5. CONCLUSION

Significant changes of C, N, P content and stoichiometric ratio in plants and soil began to appear after 7 years of alfalfa planting, indicating that the 7th year was a turning point. The C:P and N:P ratios of soil and alfalfa are positively correlated. The N:P ratio increased with the growth age of alfalfa, and it exceeded 14 in 7, 9, and 10 years, indicating that the growth of alfalfa has been severely restricted by P. Alfalfa responds to the increasing N:P ratio by increasing underground biomass and decreasing aboveground biomass, while it can improve the nutrient content and biological characteristics of the soil at the meantime. Collectively, our research combines stoichiometric characteristics with alfalfa cultivation, indicating that after 7 years of cultivation, the growth of alfalfa has seriously deteriorated, but it can significantly improve the soil fertility of Mu Us Desert edge area.
ACKNOWLEDGMENTS
This research is jointly supported by the National Key Research and Development Program of China (2017YFE0104500), the China Agriculture Research System (CARS–34), Shaanxi Academy of Forestry Science and Technology Innovation Program (SXLK2020-0204).
AUTHOR’S CONTRIBUTION
Professor Yang and Professor Xin carried out the conception and design of the study, Zhouchang Yu, Yuanying Li and Ruirui Yan conducted the entire experimental study, Wei Zhang, Yi Zhou, Zhiguo Xie and Zhouchang Yu participated in the manuscript preparation and revision,Professor Yang, Professor Xin and Zhiguo Xie provided financial support for the study.