Abstract
The effect of organic matter and charge characteristics on clay dispersibility of the soils from a newly reclaimed agricultural land, Hikigawa, Wakayama Prefecture, was investigated from the changes with the passage of six years. The adjacent forest soils were examined as a comparison. In 1987 the reduced plant growth in the reclaimed agricultural land was attributed to the unfavorable physical properties of the soil induced by high dispersibility of clay. However, continuous application of a great amount of organic matter to the surface layer of the reclaimed area since 1989, resulted in an increase in total carbon content by ten times in 1993 in comparison with that of 1987, and also favorable plant growth had been obtained. In addition, during those six years, for the surface layer, clay dispersion ratio had decreased from 25% to less than 10% ; other physical properties such as water-stable aggregate content, solid phase ratio and hydraulic conductivity had also been improved. Little clay dispersion after saturated by sodium ion indicated that the binding agent of clay particles was hardly-exchangeable organic matter rather than easily-exchangeable cations. In contrast, for the subsoil which remained in lower level of organic matter, such changes in physical properties as the surface soil were not observed. Charge characteristics of clay particles in the subsoil largely determined the dispersion behavior.
