With the growing concern over the sustainable use of soil organic matter, it is important to know the relationship between microbial activity and the physics of soil. This study measured changes in the T-C in soil aggregate and crushed aggregate at sub-atmospheric and atmospheric pressures, following substrate incorporation, to examine the effect of decompression on microbial activity in soil. The T-C decreased rapidly in the beginning and decreased more slowly at later time stages. The decrease in T-C varied with pressure. The decrease in T-C was greatest at a gauge pressure of approximately —20 kPa. The decrease also differed between the aggregate and crushed aggregate samples. These results suggest that the chemical potential of soil water changes with decompression, affecting the vital activity of microbes. Furthermore, soil aggre-gates play an important role in this activity.
