Although
interest in autoguidance dates back to the 1920s, successful systems
evolved only recently. Early systems used mechanical sensors that
sensed a crop row or furrow, followed by laser-based optical sensors.
While these systems proved the feasibility of the autoguidance concept
for agricultural tractors, they were not practical. The widespread
availability of inexpensive and powerful microcomputers and advances
in image processing led to the development of autoguidance systems
based on machine vision in the 1980s and 1990s.
These vision-based systems require a guidancy directrix (guiding
line) such as a crop row. Introduction of real-time kinematic global
positioning system (RTK GPS) to agriculture in the past decade led
to the development of a self-contained (not dependent on a crop
line or furrow wall) autoguidance system. The first successful RTK
GPS-based autoguidance system was demonstrated in spring 1996. RTK
GPS has increased in popularity because of its ability to guide
a tractor along the same path again and again not only within a
season, but also year after year at high speeds and with minimal
damage to plants, implements or drip-irrigation systems. As a result,
at least three manufacturers are currently marketing autoguidance
systems based on RTK GPS.
This technology may also lead to further reductions in costs for
row crop production. Planting and transplanting equipment can be
instrumented to sense seeds or seedlings as they are planted and
locate them precisely (to 2 inches accuracy). Such a precise plant
map can substantially target weeds using a simple greenness sensor
(any green object that is not a part of the original plant map is
considered a weed and can be sprayed).
Scientists for UC Davis initiated a project to explore the effectiveness
of an autoguidance system based on a real-time kinematic global
positioning system (RTK GPS) accurate to the centimeter (about half-inch)
in agricultural production. The objectives were to determine the
effect of spacing between cultivator disks or knives and forward
tractor speed on plant damage, and of deep tillage operations on
drip-tape damage. Two sets of split-plot field experiments were
conducted (with processing tomato transplants and direct-seeded
tomatoes) in a Yolo loam field on the UC Davis campus.
Results from their study showed no significant plant damage occurred
even at 7 miles per hour (mph) forward speed and cultivator disk
spacing of 2 inches from the plant line. In an additional split-plot
test, there was no significant damage to drip tape when the fertilizer
shank was operated 2 inches from the drip tape at 3.5 mph. This
system allows for automatic steering of the tractor and implements
along a path close to buried drip-tape and/or plants without damaging
them, even at high operational ground speeds.
