Agriculture Reference
In-Depth Information
The
Kautsky method
is not easy to apply in an online and on-the-go mode in
field operations since the sensing of its effect needs time. However, a similar stimu-
lating effect on fluorescence can be obtained with very short
laser light flashes
that
hit the canopy and saturate the photochemical system for a tiny time period of 1 s or
less. A subsequent sensing time span of 1-2 s can be realized while a tractor passes
along crop rows if recording takes place successively from the front to the rear of
the machine. Interesting approaches along this line have been dealt with by Thiessen
(
2002
) and Hammes (
2005
).
The sensing via signals of reflectance on the one hand or from steady state- or
from non steady state fluorescence on the other hand has different objectives within
plants. With reflectance sensing, the main objective is the biomass - precisely the
leaf-area-index - in combination with the chlorophyll content of the leaves. The
product of the leaf-area-index and the chlorophyll content within leaves - thus
the chlorophyll content per unit field area - is the classical objective. With
steady
state fluorescence
, the objective mostly is just the chlorophyll content within leaves
per se
and sometimes - in case of blue/green fluorescence - the phenolic material in
cell walls. Finally, with the non steady state
Kautsky fluorescence,
, the prime objec-
tive is the rate of electron transport within the photosynthesis. In this case, the bio-
mass and chlorophyll situation is taken as it is.
These differences in sensing objectives have temporal implications. The biomass
of crops and the chlorophyll content per unit field area are rather long-term phenom-
ena. Compared to these, the electron transport in the photochemical systems is a
very fast matter. And the chlorophyll content within leaves is - on a temporal basis -
in between of these extremes.
From this follows that reflectance sensing provides information about crop prop-
erties on the basis of rather long time spans,
e.g.
from several days to a few weeks.
The steady state fluorescence methods can supply signals that are related to proper-
ties for a few days. Finally, the Kautsky fluorescence is able to indicate immediate
problems in plant physiology.
A need for rapid detection exists in case of many fungal infections of crops.
A fast detection and immediate crop protection action can provide the opportunity
of preventing additional infection cycles and hence save fungicides. Because of its
physiological background, the Kautsky fluorescence can supply such immediate
control information about infections. By using indices that were derived from the
non-steady state Kautsky fluorescence, it has been possible to indicate fungal
infections on leaves several days earlier than the human eye was able to detect
them (Buerling et al.
2009
; Moshou et al.
2009
; Thiessen
2002
). So the perspec-
tives for early detection of fungi are good. However, on-the go detection from
farm machines is not yet state of the art. And since different crops, several fungi
and various environmental conditions are involved, there are still problems that
must be solved.
Crop properties will probably exist as short-term and long-term phenomena.
So both reflectance- as well as fluorescence sensing might be reasonable. Yet
since fluorescence signals are much weaker than those from reflectance, the pre-
ferred recording mode for it in the near future will be proximal- instead of remote
sensing.
