A predictive model for soil temperature during solarization and model validation at two California field sites

Soil solarization is a non-chemical alternative to fumigation whereby moist soil is covered with transparent plastic tarp, resulting in passive solar heating of the soil and reduction of weed, pathogen, and nematode inocula. Soil is typically solarized for four to six weeks during summer, when many crops are produced. Scheduling solarization to work in crop cycles and the uncertainty of the results, relative to soil fumigation, are current limitations. The overall goal of this study was to address these limitations through the development and validation of a heat transfer model to predict soil heating during solarization and thereby increase the predictability and flexibility of the process. A one-dimensional heat transfer model was developed to predict solarized soil temperatures and was validated with four weeks of data collected at depths of 5 and 15 cm for two field sites in California. The results showed that 90% to 100% of temperature predictions were within 10% of measured values, and the maximum absolute error was 3.9°C at 5 cm and 2.7°C at 15 cm. This model was very sensitive to changes in the air gap thickness between the soil surface and plastic tarp, with values of 0.6 and 0.3 cm found to minimize model error for the two field sites, indicating that this may be a site-dependent parameter. Overall, the model predicted 38 to 657 MJ m^-2 and 20 to 568 MJ m ^-2 as ratios of cumulative soil heat flux to incident solar radiation for the two field sites.