Solar Heating of the Soil: Involvement of Environmental Factors in the Weed Control Process

Solar heating (SH) of wet soil by mulching it with transparent polyethylene (PE) during the hot season increased soil temperature in a typical daily course which varied with soil depth. Annual weed species responded to soil heating in the laboratory with the same pattern as under SH conditions in the field. Rhizomes of bermudagrass (Cynodon dactylonL. Pers. ♯3CYNDA) and johnsongrass (Sorghum halepenseL. Pers. ♯ SORHA) were very sensitive to heat treatment, but purple nutsedge (Cyperus rotundusL. ♯ CYPRO) tubers were able to survive temperatures as high as 80 C for 30 min. Species having big and heavy seeds or vegetative propagules were able to emerge from deep layers of soil, thus practically escaping the lethal temperature prevailing in the upper layer. Transparent and black PE mulching effectively prevented water loss from soil, as compared with perforated PE and nonmulched control. CO2concentration in the soil atmosphere under transparent PE mulching increased rapidly during the first week and reached a maximal level which was 20-fold higher than that formed in nonmulched soil. Ethylene at 0.2 ppm was detected only in a mulched soil environment. No differences in levels of CH4or CO were detected.