|
FAQ's
|
About Resin Capsules and Their Use |
Q 1
Please provide any information you may have regarding
colorimetric analyses of ammonia, nitrate, and phosphate in the 2 M HCl
extracts.
A 1
This is the one question that most people have concerning analysis
of a 2 M HCl solution. We "neutralize" by taking an aliquot for
analysis
(e.g., for nitrate and ammonium) then add an equal quantity of 2 M
NaOH.
This will work like most other analytes for most colorimetric
determinations.
The neutralized solution can also be used for AA or ICP methods, but we
often use the HCl solution directly from the desorption for these
procedures.
Top of Page
Q 2
What is the maximum possible in situ residence time for resins without
coming too near to saturation?
A 2
For most practical purposes, the PST-1 resins are an infinite sink
for ions as compared to the amount of available ions that are usually
in
a sphere of soil near the capsule. If used in highly salty conditions,
it is possible that resin capsules may approach ion saturation after
several
days or weeks in the medium. At this time we do not know of any
situation
where the resin in UNIBEST capsules has neared saturation.
Top of Page
Q 3
Does the bead size of the resins ensure a saturated water-conductivity
similar to that of the surrounding soil?
A 3
The resin beads are similar in size to a fine sand but, all resin beads
shrink and swell in response to wetting and ion exchange. Although the
resin beads are sand-size, they are highly porous, having varying
proportions
of macro- and micropores. In this way, their water relations are
similar
to those of soils having both macro- and micropores. It is not
necessary
to have the same amount of water in the capsule as in the soil because
ions are moving along a diffusion gradient. Experience shows that there
is enough water bridging the capsule - soil interface for ion diffusion
to occur, even when soil water tensions are high.
Top of Page
Q 4
How big a problem is swelling/shrinking of the resins, does this affect
water flow or contact to the soil?
A 4
Resins do change volume depending on water content and types of ions
present. If kept wet, the amount of volume change is minimal unless a
pretty
complete change in ion saturation takes place like what happens when
stripped
of adsorbed ions with HCl. Since resin beads in the capsule have both
micro- and macro-pores they will act "similar" to soils in terms of
water movement inside the
capsule. However, we have not, measured the water relations involved.
The
WECSA access system is designed, with the spring loaded carrier
assembly,
to compensate for any in situ changes due to soil
or capsule shrink and
swell action.
Top of Page
Q 5
Several different resin adsorption systems are discussed in various
publications.
Are there any differences between the techniques?
A 5
Yes, there are important differences between various resin adsorption
systems
Suggested reading for more information is;
Skogley, Earl O. and Achim Dobermann. 1996. Synthetic
Ion-Exchange Resins:
Soil and Environmental Studies. Journal of Environmental Quality
25:13-24.
ASA, CSSA, SSSA, 677 South Segoe Rd., Madison WI 53711 USA
Top of Page
Q 6
How long should resin capsules be left in contact with the soil for
adsorption to occur?
A 6
Resin capsules respond to the same environmental conditions that affect
nutrient adsorption by plants. When a soil sample is made into a
saturated
paste in the laboratory and held at room temperature, we have obtained
satisfactory results from capsules that were in situ for 1- to 2-days.
On the other hand, in the field under cold dry conditions it will take
more time for a capsule to adsorb the available elements from the soil.
Suggested reading for more information is;
Schaff, B.E. and E.O. Skogley. 1982. Diffusion of Potassium, Calcium, and Magnesium in Bozeman Silt Loam as Influenced by Temperature and Moisture. Soil Science Society of America Journal 46:521-524.
Warrington, G. E. and E. O. Skogley. 1996. Resin Extraction
Represents
Soil Ion Bioavailability. http://www.wecsa.com/Refrence/bio_avl.htm
Top of Page
Q 7
Can the resin capsules be reused?
A 7
Regenerating and reusing capsules is not recommended for two reasons.
Foremost is that using a salt or acid to regenerate leaves the resin
saturated
with ions that do not allow the capsule to function effectively as a
"sink"
for soil ions. Second, each time the capsule is extracted,
the process
is not 100% efficient. Small, but unknown amounts of contamination
would
occur unless extreme processing was used. In practical terms, a resin
capsule
is like film in a camera, you take a picture (expose a capsule to the
soil chemistry)
then develop the film (desorb the capsule) to see the results.
Top of Page
Q 8
When the soil is washed from a capsule, will the ions be washed out
too?
A 8
All ions are adsorbed by the resin in a capsule by displacing the
counter
ions H+ and OH- from the
resin. Therefore, adsorbed ions are held in the
resin and will not be removed by a brief washing with deionized water.
Desorption of these attached ions requires a strong acid like 2M HCl
where
the H+ and Cl- replace
the NO3-N and NH4+ on the
resin. This and other characteristics
of resins are discussed in the paper;
Skogley, Earl O. and Achim Dobermann. 1996. Synthetic Ion-Exchange Resins: Soil and Environmental Studies. Journal of Environmental Quality 25:13-24.
Also, see the paper in SCIENCES of SOILS 1997 -Abstract:
Methodologies
for Resin Capsules: Capsule Storage and Ion Recovery on the web at; http://www.hintze-online.com/sos/1997/Articles/Art3/
Top of Page
Q 9
Ion availability is different for each crop and is influenced by
weather,
can the resin capsule adsorption reflect this?
A 9
Actually, ion availability is a function of the soil system. When a
resin capsule is used in situ with the soil access system, it will
respond
to the local environmental conditions. In situ sampling of the soil
allows
capsules to respond to the same soil variables of
temperature, moisture,
nutrient solubility, and transport that regulate how much of each
element
plants can take up.
Individual plant species and crops have unique requirements for nutrients and some plants are more efficient than others at taking up a particular nutrient or element. This is the basis for bioremediation, use a plant species that will accumulate an element that may be toxic to many other species and then harvest the plant to remove the element. The resin capsule adsorption would need to be correlated with the uptake by individual species to develop an interpretive data base.
Reference: Warrington, Gordon E. and Earl O. Skogley. 1994. A
Quantum
Jump in Monitoring Soil Chemistry. In; Keammerer, Warren R. and Wendell
G. Hassell, Eds. Proceedings; High Altitude Revegetation Workshop No.
11,
March 16-18, 1994, pgs 196-206. Colorado Water Resources Research
Institute.
Available from: Cooperative Extension Resource Center, General Services
Center, Colorado State University, Fort Collins, Colorado, USA 80523.
Top of Page
|
Gordon Warrington |
 |
Gordon@wecsa.com |
