Agriculture Reference
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system
physical criteria
crop criteria
reflect. sensor
comp.
special wavelengths
from the visible
and near-infrared range
of the crop's reflectance
chlorophyll-concentr.
in the leaves plus
total area of leaves
(leaf-area-index)
Kiel system
fluoresc.
sens.
comp.
chlorophyll-fluorescence
of plants, induced via
laser-radiation
chorophyll-concentr.
in the leaves
plus sometimes
the canopy-surface
DLR system
pendul.
sensor
comp.
diversion-angle of a
pendulum that is dragged
along the upper part
of the crop
plant-mass,
crop-resistance
against bending
Bornim system
Fig. 9.16 Sensor based systems for site-specific nitrogen top dressing
Three presently used commercialized systems for on-the-go nitrogen top dressing
that rely on sensing of crop properties are listed in Fig. 9.16 . The names refer to
locations of the research groups that originally developed the systems.
The Kiel system was initiated from research at the University of Kiel about two
decades ago (Heege and Reusch 1996 ). It relies on sensing and processing the vis-
ible and near-infrared reflectance of crop canopies for signals to control the nitrogen
application rate. Among the various alternatives (Fig. 9.16 ), this method is the most
frequently used in farming.
The DLR system originated from research by Günther et al. ( 1999 ) in the
Department of Optoelectromics of the DLR Research Center in Wessling near
Munich. The signals for the control of nitrogen application are based on on-the-go
sensing of the crop chlorophyll fluorescence. More details are outlined in Sect. 9.4.5 .
Finally, a mechanical pendulum sensor has been developed in the Bornim Institute
of Agricultural Engineering by Ehlert et al. ( 2004a ). The deflection angle of a pendu-
lum, which is dragged along the upper part of the crop canopy, is used to control the
application rate. This sensing system is dealt with in more detail in Sect. 9.4.6 .
Whatever sensing system is used, it will have to rely on quantitative effects of
nitrogen supply on specific crop properties. Differences based on species, varieties,
soil-conditions and prevailing weather must of course be expected.
In order to understand the functioning of optical nitrogen sensing systems, knowing
about the effects of the nitrogen supply on the chlorophyll content in the leaves and on
the leaf-area-indices of crops is fundamental. Because this knowledge helps to find the
sources of reliable signals for nitrogen sensing. The leaf-area-index is the relation
between the photo-chemically active, one-sided leaf area and the ground surface.
 
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