Deep Soil Core Micronutrients

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Soil cores were collected under mesquite (Prosopis glandulosa) trees at playa, wash, sand dune, and grassland sites on the Jornada LTER site to depths of 15, 9, 7, and 4 m. Soil cores (to 4 m) were also taken under creosote bush (Larrea tridentata) near the wash site. Soils were extracted and analyzed for micronutrients, Zn, Cu, Fe, and Mn.

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Field and electronic data sheets

*Undisturbed soil cores from the rooting zone of three trees in each ecosystem were removed using a split steel, continuous sampling tube, 1.56 m long with 6.5 cm i.d. This coring device, mounted on a truck, was modified from Kelley et al. (1947). The split-tube bit fits into an outer, rotating auger bit that served as a continuous casing to prevent cave-in. As the outer bit cut through the soil, the inner, nonrotating bit was pressed into the soil. Cores were collected at the edge of the mesquite canopy. The core retainer and the two halves of the split sampling tube were cleaned of all residual soil. Their interior surface was flame sterilized with 95% ethanol before being put together for sampling. Soil samples were removed from the surface 1 m of soil in 0.5 m increments, and thereafter in 1 m increments. Flame sterilized trowels and spatulas were used to replace each depth increment into a clean plastic bag. These were put into icecooled chests, and transported to the Univ. of California, Riverside, where they were subdivided for analysis. Drilling depth for each core was determined by either the absence of roots in two consecutive 1.56 m sampling tube lengths, or the presence of coarse, dry loose soil that could not be retained in the tube. The number of cores (three per ecosystem per sampling) collected was limited by the expense of obtaining the specialized drilling equipment used in this study. Sampling dates at New Mexico were in January 1986, the midpoint of the dormant season; late May 1986, during peak growth; and early October 1986 following the summer rains. The grassland site was not sampled on the Jan-Feb drillings. Each bag of soil representing a depth increment was mixed thoroughly before subsampling. Using trowels and spatulas flame sterilized with 95% ethanol, each soil sample was sub-divided for various analyses. Gravimetric water content of the soil samples was determined at the time of subsampling(weight of water/weight of dry soil). Soils for chemical analysis were then air-dried in a glass-house, ground to break-up clay and caliche aggregates, and passed through a 2 mm sieve. Soils from the Winter drilling were extracted with NH4HCO3-DTPA (Soltanpour et al., 1979) and analyzed for Zn, Cu, and Mn. Fall soils were extracted with DTPA (Lindsay and Norvell, 1978) and analyzed for Zn, Cu, Fe, and Mn. All analyses were made using ICP (inductively coupled plasma) emmission spectroscopy.

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*Four mesquite ecosystems were stuided: playa, coppice dune, arroyo, and grassland. An ecosystem dominated by the non-legume, Larrea tridentata, and lacking mesquite was included as a reference. The arroyo, grassland, Larrea and a playa site were loacated on the NSF Jornada Long Term Ecological Research (LTER) site situated 40 km north of Las Cruces, NM, in the northern Chihuahuan desert. A coppice mesquite dune site was located on the adjacent USDA Jornada Experimental Range about 15 km from the above sites.


Two times (January/February and September)

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