Improving tea (Camellia sinensis) quality, economic income, and environmental benefits by optimizing agronomic nitrogen efficiency: A synergistic strategy

Tea is a perennial crop widely cultivated globally. Excessive application of fertilizers is a common practice among tea farmers; however, this lowers the tea quality and consequently income and also results in serious environmental impacts. Agronomic efficiency is a vital indicator of tea yield, quality, and its environmental impact. Maximizing tea quality and economic benefits while minimizing its harmful environmental impact is an important strategy for sustainable agriculture; however, corresponding goal-oriented solutions are lacking. In this study, we used representative tea quality indicators (free amino acids), income, and global warming potential (GWP) to analyze the possibility of multi-objective synergy and explore the feasibility of achieving agronomic efficiency using the Pareto model. The Pearson correlation results indicated that the agronomic efficiency of N (AEN) was significantly (p < 0.05) associated with the free amino acid content, income, and GWP of tea. When AEN increased from 2.6 to 5.5 kg kg−1, free amino acid content and income increased by 37.2% and 80.2%, respectively, while GWP decreased by 50.9% for optimized management compared with those for conventional management using the Pareto multiple-objective optimize model. Concurrently, N fertilizer application rate was reduced from 491.4 to 237.0 kg ha−1. The results of the structural equation model revealed that the AEN had a positive pathway for income and total free amino acids content. N fertilizer application rate directly affected the GWP and AEN and indirectly affected tea leaf-free amino acid levels and production income. Reducing nitrogen fertilizer rate helps to increase AEN and further mitigates GWP and improves economic benefits and free amino acid content of tea. These findings outline a reference for tea farmers and can provide basic guidelines for a sustainable tea industry.