Soil solution samplers have certain inadequacies that limit their range of
possible applications. Passive Capillary Samplers (PCAPS), which apply suction to the
soil pore-water via a fiber glass wick, have shown promising results in preliminary
experiments in regard to collection efficiency of water and of bromide tracers. The
objectives of this study were to evaluate PCAPS under non-steady state field conditions
with respect to (1) effect of installation procedure and operational characteristics, (2)
ability to estimate the soil-water flux, and (3) ability to estimate the mean concentration
of agrochemicals. At the same time, samplers were used to (4) evaluate the effect of a
cereal rye (Secale cereale (L.)) cover crop on NO₃⁻ leaching.
Thirty-two PCAPS and 32 suction cup samplers were installed below the root
zone at a depth of 120 cm in a Willamette Variant loam wet soil (fine loamy mixed
mesic Pachic Ultic Argixeroll). Samplers were installed in an ongoing cover crop/crop
rotation study. Regarding overall performance, flux measurements were within 20 %
of the native values as determined by a water balance. The air release from the sample
bottles was a point of concern and might have slowed down the sampling rate. The
installation procedure introduced bias into volume and concentration measurements of
the part of the PCAPS closest to the refilled trench. The leachate concentration as
calculated using the arithmetic mean of suction cup sampler measurements holds a
significant bias, deviating by up to 97 % for bromide concentrations. Phosphate was
not detected by the suction cup samplers indicating that ceramic cups should not be
used for phosphate sampling. Matrix and preferential flow could clearly be
distinguished using the PCAPS, showing that PCAPS are a valuable tool to assess the
hydrology and solute transport mechanisms of a field site.
The cover crop reduced NO₃⁻-N leaching significantly at the recommended
N rate as evaluated by PCAPS. The cover crop reduced the seasonal mean NO₃⁻-N
concentration at the recommended N rate from 13.5 mg LI to 8.1 mg L⁻¹, which is
under the E.P.A. drinking water quality standard of 10 mg L⁻¹. The total NO₃⁻-N mass
lost under the fallow treatment at the recommended N rate was 48 kg N ha⁻' which
compares to 32 kg N ha⁻' under the cover crop treatment. Given the increasing
problems with nitrate contamination of ground water, programs to support the
cultivation of catch crops in conjunction with nitrogen soil testing should be considered
as a relatively easy, effective, and biologically sound means to reduce nitrate
concentrations in the recharge to the ground water in agricultural settings. / Graduation date: 1994
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/37559 |
| Date | 17 November 1993 |
| Creators | Brandi-Dohrn, Florian M. |
| Contributors | Selker, John S. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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