Wednesday, November 15, 2006

Soil Seedbank Composition in Pastures of Diverse Mixtures of Temperate Forages.

Matt Sanderson1, Sarah C. Goslee2, Keith Klement3, and Kathy J. Soder2. (1) "Bldg 3702, Curtin Rd, USDA-ARS", Pasture Research Lab, Pasture Research Lab, University Park, PA 16802-3702, United States of America, (2) USDA-ARS, Building 3702 Curtin Road, University Park, PA 16802, (3) USDA-NRCS, Ash Street, Glasgow, MT 59230

Seed banks may contribute useful or weedy species that fill gaps in the sward. In this study, we relate changes in the composition and structure of the seed bank in these same pastures to changes in the aboveground vegetation composition and structure of the planted and nonplanted species during 3 yr. In August 2001, four mixtures (2, 3, 6, and 9-species of temperate grasses, legumes and a forb) were established in replicated 1-ha pastures. Pastures were grazed from April to September in 2002 and 2003. Soil cores (1.88 cm diameter by 5 cm depth) were taken from the pastures on five dates in 3 yr to determine seed density. The total density of germinable seeds from all species did not differ among mixture treatments averaged across the five sample periods. Annual forbs accounted for 79% of the germinable seeds. Oxalis was the dominant annual forb. The 2-species mix had a higher density of germinable annual forb seeds (18, 600 seeds m-2) compared with the 3- and 9-species mixtures (11,000 seeds m-2). Seeded species contributed little to the soil seed bank with fewer than 1000 seeds m-2 total in the 3 yr. There was little relation between the species composition of the seed bank and the composition of the aboveground vegetation. Data from this study indicate that planting a diverse mix of forage species may help reduce the abundance of germinable annual forb seeds in the soil seedbank.