Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/24/2007
Publication Date: 10/23/2007
Citation: Sanderson, M.A., Klement, K., Goslee, S.C., Soder, K.J. 2007. Soil seed bank composition in pastures of diverse mixtures of temperate forages. Agronomy Journal. 99:1514-1520. Interpretive Summary: Buried seed in pasture soils (the soil seed bank) may contribute useful species to grazing management but often are reservoirs of weedy plants. In previous studies we measured changes in aboveground vegetation, forage productivity, and animal performance of four mixtures of forages differing in the number of planted species (two, three, six or nine species). In this study, we compared changes in the composition of the seed bank to change in the aboveground vegetation of these same four mixtures during three years. Pasture mixture treatment did not affect the total number of germinable seeds in the soil seed bank. There was little relationship between the plant species composition of the seed bank and the composition of the aboveground vegetation. Annual weedy species were less abundant in the seed bank of pastures planted to complex mixtures compared to the two-species mixture. Our results indicate that planting a diverse mix of forage species may reduce the abundance of annual weed seeds in the soil.
Technical Abstract: Seed banks may contribute useful or weedy species that fill gaps in pastures. In a previous study, pastures planted to complex mixtures of forages had fewer weedy species in the aboveground vegetation. In this study, we relate changes in the species composition of the seed bank to changes in the aboveground vegetation. 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 (eight total) in central Pennsylvania. Pastures were grazed by dairy cattle from April to September in 2002 and 2003. Soil cores (1.88 cm diameter by 5 cm depth) were taken in April and October in 2002 and 2003, and in April 2004 to determine the density of germinable seeds. Soil samples were placed in a greenhouse under natural light and controlled temperatures for 12 to 18 months and germinated seedlings counted regularly. The total density of germinable seeds from all species did not differ among mixtures. 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 fewer than 1000 seeds m-2 total in the 3 yr. Kentucky bluegrass (Poa pratensis L.) and white clover (Trifolium repens L.) were the most common forage species in the seed bank. 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 reduce the abundance of germinable annual forb seeds in the soil.