​INTRODUCTION

A substantial number of the most relevant studies have employed meta-analytical approaches using globally distributed datasets to quantify and synthesize the impacts of biochar application on various environmental and agricultural outcomes. For instance, a global meta-analysis of 64 studies spanning 1 to 10 years revealed that biochar significantly increased soil organic carbon (SOC), with more pronounced effects in long-term experiments. These findings emphasize the enduring impact of biochar on soil health and carbon sequestration (Gross et al., 2021).

 

Similarly, studies have examined the long-term stability of biochar, with isotopic tracer analyses estimating that over 97% of the carbon in biochar persists for centuries, underlining its potential for carbon sequestration (Wang et al., 2016). This highlights biochar’s role as a potential solution for mitigating climate change through long-term carbon storage. Further exploration of biochar's aging process has been conducted, with studies documenting how its surface chemistry and interactions with soil aggregates evolve beyond six months after application (Joseph et al., 2021).

 

The impacts of biochar on greenhouse gas (GHG) dynamics have also been extensively studied. In a meta-analysis of 3,883 paired observations, biochar was consistently found to reduce methane (CH₄) and nitrous oxide (N₂O) emissions. However, it increased carbon dioxide (CO₂) emissions under controlled experimental conditions (Jia et al., 2023). Additional research has provided valuable insights into biochar’s interaction with microbial denitrification processes, with studies reporting reduced nitrate concentrations and increased expression of denitrification genes globally (Zhang et al., 2024). However, variability in the results has been noted, with studies by Song et al. (2016) and He et al. (2017) emphasizing that CH₄ and CO₂ emission responses were influenced by land use type (e.g., rice paddies vs. uplands) and experimental design, highlighting the complexity of biochar’s environmental effects.

 

Several studies have focused on biochar’s specific effects on land systems. For instance, crop yield benefits were found to be mainly limited to tropical regions, where biochar’s ability to improve acidic and nutrient-poor soils is most evident (Jeffery et al., 2017). In contrast, datasets such as the one presented by Li et al. (2024), covering 37 countries, provides a broader understanding of biochar’s potential across diverse soil, climate, and management conditions, offering a more comprehensive foundation for comparative assessments. Despite these advances, comprehensive studies contrasting biochar’s effects across unmanaged land systems, such as forests and grasslands, remain scarce. Additionally, recent reviews have noted inconsistencies between laboratory and field-scale outcomes, particularly regarding GHG emissions (Lyu et al., 2022; Mosa et al., 2023).

​

Taken together, these studies highlight the global relevance of biochar amendments and their potential to improve specific soil properties and climate-related outcomes. However, further research is needed to provide clearer contrasts across different land system types and validate biochar's long-term effects under field conditions.