Lower CH4 Emissions Research Articles

Numerical Study on the Effects of Partial Oxidation Fuel Reforming (POFR) on the Performance of a Natural Gas Engine

Due to the issues of low flame speed and high CH4 emissions for a natural gas engine, investigations into the partial oxidation fuel reforming (POFR) method used in natural gas engines to blend H2 have become increasingly valuable. In this paper, the combustion process, engine performance, and emissions of a natural gas engine with fuel-reforming gases blended together have been numerically studied. The results show that a higher fuel-reforming ratio can effectively improve the engine combustion performance, especially at lean-burn conditions. Combustion with reformed gases can increase the thermal efficiency by almost 2% at the full-load condition, whereas fuel reforming significantly affects the natural gas engine’s power performance. Furthermore, CH4 and NOX emissions decrease significantly with increasing fuel-reforming ratio. In conclusion, fuel reforming for a natural gas engine has a promising future in reducing greenhouse gas emissions and improving economic performance.

Opportunities for mitigating net system greenhouse gas emissions in Southeast Asian rice production: A systematic review

Southeast Asia (SEA) is a key producer and exporter of rice, accounting for around 28% of rice produced globally. To effectively mitigate greenhouse gas (GHG) emissions in SEA rice systems, field methane (CH4) and nitrous oxide (N2O) emissions have been intensively studied. However, an integrated assessment of system-level GHG emissions which includes other carbon (C) balance components, such as soil organic carbon (SOC) or energy use, that can positively or negatively influence the net capacity for climate change mitigation is lacking. We conducted a systematic review of published research in SEA rice systems to synthesize findings across four main components of net system emissions: (1) field GHG emissions, (2) energy inputs, (3) residue utilization beyond the field, and (4) SOC change. The objectives were to highlight effective mitigation opportunities and explore cross-component effects to identify tradeoffs and key knowledge gaps. Field GHG emissions were the largest contributor to net system emissions in agreement with existing scientific consensus, with results showing that practices such as floodwater drainage and residue removal are sound options for CH4 mitigation. On the other hand, increasing SOC potentially provides a large GHG mitigation opportunity, with long-term continuous rice cropping and practices such as residue incorporation and biochar application promoting SOC increase. A reduction in energy inputs was mainly achieved by optimizing agrochemical use, especially N fertilizers. For residue utilization beyond the field, GHG emission mitigation mainly came from preventing open field burning through residue removal. Removed residue can subsequently be used for producing energy that offsets GHG emissions associated with conventional fuel sources (e.g. fossil fuel-based electricity generation) or substituting material used in other production systems. Integrating all four components of net system emissions into one analysis underscores the following two main takeaways. First, the components of field GHG emissions and SOC change are the biggest opportunities for reducing net system emissions and need to be considered for effective climate change mitigation. Second, the reduction of C inputs through residue removal and increased soil aeration through multiple drainage will lower CH4 emissions but may also potentially decrease SOC stocks over time. Hence, we argue that future research needs to consider cross-component effects to optimize net system emissions, specifically the “stacking” of best management practices for mitigation related to field GHG emissions or SOC change in long-term experiments.

Reoxidation of Reduced Peat Organic Matter by Dissolved Oxygen: Combined Laboratory Column‐Breakthrough Experiments and In‐Field Push‐Pull Tests

AbstractElectron transfer to peat particulate organic matter (POM) as terminal electron acceptor (TEA) in anaerobic respiration has been hypothesized to lower methane emissions from peatlands by competitively suppressing methanogenesis and/or allowing for anaerobic oxidation of methane. We herein provide evidence for two critical aspects of this hypothesis: (a) peat POM is present in a reduced state in situ in the anoxic peat subsurface, and (b) reduced POM at the oxic‐anoxic interface in peat soils can be oxidized by dissolved oxygen (DO), restoring its TEA capacity. We reacted reduced POM from three ombrotrophic bogs in Sweden with DO in soil‐packed column‐breakthrough experiments (CBEs), mimicking oxidation reactions at the oxic‐anoxic interface. Breakthrough of DO was substantially retarded relative to the inert tracer bromide, consistent with DO reduction by POM. Control experiments confirmed abiotic DO reduction and excluded DO consumption through aerobic respiration. Modeling DO breakthrough revealed fast and slowly reacting POM moieties with reaction times spanning minutes to days. Complementary push‐pull tests (PPTs) in the anoxic subsurface of one bog confirmed results from laboratory CBEs: lower recoveries of injected DO compared with bromide supported DO reduction by reduced POM. Rates of reduction of injected DO decreased with increasing number of injections, consistent with continuous oxidation of reduced POM. Electron‐donating capacities of POM to DO in CBEs and PPTs were comparable at 40–130 μmol e−/g dry POM. Our results substantiate that POM is a regenerable TEA at oxic‐anoxic interfaces in peat soils and, thereby, may substantially lower CH4 emissions from peatlands.

Global methane pledge versus carbon dioxide emission reduction

Methane (CH4) is a potent greenhouse gas whose contribution to anthropogenic radiative forcing of the climate system is second only to carbon dioxide (CO2). CH4 emission reduction has become critical to global climate mitigation policy, resulting most notably in the global methane pledge (GMP), pledging a 30% reduction of CH4 emissions by 2030. Methane is, however, much shorter-lived in the atmosphere than CO2, so emissions reductions may have different impacts on global warming over time. We quantify the difference over time in global annual mean surface temperature of the GMP versus the equivalent amount of CO2 emission reduction. The avoidance of CH4 emissions in the 2020s due to the GMP initially results in greater relative cooling than the avoidance of the equivalent amount of CO2 emissions over the same period, but less relative cooling after ∼2060, when almost all CH4 emitted during the 2020s has been removed from the atmosphere but much of the CO2 emitted during the 2020s remains. However, if the GMP places the world on a lower CH4 emissions trajectory after 2030, this results in a persistently and substantially greater reduction to global warming than the equivalent change in the CO2 emissions trajectory, with a maximum difference of 0.22 ± 0.06 ∘C in 2055 and relative cooling for well over a century. This equates to a large difference in avoided climate change damages if momentum in CH4 emission reduction from the GMP can be sustained after the 2020s. While the greatest reduction in warming is obtained by reducing both CH4 and CO2 emissions, our results underscore the striking global societal benefits of sustained reduction in CH4 emissions.

Ratoon Rice Cropping Mitigates the Greenhouse Effect by Reducing CH4 Emissions through Reduction of Biomass during the Ratoon Season.

The ratoon rice cropping system (RR) is developing rapidly in China due to its comparable annual yield and lower agricultural and labor inputs than the double rice cropping system (DR). Here, to further compare the greenhouse effects of RR and DR, a two-year field experiment was carried out in Hubei Province, central China. The ratoon season showed significantly lower cumulative CH4 emissions than the main season of RR, the early season and late season of DR. RR led to significantly lower annual cumulative CH4 emissions, but no significant difference in cumulative annual N2O emissions compared with DR. In RR, the main and ratoon seasons had significantly higher and lower grain yields than the early and late seasons of DR, respectively, resulting in comparable annual grain yields between the two systems. In addition, the ratoon season had significantly lower global warming potential (GWP) and greenhouse gas intensity-based grain yield (GHGI) than the main and late seasons. The annual GWP and GHGI of RR were significantly lower than those of DR. In general, the differences in annual CH4 emissions, GWP, and GHGI could be primarily attributed to the differences between the ratoon season and the late season. Moreover, GWP and GHGI exhibited significant positive correlations with cumulative emissions of CH4 rather than N2O. The leaf area index (LAI) and biomass accumulation in the ratoon season were significantly lower than those in the main season and late season, and CH4 emissions, GWP, and GHGI showed significant positive correlations with LAI, biomass accumulation and grain yield in the ratoon and late season. Finally, RR had significantly higher net ecosystem economic benefits (NEEB) than DR. Overall, this study indicates that RR is a green cropping system with lower annual CH4 emissions, GWP, and GHGI as well as higher NEEB.

Seasonal and annual methane and nitrous oxide emissions affected by tillage and cover crops in flood-irrigated rice

Soil tillage plays an important role in methane (CH4) and nitrous oxide (N2O) emissions in flood-irrigated rice production. Hence, this study measured the effects of soil tillage and cover crops on the seasonal and annual CH4 and N2O emissions in flood-irrigated rice. A field experiment was conducted for two agricultural years with conventional tillage (CT), minimum tillage (MT), no-tillage (NT), and NT with Persian clover (Trifolium resupinatum) (NT+PC). The effect of different tillage systems on CH4 emissions, which occur predominantly in rice cultivation, depends on the impact of tillage and the amount of straw remaining at the time of rice seeding. When straw incorporation in MT and CT reduces the quantity of straw remaining relative to NT, lower CH4 emissions occurred in the CT and MT. In contrast, when the amount of straw remaining on the soil is similar among the types of soil tillage, lower CH4 emissions occurred in the NT. The effect of tillage on annual N2O emissions was unclear, although the highest in-season N2O emissions occurred in the NT, where the highest water-filled pore space values were recorded in both years. High N2O emissions during rice cultivation occurred in the CT after nitrogen fertilization. The effect of the cover crop in the NT varied as a function of the performance of the clover. When the PC biomass production was satisfactory in the second year, annual CH4 and N2O emissions increased by 8 % and 23 %, respectively. The seasonal and annual quantification of CH4 and N2O emissions is important to reduce the uncertainty of the effect of different land management systems on CH4 and N2O emissions.

Evaluating enteric methane emissions within a herd of genetically divergent grazing dairy cows

Enteric methane (CH4) emissions of 3 genetic groups (GG) of dairy cows were recorded across the grazing season (early March to late October). The 3 GG were (1) high economic breeding index (EBI) Holstein-Friesian (HF) representative of the top 1% of dairy cows in Ireland at the time of the study (elite), (2) national average (NA) EBI, which were representative of the average HF dairy cow in Ireland, and (3) purebred Jersey (JE) cows. Enteric CH4 was recorded using GreenFeed technology. Seasonal variation in CH4 was observed, with the lowest daily CH4 emissions and CH4 expressed per unit of dry matter intake occurring in spring (253 g/d and 15.56 g/kg, respectively), intermediate in summer (303 g/d and 18.26 g/kg, respectively), and greatest in autumn (324 g/d and 19.80 g/kg, respectively). Seasonal variation was also observed in the proportion of gross energy intake converted to CH4 (Ym); in the spring the Ym was lowest at 0.046, increasing to 0.053 and 0.058 in the summer and autumn, respectively. There was no difference in daily CH4 between the elite and NA, whereas JE had lower CH4 emissions compared with the elite. When expressed per unit of milk solids (fat + protein yield; MS), the elite and JE produced 6.8% and 9.7% less CH4 per kilogram of MS, respectively, compared with NA. There was no difference between the GG for CH4 per unit of DMI or the Ym. This research emphasizes the variation in CH4 emissions across the grazing season and among cows of differing genetic merit for CH4 emission intensities but not for CH4 per unit of DMI or the Ym.

Exploring indicators of genetic selection using the sniffer method to reduce methane emissions from Holstein cows.

This study aimed to evaluate whether the methane (CH4) to carbon dioxide (CO2) ratio (CH4/CO2) and methane-related traits obtained by the sniffer method can be used as indicators for genetic selection of Holstein cows with lower CH4 emissions. The sniffer method was used to simultaneously measure the concentrations of CH4 and CO2 during milking in each milking box of the automatic milking system to obtain CH4/CO2. Methane-related traits, which included CH4 emissions, CH4 per energy-corrected milk, methane conversion factor (MCF), and residual CH4, were calculated. First, we investigated the impact of the model with and without body weight (BW) on the lactation stage and parity for predicting methane-related traits using a first on-farm dataset (Farm 1; 400 records for 74 Holstein cows). Second, we estimated the genetic parameters for CH4/CO2 and methane-related traits using a second on-farm dataset (Farm 2; 520 records for 182 Holstein cows). Third, we compared the repeatability and environmental effects on these traits in both farm datasets. The data from Farm 1 revealed that MCF can be reliably evaluated during the lactation stage and parity, even when BW is excluded from the model. Farm 2 data revealed low heritability and moderate repeatability for CH4/CO2 (0.12 and 0.46, respectively) and MCF (0.13 and 0.38, respectively). In addition, the estimated genetic correlation of milk yield with CH4/CO2 was low (0.07) and that with MCF was moderate (-0.53). The on-farm data indicated that CH4/CO2 and MCF could be evaluated consistently during the lactation stage and parity with moderate repeatability on both farms. This study demonstrated the on-farm applicability of the sniffer method for selecting cows with low CH4 emissions.

Evaluating methane emissions from rice paddies: A study on the cultivar and transplanting date

Climate change, driven by increased greenhouse gas emissions, is a pressing environmental issue worldwide. Flooded rice paddy soils are a predominant source of methane (CH4) emissions, accounting for approximately 11 % of global emissions. Factors such as rice (Oryza sativa L.) cultivar, transplanting date, water management, and soil characteristics significantly influence these emissions. This study aimed to evaluate the CH4 emissions from rice paddies in relation to the cultivar and transplanting date. The experiment included two rice cultivars (an early-maturing cultivar, Unkwang, and a medium–late-maturing cultivar, Samkwang) and four transplanting dates (Times 1–4). In the present study, CH4 emissions were higher with earlier transplanting dates and decreased significantly with delayed transplanting. Weather conditions, such as cumulative mean air temperature, cumulative soil temperature, and total sunshine hours, were positively correlated with total CH4 emissions. The recommended regional transplanting date (Time 3) resulted in the highest rice grain yields for both cultivars. However, the earlier transplanting dates (Time 1 and Time 2) were more effective in improving plant growth characteristics such as rice straw weight, root biomass weight, and chlorophyll content. A significant positive correlation was observed between the root biomass weight of the rice and CH4 emissions in both cultivars, implying that an increase in root biomass weight led to an increase in CH4 emissions. Consequently, adhering to the advised regional transplanting dates is the most sensible approach for transplanting rice seedlings. This ensured lower CH4 emissions without compromising rice productivity or quality for both cultivars. Further research should focus on identifying the most appropriate rice-transplanting dates and management practices to effectively reduce CH4 emissions without compromising rice production.

Ammonia and methane emissions from small herd cattle buildings in a cold climate

Ammonia (NH3) and methane (CH4) emission measurements that reflect local production conditions are required to track progress in national emission policies and verify emission factors. The findings can also be used to better understand key factors influencing emissions. This is especially important in Norway, which has long cold winters, and small cattle herds in mechanically ventilated buildings. However, until now, NH3 and CH4 emissions from Norwegian cattle buildings have not been reported in literature. Moreover, in other cold climates, NH3 and CH4 emissions are often taken from large dairy herds in naturally ventilated buildings, with less focus on suckler cows. The objectives were to assess indoor climate, report NH3 and CH4 emissions and examine the impact of climatic factors on NH3 and CH4 emissions in three small herd dairy and suckler cow buildings over three seasons. Three of the buildings had mechanical ventilation, while one was naturally ventilated. The suckler building had higher relative humidity (RH > 90 %) and NH3 concentrations (> 25 ppm) due to lower minimum air change rate (ACH = 1.2 h−1). The suckler building also had the highest NH3 emissions (2.04 g Livestock Unit (LU)−1 h−1) followed by the mechanically ventilated dairy building (1.92 g LU−1 h−1) with the highest ACH. These two buildings had the lowest stocking densities and floor areas. In contrast, the suckler building had the lowest CH4 emissions (6.8–10.7 g LU−1 h−1). Methane emissions from the dairy building with the supply-exhaust air mixing system (16.4–19.3 g LU−1 h−1) was higher than the other dairy buildings (11.7–13.8 g LU−1 h−1). Temperature influenced NH3 emissions however, the direction of association between temperature and NH3 emissions differed among buildings. Relationship between RH and NH3 emissions was positive, but the correlation coefficient (R2 = 0.67) was strongest in the building with the highest RH.

Impact of Haemonchus contortus infection on feed intake, digestion, liveweight gain, and enteric methane emission from Red Maasai and Dorper sheep

A study was conducted with Red Maasai and Dorper lambs to evaluate the effects of infection with the gastrointestinal nematode (GIN) Haemonchus contortus on feed intake, liveweight gain (LWG), feed energy and nitrogen partitioning, and enteric methane (CH4) emissions. Six- to seven-month-old Red Maasai (n=12) and Dorper (n=12) lambs were randomly allocated to three treatments (n=8, four lambs per breed) in a 2×3 factorial cross-over study over two periods (P1 and P2) of 36 days each. The treatments consisted of three combinations of GIN infection and feeding level: Infected + ad libitum feeding (I-adlib), uninfected + ad libitum feeding (Un-adlib), and uninfected + restricted feeding (Un-restd), across the two breeds. Lambs in the I-adlib group were trickle-infected daily with 1,000 L3 stage larvae of H. contortus for four consecutive days (Days 1–4), whereas lambs in the other experimental treatments were kept GIN free. The feed intake was measured daily. Liveweight (LW), faecal egg counts (FEC), and packed cell volume (PCV) were measured on Day 1 and weekly thereafter. On Days 29–33 total faecal and urine outputs were determined in metabolic crates. The lambs were then housed in respiration chambers for three consecutive days (Days 34–36). There was a washout period of 21 days before P2 started. Uninfected lambs (Un-adlib and Un-restd) had undetectable FEC throughout the study. On Day 36, FEC did not differ between the breeds (P>0.05). Infected lambs (I-adlib) had lower PCV than uninfected (Un-adlib and Un-restd) lambs on day 36. Neither breed nor infection influenced feed and nutrient intake, but as expected, restricted-fed lambs had a lower intake (P<0.05). The LWG of Un-adlib lambs was significantly higher than that of I-adlib and Un-restd lambs (P<0.05), whereas there was no breed difference (P>0.05). Neither breed nor infection affected feed digestibility, nitrogen retention or energy metabolisability (P>0.05). However, feed restriction decreased feed intake, LWG and N retention, whereas feed digestibility and energy metabolisability were unaffected. Neither daily CH4 emissions nor yield (per unit of feed intake) were affected by experimental infection, but Un-restd lambs had lower CH4 emissions per day. Red Maasai lambs had consistently lower daily CH4 emissions and yields than Dorper (P<0.01). This study confirmed the relative resistance of indigenous sheep (Red Maasai) to H. contortus infection, but the increased CH4 emission and yield due to GIN observed in other studies was not confirmed. Further investigations are needed to test whether in environments with multiple stress factors, local or indigenous breeds or their crossbreeds with exotic breeds may be better equipped to sustain production and simultaneously have a reduced carbon footprint than purebred exotic breeds.

Integrating low levels of organic fertilizer improves soil fertility and rice yields in paddy fields by influencing microbial communities without increasing CH4 emissions

Although organic fertilizer is usually recommended for improving soil quality and crop yields, it inevitably enhances methane (CH4) emissions. Effective measures to mitigate CH4 emissions while ensuring crop yields are urgently needed. A two-year experiment was performed to examine the effects of organic-inorganic fertilizer combinations on CH4 emissions, the CH4-related microbial community, soil biochemical characteristics, and rice yields during dual rice growing seasons in 2020–2021 at two locations (i.e., Nanning and Yulin City, Southern, China). The treatments were as follows: no N fertilizer (Neg-CF), 100 % chemical fertilizer (CF) (Pos-CF), 60 % cattle manure (CM) + 40 % CF (High-CM), 30 % CM + 70 % CF (Low-CM), 60 % poultry manure (PM) + 40 % CF (High-PM), and 30 % PM + 70 % CF (Low-PM). CH4 fluxes and related functional microorganism abundances were investigated using the closed chamber method and molecular procedures, respectively. The addition of organic manure significantly improved rice grain yields and soil properties, including total nitrogen (TN), soil organic carbon (SOC), and pH compared to the Pos-CF. Similarly, integrating organic and inorganic fertilizers led to significant increases in seasonal CH4 emissions, global warming potential (GWP), and the abundance of CH4-related soil microbes. Average increases in SOC, TN, CH4 emissions, and GWP in the High-PM treatment relative to the Pos-CF were 44.7, 36.4, 20.6, and 24.4 %, respectively, in Nanning; and 28.9, 33.3, 23.4, and 20.8 % in Yulin City, averaged across the years. Moreover, co-fertilization resulted in the highest increase in methanogenic diversity and abundance relative to Pos-CF only. Applying high proportions of manure improved the abundance of methanogenic soil archaea related to CH4 production compared with the plots with low proportions of manure. Interestingly, lower manure amendments produced the highest rice grain yields and lowest CH4 emissions while maintaining high soil qualities. In addition, regression analysis exhibited that SOC was highly positively associated with CH4 emissions. Above all, controlling the proportions of organic manure and CF may be a feasible approach for enhancing rice yields and soil quality while mitigating CH4 emissions. Of the treatments tested, the combination of 30 % organic manure (i.e., CM or PM) with 70 % CF (urea) performed the best. This study showed that combining manure and CF at a 30:70 ratio was the most effective approach for improving soil health and rice yields while ensuring environmental sustainability.

Intensive Silvopastoral Systems Mitigate Enteric Methane Emissions from Cattle

Assessments of the efficiency of grazing systems, in terms of productivity and ecological sustainability, are necessary in view of the increased demand for animal protein. In this study, the methane (CH4) emissions (sniffer methodology), dry matter (DM) yield, paddock chemical composition (AOAC and Van Soest methods), nutrient intake (dry matter, DMI; crude protein, CPI; metabolizable energy, MEI), daily milk yield (DMY), body condition score (BCS), and body weight (BW) of cattle, in intensive silvopastoral systems (ISPSs) and monoculture systems (MSs), in the tropics of Mexico were evaluated. In the ISPS, CH4 emissions (18% less) and DMY were lower than in the MS. Cows from MSs tend to disperse across higher values of CH4 emissions per kg of DMI, as well as higher milk production, while cows from the ISPS were dispersed over a higher intake (DMI, CPI, and MEI) and lower CH4 emissions. There were no differences between systems in paddock DM yield, chemical composition, cows’ BCS, and BW, regardless of whether it was the dry (April to May) and rainy (September to October) season. Based on the results obtained in this study, ISPSs contribute to the mitigation of methane emissions in cattle; forage and animal production variables in both systems were similar, with a lower use of imported inputs in the ISPS.

Quantifying methane emissions under field conditions under 2 different dairy production scenarios: Low-input versus high-input milk production

Livestock production systems with ruminants play a relevant role in the emission of the greenhouse gas CH4, which is known to significantly contribute to global warming. Consequently, it is a major societal concern to develop strategies in mitigating such emissions. In addition to breeding toward low-emitting cows, management strategies could also help in reducing greenhouse gas emissions from dairy farms. However, information is required for appropriate decision making. To the best of our knowledge, this is the first study that considers different, already available equations to estimate CH4 emissions of small-scale dairy farms in the mountain region, which largely differ from large dairy farms in the lowlands concerning management and production. For this study, 2 different production systems, both typical for small-scale dairy farming in mountain regions, were simultaneously run over 3 yr at an experimental farm as follows: (1) a high-input production system, characterized by intensive feeding with high amounts of external concentrates and maize silage, year-round housing, and high yielding Simmental cattle breed, and (2) a low-input production system, characterized by prevailing hay and pasture feeding and silage ban, thus covering most of the energy requirements by forage harvested on-farm and the use of the local Tyrolean Grey cattle breed. Results reveal that feeding management has a significant effect on the amount of CH4 emissions. The low-input production system produced less CH4 per cow and per day compared with the high-input production system. However, if calculated per kilogram of milk, the high-input scenario produced proportionally less CH4 than the low-input one. Findings of this study highlight the potential to assess in a fast and cost-effective way the CH4 emission in different dairy production systems. This information contributes to the debate about the future of sustainable milk production in mountain regions, where the production of feed resources is climatically constrained, and could be useful for breeding purposes toward lower CH4-emissions.

Variations in Methanogenic and Methanotrophic Communities Resulted in Different Methane Emissions from Paddy Soil Applied with Two Types of Manure

Organic manure application is crucial for the maintenance and improvement of soil fertility. However, it inevitably results in increased paddy CH4 emissions, restricting the use of organic manure in the rice fields. In the present study, two kinds of manures, rapidly composted manure (RCM) and non-composted manure (NCM), were investigated through a 19-week greenhouse experiment, during which the dynamics of CH4 emission, soil parameters (DOC, acetate, NH4+, NO3−, and SO42−), and communities of methanogens and methanotrophs were simultaneously measured. The results showed that NCM significantly enhanced CH4 emission, while RCM decreased CH4 emission by 65.03%; there was no significant difference with the manure-free treatment. In order to well understand the methanogenic process, the seasonal CH4 flux was divided into two periods, namely Stage 1 (before drainage) and Stage 2 (after drainage), on the basis of CH4 emission intensity. The different CH4 production abilities among the three treatments could contribute to the varied CH4 emissions at Stage 1. The much higher soil DOC concentrations were observed in the manure-amended soils (NCM- and RCM-treatments), which could correspondingly lead to the relative higher CH4 emissions compared to the control during Stage 1. Furthermore, the increased methanogenic abundance and the shifted methanogenic archaeal community characterized by the functionally stimulated growth of Methanosarcina genus were observed in the NCM-treated soils, which could consequently result in a higher CH4 emission from the NCM treatment relative to the RCM treatment. As for Stage 2, apart from the significant decrease in soil DOC, the increased contents of soil NO3− and SO42−, especially with the RCM-treated soils, were also detected following the drainage, which might retard CH4 production. The lower CH4 emission at Stage 2 could also be attributed to the vigorous aerobic CH4 oxidations, especially in the RCM-treated soils. As a support, the amount of methanotrophs revealed an increasing trend during the late rice growth period, as did the predominance of the methylotrophy of Methylophilaceae species, which showed robust co-occurrence with methanotrophs, inferring interspecies cooperation in methane oxidation.

A Longitudinal Study with a Laser Methane Detector (LMD) Highlighting Lactation Cycle-Related Differences in Methane Emissions from Dairy Cows.

Reversing climate change requires broad, cohesive, and strategic plans for the mitigation of greenhouse gas emissions from animal farming. The implementation and evaluation of such plans demand accurate and accessible methods for monitoring on-field CH4 concentration in eructating breath. Therefore, this paper describes a longitudinal study over six months, aiming to test a protocol using a laser methane detector (LMD) to monitor CH4 emissions in semi-extensive dairy farm systems. Over 10 time points, CH4 measurements were performed in dry (late gestation) and lactating cows at an Azorean dairy farm. Methane traits including CH4 concentration related to eructation (E_CH4) and respiration (R_CH4), and eructation events, were automatically computed from CH4 measured values using algorithms created for peak detection and analysis. Daily CH4 emission was estimated from each profile's mean CH4 concentration (MEAN_CH4). Data were analyzed using a linear mixed model, including breed, lactation stage, and parity as fixed effects, and cow (subject) and time point as random effects. The results showed that Holsteins had higher E_CH4 than Jersey cows (p < 0.001). Although a breed-related trend was found in daily CH4 emission (p = 0.060), it was not significant when normalized to daily milk yield (p > 0.05). Methane emissions were lower in dry than in lactation cows (p < 0.05) and increased with the advancement of the lactation, even when normalizing it to daily milk yield (p < 0.05). Primiparous cows had lower daily CH4 emissions related to R_ CH4 compared to multiparous (p < 0.001). This allowed the identification of periods of higher CH4 emissions within the milk production cycle of dairy cows, and thus, the opportunity to tailor mitigation strategies accordingly.

Greenhouse gas concentrations and emissions from a plastic-lined shrimp pond on Hainan, China

Greenhouse gas (GHG) emissions caused by food production contributed on average 23% (12 ± 2.9 P(=1015)gCO2e yr−1) to the total anthropogenic GHG emissions between 2007 and 2017. Globally, China has the largest aquatic food production and the South American white shrimp Litopenaeus vannamei (L. vannamei) is gaining more and more economic importance. Here, we set-up an GHG monitoring system within a plastic-lined L. vannamei pond on the Chinese island of Hainan and developed a simple box model to better understand processes controlling the aquatic GHG production and emission within and from the pond. Measured data in line with model results showed that an increase of the pond water pH due to liming could have turned the studied pond from a CO2 source into a CO2 sink. Nevertheless, it remained elusive whether liming would finally act as a net CO2 sink to the atmosphere, considering CO2 emissions associated with its supply and the treatment of alkaline pond waters. The transformation of mangroves into aquacultures can, in turn, be seen as a CO2 source for the atmosphere, which enhances the residence of CO2 in the climate system by reducing its burial in sediments. However, in comparison to shrimp cultures in estuaries as well as mangroves and mangroves converted into paddy fields, crab ponds as well as earthen shrimp ponds, methane (CH4) and nitrous oxide (N2O) emission were low in the pond we studied. While N2O emissions from ponds were in general low, CH4 emission in the studied pond was up to orders of magnitude lower than at the other sites. Shielding pond-waters from impacts of ambient environments such as mangrove soils and ocean waters could be one reason for the low CH4 and N2O emission. However, the still poorly understood processes controlling fluxes of N2O and CH4 in aquacultures and mangroves impede the discussion on impacts of aquacultures on the greenhouse effect and hampers the development of further, more specific strategies to lower GHG emissions from shrimp cultures.

Effect of warming on rice yield and methane emissions in a Chinese tropical double-rice cropping system

Global warming often affects crop yield and greenhouse gas emissions from cropland. However, the effects of warming on rice yield and methane (CH4) emissions from rice paddies in the tropical double-rice cropping systems are still unknown. Therefore, we conducted a field experiment to investigate the effect of warming on rice growth and CH4 emissions in a Chinese tropical double-rice cropping system, using the free air temperature increase facility. The results showed that warming did not affect the rice plant biomass, but significantly reduced the early rice yield by 5.0% and late rice yield by 6.5%. Warming trended to increase CH4 emissions, especially in the flooded stage of early rice seasons. Warming significantly stimulated the abundance of methanogens and methanotrophs, and CH4 production and oxidation potential by 93.3%, 84.3%, 29.3% and 66%, respectively. Warming non-significantly increased the soil dissolved organic carbon concentrations, but significantly reduced the soil NH4+ concentrations. Warming significantly increased yield-scaled CH4 emissions by 7–41%. Our findings suggest that warming may reduce rice yield but increase CH4 emissions from the Chinese tropical double-rice cropping systems and underline the need for agricultural practices of higher rice yield and lower CH4 emissions.

Enteric Methane Emissions in Dairy Cows with Different Genetic Groups in the Humid Tropics of Costa Rica

Enteric methane (CH4) is one of the main greenhouse gases emitted in livestock production systems with ruminants. Among the options to reduce such emissions, animal genetics is one of the factors that is taking relevance in recent years. The aim of the present study was to assess the emission of enteric CH4 in dairy cows with different genetic backgrounds. Sixteen cows belonging to the following three genetic groups were selected for this study: seven F1 (50% Jersey × 50% Gyr), five Triple cross (50% Jersey × 31% Holstein × 19% Sahiwal) and four Jersey. Enteric CH4 emissions were measured in all cows for 15 months, at the middle of each month, using the SF6 technique. Enteric CH4 emissions did not differ (p > 0.05) among genetic groups, although it varied with the stage of lactation, due to differences in milk yield and dry matter intake (DMI). Pasture DMI and the intensity of CH4 emissions (g kg-1 DMI) differed (p < 0.05) between dry and lactating cows, with higher DMI in the lactation period, while CH4 emission intensity was higher for dry cows. Cows with the highest proportion of Bos taurus genes presented a higher annual mean methane conversion factor (Ym), with 7.22, 7.05 and 5.90% for the Triple cross, purebred Jersey and F1, respectively. In conclusion, non-significant differences in enteric CH4 emissions and Ym were detected among dairy cows with different genetic backgrounds. However, F1 cows tended to show lower enteric CH4 emission and Ym, compared to those with more Bos taurus genes.

Recalculating the global warming impact of italian livestock methane emissions with new metrics

The warming impact of methane (CH4) emissions calculated using the metrics proposed by the Intergovernmental Panel on Climate Change (IPCC), which measure its global warming potential in 100 years (GWP100) expressed as carbon dioxide equivalents (CO2 e), accounts for the greatest impact in animal production chains. This work uses the new metrics, proposed to consider the difference between short living climate pollutants (SLCP), such as CH4, and long living climate pollutants (LLCP), such as carbon dioxide (CO2), which measure the warming equivalent (we) effect relative to that of CO2 in a given time frame (GWP*) and expressed as CO2 we. The GWP* was applied to CH4 emissions from all Italian livestock supply chains and compared with GWP100 for annual and cumulative assessment from 2010 to 2020 of the impact of this gas on climate change. Using official data published by Istituto Superiore per la Protezione e la Ricerca Ambientale (ISPRA) from 1990 to 2020, almost all species, except for buffalo (+272.6% of emissions calculated with the new metrics), revealed lower CH4 emissions with the greatest re-dimensioning for non-dairy cattle (-53786 kt of CO2 we of calculated with GWP* compared to +66437 kt of CO2 e estimated with the GWP100 method). The total cumulative contribution of Italian livestock production to global warming over the past 10 years, including the nitrous oxide (N2O) emissions, has been greatly negative (-48759 kt of CO2 we) compared to the data calculated using the GWP100 method (+206091 kt of CO2 e). In conclusion, the application of GWP* metric to CH4 emissions of all Italian livestock supply chains allowed to better identify the role of Italian livestock on climate change. Over the 2010–2020 time frame, the Italian animal supply chains reduced the warming impact related to its CH4 emission, with the ruminants (expect buffaloes) being the major contributor to this positive effect. HIGHLIGHTS The application of GWP* metric reduced the warming impact of CH4 emissions of Italian dairy cattle, non-dairy cattle, sheep, goats, poultry and rabbits. The reduction of CH4 emission from the major ruminant species is the major contributor to the positive effect on climate change detected over 2010–2020 time frame. The application of GWP* metric to CH4 emissions of all Italian livestock supply chains allowed to better identify the role of Italian livestock on climate change.