Improvement of Yield and Brewing Quality of Brewing Wheat Grown Under Reduced Nitrogen Fertilizer and Exogenous Melatonin Application

This study aimed to investigate the effects of exogenous melatonin on grain yield and quality of brewing wheat grown under reduced nitrogen (N) fertilizer application. Field experiments were performed using two brewing wheat cultivars, Yunong 901 and Fanmai 8. Treatments included conventional N (225 kg∙ha−1) and reduced N (150 kg∙ha−1 and 120 kg∙ha−1) levels, each with melatonin or water spray. The results demonstrated that reducing N fertilizer application led to decreased net photosynthetic rate, specific leaf N, and photosynthetic N use efficiency, while exogenous melatonin application improved corresponding photosynthetic parameters in all three N treatments. Reducing N decreased grain yield and grain endogenous hormone levels. Exogenous melatonin application increased grain yield under all N levels, with the highest increases in YN901 (10.61%) under MN and FM8 (10.27%) under LN. Melatonin partially restored grain hormone levels, particularly in the late filling stage under LN, maintaining higher filling activity. While reducing N decreased liquor volatile flavor compounds (alcohols, esters, N compounds), melatonin application significantly increased the total ester content and the relative levels of multiple volatile flavor compounds. Melatonin mitigated the adverse effects of N reduction, improving photosynthesis, grain yield, and liquor flavor quality. Comprehensively, reducing N to 150 kg∙ha−1 combined with exogenous melatonin application improves grain yield, N efficiency, and liquor flavor quality.