Geoscience Reference
In-Depth Information
Suction lysimeters were utilized during a five-year period (2001 to 2006) to obtain monthly soil
solution samples at depths of 0.6 and 1.2 m beneath the surface. The C1 test plot had six suction
lysimeters (three of 0.6 m depth and three of 1.2 m depth) installed at its one lysimeter and monitor-
ing well group location marked by a black triangle in Figure 5.16. In the C2, S1, and S2 test plots,
there were four suction lysimeters (two at 0.6 m depth and two at 1.2 m depth) installed at each
lysimeter and monitoring well group location. The average soil solution electrical conductivity val-
ues measured in the laboratory for test plots C1, C2, S1, and S2, respectively, were 1.17, 1.29, 3.28,
and 3.24 dS/m. These average soil solution electrical conductivity values initially created concern
that the practice of subirrigation might be causing a salinity buildup.
To gain further information on the possibility of a subirrigation-induced salinity increase, a
constant separation traversing resistivity survey was carried out at the site using a Veris 3100 Soil
EC Mapping System. Measurements of EC a acquired by resistivity methods are expected to be
strongly correlated with soil solution electrical conductivity. The EC a spatial pattern at the site
is shown in Figure 5.16, with the small black dots representing EC a measurement locations. The
mapped EC a pattern indicates that the larger average soil solution electrical conductivity values
found in test plots S1 and S2 are not due to subirrigation practices, but are instead the result of some
east-to-west transition in natural soil conditions causing the S1 and S2 soil solution electrical con-
ductivities to be greater than those for C1 and C2. This finding becomes more evident by focusing
strictly on the S1 test plot. If subirrigation produces a salinity increase, then the entire S1 test plot
should exhibit high EC a values, which is definitely not the case. Although the east side of the S1
test plot, where the suction lysimeters are located, does have high EC a values, the west side of the
S1 test plot has EC a values that are much lower and similar to those measured in test plots C1 and
C2. Viewing the site as a whole, the change from high to low EC a values occurs somewhat abruptly
over a short east-west distance interval passing through the center of the S1 test plot. Undoubtably,
if the S1 suction lysimeters had instead been installed on the west side of the test plot, the average
soil solution electrical conductivity value would have been substantially lower. Again, the EC a map-
ping results clearly indicate that subirrigation is not producing a salinity buildup, and the high S1
and S2 soil solution electrical conductivity values are due to the S1 and S2 suction lysimeters being
located in the part of the field research facility where natural soil conditions produce high soil solu-
tion electrical conductivities.
Finally, resistivity method applications in environmental and hydrological disciplines may also
prove useful in agriculture. Resistivity methods can be a valuable tool in regard to characterization
and leak detection for landfills and chemical disposal pits (Reynolds, 1997; Sharma, 1997). These
resistivity methods should likewise be equally useful for characterizing and detecting leaks for
animal waste storage ponds and treatment lagoons. The use of resistivity methods to determine the
trends and density of fracture systems in glacial till was previously discussed. Azimuthal rotation
surveys could also be employed to gather the same type of information on fracture systems within
the soil profile. This soil profile fracture system information might have some worth in designing
subsurface drainage systems, because orienting drain lines to intersect soil fractures will probably
improve the soil water removal efficiency of the overall drainage pipe network.
RefeRenCeS
Allred, B. J., M. R. Ehsani, and D. Saraswat. 2005. The impact of temperature and shallow hydrologic con-
ditions on the magnitude and spatial pattern consistency of electromagnetic induction measured soil
electrical conductivity. Trans. ASAE. v. 48, pp. 2123-2135.
Allred, B. J., M. R. Ehsani, and D. Saraswat. 2006. Comparison of electromagnetic induction, capacitively
coupled resistivity, and galvanic contact resistivity methods for soil electrical conductivity measure-
ment. Applied Eng. Agric. v. 22, pp. 215-230.
Banton, O., M. K. Seguin, and M. A. Cimon. 1997. Mapping field-scale physical properties of soil with electri-
cal resistivity. Soil Sci. Soc. Am. J. v. 61, pp. 1010-1017.
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