Background
Soil solarization, in the words of the author, "is a method of heating the soil by using polyethylene sheets as mulching over moistened soil, to retain solar radiation during the hot season," so that "soil-borne pathogens may be killed by lethal heat (>40°C) and weakened by sub-lethal heat (<38-40°C) to the extent that they are unable to cause damage to plants or they are more susceptible to chemical toxicants," which technique "has been successfully used to control soil-borne pathogens and weeds (Katan et al., 1976; Mahrer, 1979; Grinstein et al., 1979; Katan, 1981; Mahrer et al., 1984; Avissar et al., 1986; AL-Karaghouli et al., 1990; AL-Kayssi and AL-Karaghouli, 1991)."

What was done
AL-Kayssi conducted a laboratory experiment where "clay soil samples infested with Verticillium dahliae were exposed to different CO2 concentrations (350, 700, 1050, 1400, 1750 ppm air) and incubated in hot water baths at 35, 40, 45, 50 and 55°C," while "field plots were exposed to the same CO2 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)."

What was learned
The Iraqi researcher reports that higher than normal CO2 contents in the soil increased maximum soil temperatures while reducing the length of time required to kill 90% of the propagules of V. dahliae in natural field soil with moisture content at field capacity. As an example, he notes that this killing time parameter in soil heated to 35°C was reduced from 24 days at the normal ambient CO2 concentration to 15 days at 1750 ppm CO2; and he states that sub-lethal soil temperatures were raised to lethal levels as the soil's CO2 content was raised.

What it means
In a high-CO2 world of the future, soil solarization should become an even more viable method of controlling soil-borne pathogens and weeds than it is today.

References
AL-Karaghouli, A.A., AL-Kayssi, A.W. and Hasson, A.M. 1990. The photometric properties of different colored plastic mulches used for soil solarization. Solar and Wind Technology 7: 119-123.

AL-Kayssi, A.W. and AL-Karaghouli, A.A. 1991. Influence of different colored plastic mulches used for soil solarization on the effectiveness of soil heating. Soil Solarization 109: 297-308.

Avissar, R., Mahrer, Y., Margulies, L. and Katan, J. 1986. Field aging of transparent polyethylene mulch: I. Photometric properties. Soil Science Society of America Journal 50: 202-205.

Grinstein, A., Orion, D., Greenberger, A. and Katan, J. 1979. Solar heating of the soil for the control of Verticillium dahliae and Pratylenchus thornei in potatoes. In: Shippers, B. and Gams, W. (Eds.), Soilborne Plant Pathogens. Academic Press, London, UK, pp. 431-438.

Katan, J. 1981. Solar heating (solarization) of soil for control of soilborne pests. Annual Review of Phytopathology 19: 211-236.

Katan, J., Greenberger, A., Alon, H. and Grinstein, A. 1976. Solar heating by polyethylene mulching for the control of diseases caused by soilborne pathogens. Phytopathology 66: 683-688.

Mahrer, Y. 1979. Prediction of soil temperatures of a soil mulched with transparent polyethylene. Journal of Applied Meteorology 18: 1263-1267.

Mahrer, Y., Naot, O., Rawitz, E. and Katan, J. 1984. Temperature and moisture regimes in soils mulched with transparent polyethylene. Soil Science Society of America Journal 48: 362-367.