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primary variable (indicator transformed drainage class) and two secondary variables. The variables
found to have a significant effect on drainage class during the stepwise discrimination procedure
were further used in cokriging estimation. The cross-validation results for kriging and cokriging
procedures were further used to compare their accuracy with accuracy of discriminant analysis.
Geostatistical analysis including variogram calculation, cross-validation, kriging, and cokriging
was performed using the geostatistical software package GSLIB (Deutsch and Journel, 1998).
17.3 ReSUltS And dISCUSSIon
Mean values of the variables that were selected as significant during stepwise discriminant proce-
dure ( P = 0.15) are shown in Table 17.1. When only topographical variables (i.e., elevation, slope,
curvature, flow accumulation, and distance to drainageway) were used in the stepwise discriminant
procedure, the variables with significant effect on drainage were slope and distance to drainageway.
All the other topographical variables were not significant in discriminating between the drainage
classes for this field. When all the above listed topographical variables and both shallow and deep
EC measurements were used in the stepwise discrimination, only distance to drainageway and deep
EC were selected as significant variables.
SWPD/PD soils were located close to the drainageway, at sites with the lowest slope values
(Table 17.1). These sites were also characterized by the highest values of deep EC. One of the fac-
tors influencing the relationship between EC and soil drainage classes is soil clay content. Soil EC
was found to be positively correlated with clay content (Williams and Hoey, 1987), and at the same
time, higher clay content is one of the characteristic properties of poorly drained and somewhat
poorly drained soils in this study. Analysis of soil texture revealed that SWPD/PD soils had some-
what higher clay contents than MWD and WD soils. The differences in clay contents were most
notable at lower parts of the profile at depths 60 to 100 cm, where clay contents of WD, MWD, and
SWPD/PD soils were equal to 26.3, 28.2, and 31.3 percent, respectively. Another factor of potential
influence on the relationship between EC and soil drainage classes is soil water content. Similar to
clay content, soil water content is positively correlated to soil EC, and in the field conditions, poorly
drained soils often are characterized by higher water contents compared with MWD and WD soils.
Unfortunately, soil water content was not monitored during the EC measurements; hence, it was not
possible to separate influences of soil water content and clay content on EC data in this study. Dis-
tance to drainageway seemed to be a useful parameter in discriminating between WD and MWD
drainage classes in this field. Sites with MWD soils were located generally closer to the drainage-
way than the sites with WD soils (Table 17.1). Slopes and deep EC values of WD and MWD soils
were similar; hence, these parameters were not effective in separating WD and MWD drainage
classes using stepwise discriminant procedure.
Cross-validation results for comparing the studied methods of predicting and mapping soil
drainage classes are presented in Table 17.2. In discriminant analysis the WD and SWPD/PD soils
were predicted most accurately, with about 70 percent of each being correctly estimated based on
tAble 17.1
Mean values of the discriminant variables
Selected by Stepwise discriminant procedure
( P = 0.15) for the three Soil drainage Classes
Soil drainage
Class
distance to drain
(m)
Slope
(degree)
deep eC
(mS/m)
WD
158
1.46
33.5
MWD
125
1.45
34.0
SWPD/PD
37
1.05
49.5
 
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