Enhanced efficiency nitrogen fertilizers (EENFs) can reduce nitrous oxide emissions and maintain high grain yields in a rain-fed spring maize cropping system

Context

Enhanced efficiency nitrogen fertilizers (EENFs) have provided opportunities for the simultaneous mitigation of nitrous oxide (N₂O) emissions and increases in crop productions. However, the practice of combining EENFs with optimal fertilization under conditions of misaligned water and fertilizer inputs in rain-fed spring maize systems remains inadequately understood.

Objective

This study aims to determine the factors controlling N₂O emissions under the soil climatic conditions in rain-fed plastic mulching cropping systems treated with different nitrogen (N) fertilization rates and EENFs, and to determine the most effective N fertilization measure to reduce N₂O emissions while maintaining crop yields.

Methods

A 3-year field experiment was conducted in a spring maize system located in the semiarid rain-fed region of the Loess Plateau, applying two types of EENFs: a nitrification inhibitor dicyandiamide (DCD) and a slow-release fertilizer (SRF). It comprised five fertilization treatments: unfertilized (CK), conventional N rate (CON, 200 kg N ha⁻¹), optimal N rate (OPT, 160 kg N ha⁻¹), OPT with the addition of DCD (OPT+DCD), and OPT using SRF (OPT-SRF).

Results

The average annual cumulative N₂O emissions over the 3-year experimental period ranged from 0.74 to 1.87 kg N₂O-N ha^–1. Fertilizer N contributed 26−60% to annual N₂O emissions. The highest N₂O fluxes (50–161 μg N₂O-N m^–2 h^–1) typically occurred within the initial 10 days following fertilization, likely induced by strong nitrification processes, constituting 12–19% of the annual N₂O emissions during this brief period. In comparison to the CON treatment, the OPT, OPT+DCD, and OPT-SRF treatments resulted in significant reductions in annual N₂O emissions of 24%, 46%, and 34%, respectively, without causing any significant decrease in maize grain yields. The application of DCD led to increased ammonium (NH₄⁺-N) concentrations while reducing nitrate (NO₃^–-N). Conversely, using SRF resulted in a decrease in both NH₄⁺-N and NO₃^–-N concentrations.

Conclusions

Using EENFs at the ideal fertilization rate significantly curtailed yearly N₂O emissions without adversely affecting maize yields in a rain-fed plastic mulching spring maize system prevalent in the Loess Plateau. Most N₂O emissions occurred post-fertilization, with rainfall events further influencing these emissions.

Implications

Our findings recommend the incorporation of nitrification inhibitors, such as DCD, as the most effective fertilizer measure for reducing N₂O emissions in the rain-fed region of the Loess Plateau.