Reviewing role of biochar in controlling soil erosion and considering future aspect of production using microwave pyrolysis process for the same

Microwave-assisted pyrolysis (MAP) is considered as one of the improved biochar production options given its cost efficiency, efficient heat transfer and better-quality control. Researchers have observed that biochar can be considered as an alternative erosion control material due to its high porosity, surface area, and surface functional groups. However, as per the available literature, contradictions exist regarding some erosion control mechanisms of biochar with respect to water holding capacity (WHC), bulk density, and aggregate formation. Further, there is a lack of exploration as to how biochar produced using MAP can be adopted for erosion control. The objective of this study is to critically review existing literature on the usage of biochar for erosion control in various types of soils. In addition, the use of the MAP technique for producing biochar for erosion control is explored. Based on the review, the available experimentation research is generally of short duration with the least consideration of the long-term ageing effects of biochar. The studies on erosion control using biochar have been mostly conducted in the shallower zone (i.e., within 20 cm). The effect of different types of biochars on various soils does not seem to have been investigated systematically. It has been observed that the mechanism of washing away biochar particles and nutrients is rarely taken into account while measuring erosion. Further, the comparative analysis of biochar types produced from various feedstocks, including their physiochemical properties, is rarely explored for their applications in soil erosion. This study aims to critically analyze available literature for the erosion suppressing mechanism of biochar, limitations and the feasibility of microwave-assisted biochar production for the purpose of soil erosion control. Graphical abstract