Nitrous oxide emissions and soil profile responses to manure substitution in the North China Plain drylands

Substituting synthetic fertilizers with manures in agriculture enhances soil properties and crop yield. However, the impact on nitrous oxide (N₂O) emissions, especially from the soil profile, remains poorly understood. This study examined emissions from 2017 to 2019 on a well-established (>10-year) maize field site in the North China Plain. Three treatments were compared: 100 % synthetic nitrogen (NPK), 50 % synthetic fertilizer N + 50 % manure N substitution (50%MNS), and 100 % manure N substitution (100%MNS). N₂O emissions were monitored for three years, and in 2019, N₂O concentrations at 20 cm and 40 cm soil depths were analyzed in relation to surface N₂O fluxes and environmental factors. The results showed manure substitution resulted in about 13.8 %-25.2 % (50%MNS) and 40.3 %-72.2 % (100%MNS) reduction in N₂O emissions over the 3-year period compared with the NPK treatment. Throughout the maize growing season, the top-dressing accompanied by rainfall was responsible for the N₂O emissions. The difference in N₂O concentrations between all the treatments at 20 cm depth was insignificant, but at 40 cm depth the N₂O concentrations were significantly higher for the 50%MNS treatment than the other treatments. The N₂O fluxes and N₂O concentration were not synchronized especially in NPK. The decoupled relationship between the N₂O fluxes and the N₂O concentration in the soil profile depth suggested the contribution of N₂O produced in the soil profile to the surface N₂O fluxes is limited. This study highlights that manure substitution is an efficient measure to reduce N₂O emissions.