# Can Biochar Improve the Sustainability of Animal Production?
## 1 Introduction  
As the world population is expected to reach 9.7 billion people by 2050, the global demand for animal protein is projected to increase correspondingly [1]. The United States Agriculture Department (USDA) projects meat chicken production to increase by 5% and milk production by 9% by 2030 [2]. At the same time, fewer resources, i.e., energy, arable land, and fresh water, are available to support food production [3], which challenges the sustainability of food animal production. Animal production is challenged by significant inputs, with feed consuming the majority of water, land, and fuel inputs and associated with the largest greenhouse gas (GHG) emissions [4]. The low efficiency of converting dietary protein to animal protein (i.e., \(\sim\)33% for broilers, 23% for swine, and 18% for milk) is a primary driver for the significant production inputs per unit of protein produced [5]. Animals generate significant amounts of nutrients in manure, bedding, wastewater, excess feed, and mortalities. A large share of these nutrients become emissions that negatively impact the air, water, and soil quality. Specifically, animal production is among the largest sources of global methane emissions (32%) [6] and produces significant amounts of other gaseous emissions as demonstrated in Table 1. In addition, excess nitrogen and phosphorus from manure management and utilization is translocated from the field via runoff to surface waters or by leaching through the soil to the groundwater. Considering the significant production inputs and emissions associated with animal production, there is a critical need to advance the environmental sustainability of animal production especially with projected sector growth. Among the promising materials and technologies that could advance the sustainability of animal production is biochar. Biochar is a stable, carbon-rich product from the thermal treatment of biomass (waste or lignocellulosic) at high temperatures in the absence of oxygen. This treatment significantly alters the biomass physical and chemical properties, thereby, creating biochar with a porous structure, high surface area, and added functional groups on the surface. As a result of these changes, biochar possesses unique physical and chemical properties that can help capture pollutants (solid, liquid, or gaseous) that would otherwise be released into the environment by serving as an adsorbent [13]. Biochar can also be modified and engineered to adsorb specific contaminants through acid/base and steam treatments. For these reasons, biochar has been studied for a variety of environmental applications. Utilizing biochar in animal production also has the potential to adsorb pollutants, improve the welfare and productivity of animal growth, increase soil carbon sequestration, and increase the value of manure-based fertilizer. Biochar in animal production would increase the circularity of the industry by reusing agricultural crop or manure waste in creating biochar and reintroducing it into the system to support production and sustainability. Figure 1 visualizes the results of our literature search using Web of Science (Clarivate Analytics) for studies related to biochar and animal agriculture between 2008 and 2022 using the following search terms \"biochar AND (animal OR livestock OR poultry)\". The figure, developed using VOSviewer tool, highlights the key themes of investigation in this area, i.e., (1) producing and characterizing biochar properties and adsorptive performance, (2) incorporating biochar as an emission mitigation aid in composing-related studies, and (3) biochar soil incorporation for crop production. The figure highlights the potential for integrative research to bridge the gap across these areas to assess the life-cycle performance of biochar in animal agriculture systems. [PERSON] et al. [13] reviewed the use of biochar in animal feed, manure treatment, and land application.