Agriculture Reference
In-Depth Information
different methods of soil cultivation show more than ten amplitudes. Therefore, the
impact of each clod on the sensing tine seems to be well recorded.
Along all curves there are short instances, within which the forces become nega-
tive. This is the result of vibrations of the spring tine. The differences in the forces
before and after secondary cultivation are evident; however, those between the seed-
bed preparation by the drawn harrow tines on the one hand and the power- take-off
driven harrow on the other hand are not. Some evidence of a fi ner seedbed after
secondary cultivation by means of the power-take-off drive is given by the compari-
son of the respective mean weight diameters (see insert of Fig. 7.8 ).
However, when the erratic course of the curves is taken into account, it cannot be
expected that the mean force is the best benchmark for the site-specifi c tilth sensing.
A mean criterion can hide many details of the data from which it was obtained. A
close observation of the course of the curves suggests that concentrating the analy-
sis on the respective amplitudes, frequencies or standard deviations of the forces
might be reasonable. In a statistical analysis by Bogrekci and Godwin ( 2007b ),
which was focussed on an indicator for the soil tilth, the best results were supplied
by the standard deviation of the forces .
It should be noted, that this analysis had the mean weight diameter (MWD) of
the soil aggregates as an indicator of the soil tilth. There are several factors that
might infl uence the signals of the soil break-up that are obtained via the standard
deviation of the forces. Such factors can be the driving speed, the depth of cultiva-
tion, the soil type and the direction of cultivation compared to the direction used in
the previous primary cultivation.
The infl uence of the driving speed as well as of the soil type seem to be rather
small. As to soil type this might be expected, since - provided the clod sizes do
not differ - its effect on the mass of soil aggregates is rather small. At least this
holds, when peat soils are excluded. As to the driving speed, this might be sur-
prising, since the driving speed must have a considerable infl uence on the impact
forces. But with all implements that use drawn tines for soil cultivation, the driv-
ing speed also signifi cantly affects soil break-up. Higher driving speeds increase
the break-up as a result of the higher impact forces. So if the tilth after cultivation
is compared, the effects of the driving speed on the soil break-up as well as on
the forces exerted on the sensing tine go in the same direction and therefore prob-
ably even out.
The results shown in Fig. 7.9 are based on pooled data for driving speeds ranging
from 5 to 15 km/h and for two soil types. Despite this, the root mean square error is
only 3.5 mm for the mean weight diameter of the soil aggregates.
But the sensing-depth of the tine is important. In most cases, forces on tines
increase more than proportional with the depth of operation in the soil. So if the
cultivation implement does not provide a constant depth, a special depth control
device for the sensing tine is necessary.
It seems reasonable to compare the soil tilth that this tine sensor indicates with
results obtained by the standard sieving procedure. A correlation based on the
respective mean weight diameters that were recorded after careful calibration is
shown in Fig. 7.10 . The result is a rather simple linear relation, as might be expected
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