Agronomy and Horticulture, Department of


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Published in AGRONOMY JOURNAL, VOL. 90, JANUARY-FEBRUARY 1998. Copyright 1998. Used by permission.


Developing grazing systems requires basic information on the growth and development of adapted species. The objective of this field study was to determine seasonal tiller demographics and leaf area index (LAI) of intermediate wbeatgrass [Thinopyrum intermedium (Host) Barkw. & D.R. Dewey], smooth bromegrass (Bromus inermis Leyss.), switchgrass (Panicum virgatum L.), and big bluestem (Andropogon gerardii Vitman) tiller 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 demographics. Additionally, mean stage count (MSC), a quantified estimate of tiller population maturity, was determined at each harvest. The The LAI was indirectly measured using a canopy analyzer at 7- to 14-d intervals. Tiller density for all species generally declined as MSC increased. Tiller demographics were highly variable by year for intermediate wheatgrass and smooth bromegrass, which indicates that grazing management should be based on current tiller populations. Density of vegetative tillers declined most rapidly for smooth bromegrass, followed by intermediate wheatgrass, switchgrass, and big bluestem. Switchgrass and big bluestem tiller demographics were more uniform and predictable across years than intermediate wheatgrass and smooth bromegrass. The LAI for all species increased as MSC increased. Maximum The LAI for intermediate wheatgrass, smooth bromegrass, switchgrass, and big bluestem in 1992 was 4.7,5.1,4.9, and 5.8, respectively. Integrating tiller demographics and The LAI suggests that initial grazing readiness starts with smooth bromegrass in early spring, followed by intermediate wheatgrass in about 2 wk, switchgrass in late spring, and big bluestem in early summer.