Nitrogen and Atrazine on Shortgrass: Vegetation, Cattle and Economic Responses

Abstract

Application of nitrogen (N) fertilizer and atrazine [6-chloro-N-ethyl-N'-(l-methylethyl)-1,3,5-triazine-2,4-diamine] have each increased grazeable forage on shortgrass prairie, but their effects are unknown when applied in combination. Therefore, a 9-year study was conducted to determine effects of N and atrazine applications on 1) herbage production, 2) steer gains, and 3) profitability of grazing on shortgrass prairie in north-central Colorado. Treatments were 1) untreated control, 2) atrazine applied at 1.1 kg ha-1 in the autumn of alternate years, 3) N applied at 22 kg ha-1 each autumn, and 4) N + atrazine at the rates specified above. Pastures were stocked at 21-41 (control), 27-54 (atrazine), 24-82 (N), or 18-84 (N + atrazine) cattle-days ha-1 during summer. Pastures were stocked with yearling steers 1979-1983 and yearling steers and spayed heifers 1984-1985, using put-and-take stocking. All treatments increased total October standing crop and blue grama (Bouteloua gracilis [H.B.K.] Lag. ex Griffiths) standing crop. Nitrogen increased cool-season grass and forb standing crops; atrazine nearly eliminated cool-season grasses but did not affect forbs. Under put-and-take stocking, atrazine and/or N appeared to increase stocking rate and gain/ha, but not average daily gain or average returns to land, labor, and management. Under optimum stocking rates and grazing strategies, N or atrazine but not both together might increase returns.