Investigating the effects of soil porosity, soil water content and CO2 application on soil solarization in greenhouses

The recognition of using solar energy for soil solarization in protected agriculture is gaining ground as the ecological awareness of the public has increased. The primary effect of solarization is to increase soil temperature. Determination of soil thermal properties is important the storage and movement of heat in soils in regard to effectiveness of solarization. The effect of tillage, soil water content and carbondioxide application on soil solarization effectiviness as thermal diffusivity and volumetric heat capacity of solarized soils was investigated through an experiment conducted in greenhouses. This study was carried out in two glass greenhouses (SERA-1, SERA-2) in the Research Field of Agricultural Structures and Irrigation Department, Faculty of Agriculture, Çukurova University Adana, and in a plastic greenhouse (SERA-3) at Kazanlı town of Mersin, Turkey, during 2004 to 2005. Four different treatments of solarization were tested: (+İS) tillaged; (+İSCO2) tillaged and CO2 was applied; (-İS) none tillaged; (-İSCO2) none tillaged and CO2 was applied. Solarization was applied on individual plots of 2m×2m size using transparent polyethylene mulching, 3 to 4 weeks during summer time. Soil water status was monitored with neutron gauge. Soil temperatures were recorded continuously at 15 min. intervals, measured at 5, 20 and 30 cm depths. The soil thermal diffusivity (D) was calculated using temperature data of the soils in a temperature-amplitude equation derived from the solution of the heat transfer equation. It was observed that D increased in proportion to the increasing of water content (Pv). The highest values for soil temperatures were obtained at 20 cm and 35 cm soil depths at Pv of 0.28-0.29 cm3 cm-3 and 0.31-0.33 cm3 cm-3 under clay soil conditions (SERA-1 and SERA-2) while Pv were 0.13-0.15 cm3 cm-3 and 0.16-0.19 cm3 cm-3 for same depths under sandy soil conditions (SERA-3), respectively. Mean daily maximum soil temperature of solarized soil at 5 cm depth was varied between 55 °C and 57 °C under CO2 applied treatment in sandy soil. But, CO2 application has no positive effect on heat conduction through deep soil layers. In general, the ranks of the average maximum soil temperature of the treatments tested were found as +İSCO2 > +İS > -İS > -İSCO2. It was concluded that an effective soil solarization can be achieved under tillaged and high soil water content conditions. Keywords: Soil solarization, soil thermal properties, temperature, thermal diffusivity, greenhouse.