Agriculture Reference
In-Depth Information
from soil resistance to stress within a tine to electric signals of strain gages
stress
in MPa
23
47
70
93
117
140
164
187
210
strain gages
legs of
rake angle
horiz. force
(soil resist.)
Fig. 7.7
Sensing instrumentation for recording the soil break-up in a seedbed (From Bogrekci and
Godwin
2007b
, redrawn and altered)
With primary cultivation the main question is the
depth of operation
. The concept
is that the higher the soil resistance to a tine or a cone moving in the soil is, the more
the soil density should be reduced and the deeper the primary cultivator should
operate. Yet up to now the realization of this idea has not been successful. This
might be explained by the fact that for most soils the resistance to a tine or a cone is
predominantly infl uenced by the water content and much less by the soil density
(Fig.
7.3
). And since the water content of a soil can change fast in a spatial- as well
as in a temporal mode, the sensing objectives for the soil density hardly are met.
With secondary cultivation the situation is different: the main objective is not the
density, it is the
tilth
or break-up of the soil. The emergence of crops mainly depends
on the soil break-up within the seedbed as shown in Fig.
7.6
whenever zero tillage
methods are excluded and tillage is needed.
Bogrekci and Godwin (
2007b
) have shown that a
strain gage
located at a suitable
location on a spring tine of a cultivator can provide a reliable and an inexpensive source
of signals about the soil break-up in a seedbed. Figure
7.7
shows, at which location of
the spring tine the strain gage should be bonded. It is the highest point of the tine and
the position, where the soil resistance causes the maximum load or stress on the tine.
7.3.1.2
Results with Tilth Sensing via Impact Forces
The general situation under
ceteris paribus
conditions is that the fi ner the soil struc-
ture is, the lower the mean horizontal force on the tine is. This results from the fact that
for the fi ner soil particles it is easier to fl ow backwards around the tine. Therefore they
exert less horizontal resistance. But despite this it must be asked, whether the
mean
horizontal force is the most suitable parameter for sensing the break-up of the soil.
