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United States Department of Agriculture (USDA) 2010

EFFECTS OF REPEATED BURNING ON SOIL NITROGEN AND CHEATGRASS BIOMASS AND REPRODUCTION

Burning Nitrogel Cheatgrass

United States Department of Agriculture (USDA) Research, Education & Economics Information System (REEIS)

Titre : EFFECTS OF REPEATED BURNING ON SOIL NITROGEN AND CHEATGRASS BIOMASS AND REPRODUCTION

Identification : NEV052WY

Pays : Etats Unis

Durée : Aug 4, 2010 à Aug 3, 2015

Mots clés : cheatgrass ; soil nitrogen ; burning effects ; biomass ; reproduction

Partenaire : UNIVERSITY OF NEVADA RENO,NV 89557

Objectifs
Restoration of cheatgrass dominated rangelands depends on controlling cheatgrass while simultaneously providing the conditions necessary for native species establishment. The expansion and eventual dominance of exotic annual grasses and other invaders in semi-arid shrublands often has been attributed to fire and the increase in resource availability resulting from the death of fire intolerant shrubs (Young and Evans 1978, West and York 2002, Evangelista et al. 2004). Soil nutrients are inherently low in these systems, but can increase dramatically following fire, especially available N (NO3- and NH4+) (Stubbs and Pyke 2005) which can increase up to 12-fold (Blank et al. 1994, 1996). Cheatgrass can take advantage of the high N availability and produce significantly more shoot mass by maintaining higher growth rates than perennial grasses (Monaco et al. 2003). Recent field studies have shown the importance of available inorganic nitrogen in controlling cheatgrass establishment and growth (McLendon and Redente, 1991 ; Young et al., 1999). Although cheatgrass tends to thrive in a high nitrogen environment, it is inhibited in a low one (McLendon & Redente 1991 ; Redente et al. 1992 ; Young & Allen 1997 ; Young et al. 1999). A novel method to tie up mineral N might be to reduce total N supplies and, therefore, mineral N supplies by repeated burning. It is well documented that nearly all N contained in organic material that is burned is volatilized and lost from the system, potentially causing long-term declines in ecosystem N capital unless the N is replaced by atmospheric deposition, N-fixation, or fertilization (Blair, 1997 ; Neary et al., 1999 ; Raison et al., 1985). On the other hand, burning commonly causes short-term increases in soil ammonium levels because of the heat-induced denaturing of soil organic N (Neary et al., 1999 ; other refs). The pulse of ammonium is often followed by a pulse of nitrate and nitrate leaching once nitrifying bacteria occupy the site again. The short-term pulse of ammonium after fire is thought to be one factor favoring nitrophilic cheatgrass after rangeland fire (Monaco et al. 2003). Over the long-term, however, one would expect that repeated burning without replacement of lost N could cause reductions in soil mineral N levels, at least after the initial post-fire pulse has passed. In 2008, a 5-year study was established north of Winnemucca, Nevada on cheatgrass dominated rangeland to examine the effects of repeated burning and surface litter on soil nutrient dynamics, cheatgrass biomass and reproduction, and establishment of native species. We hypothesized that repeated burning of cheatgrass dominated areas will cause : 1. Significant reductions in soil total and mineral N levels over time, including the magnitudes of the post-fire pulses of ammonium. 2. Significant increases in the C:N ratio of litter, which will further contribute to reductions in soil available N. 3. Significant reductions in cheatgrass biomass and seed production, increasing the potential for successful restoration of native species.

Présentation : USDA

Page publiée le 24 novembre 2015, mise à jour le 9 novembre 2017