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dear Tareq
your question is not quite clear.... but here is some feedback:
On Moisture Content:
Acertain whether the instrument reads Gravimetric or Volumetric Moisture
Content.
Gravimetric : difference between wet mass of soil and oven dried to constant
mass, expressed as a percentage of dry constant mass .
To determine the moisture in kg/cub.metre you need the Bulk (Wet) Density of
the soil.
Mv
Mg = ---------------------- x 100 %
Dw - Mv
Where
Mg is gravimetric moisture content in % m/m
Mv is volumetric moisture content in kg/cub.m
Dw = Bulk or Wet density in kg/cub. m
Volumetric : Amount of water per unit volume, irrespective of the medium
(such as soil) within which it is bound, expressed as a percentage of the
volume.
ie
1000 kg/cub. m = 100% because water has an approx. Relative density of 1
300 mm = 30% m/v volumetric (300mm := 300mm/sq.m)
On Field Capacity and infiltration Rate:
I can only comment on excercises done with neutron probes, but the
principles should be similar:
Select a dry patch of soil 2m x 2m. Dam up the sides to allow for water to
be filled into the patch.
Insert an access tube (or your sensors) in the centre of the patch, with has
many sensors as will give you meaningful values up to or beyond the depth of
interest (with a neutron probe or similar you will simply have a number of
cable stop positions).
Start a clock. Fill the dammed area with water and take readings down the
access tube at the different depths. Keep the filling area full at all
times. Once the water has passed the lowest depth of interest, continue the
monitoring process until all the depths are in stasis, hydrodynamically
speaking. The moisture content values should then be the Field Capacity of
the soil at the different depths, with the water draining freely.
By plotting the change in Moisture against time at any particular depth, or
the the rate of moisture at the head as the moisture moves down, the
infiltration rate can be calculated.
I hope that this helps....but would appreciate your comments.
Carlton L.A. Weber
Director : Development - Geoquip (pty) Ltd
P.O.Box 1562
Silverton 0127
South Africa.
----- Original Message -----
From: <owner-sowacs@aqua.ccwr.ac.za>
Sent: Saturday, January 26, 2002 5:42 AM
Subject: Calculate Field capacity from percentage?
> NOTE: To get off this list, send email to majordomo@aqua.ccwr.ac.za
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>
> Dear Colleagues,
>
> Did any body out there worked with Soil moisture sensors..?
>
> If so can some one tell me how did they calculate the Field capacity of
the
> soil in volume (cm3) rather than percentage which what the sensor reads.
> Also did any body worked with sensors in calculating the infiltration rate
> specially in Sandy soils.
>
> Any feed back or case studies about the use of soil moisture sensors would
> be appreciated.
>
> Regards,
>
> Tareq
>
> UAE University
> Tareq Al-Zabet, Asst. Prof.
> United Arab Emirates
> Faculty of Science
> Geology Dept.
> Tel. 03-7064371
> P.O.Box: 18436
> T.Alzabet@uaeu.ac.ae
>
>
>