Abstract: Field experiments were conducted on a silty clay loam in Corvallis, OR during the summers of 1995 and 1996 to study the effects of soil solarization, spring-planted green manure crops, fumigation with metham, and combinations of these treatments on annual bluegrass seed survival. Annual bluegrass seeds were incorporated into the soil as a bioassay species and soil samples extracted to a depth of 15 cm to determine effects on seed survival. Soil solarization was applied over a 53- or 59-d period using a 0.6-mil clear polyethylene film. Soil samples were collected from four depths after the solarization period in both solarized and nonsolarized plots and surviving seeds germinated in a greenhouse. Maximum soil temperatures recorded at 5-, 10-, and 20-cm depths were 52, 47, and 33 C in solarized soil, respectively. Solarization reduced annual bluegrass seed survival from 89 to 100% in the upper 5 cm of soil, but did not reduce survival below 5 cm. Solarization may have enhanced seed survival below 5 cm. Cover crops of barley, rapeseed, and sudangrass generally increased survival of annual bluegrass seeds buried 2.5 to 15 cm deep in the soil. Green manure cover crops plus solarization did not improve the efficacy of solarization alone and in some cases diminished the effectiveness of solarization. Solarization significantly improved the efficacy of one-quarter rates of metham (230 L/ha) in the top 5 cm of soil, reducing overall annual bluegrass seed survival in the soil by 40% compared with metham alone (230 L/ha) but only 30% compared with solarization alone. The conventional rate of metham (930 L/ha) was the most effective and consistent treatment across all depths.
Nomenclature:Metham, methyldithiocarbamic acid; annual bluegrass, Poa annua L. #3 POANN; spring barley, Hordeum vulgare L. Micah; rapeseed, Brassica napus Dwarf Essex; sudangrass, Sorghum vulgare Trudan 8.
Additional index word: Green manures.
Abbreviations: PE, polyethylene; PNW, Pacific Northwest.