Spatial Pattern Evolution Of Soybean In Heilongjiang Province

Under the impact of genetically modified soybean,the planting area of soybean in China has fallen sharply.Research on the traditional soybean spatial pattern and dynamic changes in the main soybean producing areas is of great significance to China's soybean import and export trade and safeguarding national food security.With the Landsat TM/OLI remote sensing images from 1996 to 2016,this paper extracted the spatial distribution information of soybean planting in Songnen Plain using random forest?RF?method based on Remote Sensing?RS?and Geography Information System?GIS?techniques,and analyzed the spatiotemporal evolution characteristics of soybean planting structure from the area characteristics?the area features of time variation,spatial variation and transfer matrix?,structure characteristics based on the landscape pattern index(%LAND,PD,N_?i?).We further explored the spatial and temporal evolution characteristics of soybean spatial pattern in the counties?Nenjiang,Nehe,Keshan,Bei'an and Helen?of Songnen Plain in recent 20 years.The results were as follows:?1?Through comparative analysis,this study identified a pixel-based random forest algorithm as the optimal algorithm for extracting soybean spatial pattern information.The overall classification accuracy,Kappa coefficient,soybean leakage error,and cartographic precision of this method were89.14%,0.8718,1.58%,and 98.42%%,respectively.And the classification process for large-scale areas had high timeliness.?2?In the past 20 years,the soybean planting area in Songnen Plain showed a fluctuating characteristic with a turning point of 2006,which first increased and then decreased.In 2006,the soybean area was the largest,which was 4084.30×10³hm².There is a tendency to gather from the southeast,the southwest,to the northeast.From 1996 to 2000,the soybean area grew rapidly at an average annual rate of 491.41×10³hm²/a,which came from the conversion of other crops and green land.Structurally,in 1996,soybean cultivation had the least advantage and fragmentation degree;by2006,soybean planting dominance was gradually enhanced and planting was more concentrated;between 2006 and 2016,soybean planting area gradually decreased,and planting dispersal increased.?3?The total area of soybean in major soybean planting counties changed in 2006 as a turning point,which was consistent with the overall pattern of the study area.But there were differences in the area of soybean among the counties.The dynamic degree of soybean area of Nenjiang County was 7.35%from1996 to 2016,which was the fastest growing county.In the process of spatial transformation,all counties had common rules.Other crops were converted to soybeans in larger areas before 2006,while soybeans were mainly converted to other crops after 2006.In the spatial structure change of soybean,Nenjiang County was the county with the most dominant soybean cultivation,the smallest degree of soybean fragmentation,and the highest degree of aggregation.