Cranfield University

Field Study With Full Size Combine Harvesters
4.1.1.3 Sandy Loam Soil Shallow Tilled
The soil displacement for the shallow tilled soil pooled together is shown in Figure 52.
From the curves in the graph it was difficult to argue whether differences between treat-
ments were significant or not. Overall displacement is small due to the high soil strength.
Depth Depth (cm) (mm)
400 200 0
0
20
40
Track
Tire
High Inflation Pressure
Regression Line Track
Regression Line Tire
Regression Line High Inflation Pressure
-1 0 0
1
10
2
20
3
30
4
40
5
50
6
60
7
70
8
80
9
90
10
100
Deformation Displacement (cm) (mm)
Figure 52: Soil displacement and regression lines for sandy loam shallow tilled with
pooled groups
Table 15 illustrates that the regression lines for all treatments were significantly different
from zero, indicating that consequently soil displacement occurred. From the overlapping
CI it could be seen that the data from the track experiment had a significantly smaller in-
tercept than the data from the tyre, but the slope and hence the density increase was not
significantly different. Both intercept and slope of the regression line from the track ex-
periment were statistically different from the tyre at high inflation pressure. But the data
from the tyre at high inflation pressure was not significantly different from the one at rec-
ommended inflation pressure. The tracked combine harvester increased soil density by
approximately 7 %, the wheeled machine by approximately 9 % and at high inflation pres-
sure by about 12 %.
Before the statistical analysis was conducted the uniform distribution of the data was gen-
erally confirmed. In this particular case the data was skewed to the right due to the surface
readings suggesting a LN-transformation of the data. Yet as it can be seen from Table 15
Ph.D. Thesis Dirk Ansorge (2007)
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