In eastern Nebraska (central USA), high livestock stocking rates and season-long grazing on many prairies has led to a shift in plant composition from a warm-season native bluestem Andropogon community, to cool-season species, primarily Kentucky bluegrass Poa pratensis and smooth brome Bromus inermis. An experiment was undertaken to evaluate atrazine and glyphosate application to promote recovery of warm-season grasses through suppression of cool-season species on overgrazed, native tallgrass prairie in Gage County.
In spring (21 April) 1979, atrazine at 2.24 kg/ha or glyphosate at 1.12 kg/ha was applied (using a water solution: 189 l/ha) to plots (8.2 x 13.7 m) as a randomized complete block (replicated 4 times, including an untreated control).
Relative species composition was determined by counting basal culms in April 1979 (prior to treatment), August 1979, and May and September 1980, along a (1 m x 1 cm) belt transect.
Herbage yield was determined per plot monthly (May to September) in 1979, and four times in 1980 (June onwards). Four, randomly located quadrats (0.3 x 0.6 m) were clipped and samples separated into living plant material by species, standing dead vegetation and litter, and dried and weighed.
Both herbicide treatments significantly reduced relative species composition of smooth brome (average 17% prior to treatment; <7% in herbicide-treated plots vs. 14-16 % in controls thereafter) and Kentucky bluegrass (22-28% prior to treatment; <3% in herbicide plots vs. 21-28% in controls thereafter), and also production.
Big bluestem A.gerardii (the primary desired native species)in 1979 showed a dramatic increase from virtually zero in plots prior to treatment to 34-36% in herbicide plots (10% in control); value were similar in 1980.
In herbicide plots, warm-season herbage yield (mostly big bluestem) was higher (equivalent to 5,345 kg/ha) than the control (1,610 kg/ha), whilst cool-season grass production was reduced (1979 - 82 vs. 1,097 kg/ha; 1980 - 65 vs. 863 kg/ha).
Total herbage yield was higher on herbicide plots than controls (1979 - 6,126 vs. 3,557 kg/ha; 1980 - 4,154 vs. 3,269 kg/ha). Total, warm-season and cool-season yields were similar between atrazine- and glyphosate-treated plots.
Both herbicide treatments therefore appear to have potential for rapid recovery of overgrazed, native tallgrass prairies where sufficient warm-season tallgrass remnants are present as a source for re-establishment.
If using or referring to this published study, please read and quote the original paper, this can be viewed at: https://www.uair.arizona.edu/holdings/journal/issue?r=http://jrm.library.arizona.edu/Volume36/Number1/