Spatio-temporal evolution of traditional soybean planting structure in Songnen Plain, China in 1996-2016

Under the impacts of genetically modified soybean, the planting area of traditional soybean in China has fallen sharply. Understanding the traditional soybean planting structure and dynamics 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, we extracted the spatial distribution information of soybean planting using random forest (RF) method based on remote sensing (RS) and geographic information system (GIS) techniques and analyzed the spatiotemporal evolution characteristics of soybean planting structure in the Songnen Plain using landscape pattern index. The results showed that the soybean planting area in the Songnen Plain was fluctuating during 1996-2016. Among the area conversion with other land-use types, the interchanges between soybean and other crop lands were the most obvious. The proportion of soybean patch area to the total crop area increased first and then decreased, while the patch density index and the resolution index decreased first and then increased. In conclusion, the spatiotemporal evolution of the traditional soybean planting structure in the Songnen Plain showed the characteristics of fluctuation in planting area, increase in fragmentation, and discrete spatial distribution. The domestic and foreign markets as well as policy guidance were the important factors afecting the traditional soybean planting structure.