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Source determination of N2O has often been performed using stable isotope incubation experiments. In situ experiments with isotopic tracers are an important next step. However, the challenge is to distribute the tracers in the field as homogeneously as possible. To examine this, a bromide solution was applied as a stand‐in tracer using either a watering can, a sprayer, or syringes to a relatively dry (25% gravimetric moisture content) or wet (30%) silt loam. After 1 h, samples were taken from three soil depths (0‐10 cm), and analyzed for their water content and bromide concentration. The application with syringes was unsuccessful due to blocked cannulas. Therefore, further laboratory experiments were conducted with side‐port cannulas. Despite a larger calculated gravimetric soil moisture difference with watering can application, more Br‐ tracer was recovered in the sprayer treatment, probably due to faster transport of Br‐ through macropore flow in the wetter conditions caused by the watering can treatment. The losses of Br‐ (33% for the watering can, 28% for the sprayer treatment) are equivalent to potential losses of isotopic tracer solutions. For application of 60 at% 15NH4+, this resulted in theoretical enrichments of 44‐53 at% in the upper 2.5 cm and 7‐48 at% in 5‐10 cm. As there was hardly any NO3‐ in the soil, extrapolations for 15NO3‐ calculated enrichments were 57‐59 at% in the upper 2.5 cm and 26‐57 at% in 5‐10 cm. Overall, no method, including the side‐port cannulas, was able to achieve a homogeneous distribution of the tracer. Future search for optimal tracer application should therefore investigate methods that utilize capillary forces and avoid overhead pressure. We recommend working on rather dry soil when applying tracers, as tracer recovery was larger here. Furthermore, larger amounts of tracer lead to more uniform distributions. Further studies should also investigate the importance of plant surfaces. [ABSTRACT FROM AUTHOR]

Pure culture studies provide evidence of the ability of soil fungi to produce nitrous oxide (N2O) during denitrification. Soil studies with selective inhibition indicated a possible dominance of fungal compared to bacterial N2O production in soil, which drew more attention to fungal denitrification. Analyzing the isotopic composition of N2O, especially the [sup 15]N site preference of N2O produced (SPN[sub 2]O), showed that N2O of pure bacterial or fungal cultures differed in SPN[sub 2]O values, which might enable the quantification of fungal N2O based on the isotopic endmember signatures of N2O produced by fungi and bacteria. This study aimed to identify the fungal contribution to N2O emissions under anaerobic conditions in incubated repacked soil samples by using different approaches to disentangle sources of N2O. Three soils were incubated under anaerobic conditions to promote denitrification with four treatments of a modified substrate induced respiration with selective inhibition (SIRIN) approach. While one treatment without microbial inhibition served as a control the other three treatments were amended with inhibitors to selectively inhibit bacterial, fungal or bacterial and fungal growth. These treatments were performed in three varieties. In one variety the [sup 15]N tracer technique was used to estimate the effect of N2O reduction on N2O produced, while two other varieties were performed under natural isotopic conditions but with and without acetylene. Three approaches were established to estimate the N2O production by a fungal community in soil: i) A modification of the SIRIN approach was used to calculate N2O evolved from selected organism groups, and ii) SPN2O values from the acetylated treatment were used in the isotope endmember mixing approach (IEM), and iii) the SP/δ 18O mapping approach (SP/δ18O Map) was used to estimate the fungal contribution to N2O production and N2O reduction under anaerobic conditions from the non-acetylated treatment. The three approaches tested revealed a small fungal contribution to N2O fluxes under anaerobic conditions in the soils tested. Quantifying the fungal fraction with modified SIRIN was only possible in one soil and totaled 0.28±0.09. This was higher than the results obtained by IEM and SP/δ18O Map, which accounted zero to 0.20 of N2O produced to the fungal community. To our knowledge, this study was the first attempt to quantify the fungal contribution to anaerobic N2O production by simultaneous application of three approaches, i.e. modified SIRIN, IEM and SP/δ18O Map. While all methods coincided by suggesting a small or missing fungal contribution, further studies under conditions ensuring larger fungal N2O fluxes and including alternative inhibitors are needed to better cross-validate the methods. [ABSTRACT FROM AUTHOR]

Dairy livestock production systems rely on high‐quality forage legumes, which are widely present in grassland swards all over Europe. A future climatic scenario with higher average annual temperatures and lower precipitation is expected to affect grassland productivity in general and the productivity of the most important forage legume species Trifolium repens in particular. One way to cope with such constraints is the adoption of currently underutilized minor legume species with a higher tolerance towards drought stress. Therefore, the present study investigated legume species with lower moisture requirements than T. repens, these are Lotus corniculatus, Medicago falcata, Medicago lupulina and Onobrychis viciifolia in comparison with T. repens. Legumes were grown in containers as monocultures in a roofed open‐sided greenhouse under conditions of optimal water supply or periodic drought stress. Generally, drought stress decreased the biomass production, but species differed in their reaction. Particularly, M. lupulina and L. corniculatus had lower relative biomass losses (−26%) compared to T. repens (−43%, as averaged over drought stress periods). However, in overall biomass production T. repens still was at one level with M. lupulina and L. corniculatus under drought stress. This was related to high stomata control as indicated by the intrinsic water‐use efficiency. We conclude that there are promising future options of forage legumes as alternatives to T. repens. [ABSTRACT FROM AUTHOR]

Organic grassland farmers are caught between the pressure to operate profitably and the need to ensure ecosystem services like nature conservation. Phosphorus (P) management is at the core of this dilemma: grassland legumes, which are vital for nitrogen (N) inputs, forage quantity and quality, have high P requirements. However, rising soil P contents lead to decreased phytodiversity. We examined this 'P dilemma' based on data of a study in typical organically managed grasslands in north-eastern Germany. We found a slight, but not significant negative correlation between the soil P contents and phytodiversity. Such a negative correlation was much clearer in broader ecological studies of European grasslands, probably due to a scale effect. Despite comparably small P concentrations, we detected only moderate species richness. Thus, other factors besides P concentrations are limiting phytodiversity here, probably N concentrations. The P concentrations in the biomass of various legume species indicated P limitations for most of them. We conclude that a bundle of adapted management measures could reconcile economic and environmental requirements of organic farmers to a certain degree and thus lessen the conflict between the two ecosystem services 'biodiversity' and 'forage production'. [ABSTRACT FROM AUTHOR]

Biogas digestate (BD) is increasingly used as organic fertilizer, but has a high potential for NH3 losses. Its proposed injection into soils as a countermeasure has been suggested to promote the generation of N2O, leading to a potential trade-off. Furthermore, the effect of high nutrient concentrations on N2 losses as they may appear after injection of BD into soil has not yet been evaluated. Hence, we performed an incubation experiment with soil cores in a helium-oxygen atmosphere to examine the influence of soil substrate (loamy sand, clayey silt), water-filled pore space (WFPS; 35, 55, 75%) and application rate (0, 17.6 and 35.2mL BD per soil core, 250 cm3) on the emission of N2O, N2 and CO2 after the usage of high loads of BD. To determine the potential capacity for gaseous losses, we applied anaerobic conditions by purging with helium for the last 24 h of incubation. Immediate N2O and N2 emissions as well as the N2 = (N2OCN2) product ratio depended on soil type and increased with WFPS, indicating a crucial role of soil gas diffusivity for the formation and emission of nitrogenous gases in agricultural soils. However, emissions did not increase with the application rate of BD. This is probably due to an inhibitory effect of the high NHC 4 content of BD on nitrification. Our results suggest a larger potential for N2O formation immediately following BD injection in the fine-textured clayey silt compared to the coarse loamy sand. By contrast, the loamy sand showed a higher potential for N2 production under anaerobic conditions. Our results suggest that short-term N losses of N2O and N2 after injection may be higher than probable losses of NH3 following surface application of BD. [ABSTRACT FROM AUTHOR]

Perennial ryegrass (Lolium perenne) is a very valuable and globally widespread forage grass. The yield and quality characteristics of L. perenne depend on its growth conditions, such as soil and weather conditions. The objective of this study is to determine which soil- or weather parameters can best explain the yield and nutritive values and how they interact with different L. perenne varieties. From 2017 to 2019, field trials were carried out at 14 locations with 10 L. perenne varieties in cooperation with breeders and state institutes, as well as the Federal Plant Variety Office. In addition to yield data, the quality parameters (e.g. crude protein, crude fibre, WSC etc.) of all plant samples were determined by NIRS measurement. We present here the data of the first cut of 2017. Mixed effects model was applied to analyze the influences of soil and weather conditions on yield and various quality characteristics of L. perenne. The results showed significant influences of average temperature (T), accumulated precipitation of the growth period (NS), and field index on dry matter yield (DM). The DM increased linearly with T, while it showed an optimum curve with NS. Strong relationships of T and NS with nutritive values were also found for crude protein (CP), crude fibre (CF), and water soluble carbohydrates (WSC). However, they were also affected by further parameters, such as P2O5 content, field index, and humus level in soil. The next steps will be the statistical analysis and interpretation of the complete data set. [ABSTRACT FROM AUTHOR]

RATIONALE Fungi can contribute greatly to N2O production from denitrification. Therefore, it is important to quantify the isotopic signature of fungal N2O. The isotopic composition of N2O can be used to identify and analyze the processes of N2O production and N2O reduction. In contrast to bacteria, information about the oxygen exchange between denitrification intermediates and water during fungal denitrification is lacking, impeding the explanatory power of stable isotope methods. METHODS Six fungal species were anaerobically incubated with the electron acceptors nitrate or nitrite and 18O-labeled water to determine the oxygen exchange between denitrification intermediates and water. After seven days of incubation, gas samples were analyzed for N2O isotopologues by isotope ratio mass spectrometry. RESULTS All the fungal species produced N2O. N2O production was greater when nitrite was the sole electron acceptor (129 to 6558 nmol N2O g dw-1 h-1) than when nitrate was the electron acceptor (6 to 47 nmol N2O g dw-1 h-1). Oxygen exchange was complete with nitrate as electron acceptor in one of five fungi and with nitrite in two of six fungi. Oxygen exchange of the other fungi varied (41 to 89 % with nitrite and 11 to 61 % with nitrate). CONCLUSIONS This is the first report on oxygen exchange with water during fungal denitrification. The exchange appears to be within the range previously reported for bacterial denitrification. This adds to the difficulty of differentiating N2O producing processes based on the origin of N2O-O. However, the large oxygen exchange repeatedly observed for bacteria and now also fungi could lead to less variability in the δ18O values of N2O from soils, which could facilitate the assessment of the extent of N2O reduction. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The article reports on a study that shows long-term nitrogen fertilization can increase the release of ancient carbon (C) from deep critical zones, resulting in more carbon dioxide (CO2) emissions. It also mentions that this increase in nitrogen input resulting from anthropogenic activity is considered responsible for the activation of "sleeping" carbon in deep soils, including the need for improved nitrogen management in fertilized agricultural soils.

Nitrous oxide (N2O) is a critical greenhouse gas and an ozone-depleting substance, with a global warming potential 298–310 times greater than that of CO2. Mitigating N2O emissions from soils has environmental benefits. Recent research indicates that biochar can serve as an “electron shuttle” to reduce N2O emissions from soils. Electron shuttle is defined as organic molecules capable of reversibly receiving and donating electrons. Thus, biochar is expected to facilitate stepwise reduction of denitrification products, reducing N2O to environmentally harmless N2. However, it remains uncertain whether biochar’s capacity to mitigate N2O can be enlarged by augmenting its function as an electron shuttle. Thus, this study prepared a biochar with enhanced electron shuttle potential by loading redox-active (Fe) onto biochar. The effectiveness of this biochar in mitigating soil N2O emissions was investigated by incorporating it into the soil. The results showed that Fe-loaded biochar significantly augmented its function as an electron shuttle and dramatically reduced soil N2O emissions by 92% compared to the original biochar. The degree of decrease in N2O emissions was strongly associated with both the electron shuttle capacity and the concentration of redox-active Fe in the biochar. Additionally, Fe-loaded biochar significantly decreased the N2O/(N2O + N2) emission ratio and increased the expression of the nosZ-II gene. Our findings suggest that redox-active Fe loading in biochar is an effective strategy to enhance its electron shuttle function. The augmented electron shuttle function of biochar can successfully facilitate N2O mitigation emission by promoting complete denitrification. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N 2 O) is a potent greenhouse gas and causes stratospheric ozone depletion. While the emissions of N 2 O from soil are widely recognized, recent research has shown that terrestrial plants may also emit N 2 O from their leaves under controlled laboratory conditions. However, it is unclear whether foliar N 2 O emissions are universal across varying plant taxa, what the global significance of foliar N 2 O emissions is, and how the foliage produces N 2 O in situ. Here we investigated the abilities of 25 common plant taxa, including trees, shrubs and herbs, to emit N 2 O under in situ conditions. Using 15 N isotopic labeling, we demonstrated that the foliage-emitted N 2 O was predominantly derived from nitrate. Moreover, by selectively injecting biocide in conjunction with the isolating and back-inoculating of endophytes, we demonstrated that the foliar N 2 O emissions were driven by endophytic bacteria. The seasonal N 2 O emission rates ranged from 3.2 to 9.2 ng N 2 O-N g -1 dried foliage h -1 . Extrapolating these emission rates to global foliar biomass and plant N uptake, we estimated global foliar N 2 O emission to be 1.21 and 1.01 Tg N 2 O-N year -1 , respectively. These estimates account for 6%-7% of the current global annual N 2 O emission of 17 Tg N 2 O-N year -1 , indicating that in situ foliar N 2 O emission is a universal process for terrestrial plants and contributes significantly to the global N 2 O inventory. This finding highlights the importance of measuring foliar N 2 O emissions in future studies to enable the accurate assigning of mechanisms and the development of effective mitigation., (© 2024 John Wiley & Sons Ltd.)

Source determination of N 2 O has often been performed using stable isotope incubation experiments. In situ experiments with isotopic tracers are an important next step. However, the challenge is to distribute the tracers in the field as homogeneously as possible. To examine this, a bromide solution was applied as a stand-in tracer using either a watering can, a sprayer, or syringes to a relatively dry (25% gravimetric moisture content) or wet (30%) silt loam. After 1 h, samples were taken from three soil depths (0-10 cm), and analyzed for their water content and bromide concentration. The application with syringes was unsuccessful due to blocked cannulas. Therefore, further laboratory experiments were conducted with side-port cannulas. Despite a larger calculated gravimetric soil moisture difference with watering can application, more Br - tracer was recovered in the sprayer treatment, probably due to faster transport of Br - through macropore flow in the wetter conditions caused by the watering can treatment. The losses of Br - (33% for the watering can, 28% for the sprayer treatment) are equivalent to potential losses of isotopic tracer solutions. For application of 60 at% 15 NH 4 + , this resulted in theoretical enrichments of 44-53 at% in the upper 2.5 cm and 7-48 at% in 5-10 cm. As there was hardly any NO 3 - in the soil, extrapolations for 15 NO 3 - calculated enrichments were 57-59 at% in the upper 2.5 cm and 26-57 at% in 5-10 cm. Overall, no method, including the side-port cannulas, was able to achieve a homogeneous distribution of the tracer. Future search for optimal tracer application should therefore investigate methods that utilize capillary forces and avoid overhead pressure. We recommend working on rather dry soil when applying tracers, as tracer recovery was larger here. Furthermore, larger amounts of tracer lead to more uniform distributions. Further studies should also investigate the importance of plant surfaces., (© 2020 The Authors. Analytical Science Advances published by Wiley‐VCH GmbH.)

Biochar can reduce both nitrous oxide (N 2 O) emissions and nitrate (NO 3 - ) leaching, but refining biochar's use for estimating these types of losses remains elusive. For example, biochar properties such as ash content and labile organic compounds may induce transient effects that alter N-based losses. Thus, the aim of this meta-analysis was to assess interactions between biochar-induced effects on N 2 O emissions and NO 3 - retention, regarding the duration of experiments as well as soil and land use properties. Data were compiled from 88 peer-reviewed publications resulting in 608 observations up to May 2016 and corresponding response ratios were used to perform a random effects meta-analysis, testing biochar's impact on cumulative N 2 O emissions, soil NO 3 - concentrations and leaching in temperate, semi-arid, sub-tropical, and tropical climate. The overall N 2 O emissions reduction was 38%, but N 2 O emission reductions tended to be negligible after one year. Overall, soil NO 3 - concentrations remained unaffected while NO 3 - leaching was reduced by 13% with biochar; greater leaching reductions (>26%) occurred over longer experimental times (i.e. >30 days). Biochar had the strongest N 2 O-emission reducing effect in paddy soils (Anthrosols) and sandy soils (Arenosols). The use of biochar reduced both N 2 O emissions and NO 3 - leaching in arable farming and horticulture, but it did not affect these losses in grasslands and perennial crops. In conclusion, the time-dependent impact on N 2 O emissions and NO 3 - leaching is a crucial factor that needs to be considered in order to develop and test resilient and sustainable biochar-based N loss mitigation strategies. Our results provide a valuable starting point for future biochar-based N loss mitigation studies., (Copyright © 2018 Elsevier B.V. All rights reserved.)