Cranfield University

Field Study With Full Size Combine Harvesters
Depth Depth (cm) (mm)
600 400 200 0
0
20
40
60
Ph.D. Thesis Dirk Ansorge (2007)
Track
Tire
High Inflation Pressure
Regression Line Track
Regression Line Tire
Regression Line High Inflation Pressure
-2 0
0
2
20
4
40
6
60
8
80
10
100
12
120
14
140
Displacement Deformation (mm) (cm)
Figure 51: Soil displacement and regression lines for sandy loam subsoiled with pooled
groups
Table 13: Regression line parameters for displacement on sandy loam subsoiled soil
Treatment Intercept d0 (mm) 95% - CI Int. Slope s 95%-CI Slope R 2
Individual Groups
Tyre 1 78.9 57.7 – 100.1 -0.163 -0.235 – -0.091 0.629
Tyre 2 94.9 77.8 – 112.2 -0.206 -0.259 - -0.152 0.804
Track 1 66.6 56.0 – 77.3 -0.179 -0.216 - -0.142 0.886
Track 2 39.3 13.5 – 65.1 -0.078 -0.154 - -0.004 0.285
High 89.0 68.3 – 109.7 -0.226 -0.303 - -0.150 0.777
Combined Groups
Tyre 86.0 73.0 – 99.0 -0.182 -0.225 - -0.141 0.715
Track 49.5 35.3 – 63.7 -0.113 -0.158 - -0.068 0.462
High 89.0 68.3 – 109.7 -0.226 -0.303 – -0.150 0.777
The high inflation pressure tyre resulted in a larger slope and hence caused larger soil dis-
placement than the tyre with normal inflation pressure. Yet this difference was not statisti-
cally significant due to smaller number of replications. This emphasised the benefit of
more data points for field experiments. With natural variance, it was not possible to statis-
tically confirm results with less than 20 fish hook measurements. Overall the tracked com-
bine harvester on the subsoiled sandy loam soil increased soil density by approximately 11
%, the wheeled combine harvester by approximately 18 % and at higher inflation pressure
by 23 %. These numbers were higher than the results from the soil bin laboratory as ex-
pected due to weaker soil condition.
65