Greenhouse gas emissions from dairy manure management: a review of field-based studies

Assessment of Ammonia Emissions and Greenhouse Gases in Dairy Cattle Facilities: A Bibliometric Analysis

A deeper understanding of gas emissions in milk production is crucial for promoting productive efficiency, sustainable resource use, and animal welfare. This paper aims to analyze ammonia and greenhouse gas emissions in dairy farming using bibliometric methods. A total of 187 English-language articles with experimental data from the Scopus and Web of Science databases (January 1987 to April 2024) were reviewed. Publications notably increased from 1997, with the highest number of papers published in 2022. Research mainly focuses on ammonia and methane emissions, including quantification, volatilization, and mitigation strategies. Other gases like carbon dioxide, nitrous oxide, and hydrogen sulfide were also studied. Key institutions include the University of California-Davis and Aarhus University. Bibliometric analysis revealed research evolution, identifying trends, gaps, and future research opportunities. This bibliometric analysis offers insights into emissions, air quality, sustainability, and animal welfare in dairy farming, highlighting areas for innovative mitigation strategies to enhance production sustainability. This research contributes to academia, enhancing agricultural practices, and informing environmental policies. It is possible to conclude that this research is a valuable tool for understanding the evolution of research on gas emissions in dairy cattle facilities, providing guidance for future studies and interventions to promote more sustainable production.

In-vitro method and model to estimate methane emissions from liquid manure management on pig and dairy farms in four countries

Methane (CH4) emissions from manure management on livestock farms are a key source of greenhouse gas emissions in some regions and for some production systems, and the opportunities for mitigation may be significant if emissions can be adequately documented. We investigated a method for estimating CH4 emissions from liquid manure (slurry) that is based on anaerobic incubation of slurry collected from commercial farms. Methane production rates were used to derive a parameter of the Arrhenius temperature response function, lnA', representing the CH4 production potential of the slurry at the time of sampling. Results were used for parameterization of an empirical model to estimate annual emissions with daily time steps, where CH4 emissions from individual sources (barns, outside storage tanks) can be calculated separately. A monitoring program was conducted in four countries, i.e., Denmark, Sweden, Germany and the Netherlands, during a 12-month period where slurry was sampled to represent barn and outside storage on finishing pig and dairy farms. Across the four countries, lnA' was higher in pig slurry compared to cattle slurry (p < 0.01), and higher in slurry from barns compared to outside storage (p < 0.01). In a separate evaluation of the incubation method, in-vitro CH4 production rates were comparable with in-situ emissions. The results indicate that lnA' in barns increases with slurry age, probably due to growth or adaptation of the methanogenic microbial community. Using lnA' values determined experimentally, empirical models with daily time steps were constructed for finishing pig and dairy farms and used for scenario analyses. Annual emissions from pig slurry were predicted to be 2.5 times higher than those from cattle slurry. Changing the frequency of slurry export from the barn on the model pig farm from 40 to 7 d intervals reduced total annual CH4 emissions by 46 %; this effect would be much less on cattle farms with natural ventilation. In a scenario with cattle slurry, the empirical model was compared with the current IPCC methodology. The seasonal dynamics were less pronounced, and annual CH4 emissions were lower than with the current methodology, which calls for further investigations. Country-specific models for individual animal categories and point sources could be a tool for assessing CH4 emissions and mitigation potentials at farm level.

Cellulose-degrading bacteria improve conversion efficiency in the co-digestion of dairy and chicken manure by black soldier fly larvae

Black soldier fly larvae (BSFL) have potential utility in converting livestock manure into larval biomass as a protein source for livestock feed. However, BSFL have limited ability to convert dairy manure (DM) rich in lignocellulose. Our previous research demonstrated that feeding BSFL with mixtures of 40% dairy manure and 60% chicken manure (DM40) provides a novel strategy for significantly improving their efficiency in converting DM. However, the mechanisms underlying the efficient conversion of DM40 by BSFL are unclear. In this study, we conducted a holistic study on the taxonomic stucture and potential functions of microbiota in the larval gut and manure during the DM and DM40 conversion by BSFL, as well as the effects of BSFL on cellulosic biodegradation and biomass production. Results showed that BSFL can consume cellulose and other nutrients more effectively and harvest more biomass in a shorter conversion cycle in the DM40 system. The larval gut in the DM40 system yielded a higher microbiota complexity. Bacillus and Amphibacillus in the BSFL gut were strongly correlated with the larval cellulose degradation capacity. Furthermore, in vitro screening results for culturable cellulolytic microbes from the larval guts showed that the DM40 system isolated more cellulolytic microbes. A key bacterial strain (DM40L-LB110; Bacillus subtilis) with high cellulase activity from the larval gut of DM40 was validated for potential industrial applications. Therefore, mixing an appropriate proportion of chicken manure into DM increased the abundance of intestinal bacteria (Bacillus and Amphibacillus) producing cellulase and improved the digestion ability (particularly cellulose degradation) of BSFL to cellulose-rich manure through changes in microbial communities composition in intestine. This study reveals the microecological mechanisms underlying the high-efficiency conversion of cellulose-rich manure by BSFL and provide potential applications for the large-scale cellulose-rich wastes conversion by intestinal microbes combined with BSFL.

Production of Porous Biochar from Cow Dung Using Microwave Process

To valorize livestock manure, the present study investigated the production of biochar from cow dung (CD) by microwave pyrolysis. The pore properties and chemical characteristics of CD and CD-based biochar products were found to correlate with the process parameters like microwave power (300-1000 W) and residence time (5-20 min). The findings indicated that CD is an excellent biomass based on the richness of lignocellulosic constituents from the results of proximate analysis and thermogravimetric analysis (TGA). Higher calorific values were obtained at mild microwave conditions, giving the maximal enhancement factor 139% in comparison with the calorific value of CD (18.97 MJ/kg). Also, it can be concluded that the biochar product obtained at 800 W for a holding time of 5 min had the maximal BET surface area of 127 m2/g and total pore volume of 0.104 cm3/g, which were microporous and mesoporous in the nitrogen adsorption-desorption adsorption analysis. On the other hand, the CD-based biochar contained oxygen-containing functional groups and inorganic minerals based on the spectroscopic analyses by Fourier-transform infrared spectroscopy (FTIR) and energy-dispersive X-ray spectroscopy (EDS), thus featuring to be prone to hydrophilicity in aqueous solutions.

Methane Emissions from Dairy Operations in California's San Joaquin Valley Evaluated Using Airborne Flux Measurements

State inventories indicate that dairy operations account for nearly half of California's methane budget. Recent analyses suggest, however, that these emissions may be underestimated, complicating efforts to develop emission reduction strategies. Here, we report estimates of dairy methane emissions in the southern San Joaquin Valley (SJV) of California in June 2021 using airborne flux measurements. We find average dairy methane fluxes of 512 ± 178 mg m-2 h-1 from a region of 300+ dairies near Visalia, CA using a combination of eddy covariance and mass balance-based techniques, corresponding to 118 ± 41 kg dairy-1 h-1. These values estimated during our June campaign are 39 ± 48% larger than annual average estimates from the recently developed VISTA-CA inventory. We observed notable increases in emissions with temperature. Our estimates align well with inventory predictions when parametrizations for the temperature dependence of emissions are applied. Our measurements further demonstrate that the VISTA-CA emission inventory is considerably more accurate than the EPA GHG-I inventory in this region. Source apportionment analyses confirm that dairy operations produce the majority of methane emissions in the southern SJV (∼65%). Fugitive oil and gas (O&G) sources account for the remaining ∼35%. Our results support the accuracy of the process-based models used to develop dairy emission inventories and highlight the need for additional investigation of the meteorological dependence of these emissions.

Soil carbon sequestration in global working lands as a gateway for negative emission technologies

The ongoing climate crisis merits an urgent need to devise management approaches and new technologies to reduce atmospheric greenhouse gas concentrations (GHG) in the near term. However, each year that GHG concentrations continue to rise, pressure mounts to develop and deploy atmospheric CO2 removal pathways as a complement to, and not replacement for, emissions reductions. Soil carbon sequestration (SCS) practices in working lands provide a low-tech and cost-effective means for removing CO2 from the atmosphere while also delivering co-benefits to people and ecosystems. Our model estimates suggest that, assuming additive effects, the technical potential of combined SCS practices can provide 30%-70% of the carbon removal required by the Paris Climate Agreement if applied to 25%-50% of the available global land area, respectively. Atmospheric CO2 drawdown via SCS has the potential to last decades to centuries, although more research is needed to determine the long-term viability at scale and the durability of the carbon stored. Regardless of these research needs, we argue that SCS can at least serve as a bridging technology, reducing atmospheric CO2 in the short term while energy and transportation systems adapt to a low-C economy. Soil C sequestration in working lands holds promise as a climate change mitigation tool, but the current rate of implementation remains too slow to make significant progress toward global emissions goals by 2050. Outreach and education, methodology development for C offset registries, improved access to materials and supplies, and improved research networks are needed to accelerate the rate of SCS practice implementation. Herein, we present an argument for the immediate adoption of SCS practices in working lands and recommendations for improved implementation.

Effect of diets with different crude protein levels on ammonia and greenhouse gas emissions from a naturally ventilated dairy housing

Less crude protein (CP) in the diet can reduce nitrogen excretion of dairy cattle and lower their ammonia (NH3) and nitrous oxide (N2O) formation potential. The diet composition might also affect emissions of methane (CH4) and carbon dioxide (CO2). However, previous studies did not investigate the effect of diets with different CP levels that are customary practice in Switzerland on NH3 and greenhouse gas emissions on a practical scale. In a case-control approach, we quantified the emissions (NH3, N2O, CH4, CO2) in two separate but identical compartments of a naturally ventilated cubicle housing for lactating dairy cows over six days by using a tracer ratio method. Cows in one compartment received a diet with 116 g CP per kilogram dry matter (DM), in the other compartment with 166 g CP kg-1 DM. Subsequently, diets were switched for a second 6-day measurement phase. The results showed that the diet, aside from outside temperature and wind speed in the housing, was driving NH3 and N2O emissions. NH3 and N2O emission reduction per livestock unit (LU) was on average 46 % and almost 20 %, respectively, for the diet with low CP level compared to the higher CP level. In addition, strong relationships were observed between the CP content of the diet, N excretion in the urine and the milk urea content. An increased temperature or wind speed led to a clear increase in NH3 emissions. Differences in CH4 and CO2 emissions per LU indicated a significant influence of the diet, which cannot be attributed to the CP content. Our herd-level study demonstrated that a significant reduction in NH3 and N2O emissions related to LU, energy-corrected milk as well as DM intake can be achieved by lowering the CP content in the diet.

The intrinsic methane mitigation potential and associated microbes add product value to compost

Conventional agricultural activity reduces the uptake of the potent greenhouse gas methane by agricultural soils. However, the recently observed improved methane uptake capacity of agricultural soils after compost application is promising but needs mechanistic understanding. In this study, the methane uptake potential and microbiomes involved in methane cycling were assessed in green compost and household-compost with and without pre-digestion. In bottle incubations of different composts with both high and near-atmospheric methane concentrations (∼10.000 & ∼10 ppmv, respectively), green compost showed the highest potential methane uptake rates (up to 305.19 ± 94.43 nmol h-1 g dw compost-1 and 25.19 ± 6.75 pmol h-1 g dw compost-1, respectively). 16S, pmoA and mcrA amplicon sequencing revealed that its methanotrophic and methanogenic communities were dominated by type Ib methanotrophs, and more specifically by Methylocaldum szegediense and other Methylocaldum species, and Methanosarcina species, respectively. Ordination analyses showed that the abundance of type Ib methanotrophic bacteria was the main steering factor of the intrinsic methane uptake rates of composts, whilst the ammonium content was the main limiting factor, being most apparent in household composts. These results emphasize the potential of compost to contribute to methane mitigation, providing added value to compost as a product for industrial, commercial, governmental and public interests relevant to waste management. Compost could serve as a vector for the introduction of active methanotrophic bacteria in agricultural soils, potentially improving the methane uptake potential of agricultural soils and contributing to global methane mitigation, which should be the focus of future research.

Impact of leachate and landfill gas on the ecosystem and health: Research trends and the way forward towards sustainability

Globally, a whopping increase in solid waste (SW) generation and the risks posed by climate change are major concerns. A wide spread practice for disposal of municipal solid waste (MSW) is landfill, which swells with population and urbanization. Waste, if treated properly, can be used to produce renewable energy. The recent global event COP 27 mainly stressed on production of renewable energy to achieve the Net Zero target. The MSW landfill is the most significant anthropogenic source of methane (CH₄) emission. On one side, CH₄ is a greenhouse gas (GHG), and on the other it is a main component of biogas. Wastewater that collects due to rainwater percolation in landfills creates landfill leachate. There is a need to understand global landfill management practices thoroughly for implementation of better practices and policies related to this threat. This study critically reviews recent publications on leachate and landfill gas. The review discusses leachate treatment and landfill gas emissions, focusing on the possible reduction technology of CH₄ emission and its impact on the environment. Mixed leachate will benefit from the combinational therapy method because of its intricate combination. Implementation of circular material management, entrepreneurship ideas, blockchain, machine learning, LCA usage in waste management, and economic benefits from CH₄ production have been emphasized. Bibliometric analysis of 908 articles from the last 37 years revealed that industrialized nations dominate this research domain, with the United States having the highest number of citations.

Measurement of Methane and Ammonia Emissions from Compost-Bedded Pack Systems in Dairy Barns: Tilling Effect and Seasonal Variations

Dairy cattle contribute to environmental harm as a source of polluting gas emissions, mainly of enteric origin, but also from manure management, which varies among housing systems. Compost-bedded pack systems use manure as bedding material, which is composted in situ daily. As current literature referring to their impact on NH3 and CH4 emissions is scarce, this study aims to characterize the emissions of these two gases originating from three barns of this system, differentiating between two emission phases: static emission and dynamic emission. In addition, the experiment differentiated emissions between winter and summer. Dynamic emission, corresponding to the time of the day when the bed is being composted, increased over 3 and 60 times the static emission of NH3 and CH4, respectively. In terms of absolute emissions, both gases presented higher emissions during summer (1.86 to 4.08 g NH3 m-2 day-1 and 1.0 to 4.75 g CH4 m-2 day-1 for winter and summer, respectively). In this way, contaminant gases produced during the tilling process of the manure, especially during the warmer periods of the year, need to be taken into account as they work as a significant factor in emissions derived from compost-bedded pack systems.

Methane release from enteric fermentation and manure management of domestic water buffalo in Nepal

Methane (CH₄) emission in livestock arises from enteric fermentation (EnF) and manure management (MM). This study develops the country-specific CH₄ emission factors (EFs) in both EnF and MM for domestic water buffalo (Bubalus bubalis) and estimates total CH₄ emission in Nepal using Intergovernmental Panel on Climate Change (IPCC) Tier 2 methodology. Seasonal field data were collected on morphological characteristics, feed characteristics, and manure management practices of the buffalo. The buffalo population was divided into five age groups, and at least 35 buffalo individuals were measured from each age group in the Hilly and Plain regions of Nepal in the winter and summer seasons. Buffalo adult male (BAM) had the highest body weight of 530 ± 53 kg in the plain region and 514 ± 65 kg in the Hill region. Similarly, the weight of buffalo calf (BC) was 91 ± 25 kg in the plain region and 77 ± 26 kg in the Hill region. For different age groups of buffalo, EnF EFs ranged from 34 ± 8 to 90 ± 10 kg CH₄ head^-1 year^-1 and MM EFs ranged from 2.5 ± 0.5 to 7.5 ± 0.5 kg CH₄ head^-1 year^-1. The estimated EnF and MM EFs of buffalo were not statistically different by region (p > 0 .05). The total CH₄ flux from buffalo was 347.8 Gg year^-1 in Nepal, contributing 322.2 Gg year^-1 from EnF and 25.6 Gg year^-1 from MM. The country-specific EFs are highly recommended for precise computing of the national emissions and carrying out mitigation action.

Compaction effects on greenhouse gas and ammonia emissions from solid dairy manure

Waste management practices of solid dairy manures were evaluated under controlled conditions to study gas transport and emission inside manure piles. Three applied stresses and three moisture contents were tested to represent manure conditions managed at various pile depths. A Fourier-transform infrared spectroscopy monitor measured concentrations of greenhouses gases [methane, carbon dioxide, and nitrous oxide] and ammonia as part of gas flux rate calculations. Results showed that carbon dioxide dominated the greenhouse gas emissions under all test conditions. Gas transfer, primarily diffusion, was facilitated by manure with high mechanical strength and high permeability. Gas emission rates reduced dramatically when moisture content increased in manure with high water holding capacity, while compaction treatments did not as strongly affect the gas emission rates. Results provide fundamental insights into management strategies for reducing gas emissions from solid dairy manure.

Assessing the environmental impact of resource recovery from dairy manure

Manure management is a major contributor to environmental impacts from large-scale dairy production. In this study, technologies for recovering energy, nutrients, and water from dairy manure were evaluated using life cycle assessment (LCA) and compared to conventional practices on California dairy farms. Six scenarios were evaluated: conventional manure management practices, anaerobic digestion (AD) for biogas recovery, and four scenarios for nutrients, energy, and water integrated recovery, called NEWIR. The NEWIR system consists of hydrothermal carbonization (HTC) for energy recovery via hydrochar, algae cultivation in the HTC aqueous product for nutrient recovery and production of protein-rich cattle feed, and water recovery from algae pond effluent via membrane distillation. Four NEWIR scenarios were evaluated, each with a different species of algae. Based on the results of the LCA, AD improves GHG emissions relative to conventional practices by 82%, but has similar eutrophication impacts, posing similar concerns for nutrient management as current practices. Results for the NEWIR system are highly dependent on the algae species used. Three of the four species evaluated (Chlamydomonas reinhardtii, Chlorella vulgaris, and Scenedesmus obliquus) improve GHG emissions by 420-500 kg CO₂-eq. per functional unit, while net water consumption is increased by approximately 75% over AD and conventional practices Spirulina maxima requires more water and chemical inputs for cultivation than the other species, resulting in higher water use (21 times higher than baseline), though GHG emissions are still reduced by 85 kg CO₂-eq. per functional unit relative to conventional practices. All NEWIR scenarios improve eutrophication impacts relative to AD and conventional practices by 16-46% for marine eutrophication and 18-99% for freshwater eutrophication, depending on the algae species used. The results suggest integrated resource recovery through NEWIR is a promising treatment method for manure to mitigate GHG emissions and improve nutrient management on large-scale farms. In addition, carbon and nutrient trading policies are discussed in relation to resource recovery technologies and their potential to incentivize producers to recover products from dairy manure.

Methane emissions from California dairies estimated using novel climate metric Global Warming Potential Star show improved agreement with modeled warming dynamics

Introduction

Carbon dioxide (CO2) and methane (CH4) are two of the primary greenhouse gases (GHG) responsible for global warming. The “stock gas” CO2 accumulates in the atmosphere even if rates of CO2 emission decline. In contrast, the “flow gas” CH4 has an e-folding time of about 12 years and is removed from the atmosphere in a relatively short period of time. The climate impacts of cumulative pollutants such as CO2 and short-lived climate pollutants (SLCP) such as CH4 are often compared using Global Warming Potential (GWP), a metric that converts non-CO2 GHG into CO2-equivalent emissions. However, GWP has been criticized for overestimating the heating effects of declining SLCP emissions and conversely underestimating the heating impact of increasing SLCP emissions. Accurate quantification of the temperature effects of different CH4 emissions scenarios is particularly important to fully understanding the climate impacts of animal agriculture, whose GHG emissions are dominated by CH4.

Methods

A modified GWP metric known as Global Warming Potential Star (GWP*) has been developed to directly quantify the relationship between SLCP emissions and temperature change, which GWP cannot do. In this California dairy sector case study, we contrasted GWP- versus GWP*-based estimates of historical warming dynamics of enteric and manure CH4 from lactating dairy cattle. We predicted future dairy CH4 emissions under business-as-usual and reduction scenarios and modeled the warming effects of these various emission scenarios.

Results

We found that average CO2 warming equivalent emissions given by GWP* were greater than those given by GWP under increasing annual CH4 emissions rates, but were lower under decreasing CH4 emissions rates. We also found that cumulative CO2 warming equivalent emissions given by GWP* matched modeled warming driven by decreasing CH4 emissions more accurately than those given by GWP.

Discussion

These results suggest that GWP* may provide a more accurate tool for quantifying SLCP emissions in temperature goal and emissions reduction-specific policy contexts.

Predicting Escherichia coli levels in manure using machine learning in weeping wall and mechanical liquid solid separation systems

An increased understanding of the interaction between manure management and public and environmental health has led to the development of Alternative Dairy Effluent Management Strategies (ADEMS). The efficiency of such ADEMS can be increased using mechanical solid-liquid-separator (SLS) or gravitational Weeping-Wall (WW) solid separation systems. In this research, using pilot study data from 96 samples, the chemical, physical, biological, seasonal, and structural parameters between SLS and WW of ADEM systems were compared. Parameters including sodium, potassium, total salts, volatile solids, pH, and E. coli levels were significantly different between the SLS and WW of ADEMS. The separated solid fraction of the dairy effluents had the lowest E. coli levels, which could have beneficial downstream implications in terms of microbial pollution control. To predict effluent quality and microbial pollution risk, we used Escherichia coli as the indicator organism, and a versatile machine learning, ensemble, stacked, super-learner model called E-C-MAN (Escherichia coli-Manure) was developed. Using pilot data, the E-C-MAN model was trained, and the trained model was validated with the test dataset. These results demonstrate that the heuristic E-C-MAN ensemble model can provide a pilot framework toward predicting Escherichia coli levels in manure treated by SLS or WW systems.

The climate change mitigation potential of annual grasslands under future climates

Composted manure and green waste amendments have been shown to increase net carbon (C) sequestration in rangeland soils and have been proposed as a means to help lower atmospheric CO₂ concentrations. However, the effect of climate change on soil organic C (SOC) stocks and greenhouse gas emissions in rangelands is not well understood, and the viability of climate change mitigation strategies under future conditions is even less certain. We used a process-based biogeochemical model (DayCent) at a daily time step to explore the long-term effects of potential future climate changes on C and greenhouse gas dynamics in annual grassland ecosystems. We then used the model to explore how the same ecosystems might respond to climate change following compost amendments to soils and determined the long-term viability of net SOC sequestration under changing climates. We simulated net primary productivity (NPP), SOC, and greenhouse gas fluxes across seven California annual grasslands with and without compost amendments. We drove the DayCent simulations with field data and with site-specific daily climate data from two Earth system models (CanESM2 and HadGEM-ES) and two representative concentration pathways (RCP4.5 and RCP8.5) through 2100. NPP and SOC stocks in unamended and amended ecosystems were surprisingly insensitive to projected climate changes. A one-time amendment of compost to rangeland acted as a slow-release organic fertilizer and increased NPP by up to 390-814 kg C ha^-1  year^-1 across sites. The amendment effect on NPP was not sensitive to Earth system model or emissions scenario and endured through the end of the century. Net SOC sequestration amounted to 1.96 ± 0.02 Mg C ha^-1 relative to unamended soils at the maximum amendment effect. Averaged across sites and scenarios, SOC sequestration peaked 22 ± 1 years after amendment and declined but remained positive throughout the century. Though compost stimulated nitrous oxide (N₂ O) emissions, the cumulative net emissions (in CO₂ equivalents) due to compost were far less than the amount of SOC sequestered. Compost amendments resulted in a net climate benefit of 69.6 ± 0.5 Tg CO₂ e 20 ± 1 years after amendment if applied to similar ecosystems across the state, amounting to 39% of California's rangeland. These results suggest that the biogeochemical benefits of a single amendment of compost to rangelands in California are insensitive to climate change and could contribute to decadal-scale climate change mitigation goals alongside emissions reductions.

Is Dairy Effluent an Alternative for Maize Crop Fertigation in Semiarid Regions? An Approach to Agronomic and Environmental Effects

Simple Summary

Dairy effluent can be an environmental problem if it is not properly managed. Several application technologies exist for its reuse as a source of nutrients in agricultural crops. Our study provides new information on GHG emissions after the application of dairy effluent through a subsurface drip irrigation system on a semiarid soil of the southern Pampean Region (Argentina). In addition, some edaphic properties are compared with conventional chemical fertilization on the yield of a corn crop, contributing as a proposal for an improvement in agricultural sustainability.

Abstract

The reuse of effluents from intensive dairy farms combined with localized irrigation techniques (fertigation) has become a promising alternative to increase crop productivity while reducing the environmental impact of waste accumulation and industrial fertilizers production. Currently, the reuse of dairy effluents through fertigation by subsurface drip irrigation (SDI) systems is of vital importance for arid regions but it has been poorly studied. The present study aimed to assess the greenhouse gas (GHG) emissions, soil properties, and crop yield of a maize crop fertigated with either treated dairy effluent or dissolved granulated urea applied through an SDI system at a normalized N application rate of 200 kg N ha⁻¹. Fertilizer application was divided into six fertigation events. GHG fluxes were measured during fertigation (62-day) using static chambers. Soil properties were measured previous to fertilizer applications and at the harvest coinciding with crop yield estimation. A slight increase in soil organic matter was observed in both treatments for the 20–60 cm soil depth. Both treatments also showed similar maize yields, but the dairy effluent increased net GHG emissions more than urea during the fertigation period. Nevertheless, the net GHG emissions from the dairy effluent were lower than the theoretical CO₂eq emission that would have been emitted during urea manufacturing or the longer storage of the effluent if it had not been used, showing the need for life-cycle assessments. Local-specific emission factors for N₂O were determined (0.07%), which were substantially lower than the default value (0.5%) of IPCC 2019. Thus, the subsurface drip irrigation systems can lead to low GHG emissions, although further studies are needed.

Dairy Manure Co-composting with Wood Biochar Plays a Critical Role in Meeting Global Methane Goals

Livestock are the largest source of anthropogenic methane (CH4) emissions, and in intensive dairy systems, manure management can contribute half of livestock CH4. Recent policies such as California's short-lived climate pollutant reduction law (SB 1383) and the Global Methane Pledge call for cuts to livestock CH4 by 2030. However, investments in CH4 reduction strategies are primarily aimed at liquid dairy manure, whereas stockpiled solids remain a large source of CH4. Here, we measure the CH4 and net greenhouse gas reduction potential of dairy manure biochar-composting, a novel manure management strategy, through a composting experiment and life-cycle analysis. We found that biochar-composting reduces CH4 by 79%, compared to composting without biochar. In addition to reducing CH4 during composting, we show that the added climate benefit from biochar production and application contributes to a substantially reduced life-cycle global warming potential for biochar-composting: -535 kg CO2e Mg-1 manure compared to -194 kg CO2e Mg-1 for composting and 102 kg CO2e Mg-1 for stockpiling. If biochar-composting replaces manure stockpiling and complements anaerobic digestion, California could meet SB 1383 with 132 less digesters. When scaled up globally, biochar-composting could mitigate 1.59 Tg CH4 yr-1 while doubling the climate change mitigation potential from dairy manure management.

Quantification of methane emitted by ruminants: a review of methods

The contribution of greenhouse gas (GHG) emissions from ruminant production systems varies between countries and between regions within individual countries. The appropriate quantification of GHG emissions, specifically methane (CH4), has raised questions about the correct reporting of GHG inventories and, perhaps more importantly, how best to mitigate CH4 emissions. This review documents existing methods and methodologies to measure and estimate CH4 emissions from ruminant animals and the manure produced therein over various scales and conditions. Measurements of CH4 have frequently been conducted in research settings using classical methodologies developed for bioenergetic purposes, such as gas exchange techniques (respiration chambers, headboxes). While very precise, these techniques are limited to research settings as they are expensive, labor-intensive, and applicable only to a few animals. Head-stalls, such as the GreenFeed system, have been used to measure expired CH4 for individual animals housed alone or in groups in confinement or grazing. This technique requires frequent animal visitation over the diurnal measurement period and an adequate number of collection days. The tracer gas technique can be used to measure CH4 from individual animals housed outdoors, as there is a need to ensure low background concentrations. Micrometeorological techniques (e.g., open-path lasers) can measure CH4 emissions over larger areas and many animals, but limitations exist, including the need to measure over more extended periods. Measurement of CH4 emissions from manure depends on the type of storage, animal housing, CH4 concentration inside and outside the boundaries of the area of interest, and ventilation rate, which is likely the variable that contributes the greatest to measurement uncertainty. For large-scale areas, aircraft, drones, and satellites have been used in association with the tracer flux method, inverse modeling, imagery, and LiDAR (Light Detection and Ranging), but research is lagging in validating these methods. Bottom-up approaches to estimating CH4 emissions rely on empirical or mechanistic modeling to quantify the contribution of individual sources (enteric and manure). In contrast, top-down approaches estimate the amount of CH4 in the atmosphere using spatial and temporal models to account for transportation from an emitter to an observation point. While these two estimation approaches rarely agree, they help identify knowledge gaps and research requirements in practice.

Manure management strategies are interconnected with complexity across U.S. dairy farms

Among one of the key challenges in dairy production is the management of manure in a way that is beneficial for agricultural production, with minimal environmental and public health impacts. Manure management systems (MMS)—the entire system of handling, storage, and application of manure—are diverse in countries with developed dairy industries such as the United States, enabled by a number of different technologies. The ways in which dairy farmers manage manure is driven by varying tradeoffs, including economic, social, and environmental; however, existing research has not examined the relationships between components of MMS. Here we use data from the National Animal Health Monitoring System’s Dairy 2014 study to explore the ways in which manure handling, storage, and application are related, using a series of logistic regression models and network associations. We found significant associations between how manure is handled, stored, and applied, especially driven by the consistency of manure. For solid manure, we found highly heterogeneous systems, where farmers may have a suite of alternative manure management strategies available to them, and substitution is viable. Conversely, farms using liquid manure systems have very few substitutes in their MMS, suggesting greater investment in certain infrastructures, which are not easily changed. Such findings have important implications for shifting farmers towards management practices with minimal environmental and public health impacts, demonstrating that not all farm systems are easily changed. We highlight these results in light of current policies, which may not fully capture the relationships across the MMS, and suggest that greater financing may be necessary to shift MMS on some farms. Furthermore, we suggest that different MMS have varying tradeoffs across environmental, social, and economic aspects, which demonstrates that MMS are highly individualized to a given farm’s goals and priorities.

Agricultural Biogas Production—Climate and Environmental Impacts

Livestock manure is a major source of the greenhouse gases (GHGs) methane (CH4) and nitrous oxide (N2O). The emissions can be mitigated by production of biogas through anaerobic digestion (AD) of manure, mostly together with other biowastes, which can substitute fossil energy and thereby reduce CO2 emissions and postdigestion GHG emissions. This paper presents GHG balances for manure and biowaste management as affected by AD for five Danish biogas scenarios in which pig and cattle slurry were codigested with one or more of the following biomasses: deep litter, straw, energy crops, slaughterhouse waste, grass–clover green manure, and household waste. The calculated effects of AD on the GHG balance of each scenario included fossil fuel substitution, energy use for transport, leakage of CH4 from biogas production plants, CH4 emissions during storage of animal manure and biowaste, N2O emissions from stored and field applied biomass, N2O emissions related to nitrate (NO3−) leaching and ammonia (NH3) losses, N2O emissions from cultivation of energy crops, and soil C sequestration. All scenarios caused significant reductions in GHG emissions. Most of the reductions resulted from fossil fuel substitution and reduced emissions of CH4 during storage of codigestates. The total reductions in GHG emissions ranged from 65 to 105 kg CO2-eq ton−1 biomass. This wide range showed the importance of biomass composition. Reductions were highest when straw and grass–clover were used as codigestates, whereas reductions per unit energy produced were highest when deep litter or deep litter plus energy crops were used. Potential effects of iLUC were ignored but may have a negative impact on the GHG balance when using energy crops, and this may potentially exceed the calculated positive climate impacts of biogas production. The ammonia emission potential of digestate applied in the field is higher than that from cattle slurry and pig slurry because of the higher pH of the digestate. This effect, and the higher content of TAN in digestate, resulted in increasing ammonia emissions at 0.14 to 0.3 kg NH3-N ton−1 biomass. Nitrate leaching was reduced in all scenarios and ranged from 0.04 to 0.45 kg NO3-N ton−1 biomass. In the scenario in which maize silage was introduced, the maize production increased leaching and almost negated the effect of AD. Methane leakage caused a 7% reduction in the positive climate impact for each percentage point of leakage in a manure-based biogas scenario.

Dairy and swine manure management - Challenges and perspectives for sustainable treatment technology

Global dairy and swine production growth has increased significantly over the past decades, resulting in higher manure generation in certain areas and environmental concerns. Therefore, manure management is an essential focus for farmers and environmental regulators. Systematic selection of manure management practices can provide environmental benefits, but accounting for local constraints, economics and farming practices are significant challenges. All these factors drive the selection of appropriate manure management systems (MMSs). MMSs are highly varied for their design, partly due to individual farm settings, geography, and the end-use applications of manure. However, the benefits of technological advancements in MMSs provide higher manure treatment efficiency and co-production of value-added products such as recycled water, fiber, sand bedding, and nutrient-rich bio-solids, among others. To achieve higher environmental benefits, advanced manure treatment technologies have to be implemented, which comes with additional costs. So, there is a tradeoff between environmental benefits and cost. With the above prospects, this article reviews: 1) the different treatment technologies used in dairy and swine farms, 2) the life cycle assessment (LCA) method's importance in evaluating various treatment technologies for better environmental returns, and 3) decision support tools (DST) and their significance in MMSs prioritization. We found considerable heterogeneity in the available datasets, mainly on crucial parameters such as water consumption, types and amount of bedding materials, manure removal frequency, manure treatment technologies, and the extent of resource recovery. Thus, suitable environmental impact assessment inventory models are needed to evaluate a more comprehensive range of treatment technologies in MMSs, representing the spatial and farming system heterogeneities. There is also a need for user-friendly DST with adjustable inputs for the functional components of MMSs and evaluation criteria, which can rapidly evaluate the techno-economic feasibility of alternative systems.

Effect of feeding practices and manure quality on CH4 and N2O emissions from uncovered cattle manure heaps in Kenya

Countries in sub-Saharan Africa (SSA) rely on IPCC emission factors (EF) for GHG emission reporting. However, these were derived for industrialized livestock farms and do not represent conditions of smallholder farms (small, low-producing livestock breeds, poor feed quality, feed scarcity). Here, we present the first measurements of CH₄ and N₂O emissions from cattle-manure heaps representing feeding practices typical for smallholder farms in the highlands of East Africa: 1) cattle fed below maintenance energy requirements to represent feed scarcity, and 2) cattle fed tropical forage grasses (Napier, Rhodes, Brachiaria). Sub-maintenance feeding reduced cumulative manure N₂O emissions compared to cattle receiving sufficient feed but did not change EF_N2O. Sub-maintenance feeding did not affect cumulative manure CH₄ emissions or EF_CH4. When cattle were fed tropical forage grasses, cumulative manure N₂O emissions did not differ between diets, but manure EF_N2O from Brachiaria and Rhodes diets were lower than the IPCC EF_N2O for solid storage (1%, 2019 Refinement of IPCC Guidelines). Manure CH₄ emissions were lower in the Rhodes grass diet than when feeding Napier or Brachiaria, and manure EF_CH4 from all three grasses were lower than the IPCC default (4.4 gCH₄kg^-1 VS, 2019 Refinement of IPCC Guidelines). Regression analysis revealed that manure N concentration and C:N were important drivers of N₂O emissions, with low N concentrations and high C:N reducing N₂O emissions. Our results show that IPCC EFs overestimate excreta GHG emissions, which calls for additional measurements to develop localized EFs for smallholder livestock systems in SSA.

Provincial cattle carbon emissions from enteric fermentation and manure management in South Africa

Livestock is a major producer of agricultural greenhouse gas emissions in South Africa. Cattle methane (CH₄) from enteric fermentation is the main source of the emissions. However, due to shortage of information to guide agricultural mitigation plans in the country, the main objective of this study is to investigate causal factors of the emissions from cattle in all nine national provinces. This study calculates provincial CH₄ emission factors and factors (i.e. nitrogen excretion rate and average annual nitrogen excretion per animal) required for nitrous oxide (N₂O) emissions from cattle manure management. The study further uses these factors and other values obtained from the literature to calculate cattle CH₄ emissions from enteric fermentation and manure management. It also provides similar N₂O emissions from manure management as well as urine and dung deposited on the pasture, range and paddock. The emissions are calculated for each cattle type: commercial dairy, commercial beef, subsistence and feedlot cattle. Cattle in South Africa produced a total of 35.37 million tonnes (Mt) of carbon dioxide equivalent (CO₂e) emissions in 2019, inclusive of emissions from pasture, range and paddock. Methane from enteric fermentation accounts for 64.54% of the total emissions followed by emissions from pasture, range and paddock (27.66%). Manure management contributes 4.34% of N₂O to the total emissions while this source also produces 3.45% of CH₄ emissions. Commercial beef is responsible for 50.21% of the total emissions, followed by subsistence beef (36.72%), commercial dairy (10.52%) and feedlot cattle (2.52%). The Eastern Cape province is the highest producer of cattle emissions with 8.66 Mt CO₂e, a quarter of the emissions. It is followed by KwaZulu-Natal (7.14 Mt CO₂e, 20%) and the Free State (5.65 Mt CO₂e, 16%). Gauteng province is responsible for the lowest producer of the emissions with 0.71 Mt CO₂e (2%) of the total. South Africa's emission factors are higher than values for Africa, indicating importance of developing national factors to avoid uncertainties in emissions. As a result of national landscape and environmental conditions, the eastern provinces of the country are major sources of cattle emissions in the country.

Combination of H2SO4-acidification and temperature-decrease for eco-friendly storage of pig slurry

Owing to the economic benefit and efficiency, H₂SO₄-acidification is often applied for reducing CH₄ emissions during storage of pig slurry (PS). However, it encounters with several problems related with safety and the concomitant H₂S emissions. To reduce the required amount of H₂SO₄, in this study, the storage at low temperature (20-35 °C) was applied to the mild-acidified PS (pH 6.5 and 7.0). 55.1 kg CO₂ eq./ton PS of CH₄ was emitted from the control (non-acidified at 35 °C), which was reduced to 14.4-40.2 kg CO₂ eq./ton PS at 20-30 °C. Temperature-decrease led to the increase of the abundance of methanogens (Methanobrevibacter and Methanolobus) that can grow at low temperature and the drop of specific methanogenic activity value. To achieve 70 % CH₄ reduction, 1.6 kg H₂SO₄/ton PS was needed in PS acidification, which was decreased to 0.5 kg H₂SO₄/ton PS by decreasing temperature from 35 °C to 25 °C. CH₄ production potential of the PS stored at 35 °C-pH 6.5 and 25 °C-pH 7.0 was increased by 21-33 % compared to the control. The GHG reduction of 33.6-41.9 kg CO₂ eq./ton PS and the profit of 6.6 USD/ton PS could be attained by applying acidification or combined storage, indicating that the temperature-decrease can be effectively combined with H₂SO₄-acidification.

Estimating exposure to hydrogen sulfide from animal husbandry operations using satellite ammonia as a proxy: Methodology demonstration

Husbandry trace gases that have climate change implications such as carbon dioxide (CO₂), methane (CH₄) and ammonia (NH₃) can be quantified through remote sensing; however, many husbandry gases with health implications such as hydrogen sulfide (H₂S), cannot. This pilot study demonstrates an approach to derive H₂S concentrations by coupling in situ and remote sensing data. Using AMOG (AutoMObile trace Gas) Surveyor, a mobile air quality and meteorology laboratory, we measured in situ concentrations of CH₄, CO₂, NH₃, H₂S, and wind at a southern California university research dairy. Emissions were 0.13, 1.93, 0.022 and 0.0064 Gg yr^-1; emission factors (E_F) were 422, 6333, 74, and 21 kg cow^-1 yr^-1, respectively, for the 306 head herd. Contributing to these strong E_F were spillway emissions from a grate between the main cowshed and the waste lagoon identified in airborne remote sensing data acquired by the hyperspectral thermal infrared imager, Mako. NH₃ emissions from the Chino Dairy Complex, also in southern California, were calculated from Infrared Atmospheric Sounding Interferometer (IASI) satellite data for 2008-2017 using average morning winds, yielding a flushing time of 2.7 h, and 8.9 Gg yr^-1. The ratio of E_F(H₂S) to E_F(NH₃) for the research dairy from AMOG data were applied to IASI NH₃ emissions to derive H₂S exposure concentration maps for the Chino area, which ranged to 10-30 ppb H₂S for many populated areas. Combining remote sensing with in situ concentrations of multiple emitted gases can allow derivation of emissions at the sub-facility, facility, and larger scales, providing spatial and temporal coverage that can translate into exposure estimates for use in epidemiology studies and regulation development. Furthermore, with high fidelity information at the sub-facility level we can identify best practices and opportunities to sustainably and holistically reduce husbandry emissions.

Effects of SOP Lagoon Additive on Gaseous Emissions from Stored Liquid Dairy Manure

Animal manure is a source of greenhouse gas (GHG) emissions and other pollutants and nuisances such as ammonia and odors. There are several technologies to reduce emissions on animal farms including manure additives; however, few have been proven effective and easy to apply to dairy lagoon systems. The present research aimed at testing the ability of the commercial additive “SOP LAGOON” to reduce emissions of GHGs (i.e., carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O)), as well as ammonia (NH3) and odors from lagoon stored liquid manure. Emissions of GHGs, NH3 and odors were measured in the laboratory from barrels filled with 65 L of manure treated with SOP LAGOON or left untreated as a control. Manure was collected from a commercial dairy that is located in Solano County, California. Emissions of GHGs and NH3 were continuously measured for one week using flux chambers placed on top of the barrels and connected to a mobile air emissions laboratory. The effects of the untreated control, versus the two respective treatment additive doses of 30.8 and 61.6 g/m3 of manure were compared to each other. The low dose was selected based on the manufacturer recommendation and the high dose was selected by doubling the low dose. Results showed that SOP LAGOON applied at the high dose (61.6 g of SOP LAGOON per m3 of manure) versus the control greatly reduced (p < 0.05) emissions of CO2, CH4, N2O and NH3 by 14.7%, 22.7%, 45.4% and 45.9%, respectively. Furthermore, the high dose of SOP LAGOON treated samples versus the control samples showed less odor intensity (p < 0.05). There was no significant effect of the low dose of SOP LAGOON on the emissions of different gases. The HIGH dose of SOP LAGOON might decrease the number of methanogens and hydrolytic microorganisms and their excreted enzymes during manure storage. Further studies are needed to investigate the mechanism of emission reduction using SOP LAGOON.

Identification of parameters needed for optimal anaerobic co-digestion of chicken manure and corn stover

While studies have shown that anaerobic co-digestion of chicken manure (CM) and corn stover (CS) is an efficient method to treat these agricultural wastes, the microbial ecology of these systems and optimal parameters for the digestion process are yet to be determined. In this study, the effects of different initial substrate concentrations and CS : CM mixture ratios on co-digestion and microbial community structure were evaluated. Results demonstrated that both the highest cumulative methane yields and methane production rates were obtained from reactors with a CS : CM ratio of 1 : 1 during hemi-solid-state anaerobic digestion (HSS-AD). Cumulative methane yields and methane production rates were 24.8% and 42% lower in solid-state anaerobic digestion (SS-AD) reactors using the same CS : CM ratios. Analysis of microbial community structures revealed that cellulolytic bacteria and a diversity of syntrophic microorganisms capable of direct interspecies electron transfer (DIET) and hydrogen interspecies transfer (HIT) were enriched in the best-performing reactors. Methanosarcina species also dominated during HSS-AD, and their presence was positively correlated with methane production in the reactors.

Improving the Sustainability of Dairy Slurry by A Commercial Additive Treatment

Ammonia (NH3), methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) emissions from livestock farms contribute to negative environmental impacts such as acidification and climate change. A significant part of these emissions is produced from the decomposition of slurry in livestock facilities, during storage and treatment phases. This research aimed at evaluating the effectiveness of the additive “SOP LAGOON” (made of agricultural gypsum processed with proprietary technology) on (i) NH3 and Greenhouse Gas (GHG) emissions, (ii) slurry properties and N loss. Moreover, the Life Cycle Assessment (LCA) method was applied to assess the potential environmental impact associated with stored slurry treated with the additive. Six barrels were filled with 65 L of cattle slurry, of which three were used as a control while the additive was used in the other three. The results indicated that the use of the additive led to a reduction of total nitrogen, nitrates, and GHG emissions. LCA confirmed the higher environmental sustainability of the scenario with the additive for some environmental impact categories among which climate change. In conclusion, the additive has beneficial effects on both emissions and the environment, and the nitrogen present in the treated slurry could partially displace a mineral fertilizer, which can be considered an environmental credit.

High-rate anaerobic treatment of digestate using fixed film reactors

The effluent stream of the anaerobic digestion processes, the digestate, accommodates high residual organic content that needs to be further treated before discharge. Anaerobic treatment of digestate would not only reduce the residual organic compounds in digestate but also has a potential to capture the associated biogas. High-rate anaerobic reactor configurations can treat the waste streams using lower hydraulic retention times which requires less footprint opposed to the conventional completely stirred tank reactors. This study investigated the high-rate anaerobic treatment performance and the associated biogas capture from the digestate of a manure mixture composed of 90% laying hen and 10% cattle manures in fixed-film reactors. The results indicated that it was possible to reduce total chemical oxygen demand content of the digestate by 57-62% in 1.3-1.4 days of hydraulic retention time. The corresponding biogas yields obtained were in the range of 0.395-0.430 L_biogas/g VS_added which were found to be comparable to many raw feedstocks. Moreover, significant total phosphorus reduction (36-47%) and greenhouse gas capture (over 14.5-18.1 tCO₂e/d per m³ digestate) were also recorded in the anaerobic fixed-film reactors.

Manure storage operations mitigate nutrient losses and their products can sustain soil fertility and enhance wheat productivity

Livestock manure is a valuable source of nutrients for plants. However, poor handling practices during storage resulted in nutrient losses from the manure and decrement in its nitrogen (N) fertilizer value. We explored the influence of divergent storage methods on manure chemical composition, carbon (C) and N losses to the environment as well as fertilizer value of storage products after their application to the wheat. Fresh buffalo manure (FM) was subjected to different storage operations for a period of ∼6 months, (i) fermentation by covering with a plastic sheet (CM) (ii) placed under the roof (RM) (iii) heap was unturned (SM) to remain stacked at an open space and (iv) manure heap turned monthly (TM) to make compost. During storage, 8, 24, 45 and 46% of the initial N_total was lost from CM, RM, SM, and TM, respectively. The respective C losses from these treatments were 16, 34, 47 and 44% of the initial C content. After stored manures application to the wheat crop, mineral N in the soil remained 27% higher in CM (14.1 vs. 11.1 kg ha^-1) and 3% (10.8 vs. 11.1 kg ha^-1) lower in SM compared to FM treatment. In contrast, microbial biomass C and N was 35 (509 vs.782 mg C kg^-1 soil) and 25% (278 vs.370 mg N kg^-1 soil) lower in CM than FM treatment, respectively indicating lower N immobilization of CM in the soil. These findings could result in the highest grain yield (5166 kg ha^-1) and N uptake (117 kg ha^-1) in CM and the lowest in SM treatments (3105 and 61 kg ha^-1, respectively). Similarly, wheat crop recovered 44, 15 and 13% N from CM, TM and SM, respectively. Hence, management operations play a critical role in conserving N during storage phase and after stored manure application to the field. Among the studied operations, storing animal manure under an impermeable plastic sheet is a much better and cheaper option for decreasing N losses during storage and improving wheat yield when incorporated into the soil. Therefore, by adopting this manure storage technique, farmers can improve the agro-environmental value of animal manure in Pakistan.

Leaf-cutter ants engineer large nitrous oxide hot spots in tropical forests

Though tropical forest ecosystems are among the largest natural sources of the potent greenhouse gas nitrous oxide (N2O), the spatial distribution of emissions across landscapes is often poorly resolved. Leaf cutter ants (LCA; Atta and Acromyrmex, Myrmicinae) are dominant herbivores throughout Central and South America, and influence multiple aspects of forest structure and function. In particular, their foraging creates spatial heterogeneity by concentrating large quantities of organic matter (including nitrogen, N) from the surrounding canopy into their colonies, and ultimately into colony refuse dumps. Here, we demonstrate that refuse piles created by LCA species Atta colombica in tropical rainforests of Costa Rica provide ideal conditions for extremely high rates of N2O production (high microbial biomass, potential denitrification enzyme activity, N content and anoxia) and may represent an unappreciated source of heterogeneity in tropical forest N2O emissions. Average instantaneous refuse pile N2O fluxes surpassed background emissions by more than three orders of magnitude (in some cases exceeding 80 000 µg N2O-N m-2 h-1) and generating fluxes comparable to or greater than those produced by engineered systems such as wastewater treatment tanks. Refuse-concentrating Atta species are ubiquitous in tropical forests, pastures and production ecosystems, and increase density strongly in response to disturbance. As such, LCA colonies may represent an unrecognized greenhouse gas point source throughout the Neotropics.

Validation of mobile in situ measurements of dairy husbandry emissions by fusion of airborne/surface remote sensing with seasonal context from the Chino Dairy Complex

Mobile in situ concentration and meteorology data were collected for the Chino Dairy Complex in the Los Angeles Basin by AMOG (AutoMObile trace Gas) Surveyor on 25 June 2015 to characterize husbandry emissions in the near and far field in convoy mode with MISTIR (Mobile Infrared Sensor for Tactical Incident Response), a mobile upwards-looking, column remote sensing spectrometer. MISTIR reference flux validated AMOG plume inversions at different information levels including multiple gases, GoogleEarth imagery, and airborne trace gas remote sensing data. Long-term (9-yr.) Infrared Atmospheric Sounding Interferometer satellite data provided spatial and trace gas temporal context. For the Chino dairies, MISTIR-AMOG ammonia (NH₃) agreement was within 5% (15.7 versus 14.9 Gg yr^-1, respectively) using all information. Methane (CH₄) emissions were 30 Gg yr^-1 for a 45,200 herd size, indicating that Chino emission factors are greater than previously reported. Single dairy inversions were much less successful. AMOG-MISTIR agreement was 57% due to wind heterogeneity from downwind structures in these near-field measurements and emissions unsteadiness. AMOG CH₄, NH₃, and CO₂ emissions were 91, 209, and 8200 Mg yr^-1, implying 2480, 1870, and 1720 head using published emission factors. Plumes fingerprinting identified likely sources including manure storage, cowsheds, and a structure with likely natural gas combustion. NH₃ downwind of Chino showed a seasonal variation of a factor of ten, three times larger than literature suggests. Chino husbandry practices and trends in herd size and production were reviewed and unlikely to add seasonality. Higher emission seasonality was proposed as legacy soil emissions, the results of a century of husbandry, supported by airborne remote sensing data showing widespread emissions from neighborhoods that were dairies 15 years prior, and AMOG and MISTIR observations. Seasonal variations provide insights into the implications of global climate change and must be considered when comparing surveys from different seasons.

Mitigating Greenhouse Gas and Ammonia Emissions from Beef Cattle Feedlot Production: A System Meta-Analysis

Beef cattle production systems are the largest contributors of greenhouse gas (GHG) and ammonia (NH₃) emissions in the livestock industry. Here, we present the first meta-analysis and integrated assessment of gaseous emissions and mitigation potentials for a typical beef cattle feedlot system, including methane (CH₄), nitrous oxide (N₂O), and NH₃ losses from enteric fermentation and manure management based on data from 104 studies. A total of 14 integrated emission factors (EF) and the mitigation efficiencies (ME) of 17 available options were provided. The estimated GHG and NH₃ emissions from the baseline feedlot system were 2786 ± 108 kg carbon dioxide equivalents (CO₂-eq) per animal unit (AU) per year and 49.1 ± 1.5 kg NH₃ AU^-1 year^-1, respectively. Enteric CH₄ fermentation and manure on the feedlot contributed 67.5% and 80.8% of the total system GHG and NH₃ emissions, respectively. The highest ME values were found for lipid additives for enteric CH₄ fermentation and urease inhibitor additives (UI) for NH₃ emissions from manure on the feedlot, being -14.9% ( p < 0.05) and -59.5% ( p < 0.001), respectively. The recommended mitigation combinations of a low-crude-protein (CP) diet and a UI additive for manure on the feedlot could reduce the GHG of the system by 4.9% and NH₃ by 50.9%. The results of this study have important implications for developing sustainable beef cattle feedlot systems from the viewpoint of GHG and NH₃ mitigation.

A review of biogas and an assessment of its economic impact and future role as a renewable energy source

Anaerobic digestion (AD) is a technology that is gaining popularity because of the need for more renewable energy sources around the world. AD is a complex series of biochemical reactions that ultimately result in the formation of biogas, which is a mixture of methane and carbon dioxide with other trace elements. From large installations to small personal reactors, the underlying basic process is the same, but through research, pretreatments and substrate co-digestion are becoming more popular to enhance biogas production. Reactor design and substrate selection also vary depending on the installation’s location. Biogas cleaning and upgrading help to increase the usability of the gas for multiple applications. The economic viability depends on the location in the world and the available substrate quality and quantity. AD processes rely heavily on government subsidies to stay profitable. In developing countries, AD profitability is not a concern, as this technology provides a way to better human life in these areas. This review presents a detailed look at the AD technology, provides a discussion on the economics of AD, and suggests future studies to enhance the technology.

Dairy cattle welfare as a result of human-animal relationship – a review

Despite the various concepts of human-animal relationship, the welfarist approach to this problem is one of the most often considered in theory and used in practice. When dealing with issues related to dairy cattle welfare (DCW), it is necessary to take into account both the reality characteristic for animals used to obtain milk (e.g. the problem of automatic milking of cows) and for slaughter cattle (e.g. slaughter of culled animals). It is not surprising, therefore, that issues related to DCW are the focus of the attention of the public, researchers, breeders as well as the dairy and meat industries. The aim of this article was to possibly most comprehensively cover the above-mentioned issues, although due to its huge scope it was obviously necessary to limit the article to what I think are currently most important issues. That is why in the review I (1) characterized the issues related to the division of human responsibility for DCW; (2) discussed the importance of technology to human-animal relationship; (3) elaborated the matter of stress, emotionality of animals and their cognitive abilities in the aspect of “negative” and “positive” DCW; (4) considered the possibilities of non-invasive assessment of animal welfare in the future and (5) discussed topics related to improving the conditions of the slaughter of animals. In summary, it was proposed paying more attention than has been paid until now, to the assessment of positive DCW in scientific research and breeding practice. I also drew attention to the necessity of reliable information flow on the line of the breeder/milk producer - industry - consumer, as negligence in this area is one of the reasons for public disinformation regarding the level of animal welfare.

Milk production Life Cycle Assessment: A comparison between estimated and measured emission inventory for manure handling

Measuring emissions from manure management operations (from the barns to the land) is a challenging task, subject to different uncertainties related to the spatial-temporal variability in the process leading to gaseous release. At the same time, emissions inventory is a prerequisite of Life Cycle Assessment (LCA) studies. Manure management emissions are usually estimated using equations developed by Intergovernmental Panel on Climate Change (IPCC, in the case of greenhouse gases emissions) and European Environmental Agency (EEA) for Nitrogen-related emissions. In the present study, the environmental impacts associated to three Italian dairy farms were calculated through a comparative LCA using two different approaches for complying the emission inventory. In the "estimated" approach (E) the commonly adopted IPCC and EEA equations were used, while in the "measured" approach (M) emissions actually measured were taken as input data to quantify the emissions associated to manure management. The results showed that the IPCC equation underestimates the manure management emissions, leading to a 10-42% lower global warming potential comparing E to M approach. On the other hand, ammonia related impact categories showed higher values if they were calculated using the estimated approach, underling that a safer level of estimation is maintained.

Quantification of Methane and Ammonia Emissions in a Naturally Ventilated Barn by Using Defined Criteria to Calculate Emission Rates

Simple Summary

Defined criteria for the application of the CO₂ balance method in a naturally ventilated barn provided reliable data. This specification enabled the acquisition and quantification of CH₄ and NH₃ in a naturally ventilated dairy barn, as well as detecting decreasing NH₃ emissions affected by supplementing an Acacia mearnsii condensed tannin extract to a dairy cattle ration. Moreover, long-term measurements were possible and can be used to examine feed-related mitigation strategies at a barn level in the future.

Abstract

Extensive experimentation on individual animals in respiration chambers has already been carried out to evaluate the potential of dietary changes and opportunities to mitigate CH₄ emissions from ruminants. Although it is difficult to determine the air exchange rate of open barn spaces, measurements at the herd level should provide similarly reliable and robust results. The primary objective of this study was (1) to define a validity range (data classification criteria (DCC)) for the variables of wind velocity and wind direction during long-term measurements at barn level; and (2) to apply this validity range to a feeding trial in a naturally cross-flow ventilated dairy barn. The application of the DCC permitted quantification of CH₄ and NH₃ emissions during a feeding trial consisting of four periods. Differences between the control group (no supplement) and the experimental group fed a ration supplemented with condensed Acacia mearnsii tannins (CT) became apparent. Notably, CT concentrations of 1% and 3% of ration dry matter did not reduce CH₄ emissions. In contrast, NH₃ emissions decreased 34.5% when 3% CT was supplemented. The data confirm that quantification of trace gases in a naturally ventilated barn at the herd level is possible.

Discrepancies and Uncertainties in Bottom-up Gridded Inventories of Livestock Methane Emissions for the Contiguous United States

In this analysis we used a spatially explicit, simplified bottom-up approach, based on animal inventories, feed dry matter intake, and feed intake-based emission factors to estimate county-level enteric methane emissions for cattle and manure methane emissions for cattle, swine, and poultry for the contiguous United States. Overall, this analysis yielded total livestock methane emissions (8916 Gg/yr; lower and upper 95% confidence bounds of ±19.3%) for 2012 (last census of agriculture) that are comparable to the current USEPA estimates for 2012 and to estimates from the global gridded Emission Database for Global Atmospheric Research (EDGAR) inventory. However, the spatial distribution of emissions developed in this analysis differed significantly from that of EDGAR and a recent gridded inventory based on USEPA. Combined enteric and manure methane emissions from livestock in Texas and California (highest contributors to the national total) in this study were 36% lesser and 100% greater, respectively, than estimates by EDGAR. The spatial distribution of emissions in gridded inventories (e.g., EDGAR) likely strongly impacts the conclusions of top-down approaches that use them, especially in the source attribution of resulting (posterior) emissions, and hence conclusions from such studies should be interpreted with caution.

Revised methane emissions factors and spatially distributed annual carbon fluxes for global livestock

BACKGROUND

Livestock play an important role in carbon cycling through consumption of biomass and emissions of methane. Recent research suggests that existing bottom-up inventories of livestock methane emissions in the US, such as those made using 2006 IPCC Tier 1 livestock emissions factors, are too low. This may be due to outdated information used to develop these emissions factors. In this study, we update information for cattle and swine by region, based on reported recent changes in animal body mass, feed quality and quantity, milk productivity, and management of animals and manure. We then use this updated information to calculate new livestock methane emissions factors for enteric fermentation in cattle, and for manure management in cattle and swine.

RESULTS

Using the new emissions factors, we estimate global livestock emissions of 119.1 ± 18.2 Tg methane in 2011; this quantity is 11% greater than that obtained using the IPCC 2006 emissions factors, encompassing an 8.4% increase in enteric fermentation methane, a 36.7% increase in manure management methane, and notable variability among regions and sources. For example, revised manure management methane emissions for 2011 in the US increased by 71.8%. For years through 2013, we present (a) annual livestock methane emissions, (b) complete annual livestock carbon budgets, including carbon dioxide emissions, and (c) spatial distributions of livestock methane and other carbon fluxes, downscaled to 0.05 × 0.05 degree resolution.

CONCLUSIONS

Our revised bottom-up estimates of global livestock methane emissions are comparable to recently reported top-down global estimates for recent years, and account for a significant part of the increase in annual methane emissions since 2007. Our results suggest that livestock methane emissions, while not the dominant overall source of global methane emissions, may be a major contributor to the observed annual emissions increases over the 2000s to 2010s. Differences at regional and local scales may help distinguish livestock methane emissions from those of other sectors in future top-down studies. The revised estimates allow improved reconciliation of top-down and bottom-up estimates of methane emissions, will facilitate the development and evaluation of Earth system models, and provide consistent regional and global Tier 1 estimates for environmental assessments.

Co-digestion of agricultural and municipal waste to produce energy and soil amendment

In agriculture, manure and cotton gin waste are major environmental liabilities. Likewise, grass is an important organic component of municipal waste. These wastes were combined and used as substrates in a two-phase, pilot-scale anaerobic digester to evaluate the potential for biogas (methane) production, waste minimisation, and the digestate value as soil amendment. The anaerobic digestion process did not show signs of inhibition. Biogas production increased during the first 2 weeks of operation, when chemical oxygen demand and volatile fatty acid concentrations and the organic loading rate to the system were high. Chemical oxygen demand from the anaerobic columns remained relatively steady after the first week of operation, even at high organic loading rates. The experiment lasted about 1 month and produced 96.5 m³ of biogas (68 m³ of CH₄) per tonne of waste. In terms of chemical oxygen demand to methane conversion efficiency, the system generated 62% of the theoretical methane production; the chemical oxygen demand/volatile solids degradation rate was 62%, compared with the theoretical 66%. The results showed that co-digestion and subsequent digestate composting resulted in about 60% and 75% mass and volume reductions, respectively. Digestate analysis showed that it can be used as a high nutrient content soil amendment. The digestate met Class A faecal coliform standards (highest quality) established in the United States for biosolids. Digestion and subsequent composting concentrated the digestate nitrogen, phosphorus, and potassium content by 37%, 24%, and 317%, respectively. Multi-substrate co-digestion is a practical alternative for agricultural waste management, minimisation of landfill disposal, and it also results in the production of valuable products.

Microbial Abundances Predict Methane and Nitrous Oxide Fluxes from a Windrow Composting System

Manure composting is a significant source of atmospheric methane (CH₄) and nitrous oxide (N₂O) that are two potent greenhouse gases. The CH₄ and N₂O fluxes are mediated by methanogens and methanotrophs, nitrifying and denitrifying bacteria in composting manure, respectively, while these specific bacterial functional groups may interplay in CH₄ and N₂O emissions during manure composting. To test the hypothesis that bacterial functional gene abundances regulate greenhouse gas fluxes in windrow composting systems, CH₄ and N₂O fluxes were simultaneously measured using the chamber method, and molecular techniques were used to quantify the abundances of CH₄-related functional genes (mcrA and pmoA genes) and N₂O-related functional genes (amoA, narG, nirK, nirS, norB, and nosZ genes). The results indicate that changes in interacting physicochemical parameters in the pile shaped the dynamics of bacterial functional gene abundances. The CH₄ and N₂O fluxes were correlated with abundances of specific compositional genes in bacterial community. The stepwise regression statistics selected pile temperature, mcrA and NH₄⁺ together as the best predictors for CH₄ fluxes, and the model integrating nirK, nosZ with pmoA gene abundances can almost fully explain the dynamics of N₂O fluxes over windrow composting. The simulated models were tested against measurements in paddy rice cropping systems, indicating that the models can also be applicable to predicting the response of CH₄ and N₂O fluxes to elevated atmospheric CO₂ concentration and rising temperature. Microbial abundances could be included as indicators in the current carbon and nitrogen biogeochemical models.

Assessing the Performance of Floating Biofilters for Oxidation of Methane from Dairy Effluent Ponds

Mitigating methane (CH) emissions from New Zealand dairy effluent ponds using volcanic pumice soil biofilters has been found to be a promising technology. Because the soil column biofilter prototype previously used was cumbersome, here we assess the effectiveness of volcanic pumice soil-perlite biofilter media in a floating system to remove high concentrations of CH emitted from a dairy effluent pond and simultaneously in a laboratory setting. We measured the CH removal over a period of 11 mo and determined methanotroph population dynamics using molecular techniques to understand the role of methanotroph population abundance and diversity in CH removal. Irrespective of the season, the pond-floating biofilters removed 66.7 ± 5.7% CH throughout the study period and removed up to 101.5 g CH m h. By contrast, the laboratory-based floating biofilters experienced more biological disturbances, with both low (∼34%) and high (∼99%) CH removal phases during the study period and an average of 58% of the CH oxidized. These disturbances could be attributed to the measured lower abundance of type II methanotroph population compared with the pond biofilters. Despite the acidity of the pond biofilters increasing significantly by the end of the study period, the biofilter encouraged the growth of both type I ( and ) and type II ( and ) methanotrophs. This study demonstrated the potential of the floating biofilters to mitigate dairy effluent ponds emissions efficiently and indicated methanotroph abundance as a key factor controlling CH oxidation in the biofilter.

Greenhouse gas emissions from dairy manure management in a Mediterranean environment

Livestock agriculture is a major source of anthropogenic greenhouse gas (GHG) emissions, with a substantial proportion of emissions derived from manure management. Accurate estimates of emissions related to management practices and climate are needed for identifying the best approaches to minimize, and potentially mitigate, GHG emissions. Current emissions models such as those of the IPCC, however, are based on emissions factors that have not been broadly tested against field-scale measurements, due to a lack of data. We used a diverse set of measurements over 22 months across a range of substrate conditions on a working dairy to determine patterns and controls on soil-based GHG fluxes. Although dairy soils and substrates differed by management unit, GHG fluxes were poorly predicted by these or climate variables. The manure pile had the greatest GHG emissions, and though temperature increased and O₂ concentration decreased following mixing, we detected almost no change in GHG fluxes due to mixing. Corral fluxes were characterized by hotspots and hot moments driven by patterns in deposition. Annual scraping kept the soil and accumulated manure pack thin, producing drier conditions, particularly in the warm dry season. Summed over area, corral fluxes had the greatest non-CO₂ global warming potential. The field had net CH₄ consumption, but CH₄ uptake was insufficient to offset N₂ O emissions on an area basis. All sites emitted N₂ O with a similar or greater climate impact than CH₄ . Our results highlight the importance of N₂ O emissions, a less commonly measured GHG, from manure management and present potential opportunities for GHG emissions reductions.

Gridded National Inventory of U.S. Methane Emissions

We present a gridded inventory of US anthropogenic methane emissions with 0.1° × 0.1° spatial resolution, monthly temporal resolution, and detailed scale-dependent error characterization. The inventory is designed to be consistent with the 2016 US Environmental Protection Agency (EPA) Inventory of US Greenhouse Gas Emissions and Sinks (GHGI) for 2012. The EPA inventory is available only as national totals for different source types. We use a wide range of databases at the state, county, local, and point source level to disaggregate the inventory and allocate the spatial and temporal distribution of emissions for individual source types. Results show large differences with the EDGAR v4.2 global gridded inventory commonly used as a priori estimate in inversions of atmospheric methane observations. We derive grid-dependent error statistics for individual source types from comparison with the Environmental Defense Fund (EDF) regional inventory for Northeast Texas. These error statistics are independently verified by comparison with the California Greenhouse Gas Emissions Measurement (CALGEM) grid-resolved emission inventory. Our gridded, time-resolved inventory provides an improved basis for inversion of atmospheric methane observations to estimate US methane emissions and interpret the results in terms of the underlying processes.