2.6.3 Importance of irrigation scheduling
Some irrigation water is stored in the soil to be removed by
crops and some is lost by evaporation, runoff, or seepage. The amount of water
lost through these processes is affected by irrigation system design and
irrigation management. Prudent scheduling minimizes runoff and percolation
losses, which in turn usually maximizes irrigation efficiency by reducing
energy and water use.
Energy can thus be saved by no longer pumping water that was
previously being wasted. When water supplies and irrigation equipment are
adequate, irrigators tend to over irrigate, believing that applying more water
will increase crop yields. Instead, over irrigation can reduce yields because
the excess soil moisture often results in plant disease, nutrient leaching, and
reduced pesticide effectiveness. In addition, water and energy are wasted.
The quantity of water pumped can often be reduced without
reducing yield. Studies have shown that irrigation scheduling using water
balance methods can save 15 to 35 percent of the water normally pumped without
reducing yield (Evans et al., 1996). Maximum yield usually does not
equate to maximum profit. The optimum economic yield is less than the maximum
potential yield. Irrigation scheduling tips presented in popular farm magazines
too often aim at achieving maximum yield with too little emphasis on water and
energy use efficiencies. An optimum irrigation schedule maximizes profit and
optimizes water and energy use.
2.7 Geographic Information Systems
A geographic information system (GIS), or geographical
information system is a system which captures, stores, analyzes, manages, and
presents data that is linked to location (Chang, 2007). GIS provides a means of
measuring spatial and attribute data into a computerized database system,
thereby allowing input, storage, retrieval and analysis of geographically
referenced data (Heywood et al., 2006). It is therefore a system of
computer hardware, software, and procedures designed to support the capture,
management, manipulation, analysis, modeling, and display of spatially
referenced data for solving complex planning and management problems. In the
strictest sense, the term describes any information system that integrates
stores, edits, analyzes, shares, and displays geographic
information. In a more generic sense, GIS applications are
tools that allow users to create interactive queries (user created searches),
analyze spatial information, edit data, maps, and present the results of all
these operations. Analyzing large amount of data is a necessity for management
of irrigation projects. Data must be collected, stored and interrelated with
each other in such a way that the data are readily accessible (Dayyani et
al., 2003). The cartographic and data overlaying capability of GIS coupled
with its dynamic linking ability to models plays a vital role in water
management. In addition, its ability of writing scripts gives the decision
makers this power to produce the necessary outputs the way they need them.
GIS technology can be used for water resource management,
asset management, archaeology, environmental impact assessment, urban planning,
cartography, criminology, geographic history, marketing, logistics, scientific
investigations, prospectivity mapping, and other purposes. For irrigation
management adequate and updated information regarding the irrigation system is
needed, thus GIS tool for irrigation management provides information
interactively for decision making process. GIS have the capability of improving
water management techniques as well as decision-making (Taylor, 2005). GIS have
thus, taken a central role in analyzing, modeling, and managing a wide range of
water resource information. System GIS can analyze spatial interactions between
static and dynamic entities.
1. Spatial data management
2. Interactive visualization
3. Spatial analysis
4. Customization and decision-making support.
The importance of spatial geographic components in on-farm
irrigation system performance imposes the involvement of the capabilities to be
able to store, aggregate, manipulate, analyze and visualize a huge quantity of
data. In the recent last ten years, to this purpose, the use of GIS has been
greatly diffused. These systems, if combined to appropriate simulation models
could support the decisions of designers and/or managers (Hoogenboom et
al., 1991).
A GIS is characterized by a unique ability of the user to
overlay spatial layers, each, representing one or more physical and/or
functional characteristics of the studied
phenomenon. Each layer is related to a table, representing the
database. Using appropriate models, it is then possible to actively elaborate
the information and to present results under tabular and/or maps form.
There have been several applications of GIS in irrigation and
drainage systems around the world. Sarangi et al., (2001) used GIS in
development of input data set for a conceptual small watershed runoff
generation model. In addition, they used ARC/INFO for canal system within the
project area of Patna Canal and distributaries of Sone command area in India.
Amor et al., (2002) combined GIS with a crop growth model to estimate
the water productivity in time and space in the Philippines. Three products,
rice, corn and peanut were modeled in their research. They analyzed the water
limitation for each crop in different seasons and determined the productivity
potential in the region. In Iran, application of GIS dates as far back as the
90's in diverse fields of water sciences such as hydrology, flood control,
water erosion, and groundwater management. Daneshkar et al. (2000)
used GIS and Modflow for simulation of Ab-Barik groundwater plain. Alvankar
et al. (2000) applied GIS in watershed characterization of the Latvian
dam watershed.
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