Effects of nitrification inhibitors (DCD and DMPP) on nitrous oxide emission, crop yield and nitrogen uptake in a wheat–maize cropping system
The application of nitrification inhibitors together with ammonium-based fertilizers is proposed as a potent method to decrease nitrous oxide (N 2O) emission while promoting crop yield and nitrogen use efficiency in fertilized agricultural fields. To evaluate the effects of nitrification inhibitors, we conducted year-round measurements of N 2O fluxes, yield, aboveground biomass, plant carbon and nitrogen contents, soil inorganic nitrogen and dissolved organic carbon contents and the main environmental factors for urea (U), urea + dicyandiamide (DCD) and urea + 3,4-dimethylpyrazol phosphate (DMPP) treatments in a wheat–maize rotation field. The cumulative N 2O emissions were calculated to be 4.49 ± 0.21, 2.93 ± 0.06 and 2.78 ± 0.16 kg N ha −1 yr −1 for the U, DCD and DMPP treatments, respectively. Therefore, the DCD and DMPP treatments significantly decreased the annual emissions by 35% and 38%, respectively ( p < 0.01). The variations of soil temperature, moisture and inorganic nitrogen content regulated the seasonal fluctuation of N 2O emissions. When the emissions presented clearly temporal variations, high-frequency measurements or optimized sampling schedule for intermittent measurements would likely provide more accurate estimations of annual cumulative emission and treatment effect. The application of nitrification inhibitors significantly increased the soil inorganic nitrogen content ( p < 0.01); shifted the main soil inorganic nitrogen form from nitrate to ammonium; and tended to increase the dissolved organic carbon content, crop yield, aboveground biomass and nitrogen uptake by aboveground plant. The results demonstrate the roles the nitrification inhibitors play in enhancing yield and nitrogen use efficiency and reducing N 2O emission from the wheat–maize cropping system.