To provide a method for improving the soil, by giving immunity and resistance against pathogenic bacteria to the soil, so as to make the soil sound.

Sterilization and disinfection of the soil is realized by utilizing characteristics, such as safety, absorption, moisture retention, airtightness, and air permeability, of a composite covering sheet (composed of pulp, chitin chitosan, starch, carbon, and diatomite), and further by utilizing other characteristics of a kind of carbon (Bincho charcoal or hard charcoal) formed at 1200-1300°C or another kind of carbon (coconut shell charcoal or bamboo charcoal) formed at 700-800°C, so that the soil absorbs the sunshine, the absorbed sunshine is spread as reradiated heat of infrared rays, and the ground temperature is increased (up to 70-80°C), held, and maintained.