Assistant Prof. QUAN Zhi and Prof. FANG Yunting from the Stable Isotope Ecology Research Group of the Institute of Applied Ecology at the Chinese Academy of Sciences, cooperated with researchers at the Appalachian Laboratory of the Environmental Science Research Centre of the University of Maryland in the United States, investigated three commonly used Crop nitrogen use efficiency quantification approaches and explained why they lead to different estimate values.

Crop nitrogen use efficiency (NUE) refers to the proportion of nitrogen in fertilisers that is absorbed and used by crops, which is an important indicator to evaluate fertiliser utilisation efficiency and environmental impact of nitrogen input in farmland. However, different NUE quantification approaches produce quite different NUE values, which is not conducive to comparison between different studies.

The definition of N input is different. The nitrogen difference approach (NUE_diff) and the ¹⁵N tracer approach (NUE_15N) only consider fertiliser N, while the nitrogen balance approach (NUE_bala) considers all N input, including N input from atmospheric deposition. The NUE_diff approach and the NUE_15N approach do not consider or consider less about "the residual effect of N in the soil" (the fertiliser N remained in the soil will be used by crops in the following growing season), but the NUE_bala approach put emphasis on such effect.  

The researchers analysed the national-scale farming household survey data and the field experiment data and computed NUE of cereal crops in China. The NUE values computed with the NUE_diff, NUE_15N and NUE_bala approaches were 32%, 30%, and 52%, respectively.  

Scientists discussed in detail the differences and connections between the three NUE quantification approaches, including their individual advantages and disadvantages. They recommended that an appropriate NUE quantification approach should be chosen according to specific needs and purposes, and a uniform standard must be formulated to increase comparability between studies. 

This study, funded by the National Key Research & Development Program and the National Natural Science Foundation of China, has been published in Nature Food, entitled "Different quantification approaches for nitrogen use efficiency lead to divergent estimates with varying advantages."