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United States Department of Agriculture

Agricultural Research Service

Research Project: PROACTIVE MANAGEMENT FOR SUSTAINABLE RANGELAND PRODUCTION

Location: Livestock and Range Research Laboratory (LARRL)

Title: Fire and nitrogen fertilization effects on Purple Threeawn in vitro fermentation and gas production

Authors
item Dufek, Nickolas -
item VERMEIRE, LANCE
item WATERMAN, RICHARD
item Ganguli, Amy -

Submitted to: Society for Range Management Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: December 1, 2011
Publication Date: January 28, 2012
Citation: Dufek, N.A., Vermeire, L.T., Waterman, R.C., Ganguli, A.C. 2012. Fire and nitrogen fertilization effects on Purple Threeawn in vitro fermentation and gas production. Society for Range Management Meeting Abstracts #0160.

Interpretive Summary: Purple threeawn is a native perennial bunchgrass with poor forage quality. The grass often dominates disturbed soils and persists with continued severe grazing. N-fertilization and fire have each been used to reduce threeawn dominance. Greater utilization of threeawn by livestock is required to extend treatment life. We evaluated the effects of fire and N-fertilization on threeawn forage quality in southeastern Montana during the growing season from a completely randomized design with fire and nitrogen treatments in a 3X3 factorial arrangement. Forage quality was assessed by in vitro gas production and digestibility techniques. Asymptotic gas production was greater for sites burned during summer (68 mL/g) or fall (70 mL/g) than for non-burned sites (56 mL/g), but were not affected by fertilizer treatment. Lag time was also greater for non-burned (1.6 h) than burned sites (1.3 h). During June, average fermentation rates for threeawn differed among all fire treatments and were greatest for fall-burned (2.3 mL/h), then summer-burned (2.0 mL/h), and least for non-burned sites (1.0 mL/h). For July sample collections, average fermentation rates were similar between seasons of fire (2.3 mL/h) and continued to exceed those of non-burned sites (1.4 mL/h). Results indicate fire increases rumen microbial activity and digestibility of purple threeawn.

Technical Abstract: Purple threeawn (Aristida purpurea) is a native perennial bunchgrass with poor forage quality. The grass often dominates sites where soils have been disturbed and persists with continued severe grazing of preferred species due to livestock avoidance of threeawn. Nitrogen fertilization and fire have each temporarily reduced threeawn dominance, however, greater utilization of threeawn by livestock is required to extend treatment longevity. We evaluated effects of fire (summer, fall, no fire) and spring urea nitrogen fertilization (0 kg/ha, 40 kg/ha, 80 kg/ha) on threeawn forage quality in southeastern Montana during the growing season with a completely randomized design in a 3X3 factorial arrangement. Forage quality was assessed using a 96-h in vitro gas production. Asymptotic gas production was greater for sites burned during summer (68 mL/g) or fall (70 mL/g) than for non-burned sites (56 ± 0.9 mL/g), but was not affected by fertilizer treatment. Gas production lag time was also greater for non-burned (1.6 h) than burned sites (1.3 ± 0.08 h). During June, average in vitro gas production rates for threeawn differed among all fire treatments and were greatest for fall-burned (2.3 mL/h), then summer-burned (2.0 mL/h), and least for non-burned sites (1.0 ± 0.05 mL/h). For July sample collections, average in vitro gas production rates were similar between seasons of fire (2.3 mL/h) and continued to exceed those of non-burned sites (1.4 ± 0.05 mL/h). Results indicate that fire may enhance the rumen digestibility of purple threeawn as measured by fermentation gasses.

Last Modified: 9/29/2014