Since approximately 1976, soil solarization has been implemented in order to address the continuous cropping damage and soil blight in farmlands, and many methods have been considered. We evaluated the effect of soil sterilization because soil borne pathogens been shown to perish over elapsed times at a more-than-specific temperature at the spot stage. As for soil temperature, however, it is thought that the sterilization effect cannot be evaluated in the elapsed time due to greatly changing weather conditions during the processing period. Therefore, the positive heat-load index, which includes the heat capacity of soil's temperature rise, was proposed for the construction of a model for the sterilization effect factor with multiplication-level quantity for the rise in soil temperature above the constant temperature. This study examined the method of estimating the modeling of the solar-heating load index in order to determine the land criteria for soil solarization.
The solar-heating load index (SHLI(°C・hrs)), which indicates the effect of soil solarization, provided the model that could be estimated from the daily maximum soil temperature during a sterilization period (τ). The model is defined by the following equation:
SHLI = AΔTB ΔT = Tsmax－Tc
where A and B are constant, Tsmax is the daily maximum soil temperature (°C), and Tc is 40
°C, based on the literature.
Constant A showed a tendency to increase linearly as the measurement depth of the soil temperature increased, while constant B did not show any change in difference regarding the measurement depth of the soil temperature. Therefore, the SHLI that incorporated the measurement depth of the soil temperature is expressed by the following equation.
SHLI=(0.0746×Dr+0.7317)ΔT(0.0033×Dr+1.5878)
where Dr is the measurement depth from the surface of the ground (cm).
Our findings showed that when the SHLI of the soil solarization period exceeds 500 °C・hrs, there is little evidence of the onset of common scab of potato.
