The article is based on a long-term study of floodplain soils of the Amur River valley within the north-eastern part of the Middle-Amur Lowland. The results of field work on the soil-geomorphological profile across the Slavyansky Island, located 200 km from Khabarovsk down the Amur River, are discussed. The study analyzes the occurrence of the island's floodplain soils on riolkas[1] and their properties, with an emphasis on morphology and lithological and particle-size composition. The features of soil formation on riolkas of different genesis – alluvial and aeolian – are shown. On sandy and sandy-loam deposits of alluvial riolkas (“meadow-forest” ridges) poorly developed sod gley soils are formed. On heavy loam and clay alluvium of the “meadow“ ridges, annually flooded by river waters, sod-meadow gley soils develop under the woodreed grass stand. Sand deposits of high aeolian riolkas are characterized by a homogeneous fine-grained structure without interlayers, signs of organic matter and with a significant amount of mica. They describe poorly developed sod-forest soils under high-trunk oak forests. The formation of texture-differentiated soils on all types of riolkas was not revealed. When the floodplain reaches the position of the first terrace above the floodplain, the differences in the lithological composition and particle-size distribution, soil texture, height above the water edge and the nature of vegetation on the inherited riolkas provide a multidirectional evolution of soil formation. At the same time, the development is taking place in accordance with the zonal types of soils (sod-forest, brown-earth, texture-differentiated – soil with a bleached horizon (podbel)). The last are mainly formed on clay-loam alluvium, which can overlay not only alluvial, but also some aeolian riolkas.

[1]Riolkas are ancient, relatively high sand ridges (extended dunes) with plant cover found in Amur region (Russian Far East).