Agriculture Reference
In-Depth Information
data taken at time of third dressing
1.2
1.1
1.0
0.9
0.8
0.7
0.6
barley
(N1: 10/03; N2: 20/04; N3: 12/05)
N1 or N2 or N3 = dressing dates
± 1 stand. dev.
of 100 leaves
wheat
(N1: 10/03; N2: 21/04; N3: 03/06)
0
50
100
150
200
250
total nitrogen after two dressings (dates N1 and N2) in kg/ha
data taken 3 - 4 weeks after third dressing
barley
(N1: 10/03; N2: 20/04; N3: 12/05)
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
±
1 stand. dev.
of 100 leaves
wheat
(N1: 10/03; N2: 21/04; N3: 03/06)
N1 or N2 or N3 = dressing dates
rape
(N1: 10/03; N2: 31/03; N3: 22/04)
0
50
100
150
200
250
total nitrogen after three dressings (dates N1 + N2 + N3) in kg/ha
Fig. 9.30
Chlorophyll-fluorescence and nitrogen supply (From Thiessen
2002
, altered)
Therefore, fluorescence signals might be better at early growth stages. Restrictions
to this are outlined below. Another consideration is whether for the same reason,
fluorescence signals should be preferred for widely spaced crops such as maize,
potatoes and sugar-beets, since with these crops the canopy closes fairly late.
However, the fluorescence ratio is not
per se
influenced by the leaf-area-index, in
contrast to reflectance indices derived from the red edge and near-infrared range
(Fig.
9.19
). Since the chlorophyll concentration in the leaves often is inferior to the
leaf-area-index as an indicator of nitrogen supply (Fig.
9.17
), fluorescence sensing
has been combined with means of recording the plant density. A concept for this
approach is the combination of fluorescence sensing with a
scanning technique
.
Bredemeier and Schmidthalter (
2005
) as well as Thoren (
2007
) used such a laser-
induced fluorescence sensing combined with the recording of a “biomass index” by
scanning the field surface. The surface scanning was obtained via the
number of
fluorescence signals
per unit area that was sensed when the plants were irradiated
by pulsed red laser beams and thus were induced to emit fluorescence. Hence a rela-
tive indication of the site-specific
plant density
per unit area was obtained. The
sensors were located on the roof of the tractor and had an oblique field of view
