TILLER DEMOGRAPHICS AND LEAF-AREA INDEX OF 4 PERENNIAL PASTURE GRASSES

Developing grazing systems requires basic information on the growth an d development of adapted species. The objective of this field study wa s to determine seasonal tiller demographics and leaf area index (LAI) of intermediate wheatgrass [Thinopyrum intermedium (Host) Barkw. & D.R . Dewey], smooth bromegrass (Bromus inermis Leyss.), switchgrass (Pani cum virgatum L.), and big bluest em (Andropogon gerardii Vitman) tille r populations. This study was conducted in 1992 and 1993 near Mead, NE , on a silty clay loam soil (Typic Argiudoll) as a randomized complete block. Monocultures were harvested six times each year for tiller dem ographics. Additionally, mean stage count (MSG), a quantified estimate of tiller population maturity, was determined at each harvest. The LA I was indirectly measured using a canopy analyzer at 7- to 14-d interv als. Tiller density for all species generally declined as MSC increase d. Tiller demographics were highly variable by year for intermediate w heatgrass and smooth bromegrass, which indicates that grazing manageme nt should be based on current tiller populations. Density of vegetativ e tillers declined most rapidly for smooth bromegrass, followed by int ermediate wheatgrass, switchgrass, and big bluestem. Switchgrass and b ig bluestem tiller demographics were more uniform and predictable acro ss years than intermediate wheatgrass and smooth bromegrass. The LAI f or all species increased as MSC increased. Maximum LAI for intermediat e wheatgrass, smooth bromegrass, switchgrass, and big bluestem in 1992 was 4.7, 5.1, 4.9, and 5.8, respectively. Integrating tiller demograp hics and LAI suggests that initial grazing readiness starts with smoot h bromegrass in early spring, followed by intermediate wheatgrass in a bout 2 wk, switchgrass in late spring, and big bluestem in early summe r.