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Seasonal freezing induces large thaw emissions of nitrous oxide, a trace gas that contributes to stratospheric ozone destruction and atmospheric warming. Cropland soils are by far the largest anthropogenic source of nitrous oxide. However, the global contribution of seasonal freezing to nitrous oxide emissions from croplands is poorly quantified, mostly due to the lack of year-round measurements and difficulty in capturing short-lived pulses of nitrous oxide with traditional measurement methods. Here we present measurements collected with half-hourly resolution at two contrasting cropland sites in Ontario and Manitoba, Canada, over 14 and 9 years, respectively. We find that the magnitude of freeze–thaw-induced nitrous oxide emissions is related to the number of days with soil temperatures below 0 °C, and we validate these findings with emissions data from 11 additional sites from cold climates around the globe. Based on an estimate of cropland area experiencing seasonal freezing, reanalysis model estimates of soil temperature, and the relationship between cumulative soil freezing days and emissions that we derived from the cropland sites, we estimate that seasonally frozen cropland contributes 1.07 ± 0.59 Tg of nitrogen as nitrous oxide annually. We conclude that neglecting freeze–thaw emissions would lead to an underestimation of global agricultural nitrous oxide emissions by 17 to 28%. Large fluxes of nitrous oxide occur when frozen soils thaw. Field measurements and mathematical models suggest that freeze–thaw events are responsible for 17 to 28% of nitrous oxide emitted from agricultural soils globally.

The soil water retention curve (SWRC) shows the relationship between soil water (θ) and water potential (ψ) and provides fundamental information for quantifying and modeling soil water entry, storage, flow, and groundwater recharge processes. While traditionally it is measured in a laboratory through cumbersome and time-intensive methods, soil sensors measuring in-situ θ and ψ show strong potential to estimate in-situ SWRC. The objective of this study was to estimate in-situ SWRC at different depths under two different soil types by integrating measured θ and ψ using two commercial sensors: time-domain reflectometer (TDR) and dielectric field water potential (e.g., MPS-6) principles. Parametric models were used to quantify θ—ψ relationships at various depths and were compared to laboratory-measured SWRC. The results of the study show that combining TDR and MPS-6 sensors can be used to estimate plant-available water and SWRC, with a mean difference of −0.03 to 0.23 m3m−3 between the modeled data and laboratory data, which could be caused by the sensors’ lack of site-specific calibration or possible air entrapment of field soil. However, consistent trends (with magnitude differences) indicated the potential to use these sensors in estimating in-situ and dynamic SWRC at depths and provided a way forward in overcoming resource-intensive laboratory measurements.

The positive effect of soil organic matter (SOM) on crop yield has historically been attributed to the ability of SOM to supply crops with nitrogen and water. Whether management-induced increases in SOM meaningfully supplement water supply has received recent scrutiny, introducing uncertainty to the mechanisms by which SOM benefits crops. Here, we posit that SOM does not need to increase the supply of a growth-limiting resource to benefit crops; it only needs to facilitate root access to extant resource stocks. We highlight evidence for the ability of SOM to alleviate negative impacts of waterlogging and compaction on root development. Waterlogging restricts root aeration and, even if transient, can cause permanent downregulation of root biosynthesis. Management practices that promote SOM reduce the risk or duration of waterlogging by accelerating water infiltration, forestalling ponding, and promoting drainage. Compaction as a restriction to root development manifests in drying soils, where mechanical impedance inflates the photosynthate required to extend root tip into soil, leading to short, thick, and shallow roots. Soil organic matter reduces mechanical impedance in dry soils and is associated with root channels to the subsoil, granting crop access to deep soil water. In this framework, crop response to SOM depends on the interaction of a) crop susceptibility to waterlogging or compaction, b) soil moisture during crop maturation, and c) ‘baseline’ drainage and compaction status of soil. By exploring proposed mechanisms, future research may better constrain the context and magnitude of crop yield improvements to be expected from SOM management.

Nitrogen fertilizer application causes emissions of nitrous oxide (N O), a gas that contributes to global warming. N O emission reduction is possible given technological advances. But climate policy for N O reduction faces challenges caused by complex information, entangled risks with invisible gains, and polarized values. Behavioral factors influence farmers' decision-making, and here we argue context-dependent experimentation is needed to develop N O reduction policies, proposing crop insurance as an example policy.

The application of nitrogen (N) fertilizer to agricultural soils results in the emission of nitrous oxide (N2O), accounting for ∼40% of Canada’s and 10% of global agricultural greenhouse gas emissions. Reducing these emissions through N fertilizer best management practices (BMPs) is critical to achieve the fertilizer-related emission reduction target of 30% below 2020 levels by 2030 set by the Canadian government. However, progress is hindered by several key challenges: (1) the need to quantify N2O emission reductions associated with BMPs, (2) an incomplete understanding of the behavioral factors influencing the adoption of BMPs, (3) the lack of suitable metrics to track progress towards reduction targets, and (4) an absence of region-specific management recommendations that balance emission reduction potential with farm profitability and farmer decision-making. To address these challenges, we introduce canN2Onet, an innovative collaborative network formed in 2024 and comprising a diverse range of experts from institutions across Canada with partners representing academia, industry, government, and producer organizations. canN2Onet is focused on (1) the establishment of a national network of benchmark sites linking year-round N2O emission measurements and soil processes with behavioral economic studies on decision-making processes; (2) development and validation of robust metrics for tracking progress towards emission reduction targets by utilizing Canada’s first regional tower measurements, database development, and enhanced biogeochemical models; and (3) creation of a roadmap for emission reduction by up-scaling BMPs to the regional level, incorporating economic trade-offs and behavioral insights. This work represents the first coordinated national effort to generate a comprehensive understanding of N2O mitigation potential from improved management practices across Canada’s major grain and oilseed-producing regions. It offers actionable farm-level metrics reflective of real-world agricultural conditions and a transferable framework to guide region-specific nutrient management strategies globally, advancing both climate goals and agricultural sustainability.

Residue removal for biofuel production may have unintended consequences for N2O emissions from soils, and it is not clear how N2O emissions are influenced by crop residue removal from different tillage systems. Thus, we measured field‐scale N2O flux over 5 years (2005–2007, 2010–2011) from an annual crop rotation to evaluate how N2O emissions are influenced by no‐till (NT) compared to conventional tillage (CV), and how crop residue removal (R−) rather than crop residue return to soil (R+) affects emissions from these two tillage systems. Data from all 5 years indicated no differences in N2O flux between tillage practices at the onset of the growing season, but CT had 1.4–6.3 times higher N2O flux than NT overwinter. Nitrous oxide emissions were higher due to R− compared to R+, but the effect was more marked under CT than NT and overwinter than during spring. Our results thus challenge the assumption based on IPCC methodology that crop residue removal will result in reduced N2O emissions. The potential for higher N2O emission with residue removal implies that the benefit of utilizing biomass as biofuels to mitigate greenhouse gas emission may be overestimated. Interestingly, prior to an overwinter thaw event, dissolved organic C (DOC) was negatively correlated to peak N2O flux (r = −0.93). This suggests that lower N2O emissions with R+ vs. R− may reflect more complete stepwise denitrification to N2 during winter and possibly relate to the heterotrophic microbial capacity for processing crop residue into more soluble C compounds and a shift in the preferential C source utilized by the microbial community overwinter.

The accurate measurement of greenhouse gas emissions is a challenge for atmospheric science. Long-range open-path sensors are flexible enough to be applied to a variety of complex emission sources, and single devices are often used to measure both high and low path-integrated concentrations. As this technology develops, it is important to examine potential sources of inaccuracy. A GasFinder3 open-path laser was tested with a range of path-integrated concentrations from 11.7 to 182 ppm∙m CH4 using certified standard gases. The measured path-integrated concentrations had a positive bias which was higher than 10% at low path-integrated concentrations (<50 ppm∙m) with a declining trend expected to be under 2% at 200 ppm∙m. A linear equation was used to correct the measured path-integrated concentrations to fit the expected values. After correction, the average bias was reduced to −0.36% and there was no relationship with path-integrated concentration. A relative bias less than ±3% was achieved above ca. 150 ppm∙m with or without calibration. Measurement campaigns may reduce error by increasing path lengths to maximize path-integrated concentration. When low path-integrated concentrations are expected, calibration over the expected range is beneficial.

Switchgrass (Panicum virgatum L.) has gained importance as feedstock for bioenergy over the last decades due to its high productivity for up to 20 years, low input requirements, and potential for carbon sequestration. However, data on the dynamics of CO2 exchange of mature switchgrass stands (>5 years) are limited. The objective of this study was to determine net ecosystem exchange (NEE), ecosystem respiration (Re), and gross primary production (GPP) for a commercially managed switchgrass field in its sixth (2012) and seventh (2013) year in southern Ontario, Canada, using the eddy covariance method. Average NEE flux over two growing seasons (emergence to harvest) was −10.4 μmol m−2 s−1 and reached a maximum uptake of −42.4 μmol m−2 s−1. Total annual NEE was −380 ± 25 and −430 ± 30 g C m−2 in 2012 and 2013, respectively. GPP reached −1354 ± 23 g C m−2 in 2012 and −1430 ± 50g C m−2 in 2013. Annual Re in 2012 was 974 ± 20 g C m−2 and 1000 ± 35 g C m−2 in 2013. GPP during the dry year of 2012 was significantly lower than that during the normal year of 2013, but yield was significantly higher in 2012 with 1090 g  m−2, compared to 790 g m−2 in 2013. If considering the carbon removed at harvest, the net ecosystem carbon balance came to 106 ± 45 g C  m−2 in 2012, indicating a source of carbon, and to −59 ± 45 g C m−2 in 2013, indicating a sink of carbon. Our results confirm that switchgrass can switch between being a sink and a source of carbon on an annual basis. More studies are needed which investigate this interannual variability of the carbon budget of mature switchgrass stands.

In cold regions, climate change is expected to result in warmer winter temperatures and increased temperature variability. Coupled with changing precipitation regimes, these changes can decrease soil insulation by reducing snow cover, exposing soils to colder temperatures and more frequent and extensive soil freezing and thawing. Freeze-thaw events can exert an important control over winter soil processes and the cycling of nitrogen (N), with consequences for soil health, nitrous oxide (N 2 O) emissions, and nearby water quality. These impacts are especially important for agricultural soils and practices in cold regions. We conducted a lysimeter experiment to assess the effects of winter pulsed warming, soil texture, and snow cover on N cycling in agricultural soils. We monitored the subsurface soil temperature, moisture, and porewater geochemistry together with air temperature, precipitation, and N 2 O fluxes in four agricultural field-controlled lysimeter systems (surface area of 1 m 2 and depth of 1.5 m) at the University of Guelph’s Elora Research Station over one winter (December 2020 to April 2021). The lysimeters featured two soil types (loamy sand and silt loam) which were managed under a corn-soybean-wheat rotation with cover crops. Additionally, ceramic infrared heaters located above two of the lysimeters were turned on after each snowfall event to melt the snow and then turned off to mimic snow-free winter conditions with increased soil freezing. Porewater samples collected from five depths in the lysimeters were analyzed for total dissolved nitrogen (TDN), nitrate (NO 3 − ), nitrite (NO 2 − ), and ammonium (NH 4 + ). N 2 O fluxes were measured using automated soil gas chambers installed on each lysimeter. The results from the snow removed lysimeters were compared to those of lysimeters without heaters (with snow). As expected, the removal of the insulating snow cover resulted in more intense soil freeze-thaw events, causing increased dissolved N loss from the lysimeter systems as N 2 O (from the silt loam system) and via NO 3 − leaching (from the loamy sand system). In the silt loam lysimeter, we attribute the freeze thaw-enhanced N 2 O fluxes to de novo processes rather than gas build up and release. In the loamy sand lysimeter, we attribute the increased NO 3 − leaching to the larger pore size and therefore lower water retention capacity of this soil type. Overall, our study illustrates the important role of winter snow cover dynamics and soil freezing in modulating the coupled responses of soil moisture, temperature, and N cycling.

Crops can uptake only a fraction of nitrogen from nitrogenous fertilizer, while losing the remainder through volatilization, leaching, immobilization and emissions from soils. The emissions of nitrogen in the form of nitrous oxide (N2O) have a strong potency for global warming and depletion of stratospheric ozone. N2O gets released due to nitrification and denitrification processes, which are aided by different environmental, management and soil variables. In recent years, researchers have focused on understanding and simulating the N2O emission processes from agricultural farms and/or watersheds by using process-based models like Daily CENTURY (DAYCENT), Denitrification-Decomposition (DNDC) and Soil and Water Assessment Tool (SWAT). While the former two have been predominantly used in understanding the science of N2O emission and its execution within the model structure, as visible from a multitude of research articles summarizing their strengths and limitations, the later one is relatively unexplored. The SWAT is a promising candidate for modeling N2O emission, as it includes variables and processes that are widely reported in the literature as controlling N2O fluxes from soil, including nitrification and denitrification. SWAT also includes three-dimensional lateral movement of water within the soil, like in real-world conditions, unlike the two-dimensional biogeochemical models mentioned above. This article aims to summarize the N2O emission processes, variables affecting N2O emission and recent advances in N2O emission modeling techniques in SWAT, while discussing their applications, strengths, limitations and further recommendations.