Abstract: In order to explore the characteristics and the main causes of soil nitrogen mineralization in western Qilian Mountains,Gansu Prouince,China,the experiments were conducted in the grassland there utilizing the PVC pipe culture method in the field to measure the soil nitrogen and its associated physical and chemical elements.The nitrogen mineralization amount and the nitrogen mineralization rate were calculated in order to understand the main environmental variables that cause soil nitrogen mineralization.The results showed that,there were significant differences (P<0.05) in total nitrogen and pH value along with the altitude while the difference in organic matter was not significant (P>0.05).There were obvious differences in NH₄⁺-N at various elevations including 2 700 m,2 800 m,2 850 m,2 900 m,3 000 m,and 3 050 m (P<0.05),while no significant difference for NO₃^--N along with the altitude (P<0.05).(The soil nitrogen mineralization was promoted by field culture)The value of mineralization rate was following a quadratic polynomial in altitude.The impacts of physicochemical elements on the rate of soil nitrogen mineralization appeared in the sequence as follows based on descending order of influencing extent:pH value,K,NH₄⁺-N,total nitrogen,the water content,the temperature and soil bulk density.For the soil nitrogen mineralization rate,there were a significant correlation (P<0.05) with total nitrogen,K,pH value,NH₄^--N and water content as a quadratic polynomial correlation,a significant positive linear correlation with the pH value,a logarithm positive correlation with the soil bulk density,and a power function positive correlation with the soil temperature.However the correlation between the soil nitrogen mineralization rate and the latter two was not strong.The study also found that,the value ranges of the variable factors that can promote soil nitrogen mineralization were,pH value from 7.2 to 8.4,water content from 21.8% to 33.27%,and soil temperature from 4.41℃ to 8.91℃.

Key words: soil nitrogen mineralization, influence factors, correlation, grassland in western Qilian Mountains