Optimized chamomile–derived bioinhibitor (CCO) for enhanced maize production: Balancing nitrogen efficiency and reducing gaseous emissions

2-Cyclopenten-1-one (CCO), a bioinhibitor derived from Chamomila recutita L., is being evaluated as an alternative to synthetic nitrogen inhibitors. To facilitate its practical application, this study assessed the effects of CCO on nitrogen dynamics, greenhouse gas emissions, maize productivity, and farm economics in Alfisols of northern China, using a randomized block design with five treatments: chemical fertilizer alone (NPK) and NPK supplemented with CCO at 0.5 %, 1.0 %, 2.0 %, and 5.0 % of total nitrogen. The abundance of the ammonia oxidizer amoA gene was also monitored to clarify nitrogen loss mechanisms and fertilizer recovery. Results showed that the 1 % CCO treatment most effectively synchronized soil nitrogen supply with crop demand, reducing NH₃ emissions by 32.5 % and N₂O emissions by 21.9 % compared with NPK alone. This dosage also enhanced ammonium availability and increased CH₄ oxidation approximately five-fold, leading to a 17 % yield increase, a 26.8 % improvement in apparent nitrogen recovery efficiency, and the highest net profit (214.3 USD ha^-1). Microbial and enzymatic analyses revealed that the 1 % dosage effectively suppressed key ammonia oxidizers, thereby reducing nitrification. In contrast, suboptimal concentrations underperformed: the 2 % dosage increased N₂O emissions by 72 % (2.08 vs. 1.21 kg ha^-1), whereas the 0.5 % dosage raised NH₃ losses by 40 % (1.89 vs. 1.35 kg ha^-1) compared with the optimal 1 % dosage. Overall, the calibrated 1 % CCO treatment markedly reduced global warming potential and greenhouse gas intensity, demonstrating its potential as a sustainable strategy to enhance nitrogen use efficiency, mitigate environmental risks, and improve farm profitability.