Global insights into nitrogen losses and efficiency in rice, wheat, and maize cultivation

Context

Nitrogen (N) use efficiency (NUE) and N losses in cereal systems are central to achieving the United Nations Sustainable Development Goals (SDGs) on food security and environmental sustainability. However, global variations in NUE across cereals, regions, and management conditions remain poorly quantified, especially in relation to the relative roles of synthetic and non-synthetic N inputs.

Objectives

This study aimed to (i) assess global differences in NUE and N losses among maize, rice, and wheat; (ii) compare efficiencies derived from synthetic versus total N inputs; (iii) evaluate regional and temporal patterns; and (iv) identify key drivers and management implications to enhance NUE and mitigate losses.

Methods

A global dataset was assembled to calculate NUE indicators including partial factor productivity of N (PFPN), agronomic efficiency of N (AEN), recovery efficiency of synthetic N (REN-S), recovery efficiency of total N (REN-T), and the fraction of N derived from non-synthetic sources (Ndfs). Synthetic and total N losses (Nloss-S and Nloss-T) were estimated. Trends were analyzed by crops, region, and time, and drivers of N loss were identified in relation to soil and management factors.

Results

Maize showed the highest NUE metrics (PFPN: 56.9 %; AEN: 21.0 %) and REN-S (45.6 %), while rice recorded the highest REN-T (63.6 %). On average, REN-S was 17 % lower than REN-T, indicating overestimation of N losses when only synthetic N is considered. Rice exhibited the largest non-synthetic N contribution (Ndfs: 57.1 %) and the strongest legacy effect of synthetic N. Africa achieved the highest PFPN and AEN, largely due to low synthetic N inputs, and also showed improvements in NUE over time. Non-synthetic N consistently contributed more to crop uptake than synthetic N across cereals. Key drivers of N loss included synthetic N application rates, soil texture, and pH, with distinct loss pathways evident across soil types.

Conclusions and Implications

Global differences in NUE and N losses highlight the importance of crop- and region-specific management. Accounting for both synthetic and non-synthetic N inputs provides a more accurate assessment of NUE and N losses, avoiding systematic overestimation. Strategies to improve NUE should focus on optimizing non-synthetic N use, leveraging legacy effects, and tailoring practices to soil and environmental conditions. Holistic approaches—including improved irrigation and precise N placement—are essential to enhance productivity while reducing environmental impacts. Future research should prioritize region-specific solutions and sustainable integration of non-synthetic N sources to support both food security and environmental goals.