Trade-offs between agronomic and environmental benefits: A comparison of inhibitors with controlled release fertilizers in global maize systems

Context or problem

The application of enhanced efficiency fertilizers (EEFs) is widely considered as an effective approach to decrease reactive nitrogen (Nr) losses and improve crop yield. Although the effectiveness of EEFs is influenced by soil properties and management practices, the main drivers on global maize (Zea mays L.) systems are still unclear.

Objective or research question

The aims of this study were to: (i) determine the effectiveness of EEFs on maize productivity, nitrous oxide (N₂O) emissions, ammonia (NH₃) volatilization, and nitrate (NO₃^-) leaching; (ii) explore the EEFs efficacy under different management and environmental factors; and (iii) estimate the economic and environmental costs of the maize production system under different fertilization treatments.

Methods

The responses of maize productivity and Nr losses to EEFs were determined based on the data from 191 studies (1039 pairs of observations) worldwide using meta-analysis. Five types of EEFs include nitrification inhibitor (NI), urease inhibitor (UI), double inhibitors (NIUI), controlled release urea (CRU), and controlled release bulk blending fertilizer (CRBF). The major drivers regulating EEFs efficacy were analyzed by random forest analysis.

Results

The EEFs significantly increased maize grain yield, N uptake, and N use efficiency (NUE) by 8.5 %, 11.6 % and 35.8 % compared to urea alone, respectively. The UI was most effective at increasing maize yield (by 11.0 %) and CRU was most effective at improving NUE (by 43.2 %). The UI decreased NH₃ volatilization by 46.0 % across all EEFs, whereas NI and NIUI were most effective at reducing N₂O emissions (by 45.9 %) and NO₃^- leaching (by 45.3 %), respectively. The effects of EEFs on maize yields and Nr losses were most dependent on soil pH, soil organic carbon (SOC) content, soil texture, and annual precipitation. Inhibitors performed better when they were incorporated, and the suitable fertilizer placement for CRU and CRBF were banded. Lower total economic and environmental costs occurred when applying EEFs relative to urea alone, which was attributed to the environmental benefits.

Conclusions

Inhibitors and CRU reduced urea usage while maintaining maize yields relative to urea alone, and inhibitors decreased environmental costs over CRU, especially UI and NIUI. The yield-increasing effects were more significant when inhibitors were applied in neutral or alkaline soils, while CRU was more effective in soils with low total N.

Implications or significance

The EEFs should be used with appropriate management practices targeting different environmental conditions to strike a balance between pollution reduction and crop productivity improvement.