Characteristics of saline-alkali land and resources based on three-layer fusion of saline-alkali soil in Songnen Plain of China

Saline-alkali land has been one of the most important reserve resources for the cultivated land in China. Rational and efficient utilization of land source is of great significance to the national food security in recent years. In this study, a systematic framework was constructed to classify the saline-alkali land resources, according to the key belt of the earth. Three layers were firstly fused, including the utilization, the soil, and discrete-element modeling (DEM) layer. The specific types were then defined to determine the saline-alkali land and soil. Furthermore, the GIS overlay analysis was implemented to acquire the land use status, the soil, and DEM maps for the characteristics of saline-alkali land resources in Songnen Plain. Finally, the three-layer fusion system was verified in the saline-alkali land. The results showed that: 1) The improved three-layer fusion system of saline-alkali land resources was achieved with the three-dimensional space as the organizing and connecting link to all levels. The digital elevation was also served as the base, according to the vertical and horizontal latitudes in the Earth's critical zone. An accurate classification was clearly defined as the regional characteristics of saline-alkali soil and land resources; 2) The soil types of saline-alkali soil included 6 categories: saline-alkali cultivated land, forest land, grassland, wetland, wasteland, and other saline-alkali land; The simple saline-alkali soil was belonged to three types: saline, alkaline, and saline-alkaline soil; 3) The data superposition showed that the total area of the saline-alkali land was 2.547 7 million hm2 that concentrated in the west of the study area. Wherein the largest area of saline-alkali farmland was 0.965 5 million hm2 mainly located in the southern Tongyu County. The saline-alkali wasteland, grassland, wetland, and other saline-alkali land were found with the area of 0.640 90, 0.473, 0.322 9, and 0.083 million hm2; respectively. In addition, the largest areas of saline-alkali, alkaline, and saline soil were 1.996 5, 0.439 3, and 0.111 9 million hm2. 4) The elevation of saline-alkali cultivated land was in the range of 100-200 m. A gradual increase of the elevation was observed from the middle to the surrounding area. The relatively gentle slope was concentrated below 6°. The pattern of slope gradually increased from the west to the east. By contrast, the saline-alkali unused land was mostly distributed in the southern, with the altitude in the range of 100-150 m. Most of the slopes were below 2° in the saline-alkali unused land, indicating the low terrain, slow slope, and excellent development conditions. Consequently, a saline-alkali land system can be expected to accurately characterize the saline-alkali land resources, and then to clarify the concept and relationship between saline-alkali land and soil. This finding can provide the theoretical and methodological reference to determine the saline-alkali land resources for the rational development, particularly for the Third National Soil Census on the saline-alkali land in Songnen plain.