See the pdf document
(\"standalone_hydraprobe_protocol.pdf\") attached to this
package for detailed information on the methods for this study. These
methods are summarized below.
Monthly soil water content measurements are made at 5 depths (where
possible) at probe access tubes along the LTER-I Treatment and Control
transects. The parallel transects are 2.7 km long and extend from
College Playa to the base of Mt. Summerford. Each transect is 30
meters wide with a 45-meter buffer zone between each transect. The
Treatment transect was treated annually with NH4NO3 in a concentration
equal to 10g N/m2 until 1987. On 17 July 1986 the Control Transect was
aerially fertilized by mistake with granular NH4NO3 instead of the
Treatment Transect. As a result of this mistake, the Treatment
Transect was subsequently fertilized by hand with a team of 12 persons
using mechanical spreaders. The study site has a history of moderate
to heavy livestock grazing for 100 years before 1982.
Soil water content measurements were made at each of the 89 access
tubes on the Control transect (n=89) and at every
5
th
station on the nitrogen fertilized
Treatment transect (n= 19). Each aluminum access tube is installed 1
meter from the station marker and 30 meters apart from the next tube.
Measurements are taken at 30cm, 60cm, 90cm, 110cm, and 130cm when
possible. In addition to these measurements, mini-lysimeters readings
and standards are taken throughout each transect. If fewer depths were
measured, the missing depths have a zero in the raw data set of count
values. The occurrence of any other zero is a missed depth reading.
The hydroprobe currently used is Hydroprobe Model CPN503DR (Campbell
Pacific Nuclear, Pacheco, CA) with data logger. This probe has a 50
mCi 241 Am-Be source and a 3He detector. Neutrons encountering
hydrogen become thermalized. The detector totals the returning
thermalized neutrons over a 16 second sample time which is the raw
count value displayed. The raw count value is then substituted into
the proper regression equation to calculate cubic centimeters of water
per cubic centimeter of soil.
