Residual effects of surface applications of organic matter and calcium salts on the subsoil of a red-brown earth

The effects of surface soil applications of organic matter and calcium salts on the subsoil (200-280 mm) of a red-brown earth (Natrixeralf) were investigated in a field experiment. The calcium treatments included gypsum, lime or nil-calcium added to the surface soil. To these calcium treatments, organic matter or nil-organic matter was added. Three years after final applications of organic matter and calcium salts to the surface soil, the physical and chemical properties of the subsoil were measured. The bulk physical measurements of the subsoil (penetrometer resistance, bulk density, macroporosity and plastic limit) were not significantly influenced by the treatments. The electrical conductivity of the subsoil was greater in the gypsum-treated soil than in the lime- or nil-calcium-treated soils. Subsoil pH values were lower in the gypsum-treated soil than in the lime- or the nil-calcium-treated soil. Dispersion (spontaneous and mechanical) of the clay subsoil decreased with gypsum-treated surface soil. In treatments where both organic matter and gypsum were added to the surface soil, the subsoil showed an increased concentration of exchangeable calcium and decreased spontaneous dispersion of the clay.