Response of Central Plains tallgrass prairies to fire, fertilizer, and atrazine.

Abstract

Tallgrass prairies are an important forage resource in the eastern Central Great Plains. The effect of spring burning, fertilization, and atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine] on standing crop of selected herbaceous species and categories of vegetation was determined in 6 tallgrass prairie environments located near Lincoln and Virginia, Neb., from 1987 through 1989 and 1 site near Bloomfield, Neb., in 1987. The grasslands were in good to excellent condition at the time these studies were conducted. Portions of each site were burned in mid-to late spring, atrazine was applied at a rate of 2.2 kg a.i. ha-1 in late April to early May, and fertilizer was applied in mid-May. Despite below-normal precipitation at 6 of the 7 sites, burning combined with fertilization improved warm-season grass standing crop by 50 to 127% in 5 of the 7 grassland environments studied. This reflected the positive response of the dominant warm-season grasses, big bluestem (Andropogon gerardii Vitman var. gerardii Vitman) and indiangrass [Sorghastrum nutans (L.) Nash], to burning or fertilization. Atrazine increased warm-season grass standing crop at only the site near Bloomfield. Kentucky bluegrass (Poa pratensis L.) and annual bromes (Bromus spp.) were more susceptible to atrazine than smooth brome (Bromus inermis Leyss.). Forb standing crop was significantly reduced by atrazine alone or by burning followed by atrazine application in 4 of the 7 prairie environments. Burning combined with fertilizer application improved warm-season grass standing crop in good to excellent condition grasslands and obviated the need to use atrazine.