No-tillage (NT), a practice that has been shown to increase carbon sequestration in soils, has resulted in contradictory effects on nitrous oxide (N 2 O) emissions. Moreover, it is not clear how mitigation practices for N 2 O emission reduction, such as applying nitrogen (N) fertilizer according to soil N reserves and matching the time of application to crop uptake, interact with NT practices. N 2 O fluxes from two management systems [conventional (CP), and best management practices: NT 1reduced fertilizer (BMP)] applied to a corn (Zea mays L.), soybean (Glycine max L.), winter-wheat (Triticum aestivum L.) rotation in Ontario, Canada, were measured from January 2000 to April 2005, using a micrometeorological method. The superimposition of interannual variability of weather and management resulted in mean monthly N 2 O fluxes ranging from À1.9 to 61.3 g N ha À1 day À1 . Mean annual N 2 O emissions over the 5-year period decreased significantly by 0.79 from 2.19 kg N ha À1 for CP to 1.41 kg N ha À1 for BMP. Growing season (May-October) N 2 O emissions were reduced on average by 0.16 kg N ha À1 (20% of total reduction), and this decrease only occurred in the corn year of the rotation. Nongrowing season (November-April) emissions, comprised between 30% and 90% of the annual emissions, mostly due to increased N 2 O fluxes during soil thawing. These emissions were well correlated (r 2 5 0.90) to the accumulated degree-hours below 0 1C at 5 cm depth, a measure of duration and intensity of soil freezing. Soil management in BMP (NT) significantly reduced N 2 O emissions during thaw (80% of total reduction) by reducing soil freezing due to the insulating effects of the larger snow cover plus corn and wheat residue during winter. In conclusion, significant reductions in net greenhouse gas emissions can be obtained when NT is combined with a strategy that matches N application rate and timing to crop needs.

Alongside the steep reductions needed in fossil fuel emissions, natural climate solutions (NCS) represent readily deployable options that can contribute to Canada’s goals for emission reductions. We estimate the mitigation potential of 24 NCS related to the protection, management, and restoration of natural systems that can also deliver numerous co-benefits, such as enhanced soil productivity, clean air and water, and biodiversity conservation. NCS can provide up to 78.2 (41.0 to 115.1) Tg CO2e/year (95% CI) of mitigation annually in 2030 and 394.4 (173.2 to 612.4) Tg CO2e cumulatively between 2021 and 2030, with 34% available at ≤CAD 50/Mg CO2e. Avoided conversion of grassland, avoided peatland disturbance, cover crops, and improved forest management offer the largest mitigation opportunities. The mitigation identified here represents an important potential contribution to the Paris Agreement, such that NCS combined with existing mitigation plans could help Canada to meet or exceed its climate goals.

The importance of spring thaw nitrous oxide (N2O) fluxes to the total N2O emission budget in cold climates has been recognized recently. Two mechanisms have been proposed to explain the burst in N2O fluxes due to soil freezing and thawing: enhanced microbial activity due to increased nutrient availability at spring thaw, and release of N2O trapped at depth during winter. The objective of this study was to determine whether increased surface N2O fluxes were due to physical release at spring thaw of N2O accumulated all winter at depth in the soil profile, or whether fluxes were due to rapid N2O production in the surface layer during the thaw process. Micrometeorological flux measurements and a chamber method applied to in situ soil columns receiving 15N tracer were used in Ontario, Canada during winters of 2003 and 2004. Labeled K15NO3 fertilizer (60% excess 15N) at the rate of 100 kg N ha−1 was applied to two layers, that is, surface layer 0 to 5 cm (SL) and deep layer 12 to 17 cm (DL) in nondisturbed soil columns placed in the field during the winter. The burst in N2O fluxes from the soil surface measured by both methods occurred within the same period of soil thawing. Denitrification was the main mechanism responsible for N2O production, and conditions conducive to N2O and N2 production occurred both in the SL and DL during thawing. Despite high 15N2O concentrations at depth, the burst in N2O fluxes from DL soil columns were 1.5 to 5 times lower than that from SL soil columns as more N2O from DL was converted to N2 before diffusing out of the soil profile. Comparison of N2O fluxes originating from SL and DL soil columns indicates that the source of N2O burst at spring thaw is mostly ‘newly’ produced N2O in the surface layer, and not the release of N2O trapped in the unfrozen soil beneath the frozen layers.

Integrated Systems (IS) have been identified as an efficient land-management strategy for restoring degraded areas worldwide, increasing crops and beef yields and providing technical potential for carbon (C) sequestration in soil and trees as an option for offsetting CH 4 and N 2 O emissions from cattle production. The aim of our study is to estimate the greenhouse gas (GHG) balance and the C footprint of beef cattle (fattening cycle) in three contrasting production scenarios on the Brachiaria pasture in Brazild1) degraded pasture (DP), 2) managed pasture (MP), and 3) the crop-livestock-forest integrated system (CLFIS)dpresenting new alternatives of land use as a GHG mitigation strategy. Area-scaled total GHG emissions were highest in MP (84,541 kg CO 2 eq ha À1), followed by CLFIS (64,519 kg CO 2 eq ha À1) and DP (8004 kg CO 2 eq ha À1) over a 10-yr period. Our results note that the highest C footprint of beef cattle was in the DP, 18.5 kg CO 2 eq per kg LW (live weight), followed by 12.6 kg CO 2 eq per kg LW in the CLFIS and 9.4 kg CO 2 eq per kg LW in the MP, without taking into account the technical potential for C sequestration in MP (soil C) and CLFIS (soil and Eucalyptus C). Considering the potential for soil C sequestration in the MP and CLFIS, the C footprint of beef cattle could be reduced to 7.6 and À28.1 kg CO 2 eq per kg LW in the MP and CLFIS, respectively. The conversion of the degraded pasture to a well-managed pasture and the introduction of CLFIS can reduce their associated GHG emissions in terms of kg CO 2 eq emitted per kg of cattle LW produced, increasing the production of meat, grains and timber. This reduction is primarily due to pasture improvement and increases in cattle yields and the provision of technical potential for C sinks in soil and biomass to offset cattle-related emissions.

Best management practices are recommended for improving fertilizer and soil N uptake efficiency and reducing N losses to the environment. Few year-round studies quantifying the combined effect of several management practices on environmental N losses have been carried out. This study was designed to assess crop productivity, N uptake from fertilizer and soil sources, and N losses, and to relate these variables to the fate of fertilizer 15N in a corn (Zea mays L.)-soybean (Glycine max L.)-winter wheat (Triticum aestivum L.) rotation managed under Best Management (BM) compared with conventional practices (CONV). The study was conducted from Cumulative NO 3 leaching loss was reduced by 51% from 133 kg N ha À1 in CONV to 68 kg N ha À1 in BM. About 70% of leaching loss occurred in corn years with fertilizer N directly contributing 11-16% to leaching in CONV and <4% in BM. High soil derived N leaching loss in CONV, which occurred mostly (about 80%) during November to April was attributable to 45-69% higher residual soil derived mineral N left at harvest, and on-going N mineralization during the over-winter period. Fertilizer N uptake efficiency (FNUE) was higher in BM (61% of applied) than in CONV (35% of applied) over corn and wheat years. Unaccounted gaseous losses of fertilizer N were reduced from 27% of applied in CONV to 8% of applied in BM. Yields were similar between BM and CONV (for corn: 2000 and 2003, wheat: 2002, soybean: 2004 or higher in BM (soybean: 2001). Results indicated that the use of judicious N rates in synchrony with plant N demand combined with other BMP (no-tillage, legume cover crops) improved FNUE by corn and wheat, while reducing both fertilizer and soil N losses without sacrificing yields.

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Monensin is a widely used feed additive with the potential to minimize methane (CH 4 ) emissions from cattle. Several studies have investigated the effects of monensin on CH 4 , but findings have been inconsistent. The objective of the present study was to conduct meta-analyses to quantitatively summarize the effect of monensin on CH 4 production (g/d) and the percentage of dietary gross energy lost as CH 4 (Y m ) in dairy cows and beef steers. Data from 22 controlled studies were used. Heterogeneity of the monensin effects were estimated using random effect models. Due to significant heterogeneity (>68%) in both dairy and beef studies, the random effect models were then extended to mixed effect models by including fixed effects of DMI, dietary nutrient contents, monensin dose, and length of monensin treatment period. Monensin reduced Y m from 5.97 to 5.43% and diets with greater neutral detergent fiber contents (g/kg of dry matter) tended to enhance the monensin effect on CH 4 in beef steers. When adjusted for the neutral detergent fiber effect, monensin supplementation [average 32 mg/kg of dry matter intake (DMI)] reduced CH 4 emissions from beef steers by 19 ± 4 g/d. Dietary ether extract content and DMI had a positive and a negative effect on monensin in dairy cows, respectively. When adjusted for these 2 effects in the final mixed-effect model, monensin feeding (average 21 mg/kg of DMI) was associated with a 6 ± 3 g/d reduction in CH 4 emissions in dairy cows. When analyzed across dairy and beef cattle studies, DMI or monensin dose (mg/kg of DMI) tended to decrease or increase the effect of monensin in reducing methane emissions, respectively. Methane mitigation effects of monensin in dairy cows (-12 ± 6 g/d) and beef steers (-14 ± 6 g/d) became similar when adjusted for the monensin dose differences between dairy cow and beef steer studies.When adjusted for DMI differences, monensin reduced Y m in dairy cows (-0.23 ± 0.14) and beef steers (-0.33 ± 0.16). Monensin treatment period length did not significantly modify the monensin effects in dairy cow or beef steer studies. Overall, monensin had stronger antimethanogenic effects in beef steers than dairy cows, but the effects in dairy cows could potentially be improved by dietary composition modifications and increasing the monensin dose.

This review examined methane (CH4) and nitrous oxide (N2O) mitigation strategies for Canadian dairy farms. The primary focus was research conducted in Canada and cold climatic regions with similar dairy systems. Meta-analyses were conducted to assess the impact of a given strategy when sufficient data were available. Results indicated that options to reduce enteric CH4 from dairy cows were increasing the dietary starch content and dietary lipid supplementation. Replacing barley or alfalfa silage with corn silage with higher starch content decreased enteric CH4 per unit of milk by 6%. Increasing dietary lipids from 3% to 6% of dry matter (DM) reduced enteric CH4 yield by 9%. Strategies such as nitrate supplementation and 3-nitrooxypropanol additive indicated potential for reducing enteric CH4 by about 30% but require extensive research on toxicology and consumer acceptance. Strategies to reduce emissions from manure are anaerobic digestion, composting, solid–liquid separation, covering slurry storage and flaring CH4, and reducing methanogen inoculum by complete emptying of slurry storage at spring application. These strategies have potential to reduce emissions from manure by up to 50%. An integrated approach of combining strategies through diet and manure management is necessary for significant GHG mitigation and lowering carbon footprint of milk produced in Canada.