Bio-manure substitution declines soil N₂O and NO emissions and improves nitrogen use efficiency and vegetable quality...

Substituting mineral fertilizer with manure or a combination of organic amendments plus beneficial soil microorganisms (bio-manure) in agriculture is a standard practice to mitigate N₂O and NO emissions while enhancing crop performance and nitrogen use efficiency (NUE). Here, we conducted a greenhouse trial for three consecutive vegetable growth seasons for Spinach, Coriander herb, and Baby bok choy to reveal the response of N₂O and NO emissions, NUE, and vegetable quality index (VQI) to fertilization strategies. Strategies included solely chemical nitrogen fertilizer (CN), 20 (M1N4) and 50% (M1N1) substitution with manure, 20 (BM1N4) and 50% (BM1N1) substitution with bio-manure, and no fertilization as a control and were organized in a completely randomized design (n = 3). Manure decreased N₂O emissions by 24-45% and bio-manure by 44-53% compared to CN. Manure reduced NO emissions by 28-41% and bio-manure by 55-63%. Bio-manure increased NUE by 0.04-31% and yields by 0.05-61% while improving VQI, attributed to yield growth and reduced vegetable NO₃^- contents. Improvement of root growth was the main factor that explained the rise of NUE; NUE declined with the increase of N₂O emissions, showing the loss of vegetable performance under conditions when denitrification processes prevailed. Under the BM1N1, the highest VQI and the lowest yield-scaled N-oxide emissions were observed, suggesting that substitution with bio-manure can improve vegetable quality and mitigate N-oxide emissions. These findings indicate that substituting 50% of mineral fertilizer with bio-manure can effectively improve NUE and VQI and mitigate N-oxides in intensive vegetable production.