We evaluated soil characteristics after a lightning-initiated fire. Following the fire in July 1998, 25 experimental plots were established on the eastern edge of MacKenzie Flats at the Sevilleta National Wildlife Refuge. Ten of these plots were located in a Bouteloua gracilis (blue grama)-dominated site, while 15 were established in another area dominated by Bouteloua eriopoda (black grama). All plots were oriented along a topographic gradient that ran in an east-west direction. At three topographic locations within each plot, soil samples were taken at two depths from an area covered by perennial grass as well as an area devoid of vegetation. Soil samples were collected in July 1998 and analyzed for moisture content and soil texture.
Experimental Design - Following a lightning-initiated fire in July 1998, 25 experimental plots were established on the eastern edge of the MacKenzie Flats area of the Sevilleta National Wildlife Refuge. Ten of these plots were located in a Bouteloua gracilis (blue grama)-dominated site, while 15 were established in another study area, where B. eriopoda (black grama) was more abundant. In the former site, five of the 10 plots were established in burned areas, and the others were positioned in unburned grassland vegetation. In the latter study area, five plots were placed in burned areas, five were positioned in unburned grasslands, and the five remaining plots were located in an area that contained a mix of burned and unburned patches of grassland vegetation.
Sampling Design - All of the plots in the Bouteloua gracilis-dominated site were 4 m x 16 m in dimension. Of the 25 plots where B. eriopoda was more abundant, nine were 4 m x 16 m, and 16 were 4 m x 25 m. Regardless of site, all plots were oriented such that the long axis of each was parallel to a topographic gradient that ran in an east-west direction.
We established three 1.5 m x 1.5 m quadrats at the two corners and midpoint along the south side of each plot. Each quadrat was divided into four square cells of equal area. Within a southeastern cell (northeastern cell if a shrub was present in a southeastern cell), we selected three grass clumps and three interspace areas between plants. At the center of each plant and interspace, one sample was removed at each of two depths (0 - 2.5 cm and 2.5 - 10cm). The three "grass" samples at each depth were pooled to create one composite sample; similarly, the three interspace samples at each depth were also pooled into one sample (4 composite samples in total).
Field Methods - For the 0 - 2.5 cm samples, a 2.5-cm corer (6.7 cm diameter) was driven into the ground with a mallet. Over grass clumps, the corer was inserted such that the average original soil surface was flush with the top of the corer, generally at about one-half the height of the tussock. A sharpened trowel was hammered beneath the corer to cut the roots, and the core was removed. Any soil which fell onto the new surface was scraped away.
For the 2.5 - 10 cm samples, a 25-cm corer (4.5 cm diameter) was driven to a depth of 7.5 cm below the surface created by the previous sample. The corer was then twisted and gently pulled up. The average point of break for any individual core was estimated to be within 1 - 2 mm for at least 90% of the cores. The soil was resampled if this error exceeded 3 mm.
Samples were placed into pre-labeled paper lunch bags and transferred to a cooler (without ice). They were transported to a drying shed with ambient temperature and humidity and placed on shelves within 36 hours.
Laboratory Procedures - Soil moisture was determined by the gravimetric method (Gardner 1986). Soil texture was determined by the hydrometer method (Sheldrick and Wang 1993).
Gardner, W. H. 1986. Water content. Pages 493-544 in A. Kluite (editor), Methods of soil analysis, Part 1. Physical and minerological methods, agronomy monograph no. 9, 2nd edition. American Society of Agronomy and Soil Science Society of America, Madison, WI.
Sheldrick, B.H. and C. Wang. 1993. Particle size distribution. Pages 499-557 in M.R. Carter (editor), Soil sampling and methods of analysis. Canadian Society of Soil Science, Lewis Publishers, Ann Arbor, MI.