Agriculture Reference
In-Depth Information
cotton using a mechanical guidance system substantially reduced costs by
allowing a narrower band of herbicides over the crop row.
Electronic guidance systems usually have wands that sense the presence of
the crop row. The simplest merely alert the operator when the implement
strays to one side, but most models control a steering device. Various steering
devices correct the cultivator'sposition by (i) shifting the lift arms of the three-
point hitch, (ii) shifting the cultivator laterally relative to the hitch, (iii) rotat-
ing the cultivator slightly on the hitch, (iv) turning it slightly using disk
coulters, or (v) turning the tractor steering wheel (Cramer, 1988; Bowman,
1991, 1997, pp. 30-3). The last approach results in a longer delay between
error and correction on rear-mounted machines, but it allows the driver to
watch for jamming and other problems. It is also the only approach that is
well adapted to belly- or front-mounted machines, although in principle, the
second approach could work if the implement was attached to the tractor by a
laterally sliding carriage.
Generally, crops like maize and sorghum that are flexible when young
cannot be reliably sensed until 12-15 cm tall; beans can be detected at
7-10 cm. Some systems can guide electronically off a planter-made furrow
when the crop is too small to be sensed. Tian, Slaughter & Norris (1997)
recently developed software for detecting rows of tomato seedlings by com-
puter interpretation of a video image. When incorporated into a guidance
system, this should allow guided cultivation of very young crops. Van
Zuydam, Sonneveld & Naber (1995) used a laser beacon to provide precision
tractor guidance for several types of field operation, including cultivation.
Rapid progress in the computer industry opens possibilities for further
development of automatically guided cultivators. These could potentially
operate under the control of artificial intelligence software,distinguish weeds
from crops using a variety of electronic sensors and image processing devices
(Zhang & Chaisattapagon, 1995), and selectively destroy weeds with a flexible
array of tools.Development of such machines does not require new technolog-
ical breakthroughs,but may be unnecessarily sophisticated for most cropping
systems.
Systems of mechanical weed management
Effective mechanical weed control typically requires several machines.
These need to be appropriate for the type of crop, timing of crop development,
tillage practices, and type of weed problem. That is, various mechanical weed
management practices need to be integrated into a program that in turn is inte-
grated with other ecological management methods.
A mechanical weed management program commonly used by organic
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