Date of this Version
Eastern Nebraska and neighboring areas have large amounts of depleted pastures which consist of annual bromegrasses (Bromus spp.), Kentucky bluegrass (Poapratensis L.), and numerous broadleaf weeds. Such pastures need renovation but complete seedbed preparation is expensive and may enhance erosion. The objective of our study was to determine if sod-seeding grasses offered an alternative to complete seedbed preparation. Three weedy pastures in southeast Nebraska on a Hastings silty clay loam (fine, montmorillonitic, mesic Udic Argiustoll), a Lamo silty clay loam [fine-silty, mixed (calcareous), mesic Cumulic Haplaquoll], and a Geary silty clay loam (fine-silty, mixed, mesic Udic Argiustoll) were sprayed with sod suppressing herbicides and sod-seeded with intermediate wheatgrass [Agropyron intermedium (Host) Beauv.] or switchgrass (Panicum virgatum L.). Spring herbicide treatments consisted of atrazine [2-chloro-4-(ethyl-amino)- 6-(isopropylamino)- s-triazine] plus paraquat (1, 1' dimethyl- 4, 4' bypyridinium ion) broadcast and banded at 0.3 + 2.2 kg/ha, respectively, glyphosate [N-(phosphonomethyl) glycine] broadcast and banded at 1.1 and 2.2 kg/ha, and paraquat broadcast at 0.3 or 0.6 kg/ha. In the spring experiments both intermediate wheatgrass and switchgrass were seeded. In late summer experiments the atrazine plus paraquat treatments were replaced with banded paraquat and only intermediate wheatgrass was seeded. A nonsprayed but seeded control and a seeded rototilled treatment were included at all locations and dates.
Intermediate wheatgrass stands were acceptable if aboveground herbage suppression was 65% or greater during the first 6 weeks after spraying a subirrigated pasture and 80% or greater during the first 6 weeks after spraying upland pastures in the spring. In order to successfully establish switchgrass complete sod-suppression during the first 6 weeks after spraying was required on the subirrigated pasture and 85% suppression was required on the upland pastures. Glyphosate and paraquat suppressed the sod more severely in late summer but subsequent competition with annual brome increased. Atrazine plus paraquat, or glyphosate broadcast in spring, greatly enhanced the vigor of remnant big bluestem (Andropogon gerardii Vitman) in these depleted hut unplowed pastures. In some instances the existing big bluestem was dense enough to form a complete stand once the cool-season vegetation was removed. In other situations the seeded switchgrass established around the resident big bluestem clumps.