Nitrogen 123 nitrogen 74 Article 49 Soils 47 China 44 Nitrogen oxides 40 nonhuman 32 Ecosystems 26 controlled study 26 Organic carbon 25 Forestry 24 Nutrients 24 Water quality 24 Ammonia 23 Carbon 23 Nitrogen fertilizers 20 biomass 20 phosphorus 20 Agriculture 19 Biomass 19 Phosphorus 19 Crops 18 human 18 Carbon dioxide 17 Climate change 17 Bacteria 16 Nitrogen compounds 16 male 16 unclassified drug 16 Fourier transform infrared spectroscopy 15