Two herbicide treatments were initiated in southeastern Nebraska on a Wymore silty clay loam (clayey range site) during the spring of 1979, to change species composition of overgrazed, native range from cool-to warm-season grasses. Treatments consisted of late spring applications of atrazine [2-chloro-4-(ethylamino)&(isopropylamino)-s-triazione] at 2.24 kg/ha, and glyphosrte [N-(phosphonomethyl)lycine] at 1.12 kg/ha. Both herbicide treatments significantly (P<.O5) reduced smooth brome (Bromus inermis Leyss.) and Kentucky bluegrass (Poa pratensis L.) production and relative species composition while increasing big bluestem (Andropogongerardii Vitman) in 1979 and the effects were maintained during the second growing season. Warm-season herbage yield, primarily big bluestem, was greater following herbicide treatments (5345 kg/ha) compared to control (1610 kg/ha). Herbage yields of cool-season grasses from herbicide treated plots were reduced. However, total herbage yield was higher on herbicide treated plots during the first and second year after treatment. Total, warm-season and cool-season herbage yields for both years were not different between atrazine and glyphosate treated plots. Both herbicide treatments have potential for rapid recovery of overgrazed, native tallgrass prairies in eastern Nebraska when sufficient warm-season tallgrass remnants are present. The eastern one-third of Nebraska was described as the True Prairie (Weaver 1954) and the native plant community was a tallgrass bluestem prairie, composed of warm-season vegetation. Currently, much of the area is incropland. Remaining native range occurs as small scattered tracts of land which are generally unsuited for cultivation due to rocky or shallow soils or erosion hazards. Over I million acres of native range are located in this area (Bose 1977). Over 60% of the native pasture in eastern Nebraska is in low range condition (Bose 1977). The availability of high producing cool-season species for hay and pasture and accessibility of crop residues encourage high stocking rates, often above the available summer forage supply. This imbalance in seasonal forage supply often contributes to range deterioration. High stocking rates and season-long grazing characteristic of this area contributed to a shift in species composition from the warm-season native community, to cool-season species, primarily Kentucky bluegrass (Poaprurensis L.) and smooth brome (Bromus inermis Leyss.). Although forage is readily available in the spring, fall and winter with improved cool-season species and crop residues, a void of high quality summer forage exists which could be minimized by shifting species composition ofthe native pastures to native warm-season dominants. Atrazine [Z-chloro-4-(ethylamino)-6-(isopropylamino)-striazine], a soil active herbicide, has been reported to be phytotoxic

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