The study of soil nitrogen has long been an active field, but it was generally pivoted on agricultural and forestry production, and animal husbandry. With the rapid increase in the use of fertilizer nitrogen, more attention has been paid to the relationship between nitrogen management and environmental quality and human health. In addition, the study of soil nitrogen has become more comprehensive with the development of related sciences. The quantitative study of the processes of nitrogen cycling and their interrelationships has been an important part of this project and has attracted the attention of scientists all over the world. Nitrogen is one of the most important nutrients for plant growth and the application of fertilizer nitrogen is playing an important role in agricultural production. The annual consumption of fertilizer nitrogen in the world has reached 70 million tons, and China has an annual consumption of more than 15 million tons and is the largest fertilizer nitrogen consumer in the world. However, the efficiency of fertilizer nitrogen is low and losses are large. It is estimated that nitrogen losses from agriculture in China can be as high as 40-60% of the nitrogen applied. Some of the lost nitrogen enters the atmosphere and contributes to the greenhouse effect and some enters water bodies to pollute the water. Consequently, it is important for scientists all over the world to improve the efficiency of use of fertilizer nitrogen, to promote the biological fixation of nitrogen and to increase the nitrogen-supplying potential of soils.