Biochar modulates mineral nitrogen dynamics in soil and terrestrial ecosystems: A critical review

Biochar, over the last two decades, has become the focal point of agro-environmental research given its unique functionality, cost-effectiveness and recyclability potentials. It has been studied intensively as an efficient scavenger for the decontamination of several organic and inorganic pollutants. However, the ability of biochar to modulate nitrogen (N) dynamics in soil and terrestrial ecosystems remains controversial. This work deliberates on the premise that biochar functionality enables maximizing N use efficiency by reducing the potential losses induced by volatilization/emission and runoff/leaching as well as stimulating available N inputs derived from symbiotic and nonsymbiotic biological nitrogen fixation (BNF) and N mineralization/retention. For this purpose, we carried out a critical review on different intriguing dimensions surrounding the potentiality of biochar to modulate the complicated reactions of soil N cycle with emphasis on its pros and cons. Previous studies in the literature have shown contradictory results with a noticeable significant effect of biochar toward stimulating available N inputs and reducing its losses under short-term laboratory experimentations. However, long-term field investigations have indicated minimal or negative effects in this regard. Furthermore, some of the experimentations lack appropriate controls or fail to account for inputs or losses associated with biochar particles. It is thus of great importance to contextualise lab-scale experimentations based on real field data to provide a holistic approach for understanding the complicated reactions responsible for modulating N cycle in the charosphere. Additionally, biochar functionalization should be highlighted in the foreseeable research to develop fit-for-purpose forms tailored in agro-environmental applications.