Japanese Brome Response to Atrazine in Combination with Nitrogen Fertilizer in the Mixed Prairie

Abstract

Atrazine was used to control Japanese brome in conjunction with nitrogen fertilization to determine if herbage production could be increased more than by fertilization alone. Atrazine treatments included a single application, application in alternate years, and application for two or three consecutive years. Atrazine did not significantly increase production more than fertilizer alone and caused some decreases in western wheatgrass production at low rates of N in one year at one location. Unless atrazine was applied in two or more years, Japanese brome was a prevalent the second growing season after application as where it had never been controlled. Application of atrazine in consecutive years increased shortgrass production at one location. Japanese brome (Bromus japonicus) is an introduced annual from Eurasia. A winter annual, it is similar to downy brome (II. tectorum) but becomes more abundant than downy brome as soil moisture supplies increase (Hulbert 1955). Both species occur in South Dakota, but Japanese brome is more abundant on rangeland. Japanese brome is a newcomer to parts of South Dakota. In western South Dakota, Lewis et al. (1975) observed Japanese brome in one small area of their research pastures in 195 1. By 1955 the invading grass was a major component of this rangeland. Since then the abundance of Japanese brome has been highly variable, depending on favorable fall moisture. Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)+ trazine] has been demonstrated to be effective in controlling annual bromes (Arnold and O’Neal 1972; Morrow et al. 1977). Nitrogen (N) fertilization is widely known to increase the production of cool-season species. Several studies have combined application of atrazine with N fertilization on rangeland for various reasons. Houston and van der Sluijs (1973; 1975) have shown that atrazine and nitrogen stimulated protein production on shortgrass ranges. Hyder et al. (1976) investigated the drought resistance of blue grama (Bouteloua gracilis) as affected by atrazine and nitrogen fertilizer. Nitrogen fertilization plus atrazine used to control downy brome invasion increased the 4-year average yields of Greenar intermediate wheatgrass (Agropyron intermedium) 100% over fertilization alone (Kay 1971). It was felt that control of Japanese brome in conjunction with N fertilization might result in increases in yields of western wheatgrass (A. smithii). The objectives of this experiment were: (1) to determine if western wheatgrass production could be increased by controlling Japanese brome with atrazine; (2) to determine if atrazine control of Japanese brome in combinatron with nitrogen Authors are, respectively, assistant in plant science, extension range specialist, assistant in animal science, and former assistant in plant science, South Dakota State University, West River Research and Extension Center, 801 San Francisco St., Rapid City, 5770 I. R.G. Hoeft and W.E. Arnold are gratefully acknowledged for design and initiation of the project. The research was funded in part by the Farmers Union Central Exchange Foundation. This paper was published with the approval of the Director, South Dakota Agricultural Experiment Station, as Journal No. 1627. Manuscript received April 30, 1979.