Comparison of Surface Electrochemical Properties between Purple Rocks and their Derived Soils as Related to Pedogenesis

Abstract

Soil surface electrochemical properties may have an important effect on soil fertility and genesis. Few researches are available on the changes of surface electrochemical properties of purple soils during the pedogenesis. In present work, four purple rocks and their derived soils under arable, orchard, forest and grass were collected to determine surface electrochemical properties including surface specific area, surface charge quantity, surface charge density, electric field strength, and surface potential using the kinetic method. The results indicated that soil surface specific area and surface charge quantity of soils were both significantly higher than their parent rocks. There were similar trends in surface potential, surface charge density and electric field strength of soils and parent rocks, soils derived from Shaximiao Formation (J2s) and Suining Formation (J3s) were higher than those of parent rocks, whereas the reverse trends existed in Feixianguan Formation (T1f) and Penglaizhen Formation (J3p). At the same time, surface potential of soil samples collected from four sites with different land utilization, i.e., Arable, Orchard, Forest and Grass, were determined to illustrate the various trends of soil electrochemical properties change. Under different land use patterns, the descending orders of soil surface potential in Shaximiao Formation (J2s) and Suining Formation (J3s) were both as follows: orchard > forest > arable > grass; the order in Feixianguan Formation (T1f) and Penglaizhen Formation (J3p) were as: orchard > forest > grass > arable. On the other hand, the value of soil surface charge quantity was increased with clay content and soil acidity because of the intensive physical weathering and slight chemical weathering. Therefore, the surface electrochemical properties may have some agreements with the weathering extent of the purple soils. Soil surface potential, surface charge quantity, surface charge density, electric field strength, and surface specific area could be employed as reference criteria for pedogenesis of purple soils.