Changes of fertility of cultivated land in Lingdong black soil zone of Hulunbuir city

Lingdong black soil zone of Hulunbuir city is located in the foothill belt in which mountainous region of Great Xingan Mountains transits to Songnen Plain.It is an important constituent of black soil area of Northeast China.Due to the long term development use and cultivation influence,soil physics properties and chemistry characters have had an obvious change;and the soil fertility degeneration has been serious.Combining with the implementation of the project 'national soil fertility investigation and its quality appraisal on cultivated land',a systematic investigation was carried out on a 681100 ha farming area using "3S" technique.Base on the same position paring comparison between the 927 soil chemistry sampling points in the second national soil survey in 1980—1982 and 1007 soil chemistry sampling points in the captioned project in 2002—2003,we carried out a systematic analysis on the present soil fertility on the cultivated land(mainly was black soil,dark brown soil and meadow soil) of Lingdong black soil zone.Result showed that soil fertility of cultivated land dramatically degenerated.All nutrient indexes except available P showed a decline tendency,among which soil organic matter,total nitrogen,hydrolyzed N and available K were dramatically declined.Throughout the past 20 years,soil organic matter,total nitrogen,hydrolyzed N and available K declined by 15.52 g/kg,0.813 g/kg,27.7 mg/kg and 64.3 mg/kg,and the percentage decline was 25.38%,26.3%,12.93% and 27.35%,respectively.However,soil available K showed a upward tendency with percentage increase being 105.83%,which related to long term P application.This indicated that anthropogenic disturbance had a significant influence on the variation of soil fertility and soil nutrient balance could be adjusted through rational effective nutrient supplement.