Irrigation systems should be a relevant agent to give solutions to the increasing demand of food, and to the development, sustainability and productivity of the agricultural sector. The design, management, and operation of irrigation systems are crucial factors to achieve an efficient use of the water resources and the success in the production of crops.The aim of this paper is to analyze the advances made in irrigation systems as well as identify the principal criteria and processes that allow improving the design and management of the irrigation systems,based on the basic concept that they facilitate to develop agriculture more efficiently and sustainable. The advances and management of irrigation systems at farm level is a factor of the first importance for the rational use of water, economic development of the agriculture and its environmental sustainability.
Key words: Irrigation, Design, Water Management, Operation Systems
Water required by crops is supplied by nature in theform of precipitation, but when it becomes scarce or its distribution does not coincide with demand peaks, it is then necessary to supply it artificially, by irrigation. Several irrigation methods are available, and the selection of one depends on factors such as water availability, crop, soil characteristics, land topography, and associated cost. In the near future, irrigated agriculture will need to produce two-thirds of the increase in food products required by a larger population (English et al., 2002). The growing dependence on irrigated agriculture coincides with an accelerated competition for water and increased awareness of unintended negative consequences of poor design and management (Cai et al., 2003) Optimum management of available water resources at farm level is needed because of increasing demands, limited resources, water table variation in space and time, and soil contamination (Kumar and Singh, 2003).
Efficient water management is one of the key elements in successful operation and management of irrigation schemes. Irrigation technology has made significant advances in recent years. Criteria and procedures have been developed to improve and rationalize practices to apply water, through soil leveling, irrigation system design, discharge regulations, adduction structures, and control equipment. However, in many regions these advances are not yet available at the farm stage. Irrigation systems are selected, designed and operated to supply the irrigation requirements of each crop on the farm while controlling deep percolation, runoff, evaporation, and operational losses, to establish a sustainable production process. Playán and Mateos (2006) mentioned that modernized irrigation systems at farm level implies selecting the appropriate irrigation system and strategy according to the water availability, the characteristics of climate, soil and crop, the economic and social circumstances, and the constraints of the distribution system.
Efficient irrigation equipment generally comes in two broad categories—drip and sprinkler irrigation. Both of these areas have several sub-types of equipment in them. Within drip irrigation are surface drip equipment, subsurface drip equipment and micro sprays/sprinklers. This category of drip irrigation and particularly subsurface drip irrigation (SDI) is one of the most exciting and newest technologies in irrigation. Drip irrigation has attracted tremendous interest by academics, who measure the performance of drip systems and promote drip as a water savings technology. Sprinkler equipment can also be broken down into several subcategories including wheel lines, solid set and hand move pipe, traveling guns, and mechanical move irrigation (MMI) systems, which include center pivots and linear move equipment.
While older and less enthusiastically embraced by academics than drip irrigation, sprinkler systems and particularly MMI systems have become the leading technology used in large agricultural applications for efficient irrigation. With the advent of Low Energy Precision Application (LEPA) configurations in the 1980’s, MMI systems achieve irrigation efficiencies rivaling subsurface drip. Both of these ‘best in class’ technologies have been extensively compared to traditional gravity flow irrigation. Both systems can demonstrate significantly better overall performance than traditional irrigation methods. Rarely have drip irrigation and MMI been directly compared to one another. The balance of this paper will draw comparisons between these two types of irrigation systems, and explore how appropriate each technology is for various types of farming operations.
IRRIGATION SYSTEM PERFORMANCE
Up to this point, our discussion on advances in irrigation has focused on water savings. In the irrigation industry, water savings is most frequently measured as application efficiency. Application efficiency is the fraction of water stored in the soil and available for use by the crop divided by the total water applied. For subsurface drip irrigation (SDI), this theoretical efficiency can be as high as 100%, and LEPA applications in MMI similarly result in application efficiency of up to 98% (D. Rogers, 2012). While application efficiency is a good starting point in understanding irrigation performance, efficiency measurements under ideal conditions on a test plot hardly tell the whole story about irrigation performance. In general, we can analyze irrigation performance in five categories as shown below
Researchers generally give the edge to subsurface drip irrigation SDI when they evaluate water efficiency. According to the IrrigationAssociation, subsurfacedrip irrigation (SDI) installations, if properly managed, can achieve 95% water efficiency (James Hardie, 2011). This high level of water efficiency isapproximately the same as what a LEPA center pivot or linear system achieves, at 90-95%, and definitely better than the 75-85% efficiency of center pivot with the obsolete water application method of impact sprinklers mounted to the top of the MMI system’s pipe. Gravity flow installations are typically around 40%-50% efficient. For the purpose of a farmer’s consideration, LEPA and SDI systems can be thought of as having equivalent potential efficiency. Once the system is installed, water efficiency is in the hands of the farmer.
While data on this topic is difficult to find, it seems that farmers habitually over-apply water to their fields with all types of irrigation equipment including gravity flow. Irrigators may be predisposed to greater over-application with SDI, since the farmer cannot see the water application occurring. Both systems will benefit from more sophisticated information on evapotranspiration and plant health to allow more precise application of water and reduce over-application. SDI systems typically require periodic cleaning and flushing to prevent root ingression and plugging. Such flushing is not a requirement with MMI equipment. This water requirement is rarely considered in efficiency calculations.
CROP YIELD DRIVER
In most cases, the contribution that an irrigation system can make to reaching optimal crop yields is by delivering water to plants when they need it and by applying water uniformly over the area of the field. However, when the available water supply is insufficient to fully meet the water needs of a crop, then the highest crop yields will be achieved by the irrigation system with the highest application efficiency. Uniform water application by MMI systems is determined by sprinkler package design and by the rate at which the equipment moves across the field. Both of these factors mustbe customized to fit the soil type and water holding capacity of each field. MMI experts today have a very good understanding of the relationship between soil type, water holding capacity, equipment speed, and sprinkler package design, and they have even developed several computer programs to generate highly uniform patterns of water distribution for low pressure and LEPA systems.
Changes in the elevation of terrain can beaccommodated by the use of pressure regulators. Uniformity of MMI systems is fairly constant over time. Variations among individual nozzles is significantly reduced by the movement of the equipment and by the overlap between the wetted diameters of soil irrigated by each individual sprinkler head. Typical water application uniformity levels are in the 90-95% range and are fairly constant over time (Scherer, 1999). In applications with high levels of abrasives present in the water, sprinkler packages must be replaced and redesigned every few years to maintain watering uniformity. Drip systems can also be designed to have high levels of uniformity. A typical design targets uniformity levels in the 85% range. SDI design is not as standardized as MMI system design is, and consequently the water application of any drip system is highly dependent on the skill and knowledge the technician who designed it. Unlike MMI systems, drip system uniformity can change substantially over time if proper maintenance is not performed to the drip installation.
This is particularly difficult for subsurface systems, whose emitters are more likely to suck in soil which cannot then be easily removed by hand since the emitters are buried underground. According to a South African study published in 2001, field examinations of drip systems show that water application uniformity deteriorates significantly over time.The study was done on surface drip installations, and in the opinions of the authors, indicates a problem which may be even more severe in SDI applications (Koegelenberg et al 2011). System availability and controllability is generally good with both MMI and SDI systems, since both offer the ability to irrigate at least once every 24 hours. The exception to this can be with towable pivots, where use of the equipment on multiple fields may limit its availability. Both systems support the use of sophisticated automatic controls and remote control and monitoring.
Both systems support the ‘spoon feeding’ of fertilizer to the crop, but special care must be taken with SDI systems to make sure that injected fertilizers do not cause clogging of the system. For SDI systems, soil salinization is also a significant problem in areas where salts are present in irrigation water. As salts build up in soil, crop yields decrease. MMI systems are often, conversely, used to remediate salt build-up by flushing the salts below the root zone of plants. Based on a review of available literature, itappears that in non-water limited applications, SDI and MMI systems produce equivalent yields, although the center pivot will use slightly more water in those comparisons due to losses fromsurface evaporation. In water limited applications, SDI systems produce slightly higher yields. Over time, SDI system maintenance is of great importance. A lapse in system maintenance can result in a significant and permanent degradation of watering uniformity, which in turn causes permanently higher water consumption and lower crop yields.
A lot of conflicting information exists concerning the costs of both SDI and MMI systems. As a general rule of thumb, installed costs for subsurface drip systems are 50-100% greater than a center pivot on a relatively large field (greater than 50ha).(O’Brien et al 1998). Cost depends on a number of factors including: availability of proper power, filtration type used in the drip system, the value of installation labor, towable vs. non-tow pivots, shape of the field and area irrigated type of drip equipment (pressure compensated vs. non-pressure compensated) and the use of linear move equipment, or corner arm extensions on a center pivot. Also important to the long-term cost is the expected life. Center pivots have an average life expectancy of 25 years with minimal maintenance expenses, typically less than 1% per year of the original price. In a few installations where the source water is corrosive to galvanize steel, it is important for the buyer to move to corrosion resistant products such as aluminum, stainless steel, or polyethylene lined systems. Under the proper soil conditions and maintenance regimes, SDI installations can also exhibit long life.
Some research installations have surpassed 20 years of usage with still functioning systems. Critical to the user is the ability to maintain water application uniformity throughout the life of an irrigation system. In most commercial installations, drip systems performance degrades with time due to plugging, root intrusion, and pest damage. Diagnosis and repair of SDI system problems can be expensive and challenging to perform. Typical maintenance costs range from 3% to 10% per year of the original system cost. Another advantage of MMI technology is its portability. It is not uncommon for a center pivot to be moved several times during its expected service life. Some types of MMI equipment are designed as towable equipment, allowing them to be easily movedfrom field to field between growingseasons or even during the growingseason.
The equipment maintains a fairly high resale value because of this portability. SDI systems, with the exception of some filtration and control elements, are generally not salvageable or resell able at all. In addition to maintenance and repair costs, the other significant system operating cost is energy used to pump water and field labor. Energy costs are related to the volume of water pumped and the pressure required. Research shows that these two costs are nearly equal for SDI and MMI systems. Center pivot and linear systems at research plots typically pump slightly more volume of water then SDI systems, but SDI pump outlet pressures are typically higher (3 bar vs. 1.5-2 bar).
Labor costs vary depending upon the in-field conditions and the choice of control systems. One 1990 article shows pivots to require 3 hours per hectare, while drip requires 10 hours per hectare.(Kruse et al, 1990). Even in trouble-free installations of equal control sophistication, SDI seems to require more labor because of its regularly required maintenance cycle. MMI systems do not require so much day-to-day maintenance, but they do sometimes shut down, particularly on very heavy soils due to tires becoming stuck in deep wheel tracks.
CROP SPECIFIC CONSIDERATIONS
Different crop specific characteristics favor one system type over another. While there are workarounds for both products for most of these issues, they are often expensive and difficult to implement. Drip systems or micro-irrigation are often preferred by growers when crop height may be an issue for mechanical systems as over cashew nut trees, or with planting patterns not conducive to above ground mobile irrigation equipment as with vineyards. Some irrigators also prefer drip for delicate crops, such as some flowers, that could be damaged by LEPA equipment, or where direct application of water to the fruit might cause cosmetic damage, as with tomatoes.
Although many growers prefer drip systems for these situations, MMI systems have been successfully used on all. MMI systems are preferred where surface water application isrequired to germinate seed as with carrots and onions, particularly in sandy soils. MMI systems also have an advantage in applying foliar herbicides and pesticides, and can be used for crop coolingin temperature sensitive crops such as corn. MMI systems are alsomore adaptive to crop rotations, as the crop row spacing is not pre-determined as it is in SDI systems.
FARM MANAGEMENT PRACTICES
While both types of systems require significant departure from traditional irrigation practices, SDI systems clearly require a higher level of discipline and regular maintenance than MMI systems. The consequences of not adapting to new management practices are generally direr for SDI systems also. SDI farms must commit to the regular cleaning and flushing procedures described by the system designer and the equipment manufacturers. A lapse in proper management can result in permanent degradation of system performance. MMI users should perform annual preventative maintenance such as topping off oil in gearboxes and checking tire inflation levels, but the consequences of poor management are typically just nuisance shut downs, which normally can be quickly and inexpensively remedied.
A special problem that faces owners of MMI equipment in some third world countries is theft, particularly theft of motors, controls and copper wire. To combat this problem, a number of adaptations have been made to reduce the risk of theft on the system. Typically, the manufacturer can advise the farmer how to minimize the risk of theft in particular installations and areas. MMI systems are less flexible when it comes to field configuration and water infrastructure. Farmland laid out in 2 hectare plots with canals serving the individual fields, for example, are difficult to adapt to MMI systems. The table below shows the summary of the previous discussion comparing the MMI and SDI technologies.
Analysis of SDI and MMI System Performance|
Water Efficiency * SDI has slightly higher efficiency than LEPA (95% vs. 90-95%) in research installation. * No known studies yet compare actual on-farm efficiency| Crop Yields * SDI performs better in research tests when water availability is the limiting factor, otherwise yields are equivalent between the two systems. * Uniformity of SDI systems appears to degrade over time, favoring MMI. * Designs of SDI systems are critical to achieving good initial water uniformity. * Where salinity is a problem, MMI systems have a clear edge.| Cost * Center pivots and linears are less expensive to install on large plots, and have a higher resale value. * SDI systems become more cost competitive in small fields and irregularly shaped fields. * MMI systems have long lives (25 years on average). SDI can have a life of 10-15 years if proper maintenance is performed. * Ongoing maintenance costs of SDI are 3-5 times higher than MMI.
* Operating costs for energy are similar between the two technologies, but MMI systems typically require much less labor.| Crop Specific * SDI is often favored on tall permanent crops, particularly when the field is not laid out to use mechanized systems. * MMI systems are preferred in sandy soils where surface application is necessary for germination. * Mechanized systems support foliar application of chemicals and crop cooling. * Mechanized systems are preferred where there are frequent crop rotations.| Farm Management * SDI systems are less adaptive and forgiving to poor management practices. * Theft is an issue for mechanized systems in some third world markets. * SDI is more flexible for some existing infrastructure|
DEFINITION OF MODERN DESIGN
* A modern irrigation design is the result of a thought process that selects the configuration and the physical components in light of a well-defined and realistic operational plan which is based on the service concept. * Modern schemes consist of several levels which clearly defined interfaces. * Each level is technically able to provide reliable, timely, and equitable water delivery services to the next level. That is, each has the proper types, numbers, and configuration of gates, turnouts, measurement devices, communications systems and other means to control flow rates and water levels as desired. * Modern irrigation schemes are responsive to the needs of the end users. Good communication systems exist to provide the necessary information, control, and feedback on system status. * The hydraulic design is robust, in the sense that it will function well in spite of changing channel dimensions, siltation, and communication breakdowns. Automatic devices are used where appropriate to stabilize water levels in unsteady flow conditions.
ADVANCES MADE IN IRRIGATION
During the last three decades, micro irrigation systems made major advances in technology development and the uptake of the technology increased from 3 Mha in 2000 to more than 6 Mha in 2006. Micro-irrigation is an irrigation method that applies water slowly to the roots of plants, by depositing the water either on the soil surface or directly to the root zone, through a network of valves, pipes, tubing, and emitters (see Figure below).
Fig. 1: Components of a micro-irrigation system
EARLY HISTORY OF MICRO-IRRIGATION
Drip irrigation was used in ancient times by filling buried clay pots with water and allowing the water to gradually seep into the soil. Modern drip irrigation began its development in Germany in 1860 when researchers began experimenting with sub irrigation using clay pipe to create combination irrigation and drainage systems. In 1913, E.B. House at Colorado State University succeeded in applying water to the root zone of plants without raising the water table. Perforated pipe was introduced in Germany in the 1920s and in 1934; O.E. Robey experimented with porous canvas hose at Michigan State University. With the advent of modern plastics during and after World War II, major improvements in drip irrigation became possible. Plastic micro tubing and various types of emitters began to be used in the greenhouses of Europe and the United States. A new technology of drip irrigation was then introduced in Israel by Simcha Blass and his son Yeshayahu.
Instead of releasing water through tiny holes, blocked easily by tiny particles, water was released through larger and longer passage ways by using friction to slow the water flow rate inside a plastic emitter. The first experimental system of this type was established in 1959 in Israel by Blass, where he developed and patented the first practical surface drip irrigation emitter. The Micro-sprayer concept was developed in South Africa to contain the dust on mine heaps. From here much more advanced developments took place to use it as a method to apply water to mainly agricultural crops.
ADVANTAGES OF MICRO-IRRIGATION
The advantages of drip irrigation are as follows:
* Sophisticated technology
* Maximum production per mega litre of water
* Increased crop yields and profits
* Improved quality of production
* Less fertilizer and weed control costs
* Environmentally responsible, with reduced leaching and run-off
* Labour saving
* Application of small amounts of water more frequent
DISADVANTAGES OF MICRO-IRRIGATION
The disadvantages of micro-irrigation are as follows:
* Need managerial skills
* Waste: The plastic tubing and “tapes” generally last 3-8 seasons before being replaced
* Plant performance: Studies indicate that many plants grow better when leaves are wetted as well
The biggest single change since the first irrigation symposium is the amount of land irrigated with center-pivot and linear-move irrigation machines. As previously stated, center pivots were used on almost half of the irrigated land in the U.S. in 2008 (USDA-NASS, 2012). Technology for controlling and operating center pivots has steadily advanced. Kranz et al. (2012) describe how operators can now communicate with irrigation machines by cell phone, satellite radio, and internet-based systems. New sensors are being developed to collect soil or crop information that can be used for managing
irrigation. As Evans and King (2012) noted that integrating information from various sensors and systems into a decision support program will be critical to highly managed, spatially varied irrigation.
Technology has allowed irrigators to precisely control irrigation. However, technology to precisely apply irrigation water is wasted if the water does not infiltrate into soil where it was applied. King and Bjorneberg (2012) characterize the kinetic energy applied to the soil from common center-pivot sprinklers and relate this energy to runoff and soil erosion to improve center-pivot sprinkler selection. Finally, Martin et al. (2012) describe the wide variety of sprinkler packages available for mechanical-move irrigation machines and how those sprinkler packages are selected.
Above Left: A Field VISION control panel operates one of his pivots Above Right: A computer screen display showing the exact position of the irrigation pivot, along with how much water is being sprayed on the crop
A Zimmatic Pivot Irrigation System
An Irrigation Field Covered by a Center Pivot Irrigation System
A Center Pivot Irrigation System in Action
The success or failure of any irrigation system depends to a large extent on careful selection, thorough planning, accurate design and effective management. One thing we can be certain of, the demands of irrigated agriculture will certainly not diminish, they will indeed increase almost exponentially. Advanced surface irrigation will still dominate as the primary irrigation method, but with the current trends, the area under micro-irrigation will continue to expand. Both subsurface drip and mechanical move irrigation systems have a legitimate place in agricultural water conservation plans for the future. Both systems offer significant potential water application reduction, as well as yield improvements over traditionally managed irrigation fields. In general, mechanized systems are most suitable for: broad area crops in large fields, new land development, and sandy soils.
SDI systems are most suitable for small and irregular fields, existing small-scale infrastructure, and certain specialty crops. These innovative technologies require significant investment. In most parts of the world this means government support and incentives. Mexico and Brazil are two leading countries in providing effective incentives to farmers to invest in modern efficient agricultural irrigation. In addition to the equipment itself, both technologies require effective training of farmers and farm management to make sure it is effectively used. Poor management can easily offset most of the water saving and yield gains made possible by the equipment. Employing the modern technology available for water-efficient irrigation is clearly a key to over coming the global challenges of water scarcity. Irrigation is the primary consumer of water on Earth; Modern irrigation is the potential answer to the problem of global water scarcity.
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