Assessment of the environmental impacts of an agricultural production system
requires information on both soil water quality and solute flux. Passive Capillary Samplers
(PCAPS), which sample water from the vadose zone using fiber glass wicks, have shown
potential to provide both flux and solute concentration in unsaturated zone sampling but
have not been tested under long-term, natural, rainfall conditions. The objectives of this
study are to (1) evaluate PCAPS operation under non-steady, natural rain and irrigation
fed conditions, (2) determine the samplers ability to estimate recharge, and (3) estimate
the loss of nutrients resulting from agricultural production.
32 PCAPS and 78 suction cup samplers were installed below the root zone at 16
commercial fields in Lane County, Oregon. PCAPS' were installed in positions using
ground penetrating radar such that PCAPS' were placed in homogeneous or concave
profile locations. Two PCAPS and six suction cups were installed at each site. Rain
gages and TDR probes were installed at eight of the 16 sites. These data were used to
develop a mass balance for each of the eight special study sites. Comparison to mass
balance data indicates that the PCAPS flux measurements were within 10% of the mass
balance estimated recharge. Surface runoff of potential drainage water during periods of
high rainfall was a point of concern for estimated recharge discrepancies because runoff
was not measured. The saturated hydraulic conductivity was shown to be the most
influential design parameter for matching wick and soil types. On the other hand, the incident flux, rather than conductivity, determined the ultimate ground water recharge. PCAPS collection was found to be significantly correlated (average R��=0.75) to the mass balance monthly estimated recharge. To estimate the mean monthly recharge at each site with a 30% bound on the mean and 95% confidence level, 20 PCAPS would be required at each site.
PCAPS were found to be superior to suction cup samplers for estimating ground water recharge concentrations because PCAPS were able to sample both flux and resident concentrations. Mint and row crop, organic and inorganic, production systems contributed to the largest adverse environmental impacts with average recharge concentrations for mint and row crop of 24 mg L����� and 28 mg L�����, respectively. Orchard and blueberry production systems had little impact with their seasonal concentrations averaging below the EPA water quality standard. Amounts of percolation were key in determining which management systems were inefficiently operated. Over-irrigation during the summer lead to increased losses of nitrogen for the mint production systems in the summer as well as the winter. Over-fertilization was important for creating significant differences in seasonal mass losses of nitrogen from row crop production systems. Overall, the PCAPS estimated nitrogen loss was 12% lower than that calculated using a simplified nitrogen mass balance approach. Best management practice suggestions concerning irrigation, fertilization and cover cropping were provided as a direct result of the findings of the project. With technical support and increase in concern over nitrate contamination, farmers should be able to control leaching losses without the use of quotas or allotments. / Graduation date: 1995
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/35237 |
| Date | 20 April 1995 |
| Creators | Shelby, Patrick M. |
| Contributors | Selker, John S. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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