Dear Babar Mahmood,
I like to bring your attention to the SigmaProbe. This is a device that can
be used to measure the conductivity of the pore water in the soil. The
SigmaProbe is available from Delta-T and developed by us. This probe can be
used to measure the conductivity of the pore water in the soil without the
need of extracting water from the soil. Until now it was only possible to
measure the bulk conductivity of soil that should be converted to the pore
water conductivity (the EC).
See for more information http://www.delta-t.co.uk
Max A. Hilhorst
__________
Institute of Agricultural and Environmental Engineering (IMAG-DLO)
http://www.imag.dlo.nl/ and http://www.dlo.nl
Address: Mansholtlaan 10-12, NL-6708 PA Wageningen, The Netherlands
Mailing address: Dr. Max A. Hilhorst, IMAG-DLO, P.O. Box 43, NL-6700 AA
Wageningen, The Netherlands
E-mail: m.a.hilhorst@imag.dlo.nl
Phone: +31.317.476650 or +31.317.476602
Fax: +31.317.425670
===================
With respect to Bob's difficulty in getting moisture to flow from a fine
sand into a granular matrix sensor, my guess is that over a range of
tensions there is a capillary barrier between the fine sand and the porous
material of the sensor. The moisture won't enter because the hydraulic
conductivity of the coarse sensor material, over a range of tensions, is
much less than that of the fine sand. To test this hypothesis, one could
pack the granular matrix sensor in a container of dry fine sand and put it
on a tension plate. If the tension is slowly raised (becoming wetter),
then the granular matrix sensor will start to respond at the tension where
the conductivities are similar.
I don't know of a cure, other than to change the sensor material to
something finer. Other packing materials, such as a coarse material, won't
help because the capillary barrier will then form between the fine sand and
the coarse packing material. My guess is that a finer packing material will
make the problem worse.
Paul Hutchinson.
At 21:45 30/07/99 GMT, you wrote:
>NOTE: To get off this list, send email to majordomo@aqua.ccwr.ac.za
>with the body of the message containing the line:
>unsubscribe sowacs
>
>There has been some recent discussion on materials used to backfill
>ceramic porous cup devices that are in contact with the surrounding
>soil/water environment - bentonite being mentioned as one.
>
>I am investigating the use of a connecting media between granular matrix
>sensors (for measuring soil-water tension) and sandy soils. Sandy soils
>with a small percentage of fines are often not suitable for granular
>matrix sensors due to, I believe, some difficulty in achieving
>soil-water continuity between the porous media of the sensor and the
>surrounding soil.
>
>Is there a fine material that could be used as a slurry, having good
>hydraulic conductivity, so that the sensor could communicate with the
>surrounding soil without compromising the response time?
>
>I would sure appreciate some suggestions.
>
>Thank you,
>
>Bob Mittelstadt
>Othello, WA
>
>
>
>
===================
>There has been some recent discussion on materials used to backfill
>ceramic porous cup devices that are in contact with the surrounding
>soil/water environment - bentonite being mentioned as one.
>
>I am investigating the use of a connecting media between granular matrix
>sensors
Heck , but I am falling further and further out of touch. What is the modern
definition of a GRANULAR MATRIX SENSOR ? Is it a sensor not viable in a
loam?
By using an artificial slurry are you not just transposing the contact
problem just slightly away from the sensor ? Jean/
[Bruce comments:
content from this discussion will hopefully provide copy for the sowacs page
on granular matrix sensors : www.sowacs.com/sensors/granular.html ]
===================
>I have a long frustrating experience with using bentonite for sealing around
>the access tubes / tensiometers in a clay soil. I have tried different
>depths of application with sufficient compaction. It seems to me that upon
>drying, the bentonite cracks. It is also possible that it shrinks and water
>moves along the interface between clay and bentonite.
>
>Masoud Edraki
>At 18:56 27/07/99 GMT, you wrote:
>>I am wondering what happens with the swollen bentonite in the drying cycle?
>>Would it crack and provide preferential flow paths along the tube?
>>M. Meron
Hello to all,
The problem is different if you consider soil moisture measurements or
tensions measurements.
In the case of moisture measurements, you must have arround the sensor the
soil concerned by the measure, with his characteristics of texture and
structure (porosity ...). When this soil is a cracking when drying soil, it
can be a big problem with pinpoint measurements.
In the case of tension measurements, you do not need to have close arround
the sensor the same soil as the measured soil . You only need that the
forces linking water and soil are in balance all together for measured
surrounding soil and close arround the sensor (for ex. tensiometer). So you
can put close arround the sensor non cracking material (soil), and the
measure will be good, providing you wait a sufficient time for equilibrium.
For ex. you can make a hole of 3 cm diameter, pull in the bottom a more
sandy or loamy soil (non cracking)than the soil of your field, then put the
tensiometer in the soil, and continue to fill and compact (to avaoid
preferential flow paths) with the non cracking material.
(I hope my bad english is clear enough)
best regards
Carole Isbérie
===================
There has been some recent discussion on materials used to backfill
ceramic porous cup devices that are in contact with the surrounding
soil/water environment - bentonite being mentioned as one.
I am investigating the use of a connecting media between granular matrix
sensors (for measuring soil-water tension) and sandy soils. Sandy soils
with a small percentage of fines are often not suitable for granular
matrix sensors due to, I believe, some difficulty in achieving
soil-water continuity between the porous media of the sensor and the
surrounding soil.
Is there a fine material that could be used as a slurry, having good
hydraulic conductivity, so that the sensor could communicate with the
surrounding soil without compromising the response time?
I would sure appreciate some suggestions.
Thank you,
Bob Mittelstadt
Othello, WA
===================
If it is buried 15 - 20 cm below the surface, and is at least 15 cm long,
should reduce (eliminate?) problems with cracking based on experience in a
silty-clay soil. See Oster, J. D., and L. S. Willardson. 1971. Reliability
of salinity sensors for the management of soil salinity. Agron. J.
63:695-698.
At 06:56 PM 7/27/99 GMT, you wrote:
>
>I am wondering what happens with the swollen bentonite in the drying cycle?
>
>Would it crack and provide preferential flow paths along the tube?
>
>M. Meron
>
EFFECTIVE JUNE 4 THROUGH DEC. 31, 1999
Summer/Fall Office: 32 Wishram Tr., Graeagle Ca.
P.O. Box 1344, Graeagle, Ca. 96103. 530-836-1835
FAX: none. Webpage: http://esce.ucr.edu
e-mail: Oster@mail.ucr.edu; jdoster@inreach.com
===================
I have a long frustrating experience with using bentonite for sealing around
the access tubes / tensiometers in a clay soil. I have tried different
depths of application with sufficient compaction. It seems to me that upon
drying, the bentonite cracks. It is also possible that it shrinks and water
moves along the interface between clay and bentonite.
Masoud Edraki
At 18:56 27/07/99 GMT, you wrote:
>
>I am wondering what happens with the swollen bentonite in the drying cycle?
>
>Would it crack and provide preferential flow paths along the tube?
>
>M. Meron
>
>
>
>
>
>
M.Edraki
Department of Land and Food ( St.Lucia Campus)
The University of Queensland
Brisbane, QLD 4072
Australia
ph : ++61 07 33657429
E-mail: M.Edraki@maibox.uq.edu.au , or
agmedrak@dingo.uq.edu.au
Fax : 07- 33651177
===================
I am wondering what happens with the swollen bentonite in the drying cycle?
Would it crack and provide preferential flow paths along the tube?
M. Meron
===================
Dear members: backfilling a portion (5 - 10 cm) of an oversized hole with
bentonite will stop water flowing downward along the access tube. Best
location for the bentonite is about 5 - 10 cm below the soil surface.
Bentonite swells upon wetting, and can do so to several times the volume of
the powder. Its H.C. is very low. Swollen bentonite could plug some large
pores beyond the original insertion hole.
EFFECTIVE JUNE 4 THROUGH DEC. 31, 1999
Summer/Fall Office: 32 Wishram Tr., Graeagle Ca.
P.O. Box 1344, Graeagle, Ca. 96103. 530-836-1835
FAX: none. Webpage: http://esce.ucr.edu
e-mail: Oster@mail.ucr.edu; jdoster@inreach.com
===================
Dear Said:
One potential area of error that we are investigating is that if you
have macropore or preferential flow, the water is flowing in only a very
small percentage of the total porosity. Then when you sample using a
tension-type sampler, you are only sampling the residual water which
would not necessarily be representative of the percolate water. We have
submitted a manuscript to the Trans. ASAE in May but haven't heard back
on publication status. If you have any questions, just let me know.
Regards,
Rob
--
*************************************************
Rob Malone
Research Agricultural Engineer
North Appalachian Experimental Watershed
USDA-Agricultural Research Service
P.O. Box 488
Coshocton, OH 43812-0488
malone@coshocton.com
Phone: 740-545-6349
Fax: 740-545-5125
*************************************************
===================
Re: This posting is a followup to what Said Amali at Kennedy/Jenks Consultants
Federal Way, Washington 253-874-0555 posted before.
Dear Said/ Sowacs members:
Our water quality and plant nutrient laboratory at the University of Florida
CREC (myself, A. Fares, S. Paramasivam and A.K. Alva) wrote an extensive review
article about the previlant methods and devices used in water quality sampling
for both laboratory and field conditions This article is entitled:
vadose zone solution sampling techniques to investigate pollutant transport in
soils.
It has the following subtitled:
Introduction
Soil Solution Sampling Approaches
Lab.
Field
Selection of Technique
Field Operation of Suction Lysimeters
Comparison between different Porous Material in Soil Solution Sampler
Limitation of Soil Solution Samplers
-Solution uptake by the soil solution sampler
-Solute uptake by soil solution sampler
-Effects of spatial variability on solution sampling technique
-Chemical consideration
+ volatile organics
+ trace elements
+ aluminum
+ microbiological consideration
Comparison between PL and PCSL Soil Solution Samplers
Acquisition of soil Solutions by other methods
Summary.
Please let me know if you need a copy of this I will be glad to send you one.
--
Ali Fares, Ph.D.
CREC, University of Florida
AF@GNV.IFAS.UFL.EDU
http://gnv.ifas.ufl.edu/%7Eaf/
Ph (941) 956-1151, Fax: -4631
===================
<< Said Amali
Kennedy/Jenks Consultants
Federal Way, Washington
253-874-0555
saida@kenjenfwy.com >>
If you would give me a complete mailing address I will send you our
information on our Model SSAT (suction lysimeter).
Regards, Bill Pogue, President, Irrometer Company, Inc.
===================
Hello Said Amali,
To get a good measure of the effect of macropore flow (short-circuiting) I
think the best method is to use tile drains (if possible) which integrates
over larger areas (depends on the local hydrological situation though). I
believe this is specially important on clay soils where there might be a
very high, both spatial and temporal variability in the flow pattern.
We made such a field study to evaluate nitrate movement in a structured
clay soil. It will appear in the next (?) issue of Journal of Environmental
Quality:
Larsson, M.H. & Jarvis, N.J. 1999. A dual-porosity model to quantify
macropore flow effects on nitrate leaching.
Regards Martin Larsson
_______________________________________________________
Martin Larsson
SLU
Department of Soil Sciences
Division of Water Quality Research
P.O. Box 7072
S-75007 Uppsala, Sweden
Phone: +46 18 671169
Telefax: +46 18 673430
E-mail: Martin.Larsson@mv.slu.se
http://www.mv.slu.se/Vv/slu_vv.htm
_______________________________________________________
===================
You might find some of these (pretty old) references of use:
Hansen, Edward A., and Alfred Ray Hansen. 1975. Validity of soil-water
samples collected with porous ceramic cups. Soil Sci. Soc. Am. Proc.
39:528-536.
Jackson, D.R., F.S. Brinkley, and E. A. Bondietti. 1976. Extraction of
soil water using cellulose-acetate hollow fibers. Soil Sci. Am. Proc.
40:327-329.
Levin, M.J., and D.R.Jackson. 1977. A comparison of in situ extractors
for sampling soil water. Soil Sci. Am. J. 41:535-536.
Wagner, G.H. 1962. Use of porous ceramic cups to sample soil water
within the profile. Soil Sci. 94:379-386.
We are Delta-T Devices - scientific instrument designers and
manufacturers. If it is of interest, we have a new probe, the
SigmaProbe, that can measure the conductivity of pore water. You can
find out more in the NEWS section of our website:
http://WWW.delta-t.co.uk.
In the USA we are represented by Dynamax Inc., contactable on
export@dynamax.com
Regards,
Lea Dodds
Lea Dodds
Delta-T Devices Ltd.
128 Low Rd., Burwell, Cambridge CB5 0EJ
England
Tel: Intl +44 1638 742922
Fax: Intl +44 1638 743155
E-mail: Lea.Dodds@delta-t.co.uk
Web site: www.delta-t.co.uk
===================
TONY THOMSON writes
Richard Stirzaker, CSIRO has developed an innovative new funnel-shaped
device for irrigation scheduling which also collects a water sample from the
vadose zone.
Regards
Tony
===================
Hello Said
I am evaluating and validating crop growth simulation models for wheat in South
Africa under both irrigated and rain fed conditions and have had the same
questions during my study. In the end I have used an adapted drainage lysimeter to
measure deep percolation and the ammount of nitrate in the leachate. If you read
my short communication on that; Du Toit, W.H.O. (1997) A cost effective method to
measure percolation and leaching in a lanscape. Procc. African Crop Sceince
Conference. 3:271-273 the actual method would be clear (attatched). The biggest
problem was finacial, not having enough money to measure suction in the soil
around the percolation meter (drainage lysimeter) and the construction of a suction
plate to apply the same suction at the bottom of the lysimeter. If I could have done
this I am possitive that it would be the most accurate way of measuring nitrate
leaching.
What's your opinnion about this method?
Regards
Willie
===================
Hello Said Amali !
I am measuring water flow in a heavy clay soil with bypass flow. We use
zero tension lysimeters to collect the water from the macropores as
earthworm channels and cracks. The lysimeters are samplers that are
pushed horizontally into a vertical pit under the undisturbed soil. We have,
in our special case, problems with vertical flow in the soil.
To see more about lysimeters look at:
TITUS, B.D & MAHENDRAPPA, M.K.(1996): Lysimeter system designs
used in soil research: A review. Series: Information report (Canadian
Forest Service. Newfoundland and Labrador Region); N-X-301
If you have more questions about lysimeters, Email me.
Clemens Siebner
-----------------------------------
Clemens Stephan Siebner
Institut fuer Bodenwissenschaft/
Inst. of Soil Science
von-Siebold-Str. 4, D-37075 G=F6ttingen
Tel. 0551/39-5505 Fax ++49551/39-4619
-----------------------------------
===================
Dear Said,
You may like to try posting your query on the unsaturated-soil discussion
list.
'unsaturated-soil' is a discussion list for researchers studying the
engineering behaviour of unsaturated soils. This can include experimental
work and numerical modelling concerning the mechanical and flow properties
of unsaturated soils.
To join unsaturated-soil send the following command, (typing your own
personal names instead of firstname(s) and lastname)
join unsaturated-soil firstname(s) lastname
as the only text in the body of a message addressed to:
mailbase@mailbase.ac.uk
Archives of past messages are available on the list webpage at:
http://www.mailbase.ac.uk/lists/unsaturated-soil/
Do pass on this information to anyone whom you think would be interested.
David Toll
*******************************************
Dr David Toll
Nanyang Technological University
School of Civil & Structural Engineering
Blk N1, #1A-37, Nanyang Avenue
Singapore 639798
Tel: +65-790 6429/791 1744
Fax: +65-791 0676
e-mail: cdtoll@ntu.edu.sg
WWW: http://www.ntu.edu.sg/home/cdtoll/
===================
PLEASE LOOK AT NEW ZEALAND LAND TREATMENT COLLECTIVE
PROCEEDINGS OF THE TECHNICAL SESSION NO 18
EFFECTS OF LAND-TREATED WASTES ON GROUNDWATER (PAGE NUMBER 83)
8-9 OCTOBER 1998, TAUPO, NEW ZEALAND.
C/O FOREST RESEARCH , PRIVATE BAG 3020, ROTORUA, NEW ZEALAND
:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
Babar Mahmood
Institute of Technology and Engineering. Environmental Research Group.
Massey University,Palmerston North,New Zealand. Ph: 64-6-3505372 (work)fax:
64-6-3505640.
If you are not in the lead, the view stays the same.
----------------------------------------------------------------------
