Effects of Planting Date, Seeding Rate, and Row Spacing on Lowland Switchgrass Establishment.

Switchgrass (Panicum virgatum L) is typically slow and difficult to establish. The objectives of this study were to determine the optimal planting date, seeding rate, and row spacing in southern Oklahoma. In experiment I (planting date X seeding rate), lowland switchgrass was drilled in September, February, and May of the 2006-07 and 2007-08 growing seasons at 2.24, 4.48, 6.72, 8.8.96, and 11.2 kg PLS ha-1. In experiment II (row spacing X seeding rate), lowland switchgrass was planted at two locations on 17.8, 35.6, 71.1, and 88.9 cm row spacings at 1.12, 2.24, 3.36, and 4.48 kg PLS ha-1 in May of 2007 and 2008. Treatment effects were determined by measuring seedling counts, plant height, percent ground coverage, and biomass yield at the end of the growing season in both experiments. In experiment I, the optimal planting date occurred in May, (1570 kg DM ha-1) compared to February (1137 kg ha-1) or September (95 kg ha-1). The September planting had excellent initial seedling counts, however these seedlings did not survive through the winter. Seedlings counts increased with increasing seeding rate, however switchgrass DM yield at the end of the season did not differ (P>0.05) between the five seeding rates, which ranged from 1482 to 1674 kg ha-1. In experiment II, seedling counts increased as seeding rate increased, however there were no consistent differences in seedling counts between the four row spacings. Switchgrass DM yields at the end of the season did not differ between the three lower rows spacing, while the widest row spacing (88.9 cm) had numerically and sometimes significantly lower DM yields. Switchgrass yields were generally higher with the 3.36 and 4.48 kg ha-1 seeding rates, however this was not consistent across locations. Switchgrass DM yields will be measured in the second growing season to confirm these results.