Changes of physical properties and ameliorating approaches in Mollisols farmland

Mollisols in Northeast China is one of the four major black soil regions in the world, known for its high fertility and organic matter. The region is a dominant grain production base in China, playing an important role in national food security. However, due to the intensive cultivation, the structure and eco-function of Mollisols in Northeast China worsens, and its soil fertility decreases, which threatens regional food security and ecological security. The physical properties of Mollisols changed with the increased soil bulk density as well as reduction in soil porosity, water- stable aggregates and field water holding capacity. Soil structure is closely associated with soil aeration, water and fertilizer retention properties. Effective tillage and fertilization may improve soil structure to curb the trend of soil fertility decline. This paper summarizes previous studies in terms of the changes in soil bulk density, water-stable aggregates, field water holding capacity and saturated hydraulic conductivity since Mollisols' reclamation, highlights the importance of cultivation and organic fertilizer input on soil physical properties, discusses how the different conservative measures may improve soil physical properties and enhance soil fertility, and prospects the future research to optimize tillage system and organic fertilization, to optimize crop planting mode.