Proper burning intervals for tobosagrass in west Texas based on nitrogen dynamics

  • Published source details Sharrow S.H. & Wright H.A. (1977) Proper burning intervals for tobosagrass in west Texas based on nitrogen dynamics. Journal of Range Management, 30, 343-346.


Fire benefits tobosagrass Hilaria mutica- honey mesquite Prosopis glandulosa var. glandulosa grassland communities by reducing mesquite dominance and burning off dead material which encourages fresh growth. The time required for re-establishment of pre-fire nitrogen levels in tobosagrass communities in the Rolling Plains of west Texas (southwest USA) was studied on five different ages of burns in 1973-74 in order to determine appropriate burn management intervals.

On Spade Ranch (near Colorado City), two replications of five different aged burns (time elapsed after burns one to five growing seasons) on convex and concave topographic sites were sampled for nitrogen content in July1973 and July1974. Nitrogen content in the burn plots was determined for: 1) current growth; 2) past years’ standing growth; 3) litter; 4) coarse roots; and 5) soil plus fine roots.

Total nitrogen contained in each was compared to an unburned (control) area to determine the length of time required for re-establishment of pre-fire nitrogen levels.
Prior to burns, vegetation comprised dense tobosagrass with a fairly open mesquite canopy. Tobosagrass and mesquite cover was denser on the (wetter) concave site. In 1966 mesquite on plots was top-killed with 2,4,5-T herbicide, but had reprouted to over 1.5 m tall by 1973.

Standing old growth-nitogen returned to pre-burn levels by the end of the third growing season.

Litter-nitrogen on the soil surface took 5 years to reach pre-burn levels on concave sites and an estimated 8 years on convex sites. High variation obscured any trends in root or soil nitrogen levels.
Based on results of this study, tobosagrass communities should not be burned more frequently than once every 5 years on concave sites, and once every 8 years on convex sites.
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