Impact of elevated CO 2 concentrations in the soil on soil solarization efficiency

Abstract

Solarization is a method of heating moist soil by covering it with transparent polyethylene sheets to trap solar radiation. It involves the use of heat as a lethal agent for soil-borne pathogens. Soil temperature under polyethylene sheet cover is a function of incoming radiation and thermal characteristics of the polyethylene sheets and the soil. In order to study the effect of soil CO 2 concentrations on soil solarization efficiency, clay soil samples infested with Verticillium dahliae were exposed to different CO 2 concentrations [350, 700, 1050, 1400, 1750 μL CO 2 L air −1] and incubated in hot water baths at 35, 40, 45, 50 and 55 °C. Moreover, field plots were exposed to the same CO 2 levels during soil solarization in three periods [1st of July to 30th of September, 1st of August to 30th of September, and 1st to 30th of September]. Recorded temperatures of 35–55 °C during the three soil solarization periods were lethal to V. dahliae. At 35 and 55 °C, the exposure time for LD 90 was 24 days and 6 h respectively for V. dahliae with ambient soil CO 2 content. High CO 2 content in the soil resulted in increasing maximum soil temperatures and soil heat flux while reducing the time required for LD 90. The required time for LD 90 of V. dahliae in soil heated at 35 °C, reduced from 24 days with ambient CO 2 content to 15 days at 1750 μL CO 2 L air −1. Sub-lethal soil temperatures were raised to lethal levels with increasing CO 2 content in the soil. A linear “negative” relationship existed between logarithms of times required to kill 90% of V. dahliae microsclerotia and temperatures for all soil CO 2 enrichment levels. The fungus was killed in field soil solarized for the necessary time periods. It was found that the addition of CO 2 shortens the required time to kill the fungus V. dahliae during solarization and increased the activity of the sub-lethal soil temperatures. Levels of CO 2 and temperature necessary to kill the fungus are useful for evaluating the progress of soil solarization under field conditions.