Predictive model of soil temperature and moisture during solarization in closed greenhouse

Soil solarization is a method of non-chemical disease control that employs solar radiation to heat the soil to temperatures that are lethal for soilborne pathogens. Application of this technique in closed greenhouses has allowed it to spread in areas characterized by temperate climate, such as the Mediterranean basin. Optimization of the technique requires knowledge of the physical processes inside the soil-mulch-greenhouse system that determine the thermal regimes in the soil. In this work, a one-dimensional physical model is developed for simulation of the temperature and moisture content in mulched soil during solarization treatment in a closed greenhouse. The model also calculates the air temperature and relative humidity inside the greenhouse. The model includes heat transfer in the soil by both apparent conduction (which incorporates transfer of latent heat by vapor movement under the influence of a temperature gradient) and enthalpy transport by liquid and vapor flow. The temperature and water content in the soil are calculated using coupled partial differential equations of heat and moisture diffusion. Furthermore, in the calculations of radiative fluxes, infinite reflections are considered. The input variables required are outside air temperature and relative humidity, outside solar radiation flux, wind velocity, soil texture and bulk density, and radiometric properties of the soil as well as of the covering and mulching films. The model is validated using data collected during a soil solarization treatment carried out in a full-scale commercial greenhouse. The results show good agreement between measured and modeled data, especially concerning soil temperature. A sensitivity analysis is also carried out in order to investigate soil temperature changes induced by variations in the radiometric properties of the films. The results show that the highest temperature changes in the soil are determined by the shortwave transmittance of the cover.