Agriculture Reference
In-Depth Information
Heijting et al. (
2007
) found strong spatial correlations for cockspur (
Echinochloa
crus-galli
), lambsquarter (
C. album
), goosefoot (
C. polyspermum
) and black night-
shade (
Solanum nigrum
) in 3 years continuous maize cultivation. They attributed
spatial and temporal stability of weed populations to their high recruitment
capacity.
Summing up, it can be concluded that in many cases the weed maps from 1 year
might provide the site-specifi c control basis for either pre-emergence or post-
emergence herbicide applications in next years. So it might be reasonable to use the
results of one sensing operation initially for an simultaneous in-season real-time
application followed by map based site-specifi c sprayings in next crops.
10.4
Site-Specifi c Weed Control
The weed population can vary spatially as well as on a species basis. Precise appli-
cation of herbicides thus has two objectives:
adapting the mass
to the spatial weed
density
as well as
adjusting the formulation
to the plant species
. Hence site- and
species-specifi c control might be needed.
For this purpose, a
multiple fi eld sprayer
was developed (Fig.
10.13
). Each of
the three sprayer circuits led to a boom width of 21 m divided into 7 sections of 3 m.
Each sprayer circuit and each boom section was turned on and off separately via
solenoid valves. This sprayer allowed a separate control of each hydraulic circuit
according to information from herbicide application maps. The application rate was
regulated from 200 to 290 l ha
−1
over the whole boom width of each circuit by pres-
sure variation (Gerhards and Oebel
2006
).
Another approach for site- and species specifi c weed control is to employ spray-
ers with an integrated
direct injection system
. With such injection sprayers, herbi-
cides and carrier (water) are kept separate. According to the indications of the weed
treatment map (off-line application) or the sensor data (on-line application), the
herbicides are metered into the carrier and mixed immediately before entering the
nozzles.
In both scenarios, short
reaction times
of less than 1 s and adequate mixing of
the herbicides into the carrier are basic requirements for high weed control effi cacy.
Figure
10.14
shows an experimental direct injection system with one injection point
for each boom section (3 m each). With this confi guration, a lag time of 4-7 s was
obtained. A shorter lag of approximately 1.0 s can be achieved by the injection of
the herbicide at each nozzle.
Site- and species specifi c weed control was performed in cereals, sugar beet,
maize and oil-seed rape resulting in signifi cant areas that remained untreated with
herbicides (Table
10.3
). Combinations of weed mapping and application technolo-
gies for site- and species specifi c weed control increased the potential for herbicide
savings. From the results it is obvious that the herbicide savings can be considerably
enhanced when the site-specifi c application is supplemented with species-specifi c
spraying .
