Efficient use of water in agricultural production involves accurate assessment
and control of the quantity and spatial uniformity of excess percolation. Passive
Capillary Samplers (PCAPS), which sample water from the vadose zone have shown
potential to provide superior estimates of soil water flux compared to alternative
methods. In a four-year study, 42 PCAPS installed in 21 commercial agricultural
fields in Lane County, OR, USA were monitored monthly to evaluate their operational
characteristics and ability to estimate soil solution flux. The PCAPS showed little
evidence of technical failure, with only two of the 42 installed samplers found to
operate inefficiently. Installation of 10 of the 42 samplers in locations susceptible to
high or perched water tables resulted in submersion of the samplers, rendering them
inoperable. On average, the PCAPS measured soil water flux 25% greater than that
obtained from a water balance estimate. This discrepancy was attributed to a possible
inaccuracy in water balance evapotranspiration estimates, along with a violation of the
PCAPS design assumptions which suggests over-sampling would occur in the
presence of high water tables. Analysis of the PCAPS collection ability indicates that
to estimate the mean yearly recharge at each site with a 30% bound on the mean at the
0.05 confidence level, eight PCAPS are required. This number corresponds closely to
the results of Brandi-Dohrn et al. (1996a) and is thought to be due to intrinsic
variability of percolation.
Spatial uniformity in irrigation water application is essential to reducing excess
percolation. Twelve sprinkler irrigation systems used under commercial crop
production in Lane County, OR were evaluated for equipment wear and performance.
Field measurements of sprinkler nozzle size and discharge rate were recorded for each
system and used to estimate water application patterns. New sprinkler nozzles were
installed on six of the 12 irrigation systems to compare potential application rate and
uniformity with existing system performance. Despite reducing the coefficient of
variation in discharge between sprinklers from 10% to 2%, little increase in water
application uniformity was attained by replacing the nozzles. A 13% decrease in
mean water application rate was documented when new nozzles replaced worn parts.
The over-application due to worn or mismatched nozzles gives rise to the potential for
increased surface redistribution and deep percolation, resulting in water and nutrient
losses. / Graduation date: 1998
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/33965 |
| Date | 06 January 1998 |
| Creators | Louie, Michael J. |
| Contributors | Selker, John S., Istok, Jonathan D. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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