Agriculture Reference
In-Depth Information
supply. And if the site-specifi c information about this factor can be sensed and
processed on-the-go while the control of the farming operation takes place, the
respective transfer route is very short. Mapping the situation for this transient
growth factor alone seldom will be reasonable. But mapping and in addition aver-
aging as well as further processing of signals makes sense whenever it comes to
factors or properties that are temporally stable such as topography, soil texture,
soil organic matter and immobile nutrients like phosphorus. And the transfer of
information to subsequent crops by maps anyway is reasonable only for tempo-
rally stable properties (Fig.
13.1
, bottom).
In many cases, the sensed signals do not precisely correspond to growth factors.
Instead, they hold for defi ned physical units. The sensed signals might not even
comply with single soil- or crop properties, which each in turn again might stand for
several growth factors. The texture of soils
e.g.
affects the water, oxygen and nutri-
ent supply of crops. And single crop properties also can be correlated to several
growth factors. The leaf-area-index of a crop affects its photosynthesis, but also its
energy loss via respiration and its infections. Finally, the widely sensed signals like
electrical conductivities or radiation refl ectances each are related to several soil or
between sensed signals and actual growth factors might not be simple.
However, what is essential for site-specifi c farming? The important point is that
the sensed signals are suitable
empirical indicators
for either growth factors or for
properties of soils and plants that infl uence the development of crops. The signals
must be able to serve as
surrogates
for direct indications of growth factors or of
properties of soils or crops. And if the sensed signals are correlated to several growth
factors simultaneously and counteractions between these do not occur, successful
control can be possible.
The complexity of the sensing and the transfer of information calls for solutions
that allow
simplifi cations
. Steps in this direction are concepts of sensor fusion, map
overlay and management zones in site-specifi c farming. Sensor fusion aims at getting
more information with proximal sensing within one pass through the fi eld by combin-
ing hitherto separated sensing operations. This procedure can be reasonable for sig-
nals irrespective of their temporal stability, since the control of the farming operation
might occur within real-time when this is necessary, but also in a time-delayed mode
after mapping. Methods of map overlay and of farming by management zones inher-
ently rely on temporal stability of the properties or their surrogates.
13.2
Sensor Fusion - Solutions and Approaches
The simplest example of sensor fusion has become quite common: it is used self-
evidently when any real-time soil- or crop property sensor operates in combination
with georeferencing. This mode of sensor fusion is a base of site-specifi c farming.
An additional basis is the simultaneous use of topographic information that is avail-
able either from real-time GNSS signals or from maps. These basics will be routine
matters in the future.
