Investigations of the quantity and behaviour of variable positive charges in soils of temperate climatic zone were conducted. The experiments were carried out using sodium forms of clays separated from selected acidic soils of different origin. The clay fractions investigated possess considerable quantities of positive charge connected with mineral components surfaces. It was noted that organic matter presence leads to a considerable decrease of positive charge even when the positive charge observed after organic matter removal was rather high so the organic colloidal particles strongly block the positive charge probably by electrostatic bonds. A linear relationship between iron oxide charge and surface area was obtained.
An examination of negative charge distribution among solid soil phase components and its relations to pH of the equilibrium solution was conducted by model experiments on clays separated from selected acidic soils. It was noted that negative charge blocking by iron and aluminium oxides occurs, with the most pronounced effect in brown and podzol clays. On the basis of measured values of sample charges before and after removal of organic matter the organic matter charges were calculated to have a more linear pH dependence than that seen for natural clays. This effect is attributed to the presence of positive charges in the clays investigated.
Relations among clay particle aggregation, clay composition and the pH of equilibrium solution were studied using sedimetrical scales and sodium forms of clay fractions separated from six acidic soils of different origin. Experimentally obtained sedimentation curves were numerically extrapolated to infinite time and the mass of sediment virtually deposited was taken as a basic factor characterizing aggregation. Aggregation of investigated clays was significantly influenced by the presence of particular solid phase components i.e. organic matter, iron and aluminium compounds, which are apparently connected with their surface charges (negative and positive) and their relative amounts. A pH increase lead to a decrease of aggregation for every case investigated.