Objective  Soil is composed of particles of different sizes and shapes. The particles at all levels contain valuable information on the evolution of clay minerals. The composition and evolution of clay minerals would contribute to understand the development degree and fertility level of soil, which will provide a theoretical basis for rational utilization of the soil resources in the West Liaohe River plain.

  Method  The chestnut soil and saline soil in the West Liaohe River plain were selected as the research object. Soil particles in different sizes (< 2, 0.45-2, 0.1-0.45 μm) were separated from the surface soil. X-ray diffraction (XRD) and chemical analysis were used to study the composition of clay minerals and related soil indices.

  Result  The XRD results showed that the mineral compositions of the clay particles in chestnut soil and saline-alkali soil were mainly illite, vermiculite and chlorite, with a certain amount of kaolinite and illite-montmorillonite mixed-layer mineral in chestnut soil and a certain amount of kaolinite, montmorillonite and 1.4 nm minerals in saline soil. With the decrease of the particle size in soils, the contents of chlorite, kaolinite, montmorillonite (illite-montmorillonite mixed-layer mineral) and 1.4 nm minerals decreased obviously, with the increasing contents of illite and vermiculite. There are significant differences in illite crystallinity between chestnut soil and saline-alkali soil in particles of different grain sizes. The illite crystallinity of saline soil was weeker than that of chestnut soil. With the decrease of the particle size in soil, the illite crystallinity of saline soil and chestnut soil became weeker. The chemical analysis results showed that the content of Na₂O in saline soil was higher than that in chestnut soil. The weathering degree of chestnut soil and saline-alkali soil particles increased with the decrease of particle size.

  Conclusion  The change of the components and weathering degree leads to the transition trend of clay minerals from illite to montmorillonite in the study area.