Harvest frequency and burning effects on monocultures of 3 warm-season grasses

Harvest frequency and burning can affect forage yield of monocultures of switchgrass (Panicum virgatum L.), big bluestem (Andropogon gerardii Vitman), and indiangrass [Sorghastrum nutans (L.) Nash]. Current information is based largely on results from mixed stands. A field experiment was established in 1986, and from 1988 to 1991 treatments were applied with burning in March, April, or May plus an unburned control. Growing-season yield was measured by harvesting 1 (June), 2 (June and July), or 3 (June, July, and August) times with unharvested control plots included. End-of-season standing crop from all plots was determined after plants became dormant. Treatments were applied to the same plots annually and were arranged in a split-split plot, randomized complete block design. The main plot was species, subplot was burn date, and sub-subplot was harvest frequency. Burning reduced yields (P<0.01), and yields were lowest in plots burned in May. Burning reduced yields of indiangrass most (57%) and big bluestem least (15%). In 1989, plots harvested three times produced yields similar to plots harvested once for all species. By 1991, yields of plots harvested 3 times per growing-season were reduced (P=0.08) below those of plots harvested once. Yield response of species also varied across the study. Growing-season yields in 1991 were 113, 67, and 89% of 1989 yields for switchgrass, big bluestem, and indiangrass, respectively. Regardless of burning and harvest frequency combination, switchgrass produced as much or more herbage than the other species.