Agriculture Reference
In-Depth Information
farming inputs need to be determined for each management zone or cell
based on the specific conditions. This may require the use of an expert sys-
tem that can integrate the knowledge of farmers and crop consultants with
biological, economic, and crop growth models to make better decisions.
3. Implementing management decisions. Applicators with variable rate con-
trollers are needed to apply various inputs at desired locations with correct
rates based on site-specific application maps or data from real-time sensors.
4. Evaluating economic and environmental benefits. Precision agriculture has
the potential to increase economic returns and minimize environmental
impacts, but it requires investment in new equipment and time. To facilitate
the adoption of precision agriculture, it is important to document the eco-
nomic and environmental benefits of precision agriculture operations.
This chapter provides an overview of the major technologies involved in pre-
cision agriculture, including GPS, soil sensors, crop sensors, wireless technology,
yield monitors, remote sensing, GIS, and variable rate technology. The emphasis is
placed on the principles and practice of these technologies for precision agriculture
operations.
4.2 MEASUREMENT OF SPATIAL VARIABILITY
Measurement of within-field variability is the first important step in precision agri-
culture. Unless the level of variability is known, an appropriate management decision
cannot be made. GPS is the foundation of precision agriculture operations, includ-
ing data collection and variable rate application. Various ground-based sensors inte-
grated with GPS are used to measure spatial variability in soil attributes, crop yield,
and crop pests. Airborne and high-resolution satellite imagery has become a major
data source for documenting soil and crop growth variability, because each image
provides a continuous view of all fields in the imaging area.
4.2.1 GPS
The GPS was developed by the U.S. Department of Defense for military applica-
tions, but it has been used for many other applications including precision agricul-
ture. The system became fully operational on April 27, 1995. It provides service for
positioning, navigation, and timing.
There are three segments in the GPS: space, control, and user. The space seg-
ment consists of 24 active NAVSTAR (Navigation by Satellite Timing and Ranging)
satellites with additional ones (seven more as of October 4, 2011). The satellites
are positioned in six orbital paths, at least four in each path. One revolution takes
12 hours. The space segment is designed to guarantee that users can see at least
four satellites anytime and anywhere in the world. The satellites broadcast radio
signals in 1200-1500 MHz. It is equipped with atomic clocks, which are the most
critical component, since the positioning is based on the exact timing. The control
segment receives and transmits information to the satellites and ensures the accuracy
of the satellite positions and clocks. There are several monitoring stations around the
