Weed Seed and Seedling Reductions by Soil Solarization by Transparent Polyethylene Sheets

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Abstract
Solarization by means of transparent polyethylene sheets for 1 week in mid-summer significantly (P = 0.05) reduced numbers of viable prickly sida (Sida spinosa L.), common cocklebur (Xanthium pensylvanicum Wallr.), velvetleaf (Abutilon theophrasti Medic.) and spurred anoda [Anoda cristata (L.) Schlect.] seeds remaining after burial in soil. Solarization treatments for 1 to 4 weeks significantly reduced the total weed emergence of prickly sida, pigweeds (Amaranthus species), spurred anoda, morningglories (Ipomoea species), horse purslane (Trianthema portulacastrum L.), and various grass species from natural seed populations for the growing season by 64 to 98%. Purple nutsedge (Cyperus rotundus L.) emergence was increased by solarization in some instances. It was not determined if the increased emergence was from tubers or seeds. Maximum temperatures at the 1.3-cm soil depth under the polyethylene sheets reached 65 to 69C for 3 to 4 h of the mid-afternoon on clear days as compared with 43 to 50C at 1.3 cm in the soils that were not covered. Surface soil-moisture levels were also elevated under the polyethylene covers. Although solarization did not eliminate dormant weed seeds from the germination zone, the treatment killed nondormant seeds and greatly reduced the number of weed seedlings that otherwise would have emerged.