Multi-Objective Nitrogen Optimization in Tea Cultivation: A Pathway to Achieve Sustainability in Cash Crop Systems

Excessive nitrogen fertilizer application in tea plantations is a common problem that leads to soil acidification and reductions in both yield and economic returns. To evaluate the impacts of varying nitrogen input levels (0–600 kg N ha−1 yr−1) on yield, as well as environmental and economic outcomes, a two-year field experiment was conducted. Results demonstrated that when nitrogen application exceeded 150 kg N ha−1 yr−1, key efficiency indicators—agronomic efficiency (NAE), recovery efficiency (NRE), and partial factor productivity (NPFP) declined markedly. Among all treatments, the 150 kg N ha−1 yr−1 rate achieved the highest NRE at 28.01%. Moreover, environmental burdens including global warming potential, acidification, and eutrophication intensified with increasing nitrogen input. Benefit analysis revealed that yield-based economic returns peaked between 150 and 165 kg N ha−1 yr−1, whereas the highest ecosystem economic benefit, accounting for both profit and environmental cost, occurred at 120 kg N ha−1 yr−1. Thus, 120 kg N ha−1 yr−1 is identified as the optimal application rate for maximizing integrated economic and environmental returns while maintaining yield. These findings provide valuable guidance for promoting sustainable nitrogen management in tea cultivation worldwide.