Residual effects of slow-release nitrogen fertilizer application during the wheat growing season on N₂O emission in soybean under co-elevated atmospheric CO₂ concentration and temperature

Farmland N₂O emission is a hot topic in current climate change research. Climate change (elevated CO₂ concentration and increased temperature) and farmland management measures are the key factors affecting N₂O emission in soil. Slow-release fertilizers are considered to have a positive effect on reducing N₂O emissions. It is unclear how the interaction between climate change and slow-release fertilizers would affect N₂O emissions, thus we innovatively combined the local two crop cultivation model to investigate the potential impact of applying slow-release fertilizers on soil N₂O emissions during the growing season of subsequent crops under celevated CO₂ concentration and increased temperature. In this study, two air temperatures (ambient temperature and ambient temperature +2℃) and two CO₂ concentrations (400 μmol mol⁻¹ and 600 μmol mol⁻¹) were set in the controlled chambers. Two types of fertilizers (conventional urea and slow-release urea) were applied during the wheat season under various environmental treatments in the wheat soybean rotation system, and no fertilizer was applied during the soybean growing season. CK referred to the ambient environmental CO₂ concentration and temperature simulated in the controlled chamber (the ambient environmental CO₂ concentration in this experiment was 400 μmol mol⁻¹, and the environmental temperature was controlled by the intelligent control system to be consistent with the external environment). N₂O emission during the whole growth period of soybean season, the contents of soil ammonium nitrogen and nitrate nitrogen, and the activities of enzyme involved in nitrification and denitrification at drumming stage and ripening stage in soybean-grown soil were measured. The results indicated that N₂O emissions in soybean-grown soil were mainly concentrated in the later growth period of soybean. Compared with the application of conventional urea, the application of slow-release fertilizer in wheat-grown soil reduced the total N₂O emissions by 38.46% in soybean growth period under increased temperature (ET) alone, while the application of slow-release fertilizer increased the total N₂O emissions in soybean-grown soil by 80.76%, 82.75%, and 11.96% under CK, elevated CO₂ concentration (EC) alone, and co-elevation of atmospheric CO₂ concentration and temperature (ECT) treatments, respectively. Compared with CK treatment, ET accelerated the conversion of ammonium nitrogen to nitrate nitrogen in soybean-grown soil at filling stage, thereby promoting nitrate reductase activity and increasing N₂O emissions. In addition, EC alone had no effect on N₂O emissions in soybean-grown soil compared with CK treatment. ECT resulted in a slight increase in nitrate and ammonium nitrogen content in soybean-grown soil compared with CK treatment, which mainly attributed to the increase in nitrate reductase activity that might promote N₂O emissions, but there was no significant difference in N₂O emissions in soybean-grown soil when ECT compared with ET under conventional urea. In conclusions. N₂O emission will not increase with elevated CO₂ concentration alone. N₂O emissions will increase under elevated temperature in the future, and the rational application of slow-release fertilizer in wheat-grown soil can increase the available nitrogen content in the soil, thus reducing N₂O emission in soybean-grown soil. Our study highlights that slow-release fertilizer hold a greater potential of reducing N₂O emission under climate change scenarios.