Soil in China holds a lot of nitrogen, but how much exactly is debated. Researchers estimated that China's soil nitrogen storage at one meter deep is 7.4 Pg, with an average density of 0.84 kg m^(-2). Soil nitrogen is higher in the southwest and northeast, lower in the middle, and increases from arid to semi-arid zones in the north. It also decreases from cold-temperate to tropical zones in the east. Climate and vegetation play a big role in determining soil nitrogen levels in natural areas, explaining 75.4% of the variation.