Effects of Solarization on Soil Weed Seed Populations

Clear and black polyethylene mulches were placed over raised seed beds in four studies during a 3-yr period. At intervals during treatment times of up to 12 weeks, soil samples were taken and the recovered seed were tested for germination. The number of seed killed and depths to which they were killed varied with species. The study included natural seed populations of annual bluegrass (Poa annuaL. ♯3POAAN), barnyardgrass (Echinochloa crus-galli(L.) Beauv. ♯ ECHCG), annual species ofCyperus, dayflower (Commelina communisL. ♯ COMCO), and goosegrass (Eleusine indicaL. Gaertn. ♯ ELEIN). After 40 days exposure under clear mulch, seed of dayflower were killed to a depth of 11 cm. Under the same conditions, seed of annualCyperussedges and barnyardgrass were killed only in the upper 3 to 4 cm. After 3 weeks under clear plastic, germinable seed of goosegrass were recovered only at depths greater than 5 cm. Seed in plots under clear polyethylene mulch were killed more quickly than those in plots covered with black polyethylene mulch.