Agriculture Reference
In-Depth Information
sensing principle
ultrasonic sensors
spraying nozzles not shown
Fig. 11.1
Section control of a sprayer by ultrasonic sensing of biomass. The
insert
shows the
sensing principle (From Reusch
2009
and Agri Con GmbH, Jahna, Germany, altered)
practice of applying a uniform fungicide rate across the whole fi eld, any site-
specifi c differences in crop densities are disregarded. Yet since in many cases the
leaf-area is the object of a fungal attack, it seems logical to apply the same con-
centration of fungicides per unit of leaf surface area. This is the rationale for
fungicide application according to site-specifi c crop densities or its surrogates,
the biomasses or leaf-area-indices.
Several methods of detecting the site-specifi c biomasses or leaf-area-indices are
available and have been dealt with:
•
proximal or remote
refl ectance
sensing (Fig.
6.7
)
•
•
sensing by
ultrasonics
(this section Fig.
11.1
and Sect.
9.4.6
)
.
The growth stages at which fungal infections occur can be very different. For
small grains, depending on the respective fungi, infections can develop at almost
any growth stage. But the sensing methods listed above differ in their capabilities to
detect well at various growth stages. Only the ultrasonic method can reliably sense
biomass at any growth stage (Fig.
11.2
).
With refl ectance sensing, because of soil effects in less developed canopies, the
minimum growth stage
of small grains is about EC or BBCH 30. This is when
tillering has ended. Refl ectance indices with wavelengths from the red edge range
should be preferred in order to avoid limitations at advanced growth stages for
lush crops.
