Suppression of annual bromes impacts rangeland: Vegetation responses

Presence of invading annual bromes (Bromus spp.) can alter seasonal pattern s of forage production and quality and require management changes for effic ient use of infested rangelands in the Northern Great Plains. We studied bi ological impacts of the presence of brome by comparing brome infested range land to similar sites in which brome had been suppressed with autumn applic ations of atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4- diamine] at 0.56 kg ha(-1) in 1992 and 1993. Each treatment was randomly as signed to three, 12-ha pastures. Vegetation was measured for 5 months (May to September) each year from 1993 to 1995. Each pasture was stocked with 8 crossbred steers (Bos taurus) from mid-May to mid-September 1993 and 1995 a nd to mid-August 1994. The forage base varied temporally by date and year, but generally was not less than 800 kg ha(-1). Brome suppression increased (P less than or equal to 0.05) crude protein concentration for western whea tgrass (Pascopyrum smithii Rydb. [Love]) in July (7.1 vs. 9.1%) and August (6.0 vs. 7.1%). With the variation in annual brome stands among years, as i nfluenced by growing conditions, this experiment demonstrated that improvem ent in forage nutritional quality can be expected from suppression of annua l bromes on semiarid rangelands.