Data set ID:
NO3 + NO2-N and NH4-N levels of soil samples collected at each station along transect. Moisture content of soil samples is also included.
Lab data sheets
Samples are collected near each station on alternate sides of the transect. Distances from the station and from the transect are designated prior to collection. Soil samples are collected from 0-10cm after removing surface litter. Samples are extracted in a 10:1 ratio of standing 2M KCl for 24 hours, then filtered through Whatman #42 paper. NH4-N is measured using a colorimetric salicylate procedure. NO3+NO2-N is measured by a colorimetric cadmium reduction procedure. These were performed manually through May 1984 (weeks 122-123). Beginning in September 1984 (weeks 141-142) a Scientific Instruments AutoAnalyzer was used. Moisture content is determined by oven drying at 40 degrees C for 72 hours.
In the spring of 1982, as part of the establishment of the Jornada Long-Term Ecological Research site in southern New Mexico, a 135 ha portion of a 1500 ha, internally drained, watershed was exclosed from grazing by domestic livestock. Prior to exclosure the watershed, as well as the rest of the Jornada basin, had been moderately to heavily grazed for the past 100 years. Concurrent with grazing, the vegetation had undergone a dramatic change from desert grassland, with an almost continuous cover of C4 perennial grasses, to isolated patches of the original grassland in a mosaic with desert shrub dominated plant communities (Buffington and Herbel, 1965). The exclosure lies along a northeast facing piedmont slope at the base of a steep isolated mountain peak, and covers a variety of component landforms from the foot of the mountain to the basin floor. The northeast side of the exclosure is immediately upslope of the College Playa located near the NMSU College Ranch. Three parallel transects (2.7 km in length) run from the middle of the College Playa up into the foot of Mt. Summerford. The Control transect is to the west, the Treatment transect on the east side of the Control transect, and the Alternate Control to the east of the Treatment transect. Each transect is 30 meters wide with a 45 meter buffer zone between each transect. The Treatment transect was treated annually until 1987 with NHNO3 in a concentration equal to 10g N/m2. The station markers at 30 meter intervals along each transect.
Three to four times a year