Comment on essd-2022-263

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> China ranks in the highest position for nitrogen (N) fertilizer consumption in the world. Although N fertilizer use has greatly contributed to the China's food production, this has also caused an unprecedented alteration in the biogeochemical cycles and endangered terrestrial and aquatic ecosystems. Existing use of N fertilizers in China, as shown by digital maps, is usually coarse in resolution and intermittently covered with a biased gridded dataset. Here, we have reconstructed a historical, annual N fertilizer use dataset in China and resampled it to <span class="inline-formula">5 km×5 km</span> resolution, covering the period from 1952 to 2018 by integrating improved cropland maps. Results showed that most of the N input was directly applied as N-only fertilizer, while the contribution from compound fertilizers has ranged between 16 % and 24 % since 1980. The national total N fertilizer input increased from 0.06 Tg N yr<span class="inline-formula">^−1</span> (0.05 g N m<span class="inline-formula">^−2</span> yr<span class="inline-formula">^−1</span>) in 1952 to 31.15 Tg N yr<span class="inline-formula">^−1</span> (18.83 g N m<span class="inline-formula">^−2</span> yr<span class="inline-formula">^−1</span>) in 2014 and then decreased to 28.31 Tg N yr<span class="inline-formula">^−1</span> (17.06 g N m<span class="inline-formula">^−2</span> yr<span class="inline-formula">^−1</span>) in 2018. Despite the total N input decreasing by 9.1 % (2.84 Tg N yr<span class="inline-formula">^−1</span>) from 2014 to 2018, the N input from compound fertilizers has increased by 6 % (0.43 Tg N yr<span class="inline-formula">^−1</span>) during the corresponding period. The previous Food and Agriculture Organization (FAO) data-based N fertilizer products in China overestimated N use in low cropland coverage areas but underestimated N use in high cropland coverage areas. However, our newly reconstructed data have not only corrected the existing biases and improved the spatial distribution but have also shown that vegetable and other crops (e.g., orchards), but not grain crops, are the most intensively fertilized crops in China, implying the importance of quantifying greenhouse gas (GHG) emissions from these croplands. We argue that the reconstructed, spatially explicit N fertilizer use data in this study are expected to contribute to better understanding of biogeochemical cycles, including the simulations of GHG emissions and food production in China. The spatially explicit N fertilizer use and the crop-specific N fertilizer use datasets are available via an open data repository (<a href="https://doi.org/10.6084/m9.figshare.21371469.v1">https://doi.org/10.6084/m9.figshare.21371469.v1</a>; Yu, 2022).