Agriculture Reference
In-Depth Information
limitation does not apply to harvesting machines that temporarily store in tanks - like
combines - or that load onto hitched wagons.
Driving along curved lines always is more complicated. But if the curvature is
constant - as with the guidance along concentric circles of a center-pivot irrigated
fi eld - an automatic fi xed line GPS guidance mode still is possible. With contour
farming the situation can be different, the curvature can change. The same applies
to irregular shaped fi elds (Fig. 4.6 , bottom right). Modern guidance systems allow
to switch between prior pass- and fi xed line guidance as well as between automatic-
and manual steering and hence to adapt to different fi eld shapes that might be within
a single farm or within the area of a contractor.
4.3
Economics of GNSS Based Guidance
The investment for guidance systems can vary considerably. A main factor for this
is the respective investment for the georeferencing system (Table 3.4 ) . Normally,
manual lightbar guidance systems are not combined with real-time kinematic dif-
ferential GPS. This is because typical drivers are not able to guide with an error that
is below 10 cm on the average (Heraud and Lange 2009 ). Consequently, using a
very accurate positioning system that is much more precise than this is not justifi ed.
Differential GPS that operates with carrier phase signals plus dual frequencies
would suffi ce. Based on this, the investment for a manual lightbar guidance system
can be around 10,000 Euros. On the other hand, automatic guidance systems can
steer so precisely that the accuracy of real time kinematic differential GPS can be
utilized fully. The investment for such an automatic guidance system based on
RTK-GPS can be close to 40,000 Euros.
The costs from the investment should be offset by savings that result from more pre-
cise guidance. Theoretically, the basis for these savings could be the economical effects
of fewer gaps between passes as well as of less overlapping of strips. In practice, how-
ever, savings of a result of fewer gaps between adjacent strips hardly occur. This is
because farmers hate the visual impression that gaps make and therefore by and large
prevent them by a narrower alignment of passes. A consequence is that instead of gaps
more overlapping results. Therefore, an economical analysis can concentrate on the
effects of less overlapping. These effects have an impact on either the costs of machinery
plus labour or of the fertilizers and pesticides that are applied. Since overlapping reduces
the capacity of the machinery plus the driver, it is appropriate to assess the overlapped
area with the respective costs of the operations. Undue overlapping furthermore results
in wasted fertilizer and pesticides, so these costs must be considered too.
The relative overlapping that occurs, when no GPS based guidance techniques
are used, can be different. Bombien ( 2005 ) and Reckleben ( 2008 as well as 2011 )
calculated 8 % overlapping for operations, which are carried out without some
visual aid for the driver such as cultivations or operations on grassland. When these
operations were done either with the manual lightbar- or with the automatic GPS
guidance method, the overlapping dropped to 4.4 % or to 0.96 % respectively.
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