HARVEST FREQUENCY AND BURNING EFFECTS ON VIGOR OF NATIVE GRASSES

Burning and harvest frequency can affect the vigor of switch grass (Pa nicum virgatum L.), big bluestem (Andropogon gerardii Vitman), and ind iangrass [Sorghastrum nutans (L.) Nash] A field study was established in 1986 and from 1988 to 1991 treatments were applied with burning in March, April, or May with unburned controls. Forage was harvested from plots 1 (June), 2 (June and July), or 3 (June, July, and August) time s with unharvested control plots included. Treatments were applied to the same plots annually and were arranged in a split-split plot, rando mized complete block design. The main plot was species, the subplot wa s burning, and the suh-subplot was harvest frequency. Big bluestem pro duced 147 and 122% more etiolated biomass in spring than did switchgra ss or indiangrass, respectively. Effects of harvest management on plan t vigor occurred after 1 growing-season, but changed little during the remainder of the study. Etiolated biomass declined more as harvest fr equency increased from 2 to 3 harvests than from 1 to 2 harvests (213, 205, and 162 g m(-2) for 1, 2, and 3 harvests per summer, respectivel y). Big bluestem produced 95 and 33% more tillers than switchgrass and indiangrass, respectively, and burning stimulated tillering an averag e of 32% across all species and harvest treatments. Harvest frequency increased tiller density. However, plant vigor as measured by etiolate d growth decreased as harvest frequency increased. This suggests that with these species tillering may occur at the expense of energy storag e with frequent defoliation. Vigorous spring etiolated growth and high tillering potential may partially explain the dominance of big bluest em in the tallgrass prairie.