Increasing Native Warm-Season Grass Biomass Utilizing Fire, Nitrogen, and Herbicide

Pre-European tallgrass prairie covered approximately 260 million acres in the United States. Only 1-3% of remnant prairies remains and is threatened by loss of natural disturbances and introduction, intentional or accidental, of non-native invasive species. Introduced grasses often create unfavorable conditions for native species to thrive and reproduce. Cool-season non-native species deplete nutrient resources, crowd out native root systems, and reduce photosynthetically active radiation. This study examined the use of spring burns, glyphosate, and nitrogen (N) applications at various growth stages to stimulate native species [big bluestem (Andropogon gerardii) and sideoats grama (Bouteloua curtipendula)] growth and decrease competition with non-native species [smooth brome (Bromus inermis) and Kentucky bluegrass (Poa pratensis)] at two sites (Volga and Artesian) in eastern South Dakota. Treatments were applied in Oct 2009 (glyphosate and/or N applied) and spring 2010 (fire, glyphosate, and/or N applied). Biomass was collected at the peak of cool-season non-native (June, 2010) and warm-season native (August 2010) grass growth to evaluate results. Prescribed burn treatment increased native warm-season biomass a minimum of 60% compared with untreated control areas. Site and N timing influenced herbicide effectiveness. At Artesian, warm-season biomass doubled compared with the untreated control or when April N application was followed by a May herbicide application. May herbicide application followed by June N application had increased warm-season biomass by 30% at Volga. Compared with the untreated control, warm-season grass biomass increased 41% when N was applied in June at Artesian and increased 77% with when N was applied in both October and April at Volga. Prior management (haying and winter grazing vs lack of grazing) of sites may have influenced species response