This study was conducted on the Jornada Experimental Range (JER)
from 2007-2009. The study area is located on a level upland with
flat slopes (1-5%) that were fenced from cattle grazing since 1996.
The vegetation was dominantly desert grassland (Bouteloua eriopoda,
black grama) followed by honey mesquite (Prosopis glandulosa). Soils
are coarse-textured, well-drained, sandy loams soils (Typic
Paleothids).
A randomized complete block design was employed to randomly assign
one treatment combination to each plot (2.5 × 2.5 m) within one of
three blocks. Precipitation (PPT) manipulations consisted of five
levels of PPT relative to ambient PPT: −80, −50%, control, +50,
+80%, with 12 replicates per treatment. Reduction of 50% or 80% of
rainfall was achieved using different numbers of transparent acrylic
V-shaped "shingles" per shelter. The shingles routed
incoming PPT to outside gutters. For increased PPT treatments, a
PVC-pipe irrigation system with sprinklers was installed over the
plots. Irrigation occurred the day of the rain event if PPT was >
2mm using rainfall collected off-site. Control plots received
ambient PPT and had neither shelters nor irrigation systems. In June
2009 a subset of the plots were switched to a different
precipitation treatment (see “water_09_trt” variable in the data
set) but the nitrogen treatments were not altered.
Nitrogen fertilization treatments consisted of two levels: 1) liquid
ammonium nitrate fertilizer applied twice each growing season in
mid- and late July from 2006 to 2008 (treatment), and 2) application
of the same amount of water, equivalent to a 2mm rain event
(controls). The ammonium nitrate fertilizer consisted of 10 grams of
ammonium nitrate dissolved in water per meter per year. Treatments
began in October 2006.
Volumetric soil water content was measured (VWC) to evaluate the
effectiveness of the water manipulation treatments. VWC measurements
were taken the 1st, 3rd and 5th days following any precipitation
event > 2 mm, and every 2 to 3 weeks during the period in between
rainfall events. Some VWC measurements were timed to coincide with
plant ecophysiological measurements. VWC was monitored using Decagon
ECH2O EC-5 and EC-20 moisture sensors (Decagon Devices, Pullman, WA)
at shallow (0-5 cm, EC-5) and deep (30-50 cm, EC-20) depths. Probes
were calibrated for soils at the study site following instructions
from the manufacturer. This data set contains information on the
date of data collection, the Julian Day, block number, plot number,
2007-2008 precipitation treatment, 2009 precipitation treatment,
nitrogen treatment, depth of soil probe, sensor voltage, and
volumetric water content. Soil moisture monitoring was discontinued
in 2009.
Also available are plant cover data from this study in data package
knb-lter-jrn.210278002.
For further information and results, see:
Throop, H., L. G. Reichmann, O. Sala, and S. Archer. (2012),
Response of dominant grass and shrub species to water manipulation:
an ecophysical basis for shrub invasion in a Chihuahuan desert
grassland. Oecologia 169: 373-383.
https://doi.org/10.1007/s00442-011-2217-4
Reichmann, L. G., O. E. Sala, and D. P. C. Peters. (2013), Water
controls on nitrogen transformations and stocks in an arid
ecosystem. Ecosphere 4(1):11. https://doi.org/10.1890/ES12-00263.1
