Influence of biochar on soil nitrogen dynamics: Critical review with bibliometric insights

Abstract

Excessive application of nitrogenous fertiliser poses a significant threat to environmental sustainability. Biochar has emerged as a multifunctional amendment to mitigate this environmental risk by increasing nitrogen (N) retention and nutrient use efficiency across diverse agro ecosystems. This review critically synthesises evidence from meta-analyses, incubation and field studies to elucidate how biochar influences N transformation and different loss pathways such as denitrification, leaching and volatilisation. The large surface area, porous structure and variable surface chemistry of biochar results in increasing ammonium (NH₄+) adsorption and reduction in nitrate (NO₃-) leaching, thereby enhancing N retention in soil, which is governed by several factors, such as application rate, feedstock type, pyrolysis temperature and soil condition. To contextualise this evidence, a bibliometric review of 1026 scopus-indexed articles published between 2017–26 was carried out using bibliometrix with biblioshiny and VOSviewer. The findings indicated a rapid diversified growth of scientific production and a transition from broad subjects, e.g. soil improvement and carbon management to narrower subjects, e.g., N dynamics, microbial communities and soil health. The network analysis also indicated that the field continues to diversify into new application-oriented fields. We identified methodological inconsistencies and proposed validation through long-term studies and site-specific response models for future research.