When it comes to the use of biochar in agriculture, the majority of research conducted in the last decade has focused on its application as a soil amendment and for soil remediation. This treatment improves soil quality, increases crops yields, and sequestrates atmospheric carbon to the soil. Another widely studied aspect connecting biochar with agriculture is the composting processes of various agricultural waste with the addition of biochar. Obtaining the material via the pyrolysis of agricultural waste, including animal manure, has also been investigated. However, given the remarkable properties of biochar, its application potential could be utilized in other areas not yet thoroughly investigated. This review paper summarizes the last decade of research on biochar and its use in crop agriculture and livestock production. Knowledge gaps are highlighted, such as using biochar for the mitigation of odorous emissions from animal manure and by feeding the biochar to animals.

As airborne emissions from agricultural operations began to receive more concentrated scrutiny, the federal Task Force on Agricultural Air Quality was established in the 1996 Farm Bill and began operations in 1997 to advance research and provide solutions for sustainable agricultural operations with primary focus on particulate matter, ozone, and odors. This historical review synthesizes research conducted by institutions serving the southern and central Great Plains from the early 2000s to mid-2010s across cattle, dairy, swine, and poultry production systems, identifying three interdependent research pillars: measurement technology, emission quantification, and abatement solutions. Research priorities varied by species, with cattle and dairy operations focusing primarily on particulate matter (PM), ammonia (NH ₃ ), and greenhouse gas (GHG) emissions, while swine and poultry studies concentrated on odor and volatile organic compounds (VOCs). Measurement technology innovations proved foundational to reliable emission science. Quantification studies established baseline emission factors essential for regulatory compliance while revealing critical temporal dynamics and environmental drivers. However, persistent knowledge gaps emerged, particularly in transferring abatement solution effectiveness from controlled laboratory conditions to commercial settings, where performance declined substantially due to extreme spatial and environmental variability. Most importantly, the research field shifted from pursuing simple pollution reduction toward systematic approaches that monitor and manage multiple pollutants. We recommend that future research must develop frameworks that systematically assess pollutant trade-offs alongside economic feasibility to enable science-based mitigation strategies balancing environmental protection with agricultural sustainability.

This review described the state of the science concerning the generation, measurement, and mitigation of ammonia (NH₃) emissions from beef cattle feedyards. NH₃ emissions primarily come from urinary urea in cattle manure. In the past, constant emission factors were used to inventory NH₃ emissions. Currently, NH₃ emission factors estimated by process-based mechanistic models reflecting various factors affecting NH₃ emissions in the feedyard environment are available. This review of current literature indicated the average NH₃ emissions from a beef cattle feedyard was approximately 119 g/head/day (range 24 to 318 g/head/day), and the average NH₃ flux was approximately 58 µg/m²/s (range 2 to 185 µg/m²/s). Although more realistic estimates of NH₃ emission flux from open-lot livestock facilities were being obtained using process-based models, there was still significant variation depending on the diet composition, manure management practices, and the feedyard environment, including both seasonal weather patterns and synoptic weather events. We note the need to improve inventories of NH₃ emissions into categories of crude protein percentage, manure management implemented, and feedyard environment. Some mitigation strategies can be effective, such as diet manipulation, growth-promoting technologies, and manure or pen-surface amendments. Of those, precision diet feeding to meet but not exceed protein requirements appeared to be the most practical way to reduce ammonia emissions over the animals’ feeding period; laboratory studies suggested that shorter-term reductions in emission flux may be possible with the other approaches, but they were far more speculative at this point as to both their efficacy and their cost of implementation.

The livestock industry plays a significant role in the economic well-being of many parts of the world with a host of environmental challenges. Key amongst them is the management of gaseous emissions emitted from livestock manure. Mitigation of gaseous emissions from livestock operations such as odor, odorous volatile organic compounds (VOCs), ammonia (NH₃), hydrogen sulfide (H₂S), and greenhouse gases (GHGs) have been of research interest for the last couple of decades. Biochar, a low-cost-value byproduct of biorenewable energy and thermochemical waste processing compared with syngas and bio-oil, has been actively researched as a potential surficial treatment of manure and emissions from stored or co-composted manure. Yet, the efficacy of biochar treatment differs, partly because biochar properties vary with feedstock and thermochemical processing conditions. To date, the results from laboratory-scale trials are encouraging, but a more focused effort is needed to bring this technology closer to farm-scale applications. Therefore, this review aims to summarize and highlight current research related to mitigating gaseous emissions from manure treated with biochar. Various types of biochar, and modes of biochar applications, e.g., manure additives and co-composting, dosage, and timing, are discussed in the context of targeted gas emissions mitigation. Gaps in knowledge remain, including demonstrated larger-scale mitigation performance and verifiable technoecomics. Standardization and certification of biochar properties suitable for specific environmental management applications are recommended. The potential synergy between mitigating emissions, improving manure quality, carbon, and nitrogen cycling in animal and crop production agriculture is found. Biochar can be a comprehensive solution to gaseous emissions while also upgrading manure as a high-quality additive that could improve the sustainability of animal and crop production systems.

When it comes to air pollution complaints, odours are often the most significant contributor. Sources of odour emissions range from natural to anthropogenic. Mitigation of odour can be challenging, multifaceted, site-specific, and is often confounded by its complexity—defined by existing (or non-existing) environmental laws, public ordinances, and socio-economic considerations. The objective of this paper is to review and summarise odour legislation in selected European countries (France, Germany, Austria, Hungary, the UK, Spain, the Netherlands, Italy, Belgium), North America (the USA and Canada), and South America (Chile and Colombia), as well as Oceania (Australia and New Zealand) and Asia (Japan, China). Many countries have incorporated odour controls into their legislation. However, odour-related assessment criteria tend to be highly variable between countries, individual states, provinces, and even counties and towns. Legislation ranges from (1) no specific mention in environmental legislation that regulates pollutants which are known to have an odour impact to (2) extensive details about odour source testing, odour dispersion modelling, ambient odour monitoring, (3) setback distances, (4) process operations, and (5) odour control technologies and procedures. Agricultural operations are one specific source of odour emissions in rural and suburban areas and a model example of such complexities. Management of agricultural odour emissions is important because of the dense consolidation of animal feeding operations and the advance of housing development into rural areas. Overall, there is a need for continued survey, review, development, and adjustment of odour legislation that considers sustainable development, environmental stewardship, and socio-economic realities, all of which are amenable to a just, site-specific, and sector-specific application.