Fire resulting from natural ignition has become a more common event on the Sevilleta National Wildlife Refuge (NWR) since the exclusion of domesticated livestock. Efforts to return fire to the native landscape has resulted in the use of prescribed fire during periods that meet burn prescriptions. A prescribed fire was performed on the Sevilleta NWR in June 2003. Among the measured site and burn characteristics that were measure, this project sampled soils before and after the fire from 5 previously-sampled locations that were burned in June 2003 and from 5 newly established locations that served as controls. The controls were within an area that was sampled between 1989 and 1996 for similar properties measured in this study and had previously been tested to be similar to the locations burned in 2003. The soil properties that are repeatedly measured at the burn and control locations include: field water content; water-holding capacity; organic matter; field extractable nitrate and ammonium; and potentially mineralizable nitrogen.
The removable bridge is placed upon the end rebar and the middle pin is secured in the depression on the nail beneath the middle hole (#16). The bridge is then leveled and individual pins are inserted to the soil surface. If the surface is firm enough, the pins are left unsecured. If the surface is too soft, the pins are secured with the tip at the soil surface by attaching a clothspin above the bridge. The heights of each pin above the bridge are recorded, and cover is recorded if the pin struck vegetation when being inserted and basal cover is recorded if the pin rested upon the basal portion of a plant at the ground surface. The standard soil bridge developed for the Sevilleta was used. The bridge contains 31 holes at 5 cm intervals with the middle hole used to orientate the bridge above a nail left at the ground surface, and which provides a reference to secure the line and the bridge height. Also referenced at (http://sevilleta.unm.edu/data/contents/SEV065/).
For inorganic N extractions and potentially mineralizable N measurements, a soil core of 4-cm diameter was taken to 20-cm depth beneath two nearby grass clumps (the two cores were compostited; termed under) and from two bare soil patches (two cores were composited; termed open) within 5 m of the stake identifying each bridge or from the bridge stake with the identification tag (new control bridges). All soil samples were placed into an ice chest and transported on ice directly to the University of New Mexico UNM, where they were sieved (< 2 mm), mixed, and stored at 5 degrees C. All soil N measurements were performed at UNM.
After determining fresh water content and water-holding capacity (WHC)(White and McDonnell 1988), fresh portions of each sample were adjusted to 50% of determined WHC and subsamples of 20 g dry-weight were apportioned into plastic cups. One subsample of each sample was immediately extracted with 100-ml 2 N KCl for NH4+-N and NO3-N analyses to determine field-available N. Two additional cups were covered with plastic wrap, sealed with a rubber band, and incubated in the dark at 20 degrees C. The plastic wrap minimized water loss during incubation, yet exchange of CO2 and O2 was sufficient to keep the subsamples aerobic during incubation. Moisture content was monitored by mass loss and replenished as needed. After contact and settling for 18-24 h, the clarified KCl was filtered through a Kimwipe and analyzed for NH4+-N and NO3--N+NO2--N on a Technicon AutoAnalyzer (Technicon, Terrytown, NY) as described in White (1986). After incubation for 6 weeks, a subsample of each soil was extracted with KCl and analyzed for NH4+-N and NO3--N+NO2--N. Potentially mineralizable N was determined to be the amount of extractable N in the 6-week extraction.
Organic matter was determined by loss-upon-ignition in tin cups following heating at 500C for two hours.
Soil Physical/Chemical Properties
Soil cores were taken beneath grass clumps in which the temperature pellets were placed both before and after the fire. At least 300 g of soil were taken to a depth of 10 cm (NOTE:different depth than nitrogen cycling)
Fire temperature was determined with pellets supplied by Tempil (2901 Hamilton Blvd., South Plainfield, NJ 07080; www.tempil.com). A set of 15 foil-wrapped tablets, with melting temperatures ranging from 85 C to 1533 C, were strungon wire and suspended about 1 inch above the ground. The fire temperature was assumed to be greater than the temperature at which the corresponding pellet showed signs of melting and less than the temperature of the next highest undamaged pellet. The pellets were suspended within two clumps of dominant grasses at the site (black grama).
Pre-existing briges (1.1 through 1.5) were selected to be included within a prescribed burn area. Data collected from the bridges were consistent with existing data collection: (http//sevilleta.unm.edu/data/contents/SEV065/ ) and included soil surface elevation, plant aboveground cover and basal cover. Soils from beneath a nearby grass clump and from bare interspaces were collected for analysis of soil properties. Soil temperature pellets were placed within grass clumps from beneath which soils were collected. Pre-fire on control and expected burn plots, and post-fire on burn plots only for soil elevation, aboveground plant cover and basal cover, N mineralization potentials, field moisture, water holding capacity, and loss upon ignition for organic matter. Pre and post burn soil samples were collected beneath grass clumps at the existing bridges for analysis of soil properties (sent ot Jane Belnap). Fire temperature was measured with temperature tablets placed about 1 cm above the ground within the grass clump that was sampled for soil properties and in an adjacent grass clump of similar appearance.
Changes to the data: Data were updated to include 2007 data on 5/15/2008 by Carl White.
Additional Study Area Information
Study Area Name: Bridge 1.1
Study Area Location: north end of five bridges; black grama dominated grassland; MacKensie Flats; Site is 5 m area around bridge; Bridges setup in 1994 to monitor changes in soil surface elevations to understand the dynamics of soil particles and associatednutrients. North Coordinate: 34.3358 South Coordinate: 34.3358 East Coordinate: -106.6954 West Coordinate: -106.6954