The application of nitrogen (N) fertilizer in farmland can significantly increase crop yields. But excessive application of nitrogen may decrease nitrogen utilization efficiency, increase nitrogen losses and cause environmental pollution. Quantifying the fate and use efficiency of nitrogen fertilizers is essential for nitrogen fertilizer management in farming systems.

In order to achieve sustainable food production, researchers have developed different farming management regimes to increase crop yields and nitrogen use efficiency, and reduce environmental pollution caused by nitrogen losses. However, the fate and use efficiency of fertilizer nitrogen vary greatly across soil-climate regions and are affected by farming management regimes. Understanding the global and regional differences in nitrogen use efficiency and the factors controlling them can help us better manage nitrogen fertilizer application, improve resource utilization efficiency, and reduce environmental pollution caused by nitrogen losses. 

In view of this, Project Associate Researcher QUAN Zhi and Prof. FANG Yunting from the Institute of Applied Ecology (IAE) of the Chinese Academy of Sciences, and Associate Professor ZHANG Xin from the Environmental Science Center of the University of Maryland in the United States, conducted a meta-analysis of literature investigating the fate of nitrogen fertilizer in corn production systems. 

The researchers extracted a total of 366 observation data from 74 research papers that conducted field ¹⁵N tracer tests. They examined regional differences in the fate and used efficiency of fertilizer nitrogen in conventional farming systems, and analyzed the impacts of different corn field management options.  

They found that, an average of 41% of the fertilizer nitrogen applied to the corn systems is absorbed by crops during the current season, 31% remains in the soil, and 28% is lost (into the water body and the atmosphere). The absorption and utilization of nitrogen by crops show obvious regional differences, with significantly higher use efficiency in European and American countries (42-54%) than in China (33%).

The researchers believed that the lower nitrogen use efficiency in China may be related to the lower soil organic matter content. 

They also found that deep application of nitrogen fertilizer and multiple applications of nitrogen fertilizer can significantly increase corn yield, nitrogen uptake and nitrogen use efficiency, and reduce nitrogen losses. 

This research helps increase understanding of the fate of nitrogen fertilizer in natural and farming systems, and provides a solid scientific basis for improving nitrogen fertilizer management in farming systems. 

It was funded by the National Key Research and Development Program of China, the National Natural Science Foundation of China and the Liaoning Revitalization Talents Program. The results have been published in the journal Earth's Future entitled "Fates and use efficiency of nitrogen fertilizer in maize cropping systems and their responses to technologies and management practices: A global analysis on field ¹⁵N tracer studies." 

Fig. 1. Global distribution sites of field ¹⁵N tracer experiments conducted in corn production systems (Image by QUAN Zhi)

Fig. 2. Global and regional differences of the fate of nitrogen fertilizer in conventionally managed corn fields (field ¹⁵N tracer tests) (Image by QUAN Zhi)