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Vadose
Zone Monitoring for Nitrate Leaching.
Conservation
Districts currently monitor nitrate leaching by
using the industry standard of "suction
lysimeters". This methodology has many problems and
limitations, all of which can be averted by using
the UIC resin capsule approach. UIC has conducted
studies to compare side-by-side results from
lysimeters with results from resin capsules.
Results illustrate the benefits to be gained when
testing with the UIC supplied resin
capsules.
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Suction
lysimeters are problematic, in several ways. 1)
Solutions collected through porous cups may poorly
represent the actual soil solution. Lowered
pressure due to suction can cause degassing with
resultant pH and solubility changes, altered
seepage rates, channeling through larger pores, and
incorrect solution electrical conductivity's. 2)
Any soil must be quite moist for this sampling
method to work at all, and it is often difficult to
collect enough solution for analysis in clay soils,
even at low soil hydraulic potential. 3) Porous
cups can exhibit a "filter effect" and they may
become plugged by particles in certain soils,
preventing their extended use. 4) Continuous system
dynamics cannot be known unless extraction is
continuous.
The
resin capsule technology can be applied to
circumvent these limitations. Resin capsules
provide a simplified soil "extraction" based on
accumulation of solutes by capsules placed into the
soil. The capsule acts as a "sink" to accumulate
solutes that reach the soil-capsule interface by
diffusion or mass transport. No extraneous forces
are introduced, and the process simulates ion
dynamics in the soil-root system. The capsules will
function whenever soil conditions allow water
transport or ion diffusion, even though the soil
may be too dry to allow vacuum extraction. Also,
solute accumulation is continuous, rather than
intermittent. These properties provide the basis
for a more accurate, simplified method to study
solute movement through soils, including the
leaching of nitrate below crop rooting
zones.
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