Biochar amendments for sustainable soil management

Biochar is a carbon-rich product that is generated when a sustainable source of biomass such as wood, crop residues, or manure is thermally degraded at high temperatures under oxygen-limited conditions. The first evidence of biochar use as a soil amendment comes from paleosols in the Brazilian Amazon and is estimated to have begun more than 2000 years ago. Modernday research finds that adding biochar to nutrientimpoverished tropical soil can improve soil properties and crop productivity because biochar increases soil pH and reduces aluminum toxicity. However, soils in cold temperate regions may have a higher pH, higher soil organic matter and nutrient content, high activity clays, and lower oxide contents and are expected to respond differently to biochar than tropical soils. Adding biochar to intensively managed temperate soils is a recent agricultural innovation. Although the research is still in its infancy, there is growing interest in assessing the potential of biochar as a soil amendment for agricultural and high-valued horticultural crops in colder regions of the world. This special issue was proposed due to the enthusiastic interest in biochar research that was expressed by participants at the annual meeting of the Canadian Society of Soil Science held in Saskatoon, Saskatchewan, Canada from 9 to 13 July 2019. Our goal was to gather the most current findings that would help explain the functions of biochar in cold, temperate soils. In agroecosystems, biochar applications can boost soil nutrient availability while contributing to soil fertility (Gagnon et al. 2022; Li et al. 2022; Abedin and Unc 2022; Lévesque et al. 2022b), and influencing crop productivity (Alotaibi 2022; Hung et al. 2022; Shang et al. 2022). Research also shows that biochar is most effective in improving soil properties when it is combined or co-processed with another soil amendment such as compost, manure, paper mill sludge, or biosolids (Manirakiza et al. 2022; Ziadi et al. 2022; Hangs et al. 2022). Although the majority of biochar research has focused on soil and field crops, there is an emerging body of literature that examines the potential for biochar use in the horticultural industry for both fruit and vegetable production (Messiga et al. 2022a; Shang et al. 2022). The influence of biochar on climate change mitigation and its impact on soil and crop productivity have also been examined (Jiang et al. 2022a, 2022b; Deng et al. 2022; Weber et al. 2022). It has been proposed that biochar is a carbon-negative soil amendment and can be used as a climate change mitigation strategy in temperate agriculture (Lévesque et al. 2022a). The proposed mechanisms for climate change mitigation of biochar are a molecular structure dominated by aromatic carbon blocks that make it more resistant to microbial decomposition, allowing it to persist in soil for thousands of years and potentially curbing greenhouse gas emissions (Messiga et al. 2022a, 2022b; Deng et al. 2022). Biochar physical and chemical properties have become useful in site restoration projects in forest ecosystems and urban soils due to its ability to adsorb and immobilize organic chemicals (Bieser et al. 2022). Manuscripts in this special issue help bridge our current knowledge gap and recognize the contribution of biochar in temperate agricultural soils as a way forward to sustainable crop productivity, healthy soils, and climate change mitigation.