measurements. However, N2 emission exceeded N2O emission by a factor of 21±6–220±122 at the investigated plots. This illustrates that the dominant end product of denitrification at our plots and under the given environmental conditions is N2 rather than N2O. N2 emission showed a huge variability (range: 161±64–1070±499μgNm−2 h−1), so that potential effects of microclimate or silvicultural treatment on N2 emission could not be identified with certainty. However, there was a significant effect of microclimate on the magnitude of N2O emission as well as on the mean N2:N2O emission ratio. N2:N2O emission ratios were higher and N2O emissions were lower for soil cores taken from the plots with warm-dry microclimate as compared to soil cores taken from the cool-moist microclimate plots. We hypothesize that the increase in the N2:N2O emission ratio at the warm-dry site was due to higher N2O reductase activity provoked by the higher soil pH value of this site. Overall, the results of this study show that the N2:N2O emission ratio is crucial for understanding the regulation of N2O fluxes of the investigated soil and that reliable estimates of N2 emissions are an indispensable prerequisite for accurately calculating total N gas budgets for the investigated ecosystem and very likely for many other terrestrial upland ecosystems as well. [Copyright &y& Elsevier]

Three different tropical rain forest sites in Northeast Queensland, Australia, two in the Coastal Lowlands (Pin Gin Hill and Bellenden Ker) and one on the Atherton Tablelands (Kauri Creek), were investigated for the magnitude of N2O and CO2 emissions from soils during the wet and the dry season. At all sites, mean N2O emission rates were significantly higher during the wet season (Bellenden Ker: 242.0±7.4 μg N2O–N m−2 h−1, Pin Gin Hill: 140.8±5.1 μg N2O–N m−2 h−1, Kauri Creek: 80.8±3.3 μg N2O–N m−2 h−1) as compared to the dry season when N2O-emissions were markedly lower (<20 μg N2O–N m−2 h−1) due to limitations in soil moisture. During the wet season, mean N2O emission rates of the Coastal Lowland sites Bellenden Ker and Pin Gin Hill were approximately twofold higher as compared to N2O emission rates of the Atherton Tableland site Kauri Creek. These site differences were found to be due to differences in precipitation and soil moisture, the C-to-N ratio of the organic matter, soil pH and temperature. Site and seasonal differences in CO2-emissions were not as pronounced as for N2O-emissions. Mean CO2 emission rates at the different sites were in a range of 92.2±1.8 up to 137.3±4.5 mg C m−2 h−1. Correlation analysis revealed a strong dependency of N2O and CO2 emissions on changes in soil moisture, whereas changes in soil temperature did not significantly influence the magnitude of in situ N2O and CO2 emissions. N2O emissions were positively correlated to changes in water filled pore space (WFPS) up to a threshold of 50% WFPS at the Bellenden Ker and Kauri Creek sites and up to a threshold of 60% WFPS at the Pin Gin Hill site. CO2 emission rates were positively correlated to changes in WFPS at dry to moderate soil water contents during the dry season, but were negatively correlated to changes in WFPS during the wet season. Measurements of soil air N2O-concentrations at the different sites revealed the following sequence in magnitude: Bellenden Ker>Pin Gin Hill>Kauri Creek, which is the same as found for the N2O source strengths at these sites. [Copyright &y& Elsevier]

Approximately 1/3 of vegetables in China are produced in solar greenhouses. Most farmers use conventional irrigation with over fertilisation (CIF), thereby applying approximately 2000 kg N ha−1 fertiliser over two cropping seasons per year. Here, we tested the effect of drip irrigation with reduced fertilisation (DIF) combined with straw incorporation on reducing N 2 O emissions and nitrogen leaching from solar greenhouse vegetable production systems. Over three consecutive tomato cropping seasons, N 2 O emissions and nitrogen leaching were monitored in high temporal resolution, thereby producing a unique dataset. Compared to CIF, the realised drip fertigation scheme reduces N 2 O emission and nitrogen leaching of nitrate and dissolved organic nitrogen by approximately a factor of 5–10 (N 2 O-DIF: 10.3, CIF: 47.5 kg N ha−1 yr−1; N leaching-DIF: 83.6, CIF: 863 kg N ha−1 yr−1). Straw incorporation in CIF, though advantageous for soil health, resulted in pollution swapping as soil N 2 O emissions increased while NO 3 − leaching losses decreased. On the contrary, no significant negative environmental N effects of straw incorporation were found for DIF. As crop productivity was not affected by straw incorporation, neither for CIF nor for DIF, our study provides a sound basis for policy advice to recommend farmers to adopt drip fertigation combined with straw application. Wide scale adoption of this technique will result in reductions of environment N losses, alleviate major soil degradation signs, including soil acidity, nutrient imbalance and deterioration of soil microbial community structure, while allowing to maintaining high yields of vegetables in solar greenhouse production systems. Image 1 • Drip fertigation significantly reduced N 2 O emission by 80% and N leaching by 90%. • Most N 2 O emission and N leaching occurred in the first 20-day after basal fertigation. • Total environment N losses was higher in autumn-winter than in winter-spring season. • Straw addition increased N 2 O emissions and decreased N leaching in flood fertigation. • Straw addition had no effects on environmental N loss in drip fertigation. Drip fertigation combined with straw incorporation significantly reduces N 2 O emission and N leaching, improves soil health, while sustaining high yields. [ABSTRACT FROM AUTHOR]

Vegetable production in greenhouses is often associated with the use of excessive amounts of nitrogen (N) fertilizers, low NUE (15–35%), and high N losses along gaseous and hydrological pathways. In this meta-analysis, we assess the effects of application rate, fertilizer type, irrigation, and soil properties on soil N 2 O emissions and nitrogen leaching from greenhouse vegetable systems on the basis of 75 studies. Mean ± standard error (SE) N 2 O emissions from unfertilized control plots (N 2 O control) and N leaching (NL control) of greenhouse vegetable systems were 3.2 ± 0.4 and 91 ± 20 kg N ha−1 yr−1, respectively, indicating legacy effects due to fertilization in preceding crop seasons. Soil organic carbon concentrations (SOC) and irrigation were significantly positively correlated with NL control losses, while other soil properties did not significantly affect N 2 O control or NL control. The annual mean soil N 2 O emission from fertilized greenhouse vegetable systems was 12.0 ± 1.0 kg N 2 O–N ha−1 yr−1 (global: 0.067 Tg N 2 O–N yr−1), with N 2 O emissions increasing exponentially with fertilization. The mean EF N2O was 0.85%. The mean annual nitrogen leaching (NL) was 297 ± 22 kg N ha−1 yr−1 (global: 1.66 Tg N yr−1), with fertilization, irrigation, and SOC explaining 65% of the observed variation. The mean leaching factor across all fertilizer types was 11.9%, but 18.7% for chemical fertilizer. Crop NUE was highest, while N 2 O emissions and N leaching were lowest, at fertilizer rates <500 kg N ha−1 year−1. Yield-scaled N 2 O emissions (0.05 ± 0.01 kg N 2 O–N Mg−1 yr−1) and nitrogen leaching (0.79 ± 0.08 kg N Mg−1 yr−1) were lowest at fertilizer rates <1000 kg N ha−1 yr−1. Vegetables are increasingly produced in greenhouses, often under management schemes of extreme fertilization (>1500 kg N ha−1 yr−1) and irrigation (>1200 mm yr−1). Our study indicates that high environmental N 2 O and N leaching losses can be mitigated by reducing fertilization rates to 500–1000 kg N ha−1 yr−1 (mean: ∼762 kg N ha−1 yr−1) without jeopardizing yields. Image 1 • Global greenhouse vegetables contribute 0.067 Tg N 2 O–N yr−1 to atmospheric N 2 O. • N leaching from greenhouse vegetable production contributes 1.66 Tg N yr−1 to groundwater pollution. • N 2 O emissions were higher, and N leaching lower if chemical + organic fertilizers were used. • Low N losses and high N use efficiency were detected at N fertilization rates <500 kg N ha−1 yr−1. • Yield-scaled N 2 O emission and N leaching was lower at N fertilization rates <1000 kg N ha−1 yr−1. [ABSTRACT FROM AUTHOR]

Polluted urban river systems might be a strong source of atmospheric methane (CH 4) and nitrous oxide (N 2 O), but so far only a few urban river systems have been quantified with regard to their source strength for greenhouse gases (GHGs). In this study, we measured loads of dissolved inorganic nitrogen and organic carbon, dissolved oxygen (DO) concentrations, and fluxes of CH 4 and N 2 O from an urban river in Beijing, China during the course of an entire year. Fluxes calculated using the floating chamber approach or via the diffusion method with measurements of river water GHG concentrations showed comparable temporal variations. However, the flux magnitude based on the diffusion method was found to strongly depend on the underlying parameterization of the gas transfer velocity. In view of the large differences while applying different methodologies to estimate surface water GHG fluxes further studies are still needed to prove and eventually quantify the systematic errors which are likely caused by either the chamber technique or the approaches of individual diffusion models. For both the floating chamber and the diffusion-based flux estimates, strong seasonal variations in CH 4 and N 2 O fluxes from the river surface were observed, with fluxes ranging from 3 to 8374 μg C m−2 h−1 for CH 4 and 1–3986 μg N m−2 h−1 for N 2 O. The CH 4 fluxes were strongly negatively correlated with the DO concentration (P < 0.01). The highest N 2 O fluxes were observed at times with low CH 4 fluxes (i.e., in spring and autumn). Annual CH 4 and N 2 O fluxes totaled 19.3–79.4 and 17.4–44.8 kg C (N) ha−1 yr−1, respectively. These high fluxes are in agreement with estimates from the few other studies carried out for urban river systems to date and indicate that urban polluted river systems are a significant regional source of atmospheric GHGs. Image 1 • The polluted Xiaoyue River is a strong source of atmospheric CH 4 and N 2 O. • Dissolved oxygen was the primary factor controlling the river CH 4 fluxes. • River CH 4 and N 2 O concentrations and fluxes were inversely correlated seasonally. • Existing diffusion models contribute to the uncertainty in flux estimates. The polluted Xiaoyue River is a strong source of atmospheric CH 4 and N 2 O, whose fluxes do vary substantially depending on different methods used. [ABSTRACT FROM AUTHOR]

Grasslands cover more than one fifth of total land area in Europe and contribute significantly to the total greenhouse gas budget. The impact of management and land use on the carbon cycle and carbon sequestration in grasslands has been well-studied, however effects on emissions of N 2 O and CH 4 remain uncertain. Additionally, the majority of studies have focussed on management differences between intensively managed grasslands, with few results available for lightly managed grasslands and in particular grassland abandonment. We present N 2 O and CH 4 flux measurements for an abandonment trajectory at low land-use intensity, comparing meadow (fertilized and cut), pasture (grazed) and abandoned (unmanaged since 1983) grassland sites located in the Austrian Alps. Mean growing season N 2 O fluxes were 0.07, 0.07 and − 0.13 nmol m −2  s −1 and CH 4 fluxes were − 1.0, − 0.5 and − 1.6 nmol m −2  s −1 for the meadow, pasture and abandoned sites respectively. Variability for both gases at the abandoned site was dominated by ‘hot moments', while ’hot spots' dominated at the managed meadow and pasture sites. Consideration of the diurnal cycle observed at the abandoned site, linear correlations within all data sets, and principal components analyses of the full data set revealed increased consumption of both N 2 O and CH 4 with increasing temperature, but hardly any relationship between fluxes and soil moisture. Upscaled over a year, the observed fluxes correspond to enhanced non-CO 2 greenhouse gas uptake of 172 g CO 2 -equiv. m −2  y −1 following abandonment. These results show that non-CO 2 greenhouse gases form an important part of the total climate impact of land use change and grassland abandonment, such that abandoned grassland is a net sink for both CH 4 and N 2 O. [ABSTRACT FROM AUTHOR]