Agriculture Reference
In-Depth Information
Fig. 9.33
Sensing the canopy resistance against bending in a small cereal crop by a pendulum that
operates in front of a tractor (From Thoele and Ehlert
2010
, altered)
The
resistance of the canopy against bending
is sensed via the deflection of a
pendulum that operates in front of a tractor (Fig.
9.33
). The deflection of this pen-
dulum is indicated by its angle to the vertical via a potentiometer. And the use for
site-specific farming is based on the correlation between this angle and the biomass
or the
leaf-area-index
of crops. Actually, the coefficients of determination (r
2
)
between the pendulum deflection angles and the biomasses were 0.89 or higher
(Ehlert et al.
2003
) and those for leaf-area-indices were between 0.64 and 0.91
(Dammer et al.
2008
). However, there are limits of precise sensing in rough fields
because of vibrations or in areas with varying slope.
This rather simple method of sensing crop properties is state of the art in farming
and aims at applications in the site-specific control of both
nitrogen fertilizing
and
fungicide spraying
. The results that have been obtained are encouraging (Dammer
et al.
2008
; Thoele and Ehlert
2010
) despite the fact that this method inherently
leaves out any influence of chlorophyll on applications of agrochemicals.
A serious limitation is that it needs advanced growth stages. With small cereals,
a growth stage of at least EC or BBCH 35 is essential (Ehlert et al.
2004b
), whereas
with reflectance sensing the minimum growth stage is about EC or BBCH 30. This
means, the earliest time for sensing by the pendulum is when the first flag leaf - still
rolled - has appeared, while reflectance sensing can already start when the tillering
has ended.
Another concept that also leaves out any direct influence of plant ingredients is
based on sensing the apparent
crop height
by an ultrasonic transducer. This
method relies on distance recording as shown in Fig.
8.7
and operates similar to
well known applications in automobiles as driver aids for parking. Reusch (
2009
)
has shown that an ultrasonic transducer, which is pointing vertically downwards
from a front mounting of a vehicle towards the crop canopy, simultaneously can
