ASM01 Soil water content measured by neutron probe at Konza Prairie


Data set contains measurements of soil moisture (%volume) at various depths (25-200 cm) in deep (lowland) soils collected on LTER grazed and ungrazed watersheds burned at 1-, 4-, and 20-year intervals. Soil moisture measured by the neutron probe method.

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To monitor spatial and temporal patterns of soil moisture in nine Konza Prairie LTER watersheds.


Location of Sampling Stations: All access tubes are located in Tully soils. Two tubes are in: R01A, R20A, 004B, 020B, R20B, 001D, R01B, and N04D. N20B has four holes. All tubes are located near species composition transects and are marked with conduit. Maps of all locations are available in Bushnell 207.
Frequency of Sampling: Soil moisture is taken every two weeks from April 1 to November 1. November to March, readings are taken monthly when the temperature is above 20oF and there is no snow cover.

Preferred method is for all sites to be measured on the same day. It will take two technicians 4-5 hours to complete all sites. A solitary technician will need 6+ hours. If readings are interrupted by significant rainfall, all sites must be re-done. A standard count is taken at the beginning of every session. At every site, the technician will check for water. If water is present, the lower depth reading(s) may not be taken. The probe must NOT be inserted into water. Tube depths vary from 75 cm to 200cm. Holes were dug as deep as possible. Inserted into each hole is an aluminum access tube. The unit must be seated securely on top of the tube. The probe is then lowered to the varying depths at 25 cm increments and a reading is made and recorded. Each hole is closed off between readings with a rubber stopper and a metal top. Occasionally, these go missing due to animal activity. They will be replaced as soon as possible. Holes in the bison area are surrounded by an open metal framework 1.5 m x1.5 m x 1 m to protect the access tubes from bison damage.

The neutron probes (Troxler, Model 4300) are stored in Bushnell Hall. Batteries are charged as needed. A single charge will last 3-4 months.

Maps of all soil moisture sites are located in Bushnell 215.

Precautions: Only authorized technicians are permitted near the probes. All technicians are issued radiation badges that must be worn when using the probes. If recommended procedures are followed and the unit is not abused, operating the neutron probe is not hazardous. Make sure the probe is firmly latched in the unit before removing from the access tube. Do not immerse the probe into water. Specific safety and security procedures must be followed when transporting the probes via state and city roads.

Summary of All Changes:

1984: Tubes in 001C were added.

1989 January: a measuring stick was dropped into 020B #1, restricting depth readings to 75 cm. The stick lodged in the mud and could not be removed.

1989 July: tube #1 in 004B was damaged by a truck; it was replaced approximately 2 m away in December 1991. The new tube extended 23 cm above the ground instead of the normal 8 cm. In January 1993, the tube was cut to an 8 cm protruding height to conform to heights of other tubes. Thus readings from December 1991 to December 1992 were actually 15 cm above their indicated depth (i.e. 10, 35 and 60cm instead of 25, 50 and 75).

1992: Four tubes in N01B were abandoned because of potential contact problems between humans and bison. There are readings from 1983 until April 1992.

1998: Old probes (#1 and #2; Troxler, Model 3400) were replaced with Troxler, Model 4300. #3 arrived in January and #4 arrived in May.

1998 May to December: problems with access tube at N04D #2 tube-no readings.

1998 June: tubes in R01A (was 020A), R01B (was 020D) and R20A (was 001A) were added.

2001 Spring: fire reversal experiment began. This impacted the burn schedule of 4 watersheds. 001A became R20A. 001C became R20B. 020A became R01A. 020D became R01B.

2001: Continued, intermittent problems with N04D #2 from September 2001 to May 2002 and October 2002 to May 2003-no readings. From late May 2003 to March 2004, able to get readings but the probe was NOT completely seated on the access tube. Cause of problem, damage to access tube from bison activity.

2004 March: Unable to get readings from either N04D tube-both damaged by bison activity.  In late May, cut off the upper edge of access tubes (less than 2 cm removed from top). Bison barriers put out around all tubes in the bison area (N04D and N20B).

June 2005 to June 2006: Chronic problems with #3. The unit was in and out of Troxler’s TX and SC repair shop. During this time, readings were predominantly done by #4.

June 2006 to February 2009: chronic problems with #4. In and out of Troxler’s SC repair shop. During this time, readings were predominantly done by #3.

2006: New stand for taking standard counts has been built. The original stand was 25 cm. According to the Troxler manual, it should have been 25 inches. There have been no changes in the readings.

2010: July - All access tubes were supposed to have a standardized height of 8cm (protruding aboveground). Most of the tubes were not at this height. On July 14, all tubes were measured and those needing adjustment were cut with a hack-saw. Note that 3 sites, (N20B #1, N04D #1, and N04D #2) are below the standardized height. Both N04D sites were cut in May 2004 due to bison damage.2010: September 3, R01A was discontinued due to damage when cutting.

2015: Fall - No soil moisture readings from August through November 2015. Troxler machines no longer working. A new machine has been ordered.

2015: December - Soil moisture readings done with new machine. There are some differences from the old machine. 1.The new probe is slightly longer, and 2.There are only 7 depth markers. Therefore, 200cm depths will no longer be done. The new machine reports in g/cc. All data sheet measurements will be multiplied by 1000 to maintain the historic use of kg/m3

2015: new soil moisture probe. InstroTek CPN 503 Elite Hydroprobe. The new machine only had 7 stops; the Troxler machines had 8. The probe is slightly longer on the Hydroprobe. Also, measurements are given in g/cc; all readings are multiplied by 1000 to maintain the records in kg/m³

2017: August 25 - bison damaged access tube #1. Top 0.5 inch has been cut off to repair the damage.

2018: April 12 - bison damaged access tube #1 again. Top 0.25 inch has been cut off to repair the damage. In addition, the Konza Staff made us 8 new spikes to help hold the barrier fence in place.

2018: August 9 - 2 cm of pipe removed from 0001d #2 to repair damage that was preventing the probe from fitting for readings.

2019: May 30 - Hole #1 at N4d. On May 30, techs were taking readings. The probe separated from the cable and dropped to the bottom of the hole. Hole #2 was 2m deep and the techs had detected 11cm of water in the bottom. We contacted Patrick O’Neal/KPBS and he tried a couple of ideas (magnet-all aluminum and a “snag”). He tried to pull the access pipe with a post puller and it would not budge. It also crimped the top of the pipe ending any hopes of getting the probe out via the pipe. The 4 techs began digging down around the pipe in hopes of wiggling it loose and pulling out the pipe and probe. They eventually hit rock/clay and could not make further progress. Plans were made with Patrick to bring in a backhoe on May 31. 
2019: May 31 at 1:00 p.m. - KSU Radiation Safety was present; they requested being present at the time of removal to inspect the probe. Patrick began digging a trench alongside the hole that was dug on May 30; he dug down 2m. The end of the pipe was firmly stuck in clay so it was decided to employ a chain and pull the pipe up and out. The pipe came right out and the probe was inside. RSO Dr. Bridges declared the probe undamaged. Patrick pushed all the dirt back into the hole and drove over it a few times to pack it down.
2019: June 11 - A new hole was bored for N04d #1. A GeoProbe Soil Corer was used to dig the hole. Absolute depth is 201 cm. The pipe was cut to 8 cm above-ground height. The new location has been GPS-ed. 
2019: June/July - A new cable was installed 190604. The technicians noticed that the probe was not able to go down as far as expected. On checking, all of the cable stoppers were off by ~16 cm. Readings for June 4, June 18, and July 2, 2019 were 16 cm too deep.
2021: October - the access pipe at n04d #1 has been pushed down and is now flush with the soil surface due to bison activity. Access pipes are set at 8cm above the soil surface.
2022: April - technician noticed that some of the cable stops were slipping during the 220406 readings. All of the cable stops have been measured for distance and tightened. All of the cable stops were adjusted. I have spoken to all previous users and none of them noticed any issues. Hopefully, this was a recent problem. (AKuhl)

25cm – cable stop off by 5cm too low (the readings done at ~30cm)
50cm – cable stop off by 2.5 cm too low
75cm – cable stop off by 2.5 cm too low
100cm – cable stop off by 5 cm too low
125 cm – cable stop off by 2.5 cm too high
150 cm – cable stop off by 2.5 cm too high
175 cm – cable stop off by 10 cm too high

2023: January – during the 2022 season, seven sites routinely showed a change in depth. The change in actual depths range from 1-10cm but the data sheet has been changed so that all readings are measurements where the probe is hanging freely and not touching the soil. Seven sites have been officially changed and we are watching 3 others (changed depth for ro1a-tube2 from depth 75 to depth 50).
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