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This investigation presents a new approach for evaluating soil organic carbon (SOC) content in farming soils using a photocatalytic chemical oxygen demand (PeCOD) analyzer combined with geographic information system (GIS) technology for spatial analysis. Soil samples were collected at various sites throughout Canada and were analyzed using sieve analysis, followed by further SOC evaluation using three distinct techniques: loss on ignition (LOI), Walkley-Black, and PeCOD. The PeCOD system, which relies on the photochemical oxidation of organic carbon, showed an exciting correlation between its evaluations and SOC content, making it a prompt and reliable method to evaluate SOC. In this investigation, finer materials such as clayey soils (soil fractions of (<50 µm)) demonstrated high SOC content compared to coarser ones (soil fractions of (>75 µm)) and decreased SOC content with increased soil depth, generally below the 30 cm mark. It should be noted that this investigation revealed that other variables, such as land management practices, precipitation, and atmospheric temperature, have drastic effects on the formation and residence time of SOC. GIS georeferencing еnablеd mapping of the SOC distribution and identification of hotspot areas with high SOC content. The results of this study have implications for sustainable farming, climate change mitigation, and soil health operations by providing farmers with schemes that amplify carbon sequestration while simultaneously improving soil health. [ABSTRACT FROM AUTHOR]

We examined soil properties and accumulation rates over the last ca. 100 years in four swamps and four marshes in southern Canada where these wetlands are common but under increasing anthropogenic pressure. One 50‐cm long core was collected from each wetland and analyzed to determine bulk density (BD) and organic matter (OM). Lead‐210 and cesium‐137 dating were used to estimate sediment accumulation rates. In the datable portion of each core, we determined the organic carbon (Corg), nitrogen (N), Corg/OM, Corg/N, Corg density, Corg stocks, and Corg accumulation rates. All parameters but one—Corg accumulation rates—were significantly different in swamps compared to marshes and between seasonally wet soils and those regularly flooded. Since 1950, Corg stocks varied from 6 to 13.6 kg m−2 with ≈23% more Corg in swamps than in marshes. When hydrology and deeper soils where considered, Corg stocks in regularly flooded wetlands were 60% higher than those of seasonally wet systems, emphasizing the role of hydrology in building up C stocks long‐term. Our measurements are within the wide range reported for similar systems in North America. The average rate of Corg accumulation in the studied wetlands (112 ± 87 g m−2 yr−1) is ≈50% higher than that of oligotrophic/ombrotrophic peatlands, but ≈47% lower than in tidal marshes from eastern Canada. Our study lends support to the case for wetland restoration through re‐wetting as an important nature‐based climate solution for mitigation of GHG emissions in areas where they were drained for agriculture and other purposes. Plain Language Summary: Wetlands are important ecosystems because they have an enhanced capacity to extract carbon dioxide—a greenhouse gas—from the atmosphere and store it in the ground as partly decomposed plant carbon. This ground storage is vital because it keeps carbon dioxide from increasing in the atmosphere where it causes global warming. Among the Earth's wetlands, freshwater marshes and swamps from temperate climates are among the least understood. To address this limitation, we conducted a study in southern Canada, where these wetlands are common but under increasing pressure from farming and urban development. Our results indicate that while marshes (dominated by grasses and sedges) form mostly mineral soils with less carbon stocks than swamps (vegetated with shrubs and trees), which form organic soils, the rate at which they accumulate carbon in their soil is similar. We also show that the wetlands we studied are 50% more effective in storing carbon than the cold climate bogs (vegetated by mosses), but they are less effective than salt marshes which form along the shores of temperate seas. We suggest that if freshwater marshes and swamps are protected, they can be important natural solutions in the mitigation of carbon dioxide emitted by human activity. Key Points: Carbon stocks in eight nutrient‐rich freshwater wetlands ranged 18–40 kg m−2, with organic soils averaging ≈60% more than mineral soilsMean carbon accumulation rate over the last 100 years was 112 g m−2 yr1, with no significant differences between swamps and marshesCarbon accumulation rates were higher than in oligotrophic/ombrotrophic wetlands (bogs) but lower than in tidal salt marshes [ABSTRACT FROM AUTHOR]

The Hudson Bay Lowlands (HBL) stores a significant proportion of the northern peatland carbon pool, and constraints on the factors controlling local‐scale variation are needed to better predict soil carbon stocks. We investigated two treed peatland sites, a fen and a bog, to understand how local ecohydrological factors impacted long‐term carbon storage. Ecohydrological conditions were reconstructed using quantitative water table depth reconstructions from testate amoebae (TA) and broad peat type classifications. We also linked these factors and carbon storage to changes in TA community structure through the investigation of morphological and functional traits. Both sites have high rates of peat vertical accretion during the warmer Middle Holocene. A shift to a drier, Sphagnum‐dominated habitat after 7400 cal a bp at the bog site, however, led to lower apparent carbon accumulation rates (aCARs) than at the fen site. aCARs decreased with the transition to a cooler Late Holocene climate at both sites. Both sites have higher total carbon masses (kg m−2) than other more open and younger HBL localities, demonstrating the potential importance of treed peatlands in regional carbon storage. Shifts in the frequency of TA traits corresponded to changing ecohydrological conditions and provided insights into the role of TA in carbon storage. [ABSTRACT FROM AUTHOR]

Measuring soil organic carbon (SOC) in riparian forest soils affected by floods is crucial for evaluating their concentration and distribution along hydrological gradients (longitudinal and transversal). Hydromorphological factors (e.g., sedimentation vs. erosion, size of floodplain, flood recurrence) may be the cause of major variations in the concentration of organic matter and SOC in soils and could have a direct impact on C levels in soil profiles. For this study, SOC concentrations were assessed in riparian soils collected along transects perpendicular to the riverbanks which cross through inundated and non-inundated zones. Other soil properties (e.g., acidity, nitrogen, texture, bulk density) that may affect the concentration of SOC were also considered. The main purpose of this study was to assess SOC concentrations in soils subjected to flooding with those outside the flood zones, and also measure various soil properties (in surface soils and at various depths ranging from 0 to 100 cm) for each selected area. Across the various areas, SOC shows marked differences in concentration and spatial distribution, with the lowest values found in mineral soils affected by successive floods (recurrence of 0-20 years). SOC at 0-20 cm in depth was significantly lower in active floodplains (Tukey HSD test), with average values of 2.29 ±1.64% compared to non-inundated soils (3.83 ±2.22%). The proportion of C stocks calculated in soils (inundated vs. non-inundated zones) was significantly different, with average values of 38.22 ±10.40 and 79.75 ±29.47 t·ha-1, respectively. Flood frequency appears to be a key factor in understanding the low SOC concentrations in floodplain soils subjected to high flood recurrence (0-20 years). [ABSTRACT FROM AUTHOR]

• There was no relationship between tree productivity and soil organic carbon. • Soil organic carbon stocks were different between poplar clones. • Soil organic carbon increased with decreasing sampling distance from trees. • Tree roots could play a significant role in SOC sequestration in deep soil. Increasing soil organic carbon (SOC) storage is one of the promising solutions to mitigate climate change. Fast-growing trees are a potential tool in this context as they rapidly accumulate C in their biomass and could transfer more organic matter (OM) into the soil. However, the relationship between aboveground productivity and SOC storage remains poorly understood. Five clones with different growth rates were selected from a 14-year-old hybrid poplar plantation located in New Liskeard, ON, Canada. We collected soil cores at 87.5 and 175.0 cm distance from the stem and at 0–20, 20–40 and 40–60 cm soil depth for soil C concentration analysis. The most productive clone DN2 (Populus deltoides × P. nigra) stored less SOC (83 Mg ha−1) between 0 and 60 cm depth than the mid-productive clones 1079 (Populus × jackii (P. balsamifera × P. deltoides)) and 915005 (P. maximowiczii × P. balsamifera) (95 and 96 Mg ha−1 respectively), while the least productive clone 747210 (P. balsamifera × P. trichocarpa) also had a lower SOC stock (85 Mg ha−1) compared to the other clones, but not significantly. There was no relationship between aboveground productivity and SOC stocks and total SOC stocks increased by 6 % when the sampling distance was closer to the tree stems. The difference in SOC stocks between clones was mostly observed at the 20–40 cm depth suggesting the significant effect of roots on SOC storage. Soil C/N ratios were significantly different between clones at 0–20 and 20–40 cm depths suggesting differences in OM decomposition rates between clones. There could be a trade-off between aboveground productivity and litter decomposition rate to increase SOC storage. [ABSTRACT FROM AUTHOR]

• Boreal forest soils store about four times more SOC under continuous permafrost. • Permafrost and soil moisture control SOC stocks and quality of mineral soils. • SOC stocks of boreal mineral forest soils can be predicted from mid-infrared spectroscopy. High-latitude soils store a large amount of the global soil organic carbon (SOC). The SOC stocks in mineral soils under different permafrost conditions, however, are underrepresented in global carbon databases. We sampled mineral forest soils under continuous and discontinuous to sporadic permafrost conditions on the Canadian Boreal and Taiga Plain. We determined the SOC stocks in the upper 60 cm of 94 soil pits across eleven sites (5–9 pits per site) and SOC quality using 13C isotopic signatures, C:N ratios and composition of aliphatic/aromatic and cellulose/lignin-like compounds obtained from mid-infrared spectra analyses. Lastly, we evaluated the prediction of SOC stocks in these soils using mid-infrared spectra and partial least square regression modelling (PLSR). The SOC stocks were on average four times higher in soils under continuous permafrost conditions (93.7–203.8 Mg SOC ha−1 in 0–45 cm) compared to soils under discontinuous to sporadic permafrost conditions (26.7–60.2 Mg SOC ha−1 in 0–60 cm). In addition, the SOC stocks were larger at moist and wet locations compared to dryer locations and varied significantly between sites, stressing the importance of small-scale geomorphic differences in controlling SOC in boreal mineral forest soils. Continuous permafrost SOC had a lower degree of decomposition compared to soils under discontinuous and sporadic permafrost. This indicates a potentially large proportion of SOC in boreal mineral soils to be vulnerable to warming associate increases in decomposition. The combination of mid-infrared with PLSR was suitable to predict the SOC stocks (R2 > 0.8) with an average uncertainty of 14–23%, which was less than the observed spatial variability of the field replicates (29–41%). Mid-infrared spectroscopy can thus offer an alternative to fill SOC data gaps of high latitude mineral forest soils and reduce uncertainties originating from the limited number of currently available SOC observations of Canadian boreal mineral forest soils. [ABSTRACT FROM AUTHOR]

We have analyzed and compared concentrations of soil organic carbon (SOC), soil total nitrogen (STN) and other soil properties in different inundated areas based on governmental flood risk maps (recurrence intervals of 0–20years and 20–100years). In this case study, a paired-site approach was used to determine the impact of periodic floods on soil properties (organic carbon, total nitrogen, pH, cation exchange capacity (CEC), phosphorus, potassium and grain size particles) in riverine areas located in the mid section of the Saint-François River (southern Québec). Two specific flood-risk zones, i.e. Frequent flood zones (FFz) and Moderate flood zones (MFz), in connection with the flood recurrence intervals (20-year vs 100-year flood) were considered to evaluate the variability of different soil properties. Sampling sites located outside (NFz: No-flood zones) of the two flood-risk zones were also selected for a cross-comparison. In this study area of the Saint-François river catchment, an increase in the flood rate was noted over the last few decades, especially from 1970 to 2000, which has the effect of modifying the hydrogeomorphic conditions and pedogenetic processes. The results show that alluvial soils subject to frequent flooding (FFz) have a lower concentration in soil organic carbon (SOC%) and soil total nitrogen (STN%) than soils in non-inundated zones. The average values obtained for surface horizons (0–20cm depth) range from 1.79±0.83 to 2.16±1.28 (SOC%) and from 0.14±0.05 to 0.17±0.07 (STN%) for soils in frequent flood zones (FFz), while for soils in no-flood zones (NFz), the values range from 5.17±2.99 and 3.82±1.88 (SOC%), and from 0.30±0.28 to 0.24±0.10 (STN%). The t-student tests conducted among the various zones confirm this trend of depletion in soil organic carbon and soil total nitrogen for the soils found in the Frequent Flood Zones (FFz). A lower concentration of nutrients was also noted for the soils affected by floods. Soil acidity is higher in the no-flood zones, which could be attributed to the acidifying input of the litter, which is more abundant and better formed (LFH layers) in the no-flood forest zones. The soil textural matrices are relatively similar among the three zones under study, although the textures are generally coarser for the soils outside the flood zones. Lastly, if the current hydrological conditions are maintained (i.e. an increase in the flood rate), one can expect a nutrient storage depletion that could restrict the regeneration of forest stands and the vitality of riverside ecosystems. [ABSTRACT FROM AUTHOR]

Abstract: Mountain environments are heterogeneous and dynamic geomorphic environments sensitive to land use and climate change. Heterogenic environmental conditions result in a large variability of mountain soil properties, and thus in large uncertainties of inventories of soil organic carbon (SOC). In this study we analyzed the variability of soil properties associated with the calculation of a SOC inventory in a mountain environment in the Canadian Rocky Mountains (Alberta). Therefore, we calculated the analytical uncertainty and spatial variability of SOC stocks using Gaussian error propagation and Taylor series expansion along seventeen 36m long transects to identify major sources of uncertainty. SOC stocks in the upper 10cm and 30cm are 2.4±0.7kgCm−2 and 6.4±5.6kgCm−2, respectively. The bulk densities generated the largest uncertainty associated with the analytical precision (10.0%). However, analytical uncertainties (ranging between 2.3 and 24.2%) are much smaller than the uncertainty introduced by the spatial variability, for instance of the coarse fraction (63.8%) and SOC concentration (40.1%). This study contributes to insufficiently considered analysis of uncertainties in SOC stocks and demonstrate the high potential of nested sampling approaches to identify sources of uncertainties of SOC stocks. To reduce the uncertainties associated with heterogeneous mountain environments, we propose to apply more sophisticated statistics (e.g. regression analysis considering frequency distributions of measured coarse fractions in different geomorphic environments) rather than simple mean per unit approaches, as frequently applied in regionalization studies of soil properties. [Copyright &y& Elsevier]

Climate is the major determinant of soil biological activity, including the decomposition rates of soil organic carbon (SOC) components. The objective of this study was to estimate the influence of climate on SOC dynamics, using long-term standard weather station data for Canadian Agricultural Ecoregions and the Introductory Carbon Balance Model for regional applications (ICBMregion). Mean daily temperature, total precipitation and potential evapotranspiration data were used in pedotransfer, soil water balance and biological activity functions to calculate a climate factor, r e_clim, used to describe both inter-(1970–1999 data, daily r e_clim) and intra-annual variation (1903–2000 data, mean annual r e_clim) of the effects of climate on SOC decomposition rates across the country. When r e_clim =1.0 the SOC decomposition rate is equal to that at a reference site in Central Sweden: when it is <1.0 the relative SOC decomposition rate is lower, and when it is >1.0 it is higher. The results show that the cool and humid eastern Canadian Agricultural Ecoregions are characterized by higher SOC decomposition rates (average r e_clim =1.20), compared to the semi-arid regions of western Canada (average r e_clim =0.95). In other words, more C input is needed to maintain a certain SOC level in eastern than in western Canada. Inter-annual variation (the difference between minimum and maximum values) in r e_clim for a given agricultural ecoregion was ≈±20%. The patterns of variation in intra-annual r e_clim values differed between Agricultural Ecoregions: for eastern Canada r e_clim reached a peak of ≈3.5 in mid-summer, and that of western Canada peaked at ≈2.5. This concept of r e_clim was tested and used in other climate zones such as northern Europe and Sub-Saharan Africa, and enabled us to integrate large data sets concerning climate and SOC dynamics and to characterize Canadian Agricultural Ecoregions by one variable, r e_clim. [Copyright &y& Elsevier]

Soil organic carbon (SOC) in Canadian agricultural soils plays an important role in the global cycle of C, and management can influence its fate. Although the scientific literature suggests that practicing no-till (NT) can sequester C, this is not always the case. Furthermore, there are many other factors including climate, management history, soil type and soil landscape processes that may affect the dynamics of SOC under NT. We measured the changes in SOC under NT in southern Ontario, at varying positions in the landscape in Gleyic and Orthic Luvisols at the end of a 15-year-period. Soil cores taken to depths beyond the solum, were segmented with depth, and total SOC was determined for each segment on an equivalent mass basis. When the entire soil column was considered, there was a loss of SOC in more profiles than there were gains. Furthermore, the erosion/deposition history at each landscape position appeared to influence the dynamics of SOC. In depression areas where Ap horizons were greater than 27 cm thick due to a history of soil deposition from upslope and local hydrology, there was a loss of total SOC after 15 years of NT. While where the Ap thickness was less than 27 cm, there were 18 profiles with SOC gains and 15 with net losses. Multiple linear regression analysis revealed that the change in SOC after 15 years was negatively related to the initial total SOC content and positively related to mass of clay. The results of this study suggest that landscape position and erosion/deposition history play a significant role in the ability of NT soils to sequester SOC. Interpretations of long-term SOC monitoring studies must take into account the location of samples within fields if useful information is to be gained on C dynamics in agricultural soils. [Copyright &y& Elsevier]

• A 3D machine learning approach predicted SOC concentration with 83% of accuracy. • Quantile regression was used to build uncertainty map of SOC distribution for 0–100 cm depth. • Soil depth and surface temperature were the most important covariates to predict SOC in Canada. • Peatlands showed high SOC in all soil depths while forests only in the top layers. Canada has extensive forests and peatlands that play key roles in global carbon cycle. Canadian soils and peatlands are assumed to store approximately 20% of the world's soil carbon stock. However, the spatial and vertical distributions of the soil organic carbon (SOC) concentration in Canada have not been systematically investigated. SOC concentration, expressed in g C kg−1 soil, affects the chemical and physical properties of the soil, such as water infiltration ability, moisture holding capacity, nutrient availability, and the biological activity of microorganisms. In this study, we tested a three dimensional (3D) machine learning approach and 40 spatial predictors derived from 20 years of optical and microwave satellite observations to estimate the spatial and vertical distributions of SOC concentration in Canada in six depth intervals up to 1 m. A quantile regression forest method was used to build an uncertainty map showing 80% of prediction intervals. Results showed that a random forest model associated with 25 covariates was successful in capturing 83% of spatial and vertical SOC variation over the country. Soil depth was the most important covariate to predict SOC concentration, followed by surface temperature and elevation. The SOC concentration in forested areas was highest in the top layers (0–5 cm), but soils located in peatlands showed higher C concentration in all soil depths. Among the terrestrial ecozones of Canada, Pacific Maritime and the Hudson Plain mostly covered by forest trees and peatlands, respectively, show highest SOC concentration, while the lowest concentration are observed in the Prairies and Mixed Wood Plain ecosystems that are the agricultural areas of the country. This study provides a deeper understanding of the major factors controlling SOC concentration in Canada and shows potential areas with high carbon reserves, which are crucial in view of the ongoing climate change. In addition, the presented methodological framework has great potential to be used in future soil carbon storage inventories using satellite observations. Mapping SOC concentration and associated uncertainties in Canada are fundamental to detect trends of gains or losses in SOC linked to recent and future national or global policy decisions related to soil quality and carbon sequestration. [ABSTRACT FROM AUTHOR]

Tillage and crop residue management can have large impacts on soil organic carbon (SOC) sequestration, as well as additional feedbacks on crop productivity and agricultural sustainability. The objectives of this study were to (i) evaluate the effects of summer fallow, legume green manure, pea or canola in rotation with spring wheat on crop yields, biomass production and SOC dynamics (0–15 cm) from six long-term cropping systems under semiarid conditions in western Canada, (ii) calibrate and validate three process-based models (DNDC, DayCent and DSSAT) using experimental data, and (iii) investigate the long-term impacts of tillage (no-tillage (NT) vs. conventional tillage (CT)) and straw residue (returned vs. removal) on SOC changes from diverse rotation systems. Over the experimental period from 1987 to 2015, the average wheat yields in Wheat (W)-Canola (C)–W-Pea (P) and legume green manure (LGM)-W-W rotations increased by 33.5 and 10.8%, respectively, compared to the continuous wheat (ContW) cropping systems. Higher SOC sequestration rates were found under ContW, LGM-W-W and W–C–W–P cropping systems mainly due to higher residue C input and larger nitrogen (N) inputs/fixation when compared to fallow-wheat systems. All three models performed "fair" to "good" in simulating crop yield, biomass and SOC content over time across all treatments. DSSAT had the lowest errors of prediction for yields (e.g., normalized RMSE (nRMSE) ≤ 27.2%, index of agreement (d) ≥ 0.79), while DNDC had better estimates of SOC content (e.g., nRMSE ≤ 4.5%, d ≥ 0.74). Long-term scenario analysis demonstrated that the mean annual changes in SOC across rotations based on model ensemble ranged from 0.03 Mg C ha−1 y−1 under CT with straw removal to 0.31 Mg C ha−1 y−1 under NT with straw returned. Predicted SOC sequestration potential of NT was relatively small compared to crop straw return for all rotation systems. This study suggests that diverse crop rotations which include canola and legume crops have the potential to store more SOC than traditional wheat-based cropping (e.g., fallow-wheat, ContW) for the semiarid prairies of Canada. These diverse rotations are already becoming more common and can help to enhance crop yields and maximize SOC sequestration when they are coupled with NT and residue management. • DNDC, DayCent and DSSAT well predicted grain yield and SOC for diverse rotations. • Wheat (W) yield and SOC increased when in rotation with canola and legumes. • DNDC more accurately simulated SOC in comparison to DSSAT and DayCent. • Higher SOC sequestration rates were estimated for straw return than for no-tillage. • Long-term rotations W–C (canola)-W-C and C–C–C–P (pea) had the largest increases in SOC. [ABSTRACT FROM AUTHOR]

• Tree planting on degraded land has been identified as an effective carbon capture strategy. • Unclear how associated restoration treatment influence carbon sequestration. • Tree carbon pool increased with greater restoration effort. • Existing site characteristics influence carbon sequestration potential. • Land managers must balance restoration cost with carbon sequestration. Landscape carbon storage is a key component of climate change mitigation. Tree planting on degraded land has been identified as an effective carbon capture strategy, but it is unclear how various associated restoration treatments influence carbon sequestration. In this study, we measured carbon pools in jack pine (Pinus banksiana Lamb.) stands subject to different restoration treatments within severely damaged upland areas in the metal mining region of Sudbury, Ontario, Canada. Treatments included: i) soil amendment (liming, fertilizing and grass/legume seeding) followed by jack pine planting, ii) jack pine planting alone, iii) soil amendment only, and iv) untreated plots with some natural regeneration as a result of improving air quality in the region. Twenty-four years after the initial treatments, we measured the carbon storage in coarse and fine woody debris, herbs, shrubs, forest floor (LFH), mineral soil, and trees. The carbon pool in planted trees was 1.5 times higher in plots when soil amendments were applied. This increase in the tree carbon pool was the result of greater carbon sequestration per individual jack pine tree rather than changes in tree density or arrival of new species. Similarly, naturally regenerated white birch (Betula papyrifera Marshall) in the amended plots stored 1.7 times more carbon than white birch in the untreated plots. Tree planting proved essential on this landscape with natural tree regeneration rates very low even 50 years after local pollution was massively reduced. However, tree planting surprisingly did not significantly affect total carbon storage in these exposed upland sites. Total ecosystem carbon varied from 21.4 Mg ha−1 to 124.5 Mg ha−1 across all plots (mean of 67.6 ± 4.8 Mg ha−1) but no statistically significant differences were observed among the treatments. Soil organic carbon (SOC) proved to be the largest carbon pool across plots and stored on average 66% of total ecosystem carbon. However, at this early stage the restoration treatments had no influence on SOC pools on this highly degraded landscape, which still appears to be severely affected by ongoing erosion of surface soil and metal contamination. The restoration treatment also did not significantly affect the understory or downed woody debris carbon pools. This study demonstrates that the current restoration treatments used in Sudbury do influence the amount of carbon sequestrated mainly through tree restoration on this industrially degraded landscape, but long-term storage potential is still limited by poor soil conditions. [ABSTRACT FROM AUTHOR]

Different silvicultural treatments that are applied at plantation establishment may drive different vegetation succession pathways. These divergent vegetation types subsequently feed back to influence soil carbon and nitrogen cycles. One potential mechanism of feedback is through litter decomposition, and in particular fine root decomposition (FRD; <2 mm roots). In the present study we investigated how blade scarification, fertilization, and vegetation control influenced over- and understory vegetation 27 years after plantation, and whether these different vegetation communities affected FRD. In a design using factorial combinations of the three treatments at the Petawawa Research Forest (Laurentian Hills, ON, Canada), we conducted an in situ FRD experiment, with fine roots from the entire vegetation community (both over- and understory) of each plot. The different silvicultural treatments affected overstory basal area, understory species richness and FRD. No correlation was noted between understory species richness and FRD. Instead, we found that understory vegetation (especially fern and herb) cover best explained FRD. We conclude that silvicultural treatments affect FRD through subsequent vegetation succession and that this effect is more likely due to species-specific effects inducing a favorable soil environment than to a higher species richness per se. [ABSTRACT FROM AUTHOR]

• No-till (NT) stores more soil organic C in Western Canadian conditions. • The rate of C gain with NT decreases over time. • Soil texture influences the rate of C change under NT. Accurate estimates of soil organic carbon (SOC) stock change as influenced by tillage practices are prerequisites to quantify the impact of mitigation measures on greenhouse gas emissions associated with crop production. In this study, we compiled SOC stock change data as influenced by tillage practices, i.e. no-till (NT) versus conventional tillage (CT), on agricultural soils in Canada. We determined the rate of C change as a function of soil texture and climate stratified by time since the management change. In the cool and humid climates of Eastern Canada, the impacts of NT were inconsistent and resulted in a decline in C storage rate in the years shortly following management change, but SOC recovered over time. Carbon losses were particularly high on fine and coarse textured soils, whereas in medium textured soils NT tended to increase SOC. On the Canadian prairies NT consistently increased SOC. The rate of gain in SOC under NT decreased over time with higher rates in the 3−10 years following a change to NT at a rate of 740 kg C ha−1 yr−1 or 1.3 % yr−1. Rates declined to 260 kg C ha−1 yr−1 or 0.87 % yr−1 for periods from 11–20 years after tillage change, and to 95 kg C ha-1 yr−1 or 0.23 % for periods longer than 20 years. The results of this work clearly show climate, soil texture and duration of management as main drivers of SOC change under NT in Canada and key factors that must be considered in the development of either national or regional SOC models. The results of this study suggest that more detailed stratification of soil texture, climate and duration of NT adoption is required for more accurate estimates of SOC storage rates associated with NT for Canada. [ABSTRACT FROM AUTHOR]

Grazing of natural rangeland and seeded pasture is an important feeding strategy for the Canadian beef cattle industry. As a consequence, beef cattle population has a direct influence on the proportion of land base maintained as perennial forage, which in turn changes soil organic carbon (SOC) stocks. We examined historical relationships between the net change in SOC resulting from perennial/annual crop conversion and beef cattle populations. We observed strong negative linear relationships, both regionally and nationally, between the population of beef cattle and the estimated change in SOC (negative sign indicating soil C sink) resulting from the conversion of annual crops and vice versa. These relationships indicate that as beef cattle population declines there is a corresponding loss of SOC resulting from a reduction in the relative proportion of perennial to annual crops on the landscape. The annual C loss resulting from land use conversion was roughly equivalent to 62% (±13%) of the combined enteric and manure annual emissions of CH 4 and N 2 O [(1400 (±440) kg CO 2 eq head -1  yr -1 ] resulting in net greenhouse gas emissions of 850 (±360) kg CO 2 eq head -1  yr -1 . These results highlight the importance of an integrated analysis that considers land use conversion and its impact on SOC when assessing the environmental footprint associated with beef cattle production., (Copyright © 2020 Elsevier B.V. All rights reserved.)