Effects of nitrogen fertilization on forage production, animal performance, and greenhouse gas emissions in tropical pastures: A systematic review

This systematic review aimed to synthesize evidence on the effects of nitrogen (N) fertilization on forage production, animal performance, and greenhouse gas emissions in tropical pastures. The research question was developed based on the PICOS strategy. A total of 84,629 documents were retrieved from six databases, of which 34 studies met the inclusion criteria due to their methodological robustness. Most studies were conducted under grazing conditions (69.7%), using Brachiaria brizantha (52.9%) and Panicum maximum (26.5%). Urea (53.2%) and ammonium nitrate (25.5%) were the most evaluated N sources, with application rates ranging from 0 to 1000 kg ha⁻¹ , often split into three applications. Nitrogen use increased stocking rate (157.7%), gain per area (189.4%), and average daily gain (31.0%) when application rates rose from 0 to 300 kg ha⁻¹ . Overall, N fertilization has potential to improve forage productivity and animal performance in tropical pastures; however, responses vary depending on rates, sources, and experimental conditions. Splitting N rates (20–60 kg ha⁻¹) and synchronizing applications with plant demand are effective strategies to reduce NH₃ and N₂O losses, enhance fertilizer use efficiency, and mitigate environmental impacts. Future research should focus on evaluating the effects of different N sources and doses on soil CO₂ and CH₄ emissions, enteric CH₄, and C/N dynamics within the soil–plant–animal system, as well as expanding studies to other forage and animal species representative of tropical grazing systems. • Most N fertilization studies in tropical pastures focus on species of the genus Brachiaria . • Splitting N doses (20–60 kg/ha) reduces NH₃ losses and N₂O emissions. • Isolated results hinder understanding of N effects on forage, animals, and GHGs. • More research is needed on N fertilization impacts on soil GHGs and small ruminants.