Fire and nitrogen effects on Aristida purpurea mineral concentrations

Authors: Dufek, Nickolas; Vermeire, Lance; Waterman, Richard; GANGULI, AMY - NATIONAL INSTITUTE OF FOOD AND AGRICULTURE (NIFA)

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/31/2022
Publication Date: 12/2/2022
Citation: Dufek, N.A., Vermeire, L.T., Waterman, R.C., Ganguli, A.C. 2022. Fire and nitrogen effects on Aristida purpurea mineral concentrations. Rangeland Ecology and Management. 86:44-49. https://doi.org/10.1016/j.rama.2022.10.006.
DOI: https://doi.org/10.1016/j.rama.2022.10.006

Interpretive Summary: Purple threeawn (Aristida purpurea Nutt.) is a perennial bunchgrass native to much of North America that may dominate disturbed or previously overgrazed rangelands and is mostly avoided by herbivores as forage. Management of threeawn using fire and nitrogen addition can increase forage quality and likelihood of selection by livestock. We assessed effects of fire, nitrogen fertilizer addition, and growth stage on purple threeawn mineral concentrations the first growing season after fire on two similar sites in southeastern Montana. Fire (no fire, summer fire, fall fire) and rate of nitrogen fertilizer addition (0, 46, 80 kg N•ha-1) were assigned to test each unique combination of treatments. Samples were collected at five growth stages throughout each growing season. Minerals were evaluated using laboratory analysis of potassium (K), calcium (Ca), phosphorus (P), sulfur (S), magnesium (Mg), iron (Fe), zinc (Zn), manganese (Mn), and copper (Cu) concentrations. With no nitrogen addition, summer and fall fire increased Ca from 0.22 to 0.38 and 0.31%, respectively, S from 0.08 to 0.15 and 0.13%, and Mg from 0.06 to 0.14 and 0.12%, while fall fire decreased Fe from 289 to 176 ppm. In the vegetative stage, fire (fall and summer averaged) increased K from 0.38 to 1.08%, Ca from 0.22 to 0.35%, P from 0.10 to 0.23%, S from 0.08 to 0.16%, Mg from 0.05 to 0.13%, Zn from 19.2 to 35.8 ppm and Cu from 2.8 to 6.2 ppm. Increasing rate of nitrogen addition and advancing growth stage had little to no effect on mineral concentrations relative to fire effects. Results indicate prescribed fire can increase mineral concentrations from deficient levels to exceeding requirements for growing cattle, providing more evidence supporting use of prescribed fire to increase forage quality and potential herbivore utilization of purple threeawn within one-year following fire.

Technical Abstract: Purple threeawn (Aristida purpurea Nutt.) is a perennial bunchgrass indigenous to much of North America that may dominate disturbed or previously overgrazed rangelands and is mostly avoided by herbivores as forage. Management of threeawn using fire and nitrogen addition can increase its forage quality and likelihood of selection by livestock. We assessed effects of fire, nitrogen fertilizer addition, and phenological stage on purple threeawn mineral concentrations the first growing season postfire on two similar sites in southeastern Montana. Fire (no fire, summer fire, fall fire) and rate of nitrogen fertilizer addition (0, 46, 80 kg N•ha-1) were arranged in a completely randomized, fully factorial design. Samples were collected at five phenological stages throughout each growing season. Minerals were evaluated using laboratory analysis of potassium (K), calcium (Ca), phosphorus (P), sulfur (S), magnesium (Mg), iron (Fe), zinc (Zn), manganese (Mn), and copper (Cu) concentrations. With no nitrogen addition, summer and fall fire increased Ca from 0.22 to 0.38 and 0.31%, respectively, S from 0.08 to 0.15 and 0.13%, and Mg from 0.06 to 0.14 and 0.12%, while fall fire decreased Fe from 289 to 176 ppm. In the vegetative stage, fire (fall and summer averaged) increased K from 0.38 to 1.08%, Ca from 0.22 to 0.35%, P from 0.10 to 0.23%, S from 0.08 to 0.16%, Mg from 0.05 to 0.13%, Zn from 19.2 to 35.8 ppm and Cu from 2.8 to 6.2 ppm. Increasing rate of nitrogen addition and advancing phenological stage had little to no effect on mineral concentrations relative to fire effects. Results indicate prescribed fire can increase mineral concentrations from deficient levels to exceeding requirements for growing cattle, providing more evidence supporting use of prescribed fire to increase forage quality and potential herbivore utilization of purple threeawn within one-year following fire.