Atrazine and burning in tallgrass prairie infested with prairie threeawn

Published source details Engle D.M., Bidwell T.G., Stritzke J.F. & Rollins D. (1990) Atrazine and burning in tallgrass prairie infested with prairie threeawn. Journal of Range Management, 43, 424-427.
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Summary

Prairie threeawn Aristida oligantha is an annual grass of dry, low fertility sites in eastern USA. It commonly occurs on abandoned cropland, overgrazed ranges and degraded tallgrass prairies. It can maintain dominance for many years (due to low nutrient requirements, allelochemical production and low palatability), restricting recovery of other graminoids and herbs. Three studies were undertaken on two tallgrass prairie hay meadows infested with prairie threeawnnear the city of Stillwater, Oklahoma (south central USA). The effect of atrazine, a dormant season burn, and atrazine plus burning on prairie threeawn yield and desirable plants, was investigated.

Hay was harvested in mid-July each year. Each study comprised a randomized block design with treatments (factorial arrangement, 4 replications per treatment) applied to 10 x 10 m plots in1986 or 1987: burning in November, February or April; atrazine application in March at 0 (control) or 1.12 kg/ha.

As a measure of vegetation response, standing crop was determined by clipping (at ground level in 5, 0.5 x 0.2 m quadrats/plot) in mid-summer (late June-early July). Residual treatment effects (i.e. second year after treatment) in two studies (1 and 3) were assessed, again by clipping. Clippings were separated into current year (live) and old (litter) material. Live material was separated into tallgrasses, little bluestem Schizachyrium scoparium, other perennial grasses, prairie threeawn, and forbs, and dried and weighed.

Atrazine significantly reduced prairie threeawn in all three studies, effect (standing crop kg/ha) was most pronounced in study 1:

Study 1: unburnt (no atrazine) - 3,010 kg; atrazine alone - 100 kg; February burn - 2,800 kg; February burn + atrazine 770 kg; April burn - 660 kg; April burn + atrazine 110 kg; study 2: 140 kg/ha vs. 370 kg/ha (averaged over burn date); and study 3: 230 kg/ha vs. 430 kg/ha (averaged over years and burn date).

April burning reduced threeawn in one study. February or November burning did not reduce threeawn. Atrazine and burning combined controlled threeawn no better than atrazine alone when burns were several months before or after atrazine application.

Atrazine application (no burn) in two of the studies significantly increased desirable tallgrass prairie species yields (e.g. big bluestem Andropogon gerardii, little bluestem, switchgrass Panicum virgatum and indiangrass Sorghastrum nutans) compared with controls:

Study 1 (year 1): 3,040 vs. 1,870 kg/ha; no significant residual effect in year 2;

Study 3 (year 1): 1,630 vs. 1,440 kg/ha (not significant); significant residual effect (year 2): 1,940 vs. 1,610 kg/ha.

Burning alone or burning plus atrazine did not increase desirable species.

Note: 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/Volume43/Number5/