Distributions Of Rock Fragments And Their Impacts On Soil Water Properties In Purple Soils

Rock fragments are the coarse fraction (>2 mm) in soil, which widely exist in hilly purple soils of Sichuan basin. The presence of rock fragments modifies the soil physical and chemical properties, as well as the agronomical characteristics, and restricts a series of soil process. The previous researches on purple soils neglected the properties of rock fragments, the distributions of rock fragments, and the influence on soil physical and chemical properties. Utilizing representative purple soils (red-brown purple soils, brown purple soils, grey-brown purple soils and coarse dark purple soils) in Sichuan basin, we researched the properties, the spacial distributions, and the influences of rock fragments on water retention ability, water infiltration and water evaporation. The main results were as followed:(1) There were dissimilarity for the mineral components, chemical compositions and physical properties of different lithological rock fragments, and the rock fragments had definite distribution rules in soil, soil profiles and slope positions. The clay minerals of purple rock fragments contained the mica primarily (50-90%), the next were the kaolinite and the chlorite. The chemical elements of purple rock fragments contained much SiO₂(average content > 60%), the next was Al₂O₃; The Fe₂O₃, MgO, MnO contents were relatively stabilization, while the variation of CaO and TiO₂ contents were bigger. The average bulk densities of those rock fragments were: rock fragments in coarse dark purple soil>rock fragments in grey-brown purple>rock fragments in red-brown purple soil>rock fragments in brown purple soil; The saturation moisture contents and the field capacities of all rock fragments were 2.42-4.57% and 2.13-4.28%, respectively; and rock fragments in red-brown purple soil >rock fragments in brown purple soil > rock fragments in grey-brown purple>rock fragments in coarse dark purple soil. In the course of whole dehydration (0³0 kpa), the rock fragments in grey-brown purple soils released the most water; and those in coarse dark purple soils released the least water. In purple soils, the total rock fragments contents ranged from 5.27% to 57.78%, and coarse dark purple soil>brown purple soil >red-brown purple soil >grey-brown purple. The relative contents of medium rock fragment (2-5 mm) exceeded 50%...