Urea-based nitrogen fertilization in agriculture: a key source of N2O emissions and recent development in mitigating strategies

Agricultural land occupies nearly half of the earth’s surface, and farming activities account for nearly 60% of total anthropogenic N2O emissions. The manufactured nitrogen (N) fertilizers applied to soils are major sources of N2O emissions from agricultural systems. Among the synthetic N fertilizers, urea has the highest nitrogen content of all solid nitrogenous fertilizers and accounts for 66% of global synthetic N fertilizer use. Hence, efficient urea-N management is imperative for global N2O abatement. This review provides an update on advances in N2O-generating pathways, microbial mechanisms, abiotic and biotic regulating factors, and mitigation strategies. Nitrification inhibitors have been extensively studied as strategies to mitigate soil N2O emissions by decreasing nitrification and denitrification processes. Controlled/slow-release fertilizer formulations have been used widely to enhance fertilizer N use efficiency by regulating the release rates of N from fertilizer. Additionally, biochar, microbial inoculation with arbuscular mycorrhizal fungi (AMF), biological nitrification inhibitors (BNIs) and biological denitrification inhibitors (BDIs) may enable the development of novel and environment‐friendly strategies for practicable N2O mitigation in future.