ESTABLISHMENT OF SWITCHGRASS AND BIG BLUESTEM IN CORN WITH ATRAZINE

Switchgrass (Panicum virgatum L.) and big bluestem (Andropogon gerardi i Vitman) provide abundant forage for livestock and wildlife during ho t summer months when cool-season grass species may decline in producti on. Little biomass production for gazing may result during warm-season grass establishment because of weed competition. Chemical methods of weed control are now limited, because application of atrazine hyl-N'-( 1-methylethyl)-1,3,5-triazine-2,4-diamine] to switchgrass and big blue stem is no longer allowed according to the label. Using corn (Zea mays L.) as a companion crop could provide potential for high biomass prod uction during warm-season grass establishment, and allow the use of at razine for weed control. This study investigated the ability of switch grass and big bluestem to establish in a corn companion crop. The effe cts of corn hybrid (short- vs. long-season), population density, row s pacing, 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. Switchgrass mean stands were 26.3 pl ants 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 higher -density corn populations increased corn silage and grain yield withou t reducing warm-season grass stands. Within a season, no difference ex isted 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 gown with big bluestem (13.1 Mg ha(- 1) in 1995, and 16.6 Mg ha(-1) in 1996) for a given year. Switchgrass and big bluestem gown in corn with atrazine reduced land production lo sses during the establishment year, yet allowed adequate establishment of these grasses for future forage production.