Nitrification inhibitors (NIs) can be an effective measure to mitigate nitrous oxide (N2O) emissions from agricultural soils. Meta-analyses indicate that the efficacy of NIs is influenced by soil properties and climate, but such effects have rarely been investigated by direct comparisons across field sites. Using four experimental field sites across Denmark, this study investigated the interacting effects of fertiliser type, soil type and rainfall on N2O emissions and effects of two different NIs after spring fertilisation of spring barley in 2022 and 2023. The fertiliser materials included cattle slurry (CS), pig slurry (PS) and urea ammonium nitrate (UAN, 2022 only), applied at recommended rates with or without 3,4-dimethylpyrazole phosphate (DMPP) or 2-chloro-6-(trichloromethyl) pyridine (nitrapyrin, NP), along with an unfertilised control. Rainfall was close to the long-term average at Askov and Vejen in 2022 but below average in the six other monitoring periods. The increase in net cumulative N2O emissions from manure application without NIs varied between 0.16 and 1.5 kg N ha-1 while with UAN it was between 0.05 and 0.46 kg N ha-1. The amendment of NIs significantly reduced N2O emissions but only the coarse sandy soil at Vejen showed consistent and large reductions with NI amendment leading to average reductions of 83 %, 67 %, and 77 % for cattle slurry, pig slurry, and UAN, respectively. Specific site effects of NI were attributed to differences in gas and solute diffusivity, and NI availability, across sites and years. In this study, NI amendment to synthetic N fertiliser and, especially, manure applied to sandy soil had the greatest N2O mitigation potential, suggesting targeted use of NIs on sandy soil as a strategic N2O mitigation scenario.

Legume covercrops can partially offset synthetic N inputs by returning N-rich residues to soil for wheat production in arid regions. However, the outcomes of reducing N fertilizer remain underexplored across agronomic, nutritional, economic, and environmental dimensions. This study was conducted from 2022 to 2024 in arid northwest China to evaluate the effects of rotating a mixed-legume cover crop (hairy vetch: common vetch = 1:5) with two consecutive spring wheat (Triticum aestivum L.) under six N management strategies: conventional spring wheat without cover crops receiving 225 kg N ha−1 (TN100), and spring wheat after cover crop incorporation receiving 100

Perennialization represents a promising strategy for enhancing soil organic carbon (SOC) stocks, yet its global sequestration potential remains uncertain because experimental studies often use inconsistent methods to calculate and report SOC stock changes. The SOC stock can be calculated by either the fixed depth (FD) or the equivalent soil mass (ESM) method, and the changes can be estimated either by comparing to the initial C stock (temporal change) or to a reference treatment (reference-based change). These different approaches and their various combinations may yield divergent estimates of SOC stock changes, but their effect has not been systematically evaluated on a large scale. Here, we conducted a meta-analysis of 1022 paired observations from 70 publications to evaluate how contrasting estimation methods influence assessments of SOC stock changes under perennial cropping systems across the soil profile. We found no significant differences between the FD and ESM methods, although FD consistently produced numerically higher estimates. Temporal changes in topsoil SOC stock under perennial cropping (22.9%, 18.3-27.6%) were significantly greater than reference-based changes (5.4%, 1.7-9.2%). In contrast, temporal estimates in the subsoil (-16.7%, -23.7 to -9.1%) were significantly lower than reference-based estimates (4.8%, - 2.9-13.1%). None of the perennial systems produced significant effects on subsoil SOC stocks. Overall, our findings provide the first systematic documentation of methodological differences in estimating changes in SOC stocks following conversion from annual to perennial cropping systems. These discrepancies introduce substantial uncertainty into soil carbon sequestration estimates, potentially biasing regional and global carbon budgets, as well as estimates of mitigation measures.

Nitrous oxide (N2O) is a potent greenhouse gas (GHG) whose atmospheric concentration continues to rise, largely driven by nitrogen (N) inputs to agricultural soils. Over the past three decades, research on soil N2O emissions has advanced substantially, yet key uncertainties still constrain mitigation efforts. Here, we synthesize developments in measurement techniques, process understanding, microbial ecology, and modelling from the 1990s to the present, and identify critical gaps for future research. Advances in high-frequency measurements, laser spectroscopy, and isotopic approaches have revealed the importance of temporal "hot moments" and spatial "hotspots," challenging earlier assumptions based on sparse sampling. Concurrently, molecular and multi-omic tools have transformed our understanding of the microbial drivers of N2O production and consumption, highlighting the role of community composition, truncated pathways, and previously overlooked N2O-producing and reducing organisms. Process-based models have evolved from research tools into policy-relevant frameworks underpinning GHG inventories, with emerging integration of data assimilation, ensemble modelling, and artificial intelligence. However, despite these advances, persistent challenges remain in linking scales, reducing uncertainties, and translating mechanistic insights into scalable mitigation strategies. Closing these gaps offers a unique opportunity to translate decades of scientific progress into next-generation mitigation strategies that align agricultural productivity with climate stabilization goals.

Malting spring barley is an important commodity for Scotland’s whisky and beer industries. Meeting malting quality standards requires precise control of grain protein, which is strongly influenced by nitrogen (N) fertilization. However, N management must balance environmental impacts in addition to grain quality and profitability. Previous frameworks optimized N to reduce nitrate leaching but rarely considered nitrous oxide (N2O) emissions, which are critical under emerging carbon taxation policies. In this study, simulated N2O emissions were integrated into spatial and temporal N-rate optimization for malting spring barley using a calibrated process-based model. Ten N rates (20–200 kg N ha−1) were simulated across four yield-stability zones in an 11-ha commercial farm over 34 years. Emissions varied across zones and years: medium-yield zones (MYZ) emitted the least at high N rates; wet years (>470 mm) produced more N2O than dry years (<320 mm). Higher N inputs improved yield, grain quality, and marginal net returns (MNRav), but increased nitrate leaching and N2O emissions. Trade-offs occurred at 100 kg N ha−1 (N2O vs yield), and 140 kg ha−1 (N2O vs MNRav, grain N concentration). Multi-objective optimization identified 120–140 kg N ha−1 as optimal, with 120 kg N ha−1 favored in wet years. These findings provide a framework for integrating greenhouse gas (GHG) metrics into site-specific N management, advancing climate-smart strategies for intensive cereal systems globally.

Double-cropping rice systems account for nearly half of global rice production, yet their specific vulnerabilities to the combined effects of rising atmospheric CO2 and warming remain critically understudied compared to single-season systems. This knowledge gap poses significant risks to food security assessments, particularly as the frequency of extreme heat events intensifies. This study conducted a two-year field experiment using open-top chambers in Central China to systematically evaluate the interactive impacts of projected CO2 enrichment (similar to 550 mu mol mol(-1)) and warming (+1.5 degrees C) on crop yield, grain quality, and economic revenue. The experiment captured two distinct climatic contexts: a standard meteorological year (2021) and a year defined by record-breaking extreme heat (2022). Results indicated that during the normal conditions of 2021, elevated CO2 increased grain yield from 5.1 to 5.8 t ha(-1) in early rice and from 7.1 to 8.2 t ha(-1) in late rice, thereby largely compensating for warming-induced losses. By contrast, the extreme heat event in 2022 reduced yields from 5.1 to 2.8 t ha(-1) in early rice and from 7.8 to 5.1 t ha(-1) in late rice relative to 2021, while eliminating the CO2 fertilization effect in early rice, with the combined CO2-warming treatment failing to mitigate substantial biomass and grain reductions. Beyond yield, the heat stress severely compromised grain quality; chalkiness rates surged great increase from similar to 1% in 2021 to over 30% under warming treatments in 2022, driving significant declines in head rice rates and subsequent economic revenue. While elevated CO2 did enhance amylose content, it failed to counterbalance the drop in nutritional value. Ultimately, these findings reveal that extreme heat events can override the beneficial physiological effects of elevated CO2, nullifying potential climate resilience in double-cropping systems.

Nitrogen (N) is essential for global food production, yet its inefficient use leads to widespread environmental degradation and contributes significantly to climate change. This focus issue of Environmental Research Letters brings together a comprehensive set of studies that advance our understanding of N dynamics across scales, from field-level processes to global systems, and across sectors including agriculture, industry, and policy. The contributions provide new insights into nitrogen use efficiency, emissions, and flows through detailed subnational and national assessments, alongside methodological advances in N budgeting and accounting frameworks. Several studies address critical uncertainties in N cycling, particularly in relation to denitrification and nitrous oxide (N _2 O) emissions, highlighting gaps in measurement and modeling capabilities. Emerging integrated monitoring and modeling initiatives—including SmartField, canN _2 Onet, and N _2 Onet—demonstrate the potential for harmonized systems that improve measurement, verification, and reporting of N _2 O emissions across scales. Scenario analyses and long-term assessments of agro-food systems reveal the potential for substantial reductions in N losses through structural transformations, including dietary shifts, enhanced circularity, and improved system integration. Other contributions present underexplored opportunities for nutrient recycling, such as the recovery of N from human excreta, and examine the economic trade-offs and policy implications of N use on a global scale. Collectively, the studies emphasize the need for integrated, multi-scale approaches to N management that combine improved monitoring, robust modeling, cross-sectoral accounting, and coordinated governance. This focus issue provides a foundation for advancing N science and developing effective strategies that reconcile food production with environmental sustainability and climate change mitigation.

Afforestation can substantially alter soil organic carbon (SOC) dynamics in drylands; however, its effects on SOC fractions remain insufficiently resolved. We investigated the effect of a 25-year afforestation chronosequence in the Kubuqi Desert on SOC fractions, including acid-hydrolyzable organic carbon (LOC) and acid-resistant organic carbon (ROC) separated by a two-step sulfuric acid hydrolysis method. Compared with the mobile dune as control, SOC increased threefold from 1.54 g kg–1 after 25 years of afforestation. LOC peaked at 2.76 g kg–1 after 15 years and then declined to 1.96 g kg–1 at 25 years. In contrast, ROC increased progressively with afforestation age, reaching 4.10 g kg–1 at 25 years and becoming the dominant SOC fraction. Consequently, the ROC/LOC ratio increased over time, indicating a shift toward greater SOC persistence under prolonged afforestation. Distinct biotic and abiotic factors regulate the two fractions, leading to contrasting responses during long-term afforestation. Multiple linear regression showed that LOC was primarily associated with litter biomass, β-D-cellobiohydrolase activity, and specific bacterial ecological modules, whereas ROC was mainly linked to litter biomass, soil C/N ratio, and fungal ecological modules. Overall, long-term afforestation in temperate deserts enhances both SOC accumulation and persistence, highlighting its value as a sustainable strategy for carbon sequestration in dryland restoration.

Alpine ecosystems have vast amount of soil organic carbon (SOC) and are highly sensitive to climate change. Soil fungi play a crucial role in SOC cycling as decomposers but their contribution to alpine SOC dynamics across high elevation gradients remain poorly understood. Here, we explored fungal communities and their relationships with SOC content across an elevational gradient from 3,994 to 5,120 m on the Tibetan Plateau. We found that SOC content decreased by 28.3% from low to high elevation caused by the trade-offs between ectomycorrhizal fungi and non-ligninolytic saprotrophs. Higher elevation soils, with colder, wetter conditions and lower fertility, were dominated by ectomycorrhizal fungi at the expense of non-ligninolytic saprotrophic fungal species through environmental filtering and nutrient competition. Furthermore, ectomycorrhizal fungi are positively correlated with peroxidative enzyme activities, suggesting enhanced SOC turnover. Our work provides new evidence of, and insights into, the potential role of specific fungal guild trade-offs in shaping SOC fate in fragile alpine ecosystems.

Perennial cropping systems hold great potential to enhance soil organic carbon (SOC) stocks and contribute to climate change mitigation. However, the effects of perennial crops on SOC fractions with different stabilities remain poorly understood. Particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) are considered to have different formation mechanisms and different stabilities. Plant- and microbial-derived carbon (C) are the main origins of SOC, yet their relative contributions to POC and MAOC remain unclear. Here, based on an 11-year experiment, we compared two perennial cropping systems (festulolium and grass-clover) with an annual cropping system (maize), to investigate their effects on soil POC and MAOC, and quantify the contribution of plant- and microbial-derived C to these two soil C fractions using lignin phenols and amino sugars as biomarkers. The soil of the two perennials had higher POC and MAOC than maize at 0-20 cm soil depth, with higher proportions of POC in SOC. The higher POC of the two perennials was linked to their significantly higher fungal and bacterial necromass C in POC. Total microbial necromass C accounted for only 29% of POC and 36% of MAOC at 0-20 cm across all systems, suggesting that plant-derived C dominates these two C pools. However, no significant differences were detected in the lignin phenols content in POC and MAOC at 0-20 cm. Our results challenge the conventional assumption that microbial necromass C dominates MAOC, highlighting the role of plant-derived C in POC and MAOC, which could have a greater influence on soil C sequestration in climates with low mean annual temperature than previously assumed. Given that only two biomarkers were used, interpretations should not be extrapolated beyond their analytical scope.

Context: Increasing species richness and functional diversity in managed grasslands can enhance ecosystem services, particularly when legumes are included. However, it remains unclear whether higher species richness consistently improves productivity and stability in intensively managed grasslands under low nitrogen (N) inputs, or if species identity plays a more dominant role. Objective: This study evaluated how legume identity, non-legume identity, and species richness influence dry matter (DM) yield, N yield, and biological N2 fixation (BNF) in grass-legume-forb mixtures managed with low fertilizer inputs. Methods: In a 3-year field experiment, we tested (i) 2-species mixtures of white clover (Trifolium repens, Tr) or red clover (Trifolium pratense, Tp) with perennial ryegrass (Lolium perenne, Lp), tall fescue (Festuca arundinacea, Fa), chicory (Cichorium intybus, Ci) or ribwort plantain (Plantago lanceolata, Pl); and (ii) multi-species mixtures with 6 and 18 species. Additional 2-species mixtures of ryegrass with six clover genotypes were included. Mixtures received 75 kg N ha-1 yr-1 and were compared with ryegrass monocultures fertilized with 0-450 kg N ha-1 yr-1 . BNF was quantified using the 1 5N isotope dilution method. Results: Species identity, particularly the presence of red clover, was the primary driver of productivity, outweighing the effect of species richness. Red clover mixtures produced 14-21 t DM ha-1 yr-1 across three years, matching ryegrass fertilized with 450 kg N ha-1 yr-1 , while white clover 2-species mixtures yielded less (8-16 t DM ha-1 yr-1) but gained over time relative to red clover mixtures. N yields in red clover mixtures equaled or exceeded those of highly fertilized ryegrass, whereas white clover mixtures matched ryegrass at 300 kg N ha-1 yr-1 . BNF was greatest in red clover mixtures due to higher legume biomass, although the proportion of N derived from the atmosphere (%Ndfa) was similar or higher in white clover mixtures. Increasing species richness beyond two species did not increase yield when red clover was present, but the 18-species mixture maintained more stable legume-non-legume proportions and consistent yields across years. Conclusions: Red clover drives high productivity in low-input grassland mixtures, whereas higher species richness primarily contributes to temporal yield stability rather than increased yield. Significance: Red clover-based mixtures can replace high fertilizer N inputs while sustaining yields equivalent to intensively fertilized monocultures, offering substantial gains in N-use efficiency and reduced fertilizer-related emissions. Incorporating higher species richness may enhance long-term stability and resilience of managed grasslands, supporting more sustainable and climate-smart forage production systems.

Nitrogen-fixing (N-fixing) trees are widely planted in forests and agroforestry ecosystems due to their benefits in soil fertility and carbon sequestration. However, their effects on soil fluxes of nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2) compared to non-fixing trees remain uncertain, potentially challenging their assumed role in greenhouse gas (GHG) mitigation. Through a meta-analysis of 276 observations from 55 publications, we found that N-fixing trees increased soil N2O emissions (Hedge's d = 0.42) and enhanced CH4 uptake (Hedge's d = -0.59) without significantly affecting CO2 emissions and non-CO2 global warming potential. The type of symbiotic bacteria was critical: actinorhizal N-fixing trees increased N2O emissions (Hedge's d = 0.70) but had no effect on CH4 or CO2 fluxes, whereas rhizobial N-fixing trees increased N2O emissions (Hedge's d = 0.37), CH4 uptake (Hedge's d = -0.66) and CO2 emissions (+13%). The effects of N-fixing trees on N2O are mainly influenced by elevation and clay content, on CH4 by clay content and bulk density, and on soil CO2 fluxes by clay content, mean annual temperature, and soil organic carbon. This study highlights the importance of symbiotic relationships in N-fixing trees when designing climate change mitigation strategies, as different types have distinct effects on ecosystem GHG balances.

Legumes are central to sustainable agriculture, improving soil quality, suppressing plant diseases, and boosting crop yields. They may also reduce soil nitrous oxide (N2O) emissions, a potent greenhouse gas, by reducing dependence on synthetic nitrogen fertilizers. However, biological nitrogen fixation by legumes provides easily decomposable nitrogen-rich residues, which may stimulate N2O production through nitrification and denitrification. As a result, the net impact of legumes on N2O emissions remains uncertain. To address this knowledge gap, we conducted a global meta-analysis of 1057 observations from 149 studies. We systematically compared N2O emissions between legume and non-legume cropping systems, including cover crops, rotations, intercropping, and monocultures. Averaged across the entire dataset, legumes did not significantly alter N2O emissions. However, in systems without N fertilization, legumes increased N2O emissions by 34.5–54%. Moreover, legumes increased cash crop yield by 17.2% in rotation and cover crop systems. Soil mineral nitrogen content was the most important driver of legume-induced N2O emissions (R = 0.41, p < 0.05). We also identified environmental conditions under which legume-associated N2O emissions are elevated: cold annual temperatures (< 10 °C), high annual precipitation (> 800 mm), moderate soil bulk density (1–1.3 g cm−3), and low total soil nitrogen (< 0.5 g kg−1). Several management strategies could mitigate legume-induced emissions: minimizing tillage, using efficient irrigation systems, incorporating grain legumes into rotations or monocultures, reducing harvest frequency, reducing nitrogen fertilizers inputs to legumes, and managing legume residues through mulching or harvesting rather than incorporation. By clarifying the complex role of legumes in global N2O dynamics, this study provides a robust quantitative basis for improving predictive models and informing management strategies that align legume-based agriculture with both climate mitigation and food security objectives.

Drip fertigation is a pivotal technology for conserving water in arid and semi-arid regions across the world. Recent field studies have shown that drip fertigation may also mitigate emissions of the powerful greenhouse gas nitrous oxide (N2O). However, existing process-based models have not been evaluated for simulating N2O emissions under drip fertigation systems, limiting our capacity to predict the environmental performance of these irrigation technologies under future climatic conditions. Here, we assessed the performance of the Canadian version of the DeNitrification-DeComposition model (DNDCv.CAN) in simulating N2O emissions from drip-fertigated maize systems. The model was calibrated and validated using a comprehensive two-year dataset from a field experiment in Spain that included subsurface and surface drip irrigation with four nitrogen (N) fertigation treatments: ammonium sulfate (AS), AS with nitrification inhibitor DMPP (AS_DMPP), calcium nitrate (CN), and a control without N (N0). The calibrated model adequately simulated crop yield (RMSE < 1.84 Mg ha−1), grain N content (RMSE < 18 kg N ha−1) and cumulative N2O emissions (RMSE < 0.06 kg N ha−1) across all treatments, with R2 values of 0.3–0.7 and d-index above 0.6. The model also generally captured the observed treatment responses to N fertilizer management and irrigation placement, including the occurrence of peak N2O emissions. Compared to the baseline (1981–2010), projections using DNDCv.CAN by 2100 under SSP2–4.5, SSP3–7.0, and SSP5–8.5, indicated that both surface and subsurface drip fertigation will likely experience yield reductions (-56.2% ~ −14.6%) and increased N2O emissions (27.2% ~ 52.7%). Within these future scenarios, subsurface drip irrigation produced similar yields while reducing N2O emissions compared with surface drip systems. Among all treatments, the combination of AS_DMPP or CN fertilizers with subsurface drip irrigation performed best, achieving lower emissions without compromising yields. Increasing heat stress emerged as the primary driver of future yield losses and elevated N2O emissions due to higher residual soil N. Adaptation strategies, such as earlier sowing paired with longer‑season, higher‑yielding cultivars, may help sustain productivity but could also increase N2O emissions, highlighting important trade‑offs that must be considered when designing and implementing climate‑resilient management practices.

Upholding stable terrestrial ecosystems is integral to supporting climate regulation and planetary security. Yet, while aboveground ecosystem stability is widely described, global-scale patterns in belowground ecosystem stability and how it connects to aboveground stability remain virtually unknown. Here, we assembled a global dataset including high-resolution information on annual estimates of soil respiration from 4,544 communities and associated aboveground ecosystem productivity over the past four decades (1985-2018). We found that ecosystems with greater stability in aboveground productivity had greater long-term stability in soil respiration, with a positive and significant connection between above- and belowground stability being especially strong in arid environments. Stable temperatures played a crucial role in reinforcing the stability and coupling of above- and belowground ecosystems. Our work provides new evidence of, and insights into, the local to global connections of stability of above- and belowground biological activity, and identifies a fundamental role of temperature stability in maintaining this stability under a changing climate.

Species choice and richness in intensively managed grassland mixtures regulate soil carbon (C) input via rhizodeposition, with potential consequences for long-term soil organic carbon storage. Based on a field trial with different grass-legume-forb mixtures, we removed roots from the soil, which was then subjected to particle-size fractionation to trace fresh organic carbon (net C rhizodeposition) into particulate organic matter (POM) and mineral-associated organic matter (MAOM). We related these C input fractions to root traits. Using multiple-pulse 13C-CO2-labeling, we captured the net formation of mineral-associated organic carbon (MAOC) and particulate organic carbon (POC) at the end of the growing season. Pure stand perennial ryegrass (Lolium perenne) had higher quantities of rhizodeposited C allocated to MAOC and POC (0.21 and 0.13 g C kg-1 dry soil, respectively) compared to grass-legume-forb mixtures (ranging from 0.10 to 0.12 for MAOC and 0.05 to 0.06 g C kg-1 dry soil for POC). However, the proportion of MAOC (%MAOC of net C rhizodeposition) in relation to that of POC was higher in mixtures with legumes. Species richness did not affect the quantity of MAOC or POC, nor %MAOC. The quantities of MAOC and POC were positively associated with root length. In contrast, %MAOC was positively associated with root diameter and a lower root C:N ratio. Despite higher %MAOC in mixtures with legumes, the main driver of MAOC and POC quantities was the total amount of C rhizodeposition. These results highlight the importance of legumes in the formation of MAOC from rhizodeposition and of high root length for increasing both MAOC and POC quantities. Our study shows how plant community design can be used to increase MAOC and/or POC and facilitate soil C storage. By revealing the traits behind the relationships between plant communities and MAOC and POC formation, we provide a guide for species selection in intensively managed grasslands to mitigate climate change.

Perennial crops can be a sustainable alternative to annual crops due to plant traits and management practices that improve productivity and may contribute to soil organic carbon (SOC) sequestration. However, our understanding of the mechanisms behind the potential differences in SOC pools between perennials and annuals is incomplete, particularly in the sandy soils that dominate Danish croplands. Based on a 10-year field experiment on a temperate sandy soil with perennials (tall fescue, grass/legume mixture) and annuals (triticale monoculture, triticale in a rotation), we investigated SOC pools at depths of 0-20 cm (topsoil) and 20-50 cm (subsoil) through (i) physical fractionation into pools of particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) and (ii) chemical analysis of aliphatic-to-aromatic/carboxylic ratios via Diffuse Reflectance Infrared Fourier Transform Mid-Infrared Spectroscopy. These analyses were complemented with measurements of extracellular enzyme activities, microbial biomass, root biomass, and aboveground biomass C/N ratio. We found that tall fescue had significantly higher activities of nutrient-releasing enzymes (e.g., N-acetylglucosaminidase and acid phosphatase), and lower oxidase activities (peroxidase and phenol oxidase) in the topsoil compared to annuals. The grass/legume mixture had higher activities of C-, N-, and P-acquiring enzymes than annuals at both soil depths. Soil fractionation analyses showed no significant differences between tall fescue and annuals in POC and MAOC stocks in the topsoil. However, tall fescue exhibited a lower aliphatic to aromatic/carboxylic ratio in the topsoil compared to annuals, which correlated negatively with root biomass and phenol oxidase activity. In the subsoil, the MAOC stock in the tall fescue system tended to accumulate at a rate of 0.35 Mg ha(-1) yr(-1) compared to annual triticale, and was positively correlated to microbial biomass carbon. In contrast, the grass/ legume mixture, without N fertilization, had limited potential for SOC stock increases at both soil depths. Altogether, the results emphasize the role of microbial processes in SOC dynamics and the importance of perennial cropping systems, such as tall fescue, in enhancing SOC stability during the transition from annual to perennial crops for biorefining on sandy soils.

Static chamber-based flux measurements with gas chromatography are commonly used to estimate nitrous oxide (N2O) emissions from arable soils. The LI-COR 7820 N2O/H2O (LI-7820) enables higher-frequency in situ measurements, but side-by-side comparisons with traditional methods are limited. To address this gap, we compared non-steady-state chamber methods including non-flow-through (NFT) and flow-through (FT) chamber methods under field and laboratory conditions with plant cover or bare soil. The LI-7820 was used with the LI8200S smart chamber (FT-1: 0 20 cm) and a self-built chamber (FT-2: 60 x 60 cm), and compared to differently sized NFTs (1-4: 75 x 75, 27 x 37, 60 x 60, and 0 20 cm) with manual sampling with gas chromatography. Field experiments showed high RMSE for daily N2O fluxes within 20 days after fertilizer application between FT-1 and NFTs, particularly for maize and spring barley (183 and 214 mu g N2O-N m- 2 h- 1), which dropped sharply after 20 days (47 and 54 mu g N2O-N m- 2 h- 1, respectively). FT-2 and NFT-3 for pastures had lower RMSE and MAE, both below 40 mu g N2O-N m-2 h- 1. In the incubation experiment, bare soil showed smaller error values, remaining below 26 mu g N2O-N m-2 h- 1. Significant differences were observed between the cumulative N2O emissions measured with NFTs and FT-1, while differences were not significant between NFT-3 and FT-2. Several factors may explain these differences. The smaller chamber dimensions of FT-1 may influence water and nitrogen distribution and constrain the capture of spatial heterogeneity, while NFTs could be affected by prolonged deployment times and in-chamber pressure changes. Furthermore, the lack of water-vapor correction in NFTs, unlike the LI-7820, contributed to discrepancies between methods. Understanding these nuances including the impact of the chamber design, is essential for enhancing the comparability of N2O emissions and getting closer to achieving unbiased measurements of the true flux.

Diverse crop rotations are increasingly recognized as key to address the global food crisis and improve environmental sustainability, including reducing nitrous oxide (N2O) emissions. However, the specific effects on N2O emissions of different crops in these rotations and the underlying incidence on microbial processes remain underexplored. In a six-year field study, we compared N2O emissions from traditional wheat-maize rotation with diverse rotations, including legumes (peanut, soybean), ryegrass, sorghum, and sweet potato. We also examined the microbial functions associated with nitrogen cycling based on functional annotation of prokaryotic taxa (FAPROTAX) analysis. Our study showed that diversified crop rotations with reduced synthetic fertilization and irrigation can reduce N2O emissions by 23 %-49 % compared to conventional rotations. These reductions were supported by increases in soil organic carbon, soil carbon/nitrogen ratio and decreases in the relative abundance of denitrifying microorganisms, particularly observed in rotations with soybean and sweet potato. However, the spring maize and peanut-based rotation had higher emission factors than traditional wheat-maize rotation due to lower initial crop nitrogen uptake and lower nitrogen use efficiency, respectively. Changes in the microbial community structures of nitrification and denitrification processes, including increased activity of ammonia-oxidizing bacteria MND1 and archaea Candidatus Nitrososphaera in legume and sweet potato rotations, and a shift in denitrifying microbes of diverse rotations (a decrease in Rhodoplanes and an increase in Paracoccus), significantly contributed to the overall reductions in emissions in all other investigated rotation systems. Understanding the microbial mechanisms that control N2O emissions from agricultural soils will enable the development of more effective and crop-specific strategies to further reduce greenhouse gas emissions.

High-yielding forage grasslands frequently contain low species diversity and receive high inputs of nitrogen fertilizer. To investigate multispecies mixtures as an alternative strategy, the 26-site international LegacyNet experiment systematically varied the diversity of sown grasslands using up to six high-yielding forage species (grasses, legumes, and herbs) managed under moderate nitrogen inputs. Multispecies mixtures outyielded two widely used grassland practices: a grass monoculture with higher nitrogen fertilizer and a two-species grass-legume community. High yields in multispecies mixtures were driven by strong positive grass-legume and legume-herb interactions. In warmer sites, the yield advantage of legume-containing multispecies mixtures over grass monocultures with higher nitrogen fertilizer inputs increased. Improved design of grassland mixtures can inform more environmentally sustainable forage production and may enhance adaptation of productive grasslands to a warming climate.