Yingxia Liu defends PhD-thesis on statistical analysis and modelling of crop yield and nitrogen use efficiency in China

20 May 2022

Nitrogen fertilizer applied as a base fertilizer before sowing in Zhejian province, China. Photo credit: Jinchuan Ma.

On May 19, PhD candidate Yingxia Liu successfully defended her thesis about statistical analysis and modelling of crop yield and nitrogen use efficiency in China. Yingxia’s research was co-supported by Wageningen University and Research (WUR), ISRIC – World Soil Information and the Chinese Academy of Agricultural Sciences (CAAS).

The challenge addressed by this research is that applying nitrogen fertilizer has contributed to a large increase in yield from the world’s food production, but also introduces environmental risks. In order to achieve maximum yield, farmers tend to apply more nitrogen than needed. Excessive application of nitrogen contributes to soil acidity, greenhouse gas emissions and eutrophication of surface waters. Globally, China applies the highest rate of nitrogen for agriculture.

                     A figure from the introductory section in Yingxia’s thesis

Yingxia’s research analyzed and explained space-time patterns of crop yield and nitrogen use efficiency in China at two spatial scales, provincial and county level, for supporting the development of effective strategies and policies about nitrogen application. 

“There are large spatial and temporal variation of crop yield and nitrogen use efficiency at both provincial and county scales,” said Yingxia.

You can watch the recording of Yingxia's defense here and access her full thesis publication here.  For more information about her thesis, please contact Yingxia via the email address at the bottom of this news item.

                     A figure from Yingxia’s thesis

Advisors of this research were ISRIC senior researcher and special professor in pedometrics and digital soil mapping at Wageningen University and Research Prof. Dr. Gerard Heuvelink, ISRIC senior scientist specializing in soil and land degradation assessment and restoration Dr. Zhanguo Bai and professor at the Institute of Agricultural Resources and Regional Planning (IARRP) in the Chinese Academy of Agricultural Sciences (CAAS) Prof. Dr. Ping He.

“Yingxia’s thesis is innovative in that it analyzes a large national agronomic dataset using advanced statistical and geostatistical methods, and reveals valuable spatio-temporal patterns informative to policy and decision making” said Gerard.

“The results of the thesis could be helpful to redistribution of chemical fertilizer application among the regions under the national policy of ‘Zero Growth in Chemical Fertilizer Use by 2020,’” said Zhanguo.

After completing her PhD, Yingxia started a post-doctoral position with the Institute of Environment, Resource, Soil and Fertilizer of the Zhejiang Academy of Agricultural Sciences. She will work on projects addressing non-point source pollution and inorganic fertilizer substitution.

Access Yingxia's thesis here: https://edepot.wur.nl/565336