BLACK SOIL DEGRADATION AND INTENSITY IN NORTHEAST CHINA: Geochemical Indication

Based on the data of land quality geochemical survey in Northeast China, the paper analyzes the geochemical index variation in terms of degradation type of black soil, and also the decreased area of black soil nutrients and degradation intensity compared with that in the 1980s. The results indicate that the decrease of organic matter and salinization contribute to most of black soil degradation. The soil C/N values are less than 10.0 in both organic matter-deficient area and alkaline soil area. Besides, the indexes of total nitrogen(TN), total phosphorus (TP), total sulfur (TS) and soil organic carbon (SOC) show weak correlation; while the aluminum and iron oxides or indexes representing clay content and trace elements, which are easily adsorbed by these substances above, still keep the characteristics of "living community". By comparing the trace element contents in Hailun and Gongzhuling areas in different periods, the results show the contents of trace elements such as soil zinc and molybdenum have decreased significantly over the past 10 years, indicating that the TN, TP, TS and soil nutrients of manganese and zinc are lost to a certain extent during the process of organic matter loss and soil salinization. Since the 1980s, the reduction area of SOC in Songliao Plain has reached 54.45%, reduced by 131 Mt, among which 26.2 Mt is released into the atmosphere. In Heilongjiang Province where the reclamation is relatively late, the SOC decreases the most, while the SOC decreases relatively less with the reclamation degree increasing from north to south, reflecting the SOC tends to be stable constantly with the increase of reclamation degree. Through statistics and comparative study, it is concluded that the study of black soil degradation and development/protection should pay attention to not only the loss of soil nutrients caused by human activities, but also the trend of black soil becoming strongly acidic or strongly alkaline.