Agriculture Reference
In-Depth Information
for cross-referencing. Although irrigation timing is based on a threshold established
within the scheduling algorithm, the amount of irrigation water to apply is typically
determined from estimates of crop evapotranspiration derived from daily weather
data and crop coefficients or historical regional peak crop water use data. Once an
irrigation event is triggered, a control system executes water delivery.
Site-specific applications refer to precision crop management techniques that
include irrigation, chemigation, and fertigation. Both automated irrigation man-
agement and site-specific application methods have been under research and devel-
opment since the 1990s (King et al. 1996; Wall et al. 1996; McCann et al. 1997).
Looming issues of global water scarcity, increasing energy costs, and an exponential
rise in global population give impetus for advancing robust automation and site-
specific technologies. The recent synergy of affordable electromechanical devices,
radio frequency (RF) technology, and embedded computing systems will surely help
drive the commercialization of advanced automation. However, irrigation manage-
ment and application systems must be reliable and result in measureable savings
to the farmer either in terms of savings in labor, reduction in inputs, or improved
water use efficiency or water and energy conservation. Farmers are willing to adopt
new technology when there is an obvious expected outcome rather than information
alone (Jochinke et al. 2007). The outcomes of automation are likely to make agricul-
tural practices more sustainable.
11.2 AUTOMATION IN PRESSURIZED IRRIGATION SYSTEMS
A large portion of irrigated farmland in the United States (63%) comprises pressur-
ized systems depending on crop type, land topography, and water availability (USDA
ERS 2011). In California, about 50% of the 9.6 million irrigated acres are using sprin-
kler and micro-irrigation systems. Sprinkler and micro-irrigation systems are often
referred to as pressurized irrigation systems, and these systems typically operate under
a water pressure range of approximately 15-65 lb/in
2
. Although automation can be
facilitated to some degree in nonpressurized surface irrigation systems, for example,
programmable canal and gate controls, pressurized systems allow more flexibility for
automating irrigation management, especially for crops that require a high frequency
of irrigation (Buchleiter 2007). Automation in a pressurized irrigation system is typi-
cally achieved with a centralized decision-making control device, supported with a set
of hardware (control valves, relays) to carry out irrigation commands and sensors to
input environmental measurements for making irrigation decisions.
11.2.1 C
ONTROL
S
YSTEMS
Control systems deployed to automate pressurized irrigation systems range from a
simple on/off timer to sophisticated closed-loop operations using real-time or near
real-time feedbacks from soil (Evett 2007), plant (Wanjura et al. 1992; Jones 2004),
and meteorological variables (Doorenbos and Pruitt 1977; Howell et al. 1984). The
basic structure and components of a relatively comprehensive control system are
depicted in Figure 11.1. Automation is performed with an irrigation controller, which
