Establishment of Switchgrass and Big Bluestem in Corn with Atrazine

Switchgrass (Panicum virgatum L.) and big bluestem (Andropogon gerardii Vitman) provide abundant forage for livestock and wildlife during hot summer months when cool-season grass species may dedine in production. Little biomass production for grazing may result during warm-season grass establishment because of weed competition. Chemical methods of weed control are now limited, because application of atrazine [6-chloro-N-ethyI-N'-(l-methylethyl)-l,3,5-triazine-2,4-diamine] to switchgrass and big bluestem is no longer allowed according to the label. Using corn (Zea mays L.) as a companion crop could provide potential for high biomass production during warm-season grass establishment, and allow the use of atrazine for weed control. This study investigated the ability of switchgrass and big bluestem to establish in a corn companion crop. The effects of corn hybrid (short- vs. long-season), population density, row spacing, and harvest date on switchgrass and big bluestem stands and on corn production were quantified. Establishment of switchgrass and big bluestem in corn was successful. Switcbgrass mean stands were 26.3 plants m⁻² in 1995 and 46.4 plants m⁻² in 1996. Big bluestem stands were similar to switchgrass in 1995 (31.7 plants m⁻²), but were much lower in 1996 (5.2 plants m⁻²). Long-season corn hybrids and higherdensity corn populations increased corn silage and grain yield without reducing warm-season grass stands. Within a season, no difference existed between corn grain yields when grown with either switchgrass (6.7 Mg ha⁻¹ in 1995, 5.3 Mg ha⁻¹ in 1996) or big bluestem (6.9 Mg ha⁻¹ in 1995, 5.7 Mg ha⁻¹ in 1996). Silage dry matter yield was not different between corn grown with switchgrass (12.6 Mg ha⁻¹ in 1995, 16.1 Mg ha⁻¹ in 1996) and corn grown with big bluestem (13.1 ha⁻¹ in 1995, and 16.6 Mg ha⁻¹ in 1996) for a given year. Switchgrass and big bluestem grown in corn with atrazine reduced land production losses during the establishment year, yet allowed adequate establishment of these grasses for future forage production. Journal Paper no. J-17415 of the Iowa Agric. & Home Econ. Exp. Stn., Ames, Project no. 2899. Research supported by Hatch Act and State of Iowa funds.