Magnesium is a nutritional tool for the yield and quality of oolong tea (Camellia sinensis L.) and reduces reactive nitrogen loss

• Magnesium (Mg) fertilization raise tea yield due to increased bud density. • Mg fertilization increased amino acid content and its ratio to tea polyphenols. • Mg fertilization enhanced nitrogen and Mg accumulation in the tea harvested part. • Mg fertilization reduces nitrous oxide emission and nitrate leaching in tea garden. • The role of Mg fertilizer on the green development of tea garden cannot be ignored. Magnesium (Mg) plays an important role in controlling the biological utilization and dispersion of nitrogen (N) in crops and the environment; however, the application of Mg fertilizer is often neglected in crop nutrient management globally. Can intensified Mg management optimize the agronomic and environmental benefits of tea production? To answer this question, four trials of Mg fertilizer levels in oolong tea ( Camellia sinensis L.) garden were designed, i.e., 0 (Mg0), 35 (Mg1), 70 (Mg2) and 140 (Mg3) kg MgO ha −1 yr −1 , and the tea yield and quality, N use efficiency (NUE) and reactive N losses were assessed. Compared with Mg0, Mg applications significantly increased tea yield by an average of 14.1% (spring tea), 18.4% (autumn tea) and 15.8% (annual total tea), improved tea quality, and increased the partial factor productivity of applied N (PFP N ) and NUE by 13.9–17.2% and 17.8–25.5% after the four-year trial, respectively. The N uptake of young shoots (i.e., harvest part) in Mg1, Mg2 and Mg3 was higher than that in Mg0 by 19.5%, 25.8% and 21.5%, respectively. Simultaneously, Mg fertilization significantly decreased the N surplus and reduced the risk of reactive N loss. There was no significant difference in the indicators mentioned above or in the economic benefits among the Mg fertilizer treatments. In conclusion, if the risk of soil nitrate leaching is not considered, the recommended Mg application rate is 35 kg MgO ha -1 yr -1 ; otherwise, it is 70 kg MgO ha -1 yr -1 . These results indicated that Mg could be a key limiting factor and have positive effects on tea production, and reasonable Mg fertilization is beneficial to the sustainability of tea production.