东北黑土区和东北典型黑土区的范围与划界

Delineating the black soil region and typical black soil region of northeastern China

东北是我国重要的粮食基地,但该区土壤侵蚀和土地退化有日益严重的趋势,因此近年来保护黑土的呼声越来越大.为了制定精准保护黑土的规划,需要准确的边界划定.本文目的是界定东北黑土区的内涵,定量划定东北黑土区的边界,落实黑土区包括的县级行政区.划定方法是以土壤发生学分类的黑土、黑钙土、栗钙土和灰色森林土作为黑土区的标志土壤,将其集中分布区划为黑土区;以黑土和黑钙土作为典型黑土区的标志土壤,将其集中分布区划为典型黑土区.这些土壤大多都属于中国土壤系统分类中的均腐土(Isohumosols),或美国土壤系统分类中的软土(Mollisol),具有明显的“暗沃表层”黑土特征,同属“黑土”系列.在ArcGIS10.2软件中,用“中心引力集聚法”反复迭代,合并或舍弃边缘小图斑,形成完整的东北黑土区和东北典型黑土区.划分结果如下:东北黑土区的面积为55.6万km2,涉及146个县级行政区.东北典型黑土区的面积为33.3万km2,涉及138个县级行政区.黑土区内坡度大于0.25°的农地存在水土流失问题,是水土流失的重点防治对象,面积为8.9万km2.典型黑土区内坡度大于0.25°的农地,是水土流失的优先防治对象,面积为7.8万km2.结果可为黑土区生态文明建设特别是水土保持规划提供重要科学依据.

The black soil region in northeastern China is one of the most important grain production areas in the country,and plays a key role in food security.Large lands have been brought into cultivation in the last 100 years.Because these lands have lesser slope gradients compared to those in the loess plateau and other regions in China,soil erosion has been ignored in this area for a long time.Few soil conservation practices have been implemented.Serious soil erosion problems due to long slope lengths have been identified based on recent research and observations in the study area.The government has realized the necessity and urgency of soil conservation.However,to create policies and plans for black soil conservation,questions such as how much of the black soil region,and where in the region,erosion is a problem must be addressed.Currently,the black soil region of northeastern China is regarded as having a total area of 1.09 million square kilometers,including Heilongjiang,Jilin,the north part of Liaoning,and the east part of Inner Mongolia,in which there are also many non-black soils in mountain regions of Daxingan,Xiaoxingan,and Changbaishan.Therefore,it is difficult to determine precisely the conservation priorities for this large area.In this study,the black soils were defined and their concentrated area was delineated in northeastern China.The black soils were defined as soils with the“mollic epipedon”,which were classified as Isohumosols in Chinese Soil Taxonomy or Mollisols in the USDA Soil Taxonomy,and classified as Phaezoems,Chernozems,Kastanozems and Grayzems soils according to the Genetic Soil Classification of China(GSCC).The region dominated by these four soils in GSCC was defined as the black soil region.Because Phaezoems and Chernozems have higher organic matter contents and deeper mollic epipedon depths,and are distributed in the center of the study area,these two soils were defined as the typical black soil,and their dominate area was defined as the typical black soil region.A soil map in the scale of 1:1000000,made from the second national soil survey,was used with ArcGIS 10.2 software to delineate both black soil and typical black soil regions.A method called“central gravitational agglomeration”was developed.All of the soil polygons were selected,and the farthest and the smallest polygon were merged into its closest adjacent one if its radius was larger than the distance between it and its closest one.Otherwise it was abandoned.The same process was repeated until only a few small polygons were left and a regional outline appeared.Four soils were used to determine the exact boundaries of the black soil region,and two soils were used to determine the exact boundaries of the typical black soil region.The results showed that the area of the black soil region was 556000 km2,including 146 counties in which 33.0%was cultivated land.The area of the typical soil region was 333000 km^(2),including 138 counties in which 50.2%was cultivated land.Due to the long slopes,the soil erosion rate from the cropland with slope greater than 0.25°is estimated to be larger than soil loss tolerance of 200 t/km2.The cultivated lands with slope greater than 0.25°were regarded as sloped cultivated land or sloped cropland,which totaled 89000 km^(2),or 16.0%of the total land for the black soil region,and 78000 km^(2),or 23.4%of the total land for the typical black soil region.The sloped cultivated land in both the black soil region and typical black soil region should be targeted as key areas for soil erosion control in northeastern China.