Beef cattle production impacts soil organic carbon storage

Science of the Total Environment 718 (2020) 137273

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Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv

Beef cattle production impacts soil organic carbon storage Chang Liang a,b,⁎, J. Douglas MacDonald a, Raymond L. Desjardins b, Brian G. McConkey c, Karen A. Beauchemin d, Corey Flemming a, Darrel Cerkowniak e, Ana Blondel a a

Pollutant Inventories and Reporting Division, Environment and Climate Change Canada, PVM, 7th Floor, 351 St-Joseph Blvd., Gatineau, Quebec K1A 0H3, Canada Ottawa Research and Development Centre, Agriculture and Agri-Food Canada, Central Experimental Farm, K.W. Neatby Building, 960 Carling Avenue, Ottawa, Ontario K1A 0C6, Canada c Swift Current Research and Development Centre, Agriculture and Agri-Food Canada, 1 Airport Road, P.O. Box 1030, Swift Current, Saskatchewan S9H 3X2, Canada d Lethbridge Research and Development Centre, Agriculture and Agri-Food Canada, 5403 1st Ave. S., Lethbridge, Alberta T1J 4B1, Canada e Saskatoon Research and Development Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, Saskatchewan S7N 0X2, Canada b

H I G H L I G H T S

G R A P H I C A L

A B S T R A C T

• Proportions of perennial crops in Canadian croplands vary with beef populations. • Beef cattle in Canada emit CH4 and N2O equivalent to about 2250 kg CO2 yr−1 head−1 • Soil C retention associated with beef cattle accounts for 2/3 of CH4 and N2O emissions • Net greenhouse gas emissions for beef cattle are 850 kg CO2 eq yr−1 head−1

a r t i c l e

i n f o

Article history: Received 11 September 2019 Received in revised form 10 February 2020 Accepted 11 February 2020 Available online xxxx Editor: Deyi Hou Keywords: Beef cattle Greenhouse gas emissions Soil organic carbon Perennial crop Annual crop

a b s t r a c t 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 CH4 and N2O [(1400 (±440) kg CO2 eq head−1 yr−1] resulting in net greenhouse gas emissions of 850 (±360) kg CO2 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. © 2020 Elsevier B.V. All rights reserved.

⁎ Corresponding author at: Pollutant Inventories and Reporting Division, Environment and Climate Change Canada, PVM, 7th Floor, 351 St-Joseph Blvd., Gatineau, Quebec K1A 0H3, Canada. E-mail address: [email protected] (C. Liang).

https://doi.org/10.1016/j.scitotenv.2020.137273 0048-9697/© 2020 Elsevier B.V. All rights reserved.

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C. Liang et al. / Science of the Total Environment 718 (2020) 137273

1. Introduction Globally, 14.5% of anthropogenic greenhouse gas (GHG) emissions result from livestock farming (animals, manure, feed production, and expansion of lands into forested areas), with 40% (i.e. 6% of total GHG) attributed to enteric methane production (Gerber et al., 2013). Worldwide demand for meat is likely to double between 1999 and 2050 (Steinfeld et al., 2006) because of population and income growth (Delgado et al., 1999). Thus, the total number of meat-producing animals will likely increase to meet the demand, which will result in an increase in global emissions. Considering environmental challenges associated with beef production, it is important to carry out a comprehensive analysis of the GHG (CH4, N2O and CO2) emissions and removals/sinks of soil C associated with grazing animal production. Canada produces approximately 2% of the world's beef and is the 5th-largest global exporter of beef in the world, producing 1.15 million tonnes in 2017 (Canfax Research Services, 2018). Economic returns have been the primary driver of decision processes in the beef industry, and the environmental footprint of beef production has been under scrutiny from industry groups, consumers, retailers and nongovernmental organisations (Grebitus et al., 2013). Beef producers require science-based information to provide more accurate assessments of the environmental impacts of the industry and strategies to increase consumer confidence through the implementation of improved and environmentally friendly production practices. Livestock production is the world's largest user of land because the production of animal feed takes up almost 80% of the agricultural area (FAO, 2010) with beef production being responsible for a large part of this. Land use requirements vary significantly depending on the production system. Nguyen et al. (2010) showed variations in land use from 16.5 m2 kg−1 carcass for an intensive indoor dairy bull system to 42.9 m2 kg−1 on non-cultivatable land for a cow-calf operation. Analyses of the contribution of beef production to land-use change in the form of deforestation have also been estimated globally (Steinfeld et al., 2006), but similar analyses have not considered the impacts of land management and the conversion of perennial land to annual production. It is understood that changes in land management systems between perennial and annual crop production will impact terrestrial C stocks. Measurements of direct net CO2 fluxes have generally indicated that many annual cropping systems emit CO2 (Baker and Griffis, 2005; Glenn et al., 2010; Kutsch et al., 2010; Maas et al., 2013; Taylor et al., 2013), whereas perennial systems sequester CO2 (Hussain et al., 2011; Taylor et al., 2013). In general, perennial forages typically sequester C while annual crop production is prone to either C loss or lower rates of C uptake (Vellinga et al., 2011). Measures to enhance C sequestration in the soil have been identified as important global mitigation strategies (Arrouays and Horn, 2019; Dawson and Smith, 2007; Minasny et al., 2017) and maintaining land under perennial production is a viable means of increasing soil C. Nonetheless, beef production needs to achieve a net reduction in GHG emissions of the whole production system, considering soil organic carbon (SOC) changes (Beauchemin et al., 2011) and assuring that any reduction in on-farm GHG emissions is not offset by an increase in off-farm GHG emissions such as those resulting from imported feed (Kröbel et al., 2016). The Canadian beef cattle industry accounts for 3.4% to 4.3% of Canada's total GHG emissions, and has contributed approximately 41% to 53% of total agricultural emissions since 1990 (ECCC, 2019). In 2016, beef cattle produced approximately 80% of the country's enteric CH4 emissions (ECCC, 2019). The GHG budget for a beef cattle production system to the farm gate indicates that enteric CH4 is the predominant GHG (Beauchemin et al., 2010; Basarab et al., 2012; Desjardins et al., 2012). Grazing is an important component of feeding practices for the beef cattle industry in Canada, especially for cow-calf and backgrounding operations. N80% of Canadian beef cattle farms manage cattle on either natural rangeland or seeded pasture during the summer

grazing season and 58% practice winter grazing on bales and stockpiled forages (Sheppard et al., 2015). The contributions of cattle production to global GHG emissions have been well documented and C footprints have been estimated for various production systems (Beauchemin et al., 2010; Beauchemin et al., 2011). However, most analyses rarely consider the impact of land use conversion for feed production on soil C, due to the difficulty in effectively doing so. Several modelling studies reported that the C footprint of beef (kg CO2 eq kg−1 product) is larger than that of other livestock products (Dyer et al., 2010; Lesschen et al., 2011; Browne et al., 2011). In these analyses, grazing cattle are typically penalized relative to grainfed cattle, as the effect of increased consumption of forage results in an overall increase in GHG emissions because the enteric CH4 emissions are greater than the reduction in N2O emissions from the production of annual crops. However, as noted, other modelling assessments have suggested that these studies may be biased by not considering CO2 flux from the soil in the net GHG balance of livestock production systems (Vergé et al., 2012; Wang et al., 2015). To adequately assess GHG mitigation strategies, it is necessary to use a whole system modelling approach (Schils et al., 2007; Stewart et al., 2009) that includes SOC change. Obtaining an accurate estimate of the relative importance of beef cattle production to soil C is difficult. In most regions of Canada livestock and crop production compete, to a large extent, for the same land base. Depending on market-related factors, annual crop production and animal production may increase or decrease as farmers shift between these two land-use options. These shifts in land use inevitably have an impact on soil C storage. The GHG inventory in Canada has quantified the shifts in land use and emissions from beef cattle production that have occurred over the past 35 years. The objective of this study was to examine the long-term data and to develop an empirically based quantitative estimate of the relative trade-offs in net GHG emissions between non-energy-related GHG emissions from beef cattle production and changes in SOC resulting from annual and perennial crop conversion. 2. Materials and methods Beef cattle production results in GHG emissions through enteric fermentation and the excretion, storage and subsequent disposal of animal manure. Emissions are estimated using the Intergovernmental Panel on Climate Change (IPCC) Tier-2 approach (IPCC, 2006) for Canada. To develop an IPCC Tier-2 enteric fermentation emission factor (EF) for beef cattle the subcategories of provincial cattle populations (beef cows, calves, bulls, beef and dairy heifers, feed heifers, and steers) collected by Statistics Canada were further disaggregated into sub-annual production stages to isolate and quantify the effect of specific production practices on gross energy intake of animals and, as a consequence, enteric CH4 emissions. In this study, we used the IPCC definition of “non dairy” cattle to define the beef cattle population in Canada. This population represents cattle that consume forage-based diets for a large proportion of their lifetime. Also included in this population were feedlot animals because as calves and during backgrounding periods, these cattle spend a significant portion of their lives consuming forages. Furthermore, dairy young stock was considered in this group because prior to going into milk production (heifers) or feedlots (steers) the majority of their daily intake is forage-based and not concentrates. Different animal subcategory groupings were tested in the statistical analyses, but it was noted that there were no important changes to the strength or trends in statistical relationships that resulted from the different groupings that would impact the conclusions of this study. Alemu et al. (2016) characterized the predominant practices for each province, according to animal type, physiological status, age, gender, growth rate, activity level and production environment. More details on grazing practices, dietary information, feed quality, variable parameters and methods were published by Ominski et al. (2007) and

C. Liang et al. / Science of the Total Environment 718 (2020) 137273

methodologies are detailed in ECCC (2019). Briefly, the methodology is based on the 2006 IPCC Guidelines and uses CH4 conversion factors (i.e. Ym) of 6.5% of gross energy intake (GEI) for all animals fed forage-based diets and 3% for animals while in feedlots. Feed digestibility percentages for forage diets ranged from 56% to 63% depending on region and animal subcategory and from 78 to 80% for animals in feedlots. Gross energy intake was calculated as outlined in the IPCC Tier 2 methods (IPCC, 2006) including the adjustment for winter temperatures estimated as monthly weighted correction factors based on regional 30-year average temperatures. To develop IPCC Tier-2 CH4 EFs from manure management, countryspecific inputs were required that take into account climate, livestock diets and type of manure storage system. The volatile solids (VS) of manure were estimated using the digestible energy intake, ash content of manure and gross energy consumed by a given beef subcategory, and the urinary energy fraction of the gross energy intake, according to the 2006 IPCC Guidelines (IPCC, 2006). Trends in carcass weights were used as an indicator of changes in mature body weight. Boadi et al. (2004) estimated the mean body weight for each subcategory of beef cattle for 2001. Data on carcass weight are collected by the Canadian Beef Grading Agency (CBGA) and published by Agriculture and Agri-Food Canada (AAFC, 1990–2016). Body weight trends were accounted for in the calculations of GEI, VS and N excretion as outlined in the 2006 IPCC Guidelines to create a time series that explains changes in animal productivity due to feed consumption and nutrient excretion (IPCC, 2006). Nitrous oxide emissions from manure management systems result from mineralization of organic materials, nitrification and denitrification of mineral N directly and indirectly (ECCC, 2019). Soil N2O emissions from application of cattle manure on agricultural soils were estimated using the method of Rochette et al. (2008) based on a linear function of soil N2O EF with a ratio of growing season precipitation over potential evapotranspiration. Soil N2O emissions from urine and dung deposited on pasture, range and paddock by grazing cattle were estimated using the findings of Rochette et al. (2014) for Eastern Canada, and unpublished data of Lemke et al. (2012) for Western Canada. More details on specific EFs for Eastern and Western Canada are provided in Table 1. The IPCC default methods were used to estimate ammonia emissions from manure N deposited on pasture, range and paddock as well as manure N applied as fertilizers on agricultural soils (IPCC, 2006), while country specific methods were used to estimate nitrate leaching (Rochette et al., 2008), and the subsequent indirect soil N2O emissions using the 2006 IPCC Tier-1 default EFs (IPCC, 2006). The annual beef cattle population is presented as the simple mean of semi-annual surveys. These surveys are corrected by Statistics Canada to the Census of Agriculture population estimates, which are collected every five years, to assure the accuracy of the estimates. Likewise, Table 1 Beef cattle emission factors for Eastern and Western Canada in 2016. Source

Western Canada

Eastern Canada

kg CH4 or N2O-N head−1 yr−1 (kg CO2 eq head−1 yr−1) Enteric - CH4 Manure - CH4 Stored Manure - N2O Applied Manure - N2O Pasture, Range and Paddock - N2O

Direct Indirecta Direct Indirectb Direct Indirectb

73.2 (1830) 2.7 (68) 0.70 (210) 0.11 (34) 0.18 (54) 0.07 (21) 0.017 (5) 0.12 (35)

61.9 (1550) 7.3 (183) 0.70 (210) 0.12 (35) 0.50 (149) 0.13 (40) 0.16 (47) 0.09 (28)

a Ammonia volatilization and subsequent redeposition and nitrous oxide emissions using the 2006 IPCC default emission factor of 0.01 kg N2O-N kg−1 N (IPCC, 2006). b Including ammonia volatilization, subsequent redeposition and leaching of nitrate, and soil nitrous oxide emissions using the 2006 IPCC default emission factors of 0.01 kg N2O-N kg−1 N and 0.075 kg N2O-N kg−1 N, respectively (IPCC, 2006).

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areas of cropland and the split between perennial and annual crops are based on the Census of Agriculture. The area of annual crops varied from 30 Mha to 35 Mha from 1981 to 2016 while the area of perennial crops ranged from 14 Mha to 18 Mha during the same period. The area in natural rangeland was relatively stable with a decrease of 84 kha from 1981 to 2016. Management-induced changes in SOC are monitored in Canada's national inventory report of GHG emissions/removals for cropland that result from changes in tillage practices, summerfallow and conversion of annual/perennial crops. Estimates are developed using a combination of country-specific empirical C factors and modelling approach (ECCC, 2019) based on the findings of VandenBygaart et al. (2003). The Century model (Parton et al., 1987) is used to estimate the C change factors by setting the factor to fit the slope of a linear regression for the management-induced change in SOC. The C factors are estimated for each distinct soil unit within the Soil Landscapes of Canada (SLC) polygon (AAFC, 2006). The Century model was calibrated to ensure that crop yields were in line with known values for agricultural crops in Canada. The amount of SOC retained in soil represents the balance between the rates of input from crop residues and losses through decomposition. The method for quantifying the change in SOC is based on the premise that, on long-existing cropland (i.e. annual crop or perennial crop), changes in soil C stocks over time occur following changes in soil management that influence the rates of either C additions to, or C losses from, the soil. If no change in management practices occurs, the C stocks are assumed to be at a steady state, and hence the change in C stocks is deemed zero. In this study we only estimate the change in SOC for areas where there is a change in annual-perennial crop conversion or vice versa. Within semiarid regions of Western Canada, approximately 7 Mha of natural rangeland is used primarily for grazing by beef cattle. Since 1981, the loss of 84 kha of this rangeland was estimated to have been converted to cropland at a mean rate of 2.4 kha yr−1. For this study, the losses of SOC associated with the conversion of natural rangeland to annual crops were included. The dynamics of soil C after a land use conversion generally follow first-order kinetics and, consequently, the following equation was used to quantify the soil C change (VandenBygaart et al., 2008):
 ΔSOC ðt Þ ¼ ΔSOCmax • 1–e−k•t

ð1Þ

where ΔSOC(t) is the soil C change with time, t, since adoption of the land use conversion; ΔSOCmax is the maximum eventual soil C change with land use alteration and k is the rate constant for soil C change. Using Eq. 1, an effective linear soil C change factor can be derived, when multiplied by time since land use conversion. This factor, f(t), varies in value with time, t, since land use conversion and is simply Eq. 1 divided by t:
 f ðt Þ ¼ ΔSOCmax • 1–e−k•t =t

ð2Þ

Furthermore, C factors derived from exponential curves are not a single value for an activity, but rather a time dependent equation. The value of the C factor depends on how many years have passed since the onset of the specific activity. Eq. 3 was used to estimate an annual factor (year t-1 to year t): n o f ðt Þ ¼ ΔSOCmax • e−k•ðt−1Þ −e−k•t

ð3Þ

In the national inventory, perennial crops include alfalfa and alfalfa mixtures for hay, other tame (i.e. cultivated) hay and fodder crops for hay, berries, grapes, fruit and nut trees, and tame pasture. However, for this study, changes in perennials related to beef production include all hay and pasture. Production of annual crops has typically resulted in a loss of C, particularly when the use of summerfallow was prevalent (Dumanski et al., 1998). Areas of land

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C. Liang et al. / Science of the Total Environment 718 (2020) 137273

use conversion from either perennial to annual crops or vice versa were obtained from the Census of Agriculture. Census data provide information on the net change in area over five-year census periods. In practice, gross changes back and forth between annual and perennial crops are probably frequent and so net changes are smaller. Because only net change data are available at a spatial unit of Soil Landscape of Canada polygons, reversibility is assumed. This assumption means that the soil C factor associated with perennial crop converted to annual crop is considered the inverse of that associated with annual crop converted to perennial crop. The loss of natural grassland to either annual or perennial crops is considered irreversible and results in a loss of SOC. Data on the areas of annual and perennial crops are only collected through the Census of Agriculture once in every five years (i.e. 1981, 1986, 1991, 1996, 2001, 2006, 2011, and 2016) by Statistics Canada. Therefore the estimates of C loss in the form of net CO2 emissions were compiled for each of these years in parallel with beef cattle populations. The relationship between the change in SOC as a result of land use conversion from either annual to perennial crops or vice versa and beef cattle population for these years at various spatial aggregations (i.e. Reporting Zone, Eastern and Western Canada and Canada) was tested using the PROC GLM procedure of SAS (SAS Institute, 1999). Similarly, total non-CO2 emissions (CH4 and N2O) from the various classes of beef cattle on a per head yearly basis from 1990 to 2016 were also determined statistically. Error bounds for reported values are based on either the standard deviation of the slope produced by the PROC GLM analysis or from Monte Carlo analyses of agricultural emissions from the national inventory report (Karimi-Zindashty et al., 2012; ECCC, 2019).

3. Results and discussion Canada has a land mass of 9.98 million km2 that has been divided based on its ecological characteristics into 18 Ecozones, 9 of which contain significant agricultural activities (Fig. 1). Reporting zones serve as the spatial framework upon which changes in SOC stocks in Canada are compiled and reported. This framework was established to ensure the consistency and spatial integrity of inventory estimates developed for Canadian reporting of GHG emissions and removals from the land use, land-use change and forestry sector (LULUCF) (ECCC, 2019). Reporting zones are the same as Ecozones of Canada's national ecological framework (Marshall et al., 1999) with three exceptions: the Boreal Shield and Taiga Shield ecozones are split into east and west components, and the Prairies ecozone is divided along ecoregion boundaries into a semi-arid and a subhumid component (ECCC, 2019) to better reflect differences in major land-use and management practices. Across reporting zones, the area of agricultural land (cropland) in Canada remained relatively constant throughout the 1990's at approximately 50 Mha but has since gradually declined to 45 Mha beginning in 2001 (Fig. 2). Beef cattle production varies among various Reporting Zones as a consequence of differences in land value, climate, forage availability and market access. From 63 to 76% of the country's beef cattle are in Western Canada, mainly on the Canadian prairies (Boreal Plains, Subhumid Prairies, Semiarid Prairies, and Montane Cordillera) (Table 2). Since 1981 a 10% increase in the beef cattle population has occurred in the Semiarid Prairies Reporting Zone while a 10% reduction has occurred for the Mixedwood Plains and Boreal Plains Reporting Zones (Table 2). Similar to beef cattle distributions, approximately 79 to 91% of annual

Fig. 1. Ecological Reporting Zones of Canada.

C. Liang et al. / Science of the Total Environment 718 (2020) 137273

5

Area of annual and perennial crops grown in Canada (Mha)

15000 30 10000

5000

20

0 10 -5000

0 1981

1986

1991 Annual crop area

1996

2001

Perennial crop area

2006

-10000 2016

2011

Beef Cale

Beef cale populaon (x1000 head) and ∆SOC from the conversion of annual/perennial crops (kt CO2 eq)

20000

40

Delta SOC

Fig. 2. Beef cattle population and change in soil organic carbon (ΔSOC) from the conversion of perennial/annual crop from 1981 to 2016 in Canada (negative value indicates soil C sink).

cropland and 67 to 79% of perennial forage are located on the Canadian prairies (Table 2). From 1981 to 2016, overall, there was a 12% increase in areas of perennial forages on the Canadian prairies accompanied with similar increase in annual crops in Eastern Canada (Table 2). Throughout the 1990s perennial land areas increased in parallel with beef cattle population (Fig. 2). Since 2005 beef cattle populations have decreased. In 1990, beef cattle were directly responsible for emissions of 22 Tg CO2 eq. Emissions peaked at 33 Tg CO2 eq in 2005, but since have decreased to approximately 26 Tg CO2 eq in 2011, and have remained stable since then. This change in emissions parallels trends in beef cattle populations; an increase of 34% from 1990 to 2005 followed by a decrease of 22% from 2006 to 2016 (Fig. 2). An incremental increase in emissions on a per head-year over the years reflects an increase in average body weights of the various marketed animals such as heifers and steers and the relative distribution of each subcategory of beef cattle (Table 3). Greenhouse gas emissions on a per head yearly basis varied from 2100 to 2300 kg CO2 eq with a mean of 2250 kg CO2 eq (Table 3). Lower N2O emissions in Western Canada (Table 3) are mainly the result of lower soil N2O EFs from manure N either directly deposited on pasture, range and paddock by beef cattle or applied as fertilizers on agricultural soils in less humid and drier climate (Rochette et al., 2018; Rochette et al., 2008). On the other hand, lower CH4 emissions in Eastern Canada are associated with better quality forage, and thus reduced enteric CH4 EFs (ECCC, 2019). The change in SOC upon perennial/annual crop conversion also mirrored closely the beef cattle population as the soil C sink peaked in 2005, and has decreased since (Fig. 2). While uncertainties exist in the estimates, particularly in site specific rates of C loss or gain, the rates of C loss and gain used in the Canadian inventory methodology have been validated against Canadian studies in the scientific literature. The rates of C change (20-yr average factor) of the modelled perennial crop C factors were considerably lower in the two Eastern Canadian regions (East Atlantic and East Central Regions) (0.46–0.56 vs. 0.74–0.77 Mg C ha−1 yr−1) than in the three Western Canadian regions (Subhumid Prairies, Semiarid Prairies, and West Pacific Regions) (Table 4). The modelled rate constant, maximal amount of C change, and mean annual rate of change over the first 20 years for SOC upon the land use conversion among various Reporting Zones varied from 0.015 to 0.28 yr−1, from 26 to 46 Mg C ha−1, and from 0.47 to 0.75 Mg C ha−1 yr−1, respectively (Table 4). Empirically derived C factors were highly variable, ranging from 0 to N1.4 Mg C ha−1 yr−1 across Canada. The reasons for this broad range of C factors are likely due to

large variations in experiment duration, variable treatments and interactions, different soil sampling strategies and different soil types (VandenBygaart et al., 2008). Nonetheless, for the western regions the mean of the empirical factors of 0.59 Mg C ha−1 yr−1 compares favourably to the range of 0.46–0.56 Mg C ha−1 yr−1 in the modelled

Table 2 Distribution of beef cattle, annual and perennial crops among various Reporting Zones for selected census years for Canada. Reporting zone

1981

Beef Cattle Boreal Shield East Atlantic Maritime Mixedwood Plains Boreal Shield West Boreal Plains Subhumid Prairies Semiarid Prairies Montane Cordillera Pacific Maritime Eastern Canada Western Canada

% (x1000 head) 2.6 (289) 2.5 (267) 2.0 (286) 4.5 (491) 4.5 (478) 3.7 (528) 24.2 (2663) 20.0 (2147) 14.5 (2077) 0.4 (48) 0.4 (43) 0.4 (54) 14.8 (1627) 17.8 (1913) 18.9 (2713) 28.8 (3162) 30.0 (3223) 31.5 (4513) 19.7 (2160) 20.2 (2174) 25.7 (3682) 3.9 (429) 3.9 (416) 2.8 (403) 1.1 (118) 0.7 (79) 0.4 (61) 31.3 (3443) 26.9 (2891) 20.2 (2892) 68.7 (7545) 73.1 (7848) 79.8 (11426) Annual Crops - % (kha) 0.3 (117) 0.3 (103) 0.5 (147) 0.8 (278) 0.7 (243) 1.0 (296) 8.6 (2984) 8.1 (2841) 10.5 (3247) 0.2 (80) 0.2 (74) 0.2 (60) 15.3 (5278) 14.9 (5222) 14.0 (4322) 36.2 (12504) 36.5 (12807) 35.4 (10930) 38.3 (13209) 39.1 (13718) 38.3 (11827) 0.1 (44) 0.1 (50) 0.1 (37.9) 0.1 (23) 0.05 (16) 0.07 (20.7) 9.8 (3379) 9.1 (3188) 11.9 (3691) 90.2 (31138) 90.9 (31887) 88.1 (27197) Perennial Crops - % (kha) 4.5 (697) 3.9 (575) 3.0 (525) 6.1 (948) 5.5 (812) 4.3 (763) 22.3 (3438) 20.5 (3029) 13.9 (2464) 0.8 (125) 0.7 (111) 0.7 (116) 22.8 (3520) 27.1 (4009) 26.1 (4627) 30.7 (4742) 29.1 (4307) 31.2 (5518) 9.2 (1424) 9.6 (1422) 18.2 (3223) 3.0 (456) 3.2 (471) 2.4 (422) 0.5 (75) 0.4 (57) 0.2 (41) 33.0 (5083) 29.9 (4416) 21.2 (3753) 67.0 (10342) 70.1 (10377) 78.8 (13948)

Boreal Shield East Atlantic Maritime Mixedwood Plains Boreal Shield West Boreal Plains Subhumid Prairies Semiarid Prairies Montane Cordillera Pacific Maritime Eastern Canada Western Canada Boreal Shield East Atlantic Maritime Mixedwood Plains Boreal Shield West Boreal Plains Subhumid Prairies Semiarid Prairies Montane Cordillera Pacific Maritime Eastern Canada Western Canada

1991

2006

2016 1.9 (208) 3.6 (395) 14.4 (1601) 0.4 (46) 16.5 (1841) 29.6 (3298) 30.0 (3342) 3.0 (334) 0.5 (60) 19.8 (2204) 80.2 (8923) 0.6 (180) 1.0 (316) 11.3 (3660) 0.3 (83) 15.6 (5058) 35.0 (11387) 36.2 (11753) 0.1 (39) 0.1 (25) 12.8 (4157) 87.2 (28346) 3.1 (443) 4.5 (647) 13.1 (1881) 0.6 (92) 24.3 (3485) 30.4 (4368) 21.2 (3042) 2.6 (378) 0.2 (32) 20.7 (2971) 79.3 (11396)

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C. Liang et al. / Science of the Total Environment 718 (2020) 137273

Table 3 Non-CO2 greenhouse gas emissions per head of beef cattle for selected years in Eastern and Western Canada. Year

Western Canada

Eastern Canada

CH4 emissions kg CO2 eq head-year−1 1791 1990 1900 2000 1876 2005 1898 2016

N2O emissions

Total emissions

CH4 emissions

N2O emissions

Total emissions

302

2093

1668

470

2138

346

2246

1797

524

2321

339

2214

1736

498

2233

358

2256

1735

509

2244

C factors for these regions. For Eastern Canada only two empirical factors were available but appeared to also be in line with the modelled values where observed values range from 0.60–1.07 Mg C ha−1 yr−1 versus 0.74–0.77 Mg C ha−1 yr−1 for the modelled analyses. Based on these rate constants, nationally, net emissions and removals resulting from land management change between perennial and annual cropping systems have varied from a small net source of CO2 in the 1980's to a net sink in the 90's and 2000's and again have reverted to a net source in recent years (Fig. 2). When beef cattle population trends from 1981 to 2016 in Canada are presented together with the changes in SOC resulting from the land use conversion, the two independent measures mirror each other (Fig. 2). In Eastern Canada, since 1981, there has been a loss of C associated with decreased agricultural land in perennial crops as the fraction of total agricultural land has consistently declined. On the contrary, in Western Canada, the emissions and removals from soil change from a source to a sink depending on the number of beef cattle at any one time (Fig. 3). Closer examination reveals a linear relationship between these two variables on a Reporting Zone basis (Table 5). The actual magnitude of emissions/removals of C from or to soils is negatively related to the size of beef cattle population. In other words, as beef cattle populations declined there was a corresponding loss of SOC resulting from a reduction in the relative proportion of perennial to annual crops on the landscape. Significant linear relationships for all Reporting Zones except for Atlantic Maritime, Boreal Shield East and Montane Cordillera were observed, with the R2 varying from 0.62 to 0.83 (p b 0.001); Table 4). On a regional scale, the slope of the linear regression for Western and Eastern Canada is significantly different. In Eastern Canada, variations in populations resulted in a change in soil C of 2600 kg CO2 eq head−1, whereas in Western Canada, the associated change in C was 1700 kg CO2 eq head−1. Based on the observed relationships (Table 5), the reduction of the beef cattle population and associated perennial production on the landscape had a negative impact on soil C. Each beef animal in Western Canada represents avoided emissions from losses of SOC of approximately 1700 (±430) kg CO2 eq yr−1 (approximately 80% of total emissions). Likewise, in Eastern Canada (Fig. 3), the presence of beef cattle

on the landscape and associated land use conversion represents avoided losses of SOC that are more than the combined emissions of CH4 and N2O [2240 (±590) kg CO2 eq head−1 yr−1 versus 2600 (±530) kg CO2 eq head−1 yr−1]. Nationally, the maintenance of perennial crops on the landscape required to feed one beef animal preserves SOC on the landscape equivalent to 62% of the average annual emissions from each beef animal estimated at 2250 (±550) kg CO2 eq head−1 yr−1 (Table 3). It is also interesting to note from Fig. 3 that approximately 11 million beef cattle are required to maintain a balance of SOC (ΔSOC = 0) resulting from annual/perennial crop conversion in Canada. This analysis only includes a comparison of direct emissions associated with beef production. There are other sources of indirect emissions associated with beef cattle production that would need to be considered in a full life cycle analysis. Dyer and Desjardins (2006) reported that the fossil energy coefficient of electrical energy was 23 kg CO2 eq (cow. year)−1 for beef cattle production in Canada. Likewise, for improved pastures N fertilizers are also used to increase forage production, though the quantity of N fertilizers applied is generally low, varying from 1 kg N ha−1 in Saskatchewan to 17 kg N ha−1 in Quebec (Sheppard et al., 2010). Therefore emissions associated with manufacture and application of synthetic N fertilizers for forage production are relatively low. Further, because we include the full population of beef cattle in this analysis, including feeder cattle, emissions associated with fertilizer and energy use to grow crops fed to finishing cattle would contribute to the total emissions associated with beef production in a full life cycle analysis. A parallel analysis was carried out excluding feedlot animal populations from the national statistics; however, this did not improve the strength of the statistical relationship between the variables. The inclusion of feeder animals in the relationship was considered to be more representative of the beef industry's role in preserving SOC on the landscape due to the fact that feeder animals do consume a diet of mainly forages throughout the majority of their life, even though they are finished on grain. So far, very few life cycle analyses include a contribution from soil C changes in GHG emission estimations, mainly due to methodological limitations. Petersen et al. (2013) suggested how soil C changes could be included in life cycle analysis by calculating a partial C

Table 4 Rate constant (k), maximum carbon change (ΔSOCmax), and 20-year average carbon change factor for perennial/annual crop conversion based on Century simulation for the Canadian greenhouse gas inventory (Environment and Climate Change Canada, 2019). Region

Atlantic Maritime Boreal Plains Boreal Shield East Boreal Shield West Mixedwood Plains Mountane Cordillera Pacific Maritime Semiarid Prairies Subhumid Prairies

Rate constant

ΔSOCmax

k/year

Mg C ha−1

0.022 0.022 0.022 0.023 0.025 0.017 0.015 0.028 0.025

±43 ±33 ±46 ±33 ±38 ±35 ±45 ±26 ±27

Equation of soil organic C change upon perennial/annual crop conversion

Mean annual C change over first 20 years Mg C ha−1 yr−1

ΔSOC ΔSOC ΔSOC ΔSOC ΔSOC ΔSOC ΔSOC ΔSOC ΔSOC

= = = = = = = = =

43 • (1-e-0.022t) 33 • (1-e-0.022t) 46 • (1-e-0.022t) 33 • (1-e-0.023t) 38 • (1-e-0.025t) 35 • (1-e-0.017t) 45 • (1-e-0.015t) 26 • (1-e-0.028t) 27 • (1-e-0.025t)

±0.74 ±0.55 ±0.75 ±0.59 ±0.71 ±0.47 ±0.53 ±0.54 ±0.50

C. Liang et al. / Science of the Total Environment 718 (2020) 137273

7

∆SOC resulting from conversion of annual/perennial crops (kt CO2 eq)

3500 3000 2500 2000 1500 1000 500 0 2200

a. Eastern Canada ∆SOC = -2.6●BeefCattle + 8930 R² = 0.80** n=8 2400

2600

2800

3000

3200

3400

3600

∆SOC resulting from conversion of annual/perennial crops (kt CO2 eq)

4000

2000

0 6000

7000

8000

9000

10000

11000

12000

12000

13000

14000

15000

-2000

-4000

b. Western Canada -6000

∆SOC = -1.7●BeefCattle + 13530 R² = 0.72** n=8

-8000

∆SOC resulting from conversion of annual/perennial crops (kt CO2 eq)

3000 1500 0 9000

10000

11000

-1500 -3000

c. Canada -4500

∆SOC = -1.4●BeefCattle + 15700 R² = 0.63* n=8

-6000

Beef cale populaon (x1000 head)

Fig. 3. The relationship between beef cattle population and change in soil organic carbon stock (ΔSOC) resulting from the conversion of annual/perennial crop: a) Eastern Canada, b) Western Canada, and c) Canada (negative value indicates soil C sink). * and ** indicate statistical significance at p b 0.05 and p b 0.01, respectively.

budget for individual crops and combining this with the degradation and emissions of CO2 from the soil and the resulting change in CO2 in the atmosphere. Mogensen et al. (2015) illustrated how this approach can be used to include the contribution from soil C changes in estimations of the C footprint of animal feed. On a small scale, Beauchemin et al. (2011) used a whole-farm model (Holos) for assessing mitigation strategies of GHGs from beef production, and reported that soil C gain more than offset all GHGs when perennial crop in the baseline scenario was newly seeded onto previously annual crops, changing the beef production system from a net emitter to a net sink of C.

Alemu et al. (2016) investigated impacts of grazing management scenarios on GHG intensity (kg CO2 eq kg−1 beef) at the farm-gate for beef production systems in Western Canada using life cycle assessment. The rate of soil C sequestration ranged from 0.01 Mg C ha−1 yr−1 for rangeland under heavy continuous grazing to 0.46 Mg C ha−1 yr−1 for a triticale field used for swath grazing. They concluded that grazing management impacted GHG intensity of beef production by influencing diet quality, animal performance and soil C change. Likewise, it should also be noted that leguminous forages can have very significant positive impact over time on soil N (McKenna et al., 2018) and their implementation in crop rotations could result in avoided GHG emissions from N

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C. Liang et al. / Science of the Total Environment 718 (2020) 137273

Table 5 The relationship between beef cattlea population and the change in soil organic carbon(ΔSOC) resulting from the conversion of perennial/annual crops among Reporting Zones in Canada with significant agriculture. Region

Linear relationship

R2

nb

Statistical significance

Boreal Shield East Atlantic Maritime Mixedwood Plains Boreal Shield West Boreal Plains Subhumid Prairies Semiarid Prairies Mountane Cordilera Pacific Maritime

ΔSOC ΔSOC ΔSOC ΔSOC ΔSOC ΔSOC ΔSOC ΔSOC ΔSOC

0.62 0.37 0.81 0.16 0.82 0.62 0.83 0.10 0.77

8 8 8 8 8 8 8 8 8

P P P P P P P P P

a b

= = = = = = = = =

870–2.8●BeefCattle 840–1.5●BeefCattle 6525–2.5●BeefCattle 64–1.3●BeefCattle 2580–1.5●BeefCattle 8840–1.4●BeefCattle 5230–2.4●BeefCattle 40–0.06●BeefCattle 80–0.76●BeefCattle

b N b N b b b N b

0.05 0.05 0.01 0.05 0.01 0.05 0.01 0.05 0.01

Beef cattle include beef cows, beef and dairy heifers, bulls, feeder heifers, steers and calves. Number of independent observations.

fertilizer. Such complex impacts resulting from land management are rarely included in analyses of cattle production. To our knowledge the present study is the first to demonstrate at regional and national scales strong quantitative empirical evidence of a relationship between beef cattle production and associated land management impacts to SOC stocks resulting from annual/perennial crop conversion. 4. Conclusions The role of beef production in maintaining SOC has been theoretically postulated on a number of occasions. This study provides empirical quantitative evidence of the positive role of beef cattle in maintaining C stocks in soils. Carbon footprints of beef cattle production typically far exceed other animal production systems. However, most analyses are overly simplistic as they do not effectively capture the impact of beef cattle production on the landscape. Because grazing and perennial forage production is an important component of feeding practices for the beef cattle industry, especially for cow-calf and backgrounding operations in Canada, the impact of the change in SOC resulting from the conversion of annual/perennial crops needs to be accounted for. It is clear that the exclusion of the impact of changes in land management on SOC overestimates GHG emissions associated with beef production. The data presented in this study clearly demonstrate that, taking into account the impact of the losses of SOC avoided by maintaining perennial crops on the landscape accounts for approximately 62% of the direct emissions resulting from beef production. Beef cattle maintain on average 1400 (±440) kg CO2 eq head−1 yr−1 of SOC, suggesting that the net direct GHG emissions of Canadian beef cattle is approximately 850 (± 360) kg CO2 eq head−1 yr−1. This result underlines the importance of including the change in SOC for assessing mitigation measures associated with beef cattle production. CRediT authorship contribution statement Chang Liang:Conceptualization, Methodology, Writing - original draft. J. Douglas MacDonald: Conceptualization, Writing - review & editing. Raymond L. Desjardins: Writing - review & editing. Brian G. McConkey: Writing - review & editing. Karen A. Beauchemin: Writing - review & editing. Corey Flemming: Data curation. Darrel Cerkowniak: Data curation. Ana Blondel: Data curation. References [AAFC] Agriculture and Agri-Food Canada, 1990–2016. Annual Livestock and Meat Report. Available online at. www.agr.gc.ca/redmeat-vianderouge/index_eng.htm. [AAFC] Agriculture and Agri-Food Canada, 2006. Soil Landscapes of Canada Working Group. Soil Landscapes of Canada. v. 3.1. Agriculture and Agri-Food Canada, Ottawa, Ontario, Canada (digital map and database at 1:1 million scale). [ECCC] Environment and Climate Change Canada, 2019. National Inventory Report 1990–2017: Greenhouse Gas Sources and Sinks in Canada. Canada’s Submission to

the United Nations Framework Convention on Climate Change. Environment and Climate Change Canada, 351 St-Joseph Blvd., Gatineau, Quebec, Canada. [FAO] Food and Agriculture Organization, 2010. State of Food and Agriculture: Livestock in the Balance. Report by the Food and Agriculture Organization of the United Nations. FAO, Rome (180pp.). [IPCC] Intergovernmental Panel on Climate Change, 2006. 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Volume 4: Agriculture, Forestry and Other Land Use. Intergovernmental Panel on Climate Change Available online at. http://www. ipcc-nggip.iges.or.jp/public/2006gl/vol4.htm. Alemu, A.W., Janzen, H., Little, S., Hao, X., Thompson, D.J., Baron, V., Iwaasa, A., Beauchemin, K.A., Kröbel, R., 2016. Assessment of grazing management on farm greenhouse gas intensity of beef production systems in the Canadian Prairies using life cycle assessment. Agric. Syst. 158, 1–13. Arrouays, D., Horn, R., 2019. Soil carbon - 4 per mille - an introduction. Soil Tillage Res. 188, 1–2. Baker, J.M., Griffis, T.J., 2005. Examining strategies to improve the carbon balance of corn/ soybean agriculture using eddy covariance and mass balance techniques. Agric. For. Meteorol. 128, 163–177. https://doi.org/10.1016/j.agrformet.2004.11.005. Basarab, J., Baron, V., López-Campos, Ó., Aalhus, J., Haugen-Kozyra, K., Okine, E., 2012. Greenhouse gas emissions from calf- and yearling-fed beef production systems, with and without the use of growth promotants. Animals 2, 195–220. https://doi. org/10.3390/ani2020195. Beauchemin, K.A., Janzen, H.H., Little, S.M., McAllister, T.A., McGinn, S.M., 2010. Life cycle assessment of greenhouse gas emissions from beef production in western Canada: a case study. Agric. Syst. 103, 371–379. Beauchemin, K.A., Janzen, H.H., Little, S.M., McAllister, T.A., McGinn, S.M., 2011. Mitigation of greenhouse gas emissions from beef production in western Canada evaluation using farm-based life cycle assessment. Anim. Feed Sci. Technol. 167, 663–667. Boadi, D.A., Ominski, K.H., Fulawka, D.L., Wittenberg, K.M., 2004. Improving estimates of methane emissions associated with enteric fermentation of cattle in Canada by adopting an IPCC (intergovernmental panel on climate change) tier2 methodology. Final Report Submitted to the Greenhouse Gas Division, Environment Canada, by the Department of Animal Science. University of Manitoba, Winnipeg, MB, Canada. Browne, N.A., Eckard, R.J., Behrendt, R., Kingwell, R.S., 2011. A comparative analysis of onfarm greenhouse gas emissions from agricultural enterprises in south eastern Australia. Anim. Feed Sci. Technol. 166-167, 641–652. Canfax Research Services, 2018. Statistical Briefer. March 2017. Available at. http://www. canfax.ca/Samples/StatBrf.pdf. Dawson, J.J.C., Smith, P., 2007. Carbon losses from soil and its consequences for land-use management. Sci. Total Environ. 382, 165–190. Delgado, C.M., Rosegrant, H., Steinfeld, S., Courbois, C., 1999. Livestock to 2020: The Next Food Revolution. IFPRI, FAO and ILRI, Washington, D.C., USA. Desjardins, R.L., Worth, D.E., Verge, X.P.C., Maxime, D., Dyer, J.A., Cerkowniak, D., 2012. Carbon footprint of beef cattle. J. of Sustainability 4, 3279–3301. Dumanski, J., Desjardins, R.L., Tarnocai, C., Monreal, C., Gregorich, E.G., Kirkwood, V., Campbell, C.A., 1998. Possibilities for future carbon sequestration in Canadian agriculture in relation to land use changes. Clim. Chang. 40, 81–103. Dyer, J.A., Desjardins, R.L., 2006. A balance sheet for electrical energy use in Canadian agriculture with implications for greenhouse gas emissions. Biosyst. Eng. 95, 449–460. Dyer, J.A., Vergé, X.P.C., Desjardins, R.L., Worth, D.E., 2010. The protein-based GHG emission intensity for livestock products in Canada. J. Sustain. Agric. 34, 618–629. Gerber, P.J., Steinfeld, H., Henderson, B., Mottet, A., Opio, C., Dijkman, J., Falcucci, A., Tempio, G., 2013. Tackling Climate Change through Livestock – A Global Assessment of Emissions and Mitigation Opportunities. Food and Agriculture Organization of the United Nations (FAO), Rome, Italy Retrieved on 10 July 2019 from. http://www.fao. org/3/a-i3437e.pdf. Glenn, A.J., Amiro, B.D., Tenuta, M., Stewart, S.E., Wagner-Riddle, C., 2010. Carbon dioxide exchange in a northern Prairie cropping system over three years. Agric. For. Meteorol. 150, 908–918. https://doi.org/10.1016/j.agrformet.2010.02.010. Grebitus, C., Steiner, B., Veeman, M., 2013. Personal values and decision making: evidence from environmental footprint labeling in Canada. Am. J. Agric. Econ. 95, 397–403. https://doi.org/10.1093/ajae/aas109.

C. Liang et al. / Science of the Total Environment 718 (2020) 137273 Hussain, M.Z., Grünwald, T., Tenhunen, J.D., Li, Y.L., Mirzae, H., Bernhofer, C., Otieno, D., Dinh, N.Q., Schmidt, M., Wartinger, M., Owen, K., 2011. Summer drought influence on CO2 and water fluxes of extensively managed grassland in Germany. Agric. For. Meteorol. 141, 67–76. Karimi-Zindashty, Y., MacDonald, J.D., Desjardins, R., Worth, D., Vergé, X., 2012. Analysis of the uncertainty in the IPCC tier 2 Canadian livestock model: sources of uncertainty. J. Agric. Sci. 150, 556–559. Kröbel, R., Bolinder, M.A., Janzen, H.H., Little, S.M., VandenBygaart, A.J., Kätterer, T., 2016. Canadian farm-level soil carbon change assessment by merging the greenhouse gas model Holos with the Introductory Carbon Balance Model (ICBM). Agric. Syst. 143, 76–85. Kutsch, W.L., Aubinet, M., Buchmann, N., Smith, P., Osborne, B., Eugster, W., Wattenbach, W., Schrumpft, M., Schulze, E.D., Tomelleri, E., Ceschia, E., Bernhofer, C., Béziat, P., Carrara, A., Di Tommasi, P., Grünwald, T., Jones, M., Magliulo, V., Marloie, O., Moureaux, C., Olioso, A., Sanz, M.J., Saunders, M., Søgaard, H., Ziegler, W., 2010. The net biome production of full crop rotations in Europe. Agric. Ecosyst. Environ. 139, 336–345. https://doi.org/10.1016/j.agee.2010.07.016. Lemke, R.L., Baron, V., Iwaasa, A., Farrell, R., Schoenau, J., 2012. Quantifying nitrous oxide emissions resulting from animal manure on pasture, range and paddock by grazing cattle in Canada. Final Report Submitted to the Greenhouse Gas Division, Environment Canada, by. Agriculture and Agri-Food Canada, Saskatoon, SK, Canada. Lesschen, J.P., van der Berg, M., Westhoek, H.J., Witzke, H.P., Oenema, O., 2011. Greenhouse gas emission profiles of European livestock sectors. Anim. Feed Sci. Technol.166–167, 16–28. Maas, S.E., Glenn, A.J., Tenuta, M., Amiro, B.D., 2013. Net CO2 and N2O exchange during perennial forage establishment in an annual crop rotation in the Red River Valley, Manitoba. Can. J. Soil Sci. 93, 639–652. https://doi.org/10.4141/cjss2013-025. Marshall, I.B., Schut, P.H., Ballard, M., 1999. A National Ecological Framework for Canada: Attribute Data. Prepared by Environment Canada and Agriculture and Agri-Food Canada. Available online at. http://sis.agr.gc.ca/cansis/nsdb/ecostrat/1999report/ index.html. McKenna, P., Cannon, N., Conway, J., Dooley, J., 2018. The use of red clover (Trifolium pretense) in soil fertility-building: a review. Field Crop Res. 221, 38–49. Minasny, B., Malone, B.P., McBratney, A.B., Angers, D.A., Arrouays, D., Chambers, A., Chaplot, V., Chen, Z.S., Cheng, K., Das, B.S., Field, D.J., Gimona, A., Hedley, C.B., Hong, S.Y., Mandal, B., Marchant, B.P., Martin, M., McConkey, B.G., Mulder, V.L., O’Rourke, S., Richer-de-Forges, A.C., Odeh, I., Padarian, J., Paustian, K., Pan, G.X., Poggio, L., Savin, I., Stolbovoy, V., Stockmann, U., Sulaeman, Y., Tsui, C.C., Vagen, T.G., Wesemael, B.V., Winowiecki, L., 2017. Soil carbon 4 per mille. Geoderma 292, 59–86. Mogensen, L., Kristensen, T., Nielsen, N.I., Spleth, P., Henriksson, M., Swensson, C., Hessle, A., Vestergaard, M., 2015. Greenhouse gas emissions from beef production systems in Denmark and Sweden. Livest.Sci. 174, 126–143. Nguyen, T.L.T., Hermansen, J.E., Mogensen, L., 2010. Environmental consequence of different beef production systems in the EU. J. Clean. Prod. 18, 756–766. Ominski, K.H., Boadi, D.A., Wittenberg, K.M., 2007. Enteric methane emissions from backgrounded cattle consuming all-forage diets. Can. J. Anim. Sci. 86, 393–400. Parton, W.J., Schimel, D.S., Cole, C.V., Ojima, D.S., 1987. Analysis of factors controlling soil organic matter levels in Great Plains grasslands. Soil Sci. Soc. Am. J. 51, 1173–1179. Petersen, B.M., Knudsen, M.T., Hermansen, J.E., Halberg, N., 2013. An approach to include soil carbon changes in the lifecycle assessments. J. Clean. Prod. 52, 217–224.

9

Rochette, P., Worth, D.E., Lemke, R.L., McConkey, B.G., Pennock, D.J., Wagner-Riddle, C., Desjardins, R.L., 2008. Estimation of N2O emissions from agricultural soils in Canada. I. Development of a country-specific methodology. Can. J. Soil Sci. 88, 641–654. Rochette, P., Chantigny, M.H., Ziadi, N., Angers, D.A., Bélanger, G., Charbonneau, E., Pellerin, D., Liang, B.C., Bertrand, N., 2014. Soil nitrous oxide emissions after deposition of dairy cow excreta in eastern Canada. J. Environ. Qual. 43, 829–841. Rochette, P., Liang, B.C., Pelster, D., Bergeron, O., Lemke, R., Kroebel, R., MacDonald, D., Yan, W.K., Flemming, C., 2018. Soil nitrous oxide emissions from agricultural soils in Canada: exploring relationships with soil, crop and climatic variables. Agric. Ecosyst. Environ. 254, 69–81. SAS Institute, 1999. SAS/STAT User’s Guide. Version 6. SAS Institute, Cary, NC, USA. Schils, R.L.M., Olesen, J.E., del Prado, A., Soussana, J.F., 2007. A review of farm level modelling approaches for mitigating greenhouse gas emissions from ruminant livestock systems. Livest. Sci. 112, 240–251. Sheppard, S.C., Bittman, S., Bruulsema, T.W., 2010. Monthly ammonia emissions from fertilizers in 12 Canadian ecoregions. Can. J. Soil Sci. 90, 113–127. Sheppard, S.C., Bittman, S., Donohoe, G., Flaten, D., Wittenberg, K.M., Small, J.A., Berthiaume, R., McAllister, T.A., Beauchemin, K.A., McKinnon, J., Amiro, B.D., MacDonald, D., Mattos, F., Ominski, K.H., 2015. Beef cattle husbandry practices across ecoregions of Canada in 2011. Can. J. Anim. Sci. 95, 305–321. Steinfeld, H., Gerber, P., Wassenaar, T., Castel, V., Rosales, M., de Haan, C., 2006. Livestock’s Long Shadow: Environmental Issues and Options. Food and Agriculture Organization, Rome. Stewart, A.A., Little, S.M., Ominski, K.H., Wittenberg, K.M., Janzen, H.H., 2009. Evaluating greenhouse gas mitigation practices in livestock systems: an illustration of a wholefarm approach. J. Agr. Sci. 147, 367–382. Taylor, A.M., Amiro, B.D., Fraser, T.J., 2013. Net CO2 exchange and carbon budgets of a three-year crop rotation following conversion of perennial lands to annual cropping in Manitoba, Canada. Agric. Forest Meteorol. 182–183, 67–75. https://doi.org/ 10.1016/j.agrformet.2013.07.008. VandenBygaart, A.J., Gregorich, E.G., Angers, D.A., 2003. Influence of agricultural management on soil organic carbon: a compendium and analysis of Canadian studies. Can. J. Soil Sci. 83, 363–380. VandenBygaart, A.J., McConkey, B.G., Angers, D.A., Smith, W., de Gooijer, H., Bentham, M., Martin, T., 2008. Soil carbon change factors for the Canadian agriculture national greenhouse gas inventory. Can. J. Soil Sci. 88, 671–680. Vellinga, T.V., de Haan, M.H.A., Schils, R.L.M., Evers, A., van den Pol–van Dasselaar, A., 2011. Implementation of GHG mitigation on intensive dairy farms: farmers’ preferences and variation in cost effectiveness. Livest. Sci. 137, 185–195. Vergé, X.P.C., Dyer, J.A., Worth, D.E., Smith, W.N., Desjardins, R.L., McConkey, B.G., 2012. A greenhouse gas and soil carbon model for estimating carbon footprint of livestock production in Canada. Animals 2, 437–454. https://doi.org/10.3390/ani2030437. Wang, T., Teague, W.R., Park, S.C., Bevers, S., 2015. GHG mitigation potential of different grazing strategies in the United States southern Great Plains. Sustain. For. 7, 13500–13521.