Jornada Basin LTER Research

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Dataset: Soil Volumetric Water Content at the 15 NPP Sites of the Jornada Basin LTER from 1989

Related links: Neutron Moisture Meter Calibration

   File description including attribute definitions: data_Jornada_013_npp_soil_volumetric_water_content
   Original Investigator: Wesley Jarrell
   Data contact: Mike Duniway
   Duration: 1989 - ongoing
   Dataset ID: 210013003
   DOI: 10.6073/pasta/2f128c4dadcd27feec5d4e9fd0b7effc
   Abstract:

    Monthly soil water content measurements are made at 10 depths (where
    possible) at each of 10 access tubes at each of the 15 LTER-II NPP
    sites using a neutron probe (CPN Model 503DR Hydroprobe).  The counts
    of thermalized neutrons are adjusted for the decay rate of Americium
    241, then converted to soil water content using individual site
    regressions.  Soil water content is a volume/volume relationship and
    represent cm3 water/cm3 soil.  Data are provided at 30cm intervals from
    30cm to a maximum of 270cm soil depth, shallower when an impenetrable
    caliche layer is reached.  Field readings may include one at 300cm;
    however, the value for the deepest depth of each access tube is removed
    from the calculated soil water content data because of the effect of
    measuring greater soil volume directly below the probe than that of the
    more shallow depths.


   Additional information:

Site Location: LTER-II 15 NPP sites

   Methods:

    <SEE "Procedure: Soil water content readings on LTER-I Transect and
     LTER-II NPP sites using CPN Model 503DR Hydroprobe.pdf", file
     Probe-protocol.pdf>

     Initial regression equation was derived by Mahlia Nash in the early
     1980's, and after datalogger upgrade was added to hydroprobe, by David
     Hudson.  Both worked for Dr.  Peter Wierenga with David Hudson
     continuing this association into the first half of the 1990's at
     University of Tucson.

     Initial regression equation was derived for the LTER-I Transect soil
     water content study and applied to the measurements at the NPP sites.
     Between 2003 and 2007 individual site regressions were developed by
     Mike Duniway to better represent the variation in soil
     characteristics.  Once these were finalized all the data were
     recalculated using the new equations and adjusted raw counts of
     thermalized neutrons to account for the drift associated with the
     decay rate of the Americium 241/Beryllium used to generated the
     neutrons.

     Negative calculated water content values result from

     See PROBE.HIS file for probe history and regressions used for
     different data periods when different probes were used.  The
     hydroprobe used is a Hydroprobe Model CPN503DR (Instrotek, Inc.) with
     data logger.  This probe has a 50mCi 241 Am-Be source and a hydrogen
     detector.  Neutrons encountering hydrogen become thermalized.  The
     detector totals 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 for cm3 of water
     per cm3 of soil.
 

   Maintenance:

monthly