Irrigation may be defined as the process of supplying water to land by artificial means for the purpose of cultivation.Ordinarily water is supplied to land by nature through rain but generally it is not enough for the proper growth of plants.As such as the basic objective of irrigation is to supplement the natural supply of water to land so as to obtain the an optimum yield from the crop grown on the land.
In order to achieve this objective of irrigation, an irrigation system is required to developed, which involves planning, designing, construction, operation and maintenance of various irrigation works viz, a source of water supply, a distribution system for carrying water from the source to the agricultural land and its application on the land, and various other associated works.The factors which neccessitate irrigation are:
Ø Inadequate rainfall
Ø Uneven distribution of rainfall
Ø Growing a number of crops during a year
Ø Growing superior crops
1.2 METHODS OF IRRIGATION
Irrigation methods are commonly designated according to the manner in which water is applied to the land to be irrigated.
1.2.1 Surface Irrigation Methods
The water is applied by spreading in it sheets or small streams on the land to be irrigated.These methods are adopted for perennial irrigation system.
1.2.2 Sprinkler Irrigation Methods
The irrigation water is applied to the land in the form of spray, somewhat as in ordinary rain.It can be used for all the crops except rice and jute and for almost all soils except very heavy soils with very low filtration rates.
1.2.3 Sub-Surface Irrigation Methods
The water is applied below the ground surface so that it is supplied directly to the root zone of the plants.The main advantages of these methods are that the evaporation losses are considerably reduced and the hindrance caused to cultivation by the presence of borders, pipes and field channels in the other methods of irrigation is eliminated.
1.3 DRIP OR TRICKLE IRRIGATION METHOD
Drip irrigation,also known as trickle irrigation or microirrigation is one of the sub-surface irrigation method of applying water or frequent application of water to crops through small emitters in the vicinity of the root zone, wetting a limited amount of surface area and depth of soil. The theory behind drip irrigation is to apply sufficient moisture to the root of the crops to prevent water stress. A major difference between drip system and most other systems is that the balance between crop evapotranspiration and applied water is maintained over limited periods of 24 to 72 hours. The conversion from sprinkler to drip irrigation can result in water use reduction of 50% and double yield. This is a result of improved water use and fertility and reduced disease and weed pressure.
1.4 NEED OF DRIP IRRIGATION
Drip irrigation can help you use water efficiently.A well-designed drip irrigation system loses practically no water to runoff, deep percolation, or evaporation. Drip irrigation reduces water contact with crop leaves, stems, and fruit. Thus conditions may be less favorable for the onset of diseases. Irrigation scheduling can be managed precisely to meet crop demands, holding the promise of increased yield and quality.Growers and irrigation professionals often refer to "subsurface drip irrigation,"or SDI. When a drip tape or tube is buried below the soil surface, it is less vulnerable to damage during cultivation or weeding. With SDI, water use efficiency is maximized because there is even less evaporation or runoff.Agricultural chemicals can be applied more efficiently with drip irrigation. Since only the crop root zone is irrigated, nitrogen already in the soil is less subject to leaching losses, and applied fertilizer N can be used more efficiently. In the case of insecticides, less product might be needed.
COMPONENTS AND WORKING
In drip irrigation, also known as trickle irrigation, water is applied in the form of drops directly near the base of the plant. Water is conveyed through a system of flexible pipelines, operating at low pressure, and is applied to the plants through drip nozzles. This technique is also known as ‘feeding bottle’ technique where by the soil is maintained in the most congenital form by keeping the soil-water-air proportions in the optimum range. Drip irrigation limits the water supplied for consumptive use of the plant by maintaining minimum soil moisture, equal to the field capacity, thereby maximizing the saving. The system permits the fine control on the application of moisture and nutrients at stated frequencies.
Fig 2.1 Drip Irrigation System Layout and its parts (Credits:Eric Simonne)
The main components of a typical drip irrigation system are:
Ø Water Source
Ø Pumping System
Ø Distribution System
Ø Drip Tape ( Drip Tube)
Ø Filtration System
2.1 WATER SOURCE
Common water sources for drip irrigation are surface water (pond, river, and creek), groundwater, and potable water (from municipality, county orutility company). Use the water source thatwill provide the largest amount of water of greatestquality and lowest cost. Potable water is of high,constant quality, but is by far the most expensive.
Fig 2.2 Pond: Water Source (Credits:Eric Simonne)
2.2 PUMPING SYSTEM
The role of the pumping system is to move waterfrom the water source to the field through the distribution system. Pumping systems may be classified as electric powered systems, gas/diesel powered systems, and gravity systems.Gas/diesel pumps offer the greatest versatility in isolated fields.
Fig 2.3 Diesel Powered Pumping System (Credits:Eric Simonne)
2.3 DISTRIBUTION SYSTEM
The role of the distribution system is to convey the water from the source to the field. Distribution systems may be above ground (easily movable) or underground (less likely to be damaged).Pipes are most commonly made of PVC or polyethylene plastics.Aluminum pipes are also available, but are more difficult to customize, cut, and repair.The size and shape of the distribution system may vary widely from field to field and from farm to farm.
2.4 DRIP TAPE (OR DRIP TUBE)
The drip-irrigation system delivers water to each plant through a thin polyethylene tape (or tube) with regularly spaced small holes (called emitters). Selection of drip tape should be based on emitter spacing and flow rate. The typical emitter spacing for vegetables is 12 inches, but 8 inches or 4 inches may be acceptable. Dry sections of soil may develop between consecutive emitters when a wider emitter spacing (18 inches) is used on sandy soils. Flow rates are classified into low flow (<20gal/100ft/hr), medium flow (20 to 30 gal/100ft/hr) and high flow(>30 gal/100ft/hr). The risk of emitter clogging is generally higher with the lower-flow drip tapes.In the field, drip-irrigation tape should be installed with emitters upward (looking up) to prevent clogging from sediment deposits settling in the emitters between irrigation events. Drip tapes are widely available from several manufacturers.
|Fig 2.4 Drip Tapes (Credits:Eric Simonne)|
Injectors allow the introduction of fertilizer, chemicals and maintenance products into the irrigation system. Florida law requires the use of an anti-siphoning device (also called backflow-prevention device) when fertilizer, chemicals or any other products are injected into a drip-irrigation system.Backflow-prevention devices ensure the water always moves from the water source to the field. The devices prevent chemicals in the water from polluting the water source. The most common injectors used with smalldrip-irrigation systems are the Venturi (or Mazzei) injector and the Dosatron.Because Venturi injectors involve no moving parts and are less expensive, they are commonly used on small farms. The injector is typically located as close as possible to the irrigation zone, but before the filter.
2.6 FILTRATION SYSTEM
Because drip-irrigation water must pass through the emitters, the size of the particles in the water must be smaller than the size of the emitter to prevent clogging. Nearly all manufacturers of drip-irrigation equipment recommend that filters be used. The filtration system removes "large" solid particles in suspension in the water. Different types of filters are used based on the type of particles in the water. Media filters (often containing angular sand) are used with surface water when large amounts of organic matter (live or dead) need to be filtered out. Screen filters or disk filters may be used withgroundwater. A 200-mesh screen or equivalent is considered adequate
for drip irrigation.When the water contains sand, a sand separator should be used. Rapid clogging may occur when no filter or the incorrect type of filter is used. A filter needs to be cleaned when the difference in pressure across the R filter (measured before and after the filter) is greater than 5 - 8 psi. A drip-irrigation system should never be operated without a filter even if the filter requires clogged drip-tape emitters, often resulting in poor uniformity and sometimes in crop loss. The filter should be cleaned as often as needed. Efforts should be made to understand the cause of the rapid clogging, and remediation for the problem should bdeveloped. The presence of the filter after the point of fertilizer injection means totally soluble fertilizers must be used. Otherwise fertilizer particles may contribute to filter clogging.
The whole field is divided into suitable plots. A secondary line is provided for each such plot, and a number of trickle lines are connected to each secondary line. A discharge regulator is provided at the beginning of each secondary line, and its capacity is fixed in accordance with the size and the number of nozzles used. The automatic valve at the head is so adjusted to deliver the desired quantity of water and the irrigation terminates automatically after this amount is discharged.
DESIGN AND LAYOUT
3.1 HOLTICULTURAL CONSIDERATIONS
The goal of drip irrigation is to bring water to the crop. The main parameters that determine crop water use are the type of crop planted and row spacing. A drip irrigation system should be able to supply 110% - 120% of crop water needs. In other words, the system should be slightly oversized. In designing a drip-irrigation system, it is common to consider that vegetable crops ordinarily need approximately 1.5 acre-inches of water for each week of growth or approximately 20 acre-inches of water per crop. Actual crop water use will be more or less than this amount, depending on weather and irrigation efficiency.
3.2 DESIGN CONSIDERATIONS
Start with what is already available, the water source or the field. If a water source is already available (pond or well), the amount of water available may be used to calculate the maximum size of each irrigation zone.
If no water source is available, the amount of water needed by the crop, based on the size of the planted area, may be used to calculate the type of well or pond size needed.
3.3 LAY OUT OF BEDS AND ROWS
Because differences in altitudes affect water pressure, it is preferable to lay out beds perpendicular to the slope. This arrangement of rows is called "contour farming”.
Excessive water velocities (>5 feet/second) in the lines, the result of a too-small diameter are likely to create a water hammer (pressure wave), which can damage the delivery lines. Growers should be aware of the maximum acreage that can be
irrigated with different pipe sizes at a water velocity of 5 feet/second.
The maximum length of drip tape should be based on the manufacturer's recommendation and the actual terrain slope. Typically 400 - 600 feet are
maximum values for drip-tape length. Excessive length of laterals will result in poor uniformity and uneven water application. When the field is longerthan 400 - 600 feet, consider placing the secondary (submain) line in the middle of the field rather than at the end and connect drip tape on both sides.
Table 3.1 Maximum length of drip tape (feet) and maximum irrigatable field size (acre) with low- and medium-flow drip tape at awater velocity of 5-feet-per-second for selected diameters of Class 160 PVC pipes
System controls are devices that allow the user to monitor how the drip-irrigation system performs. These controls help ensure the desired amount ofwater is applied to the crop throughout the growing season.The different devices used for the control are:
Ø Pressure Regulators
Ø Water Meters
Ø Pressure Gauges
Ø Soil moisture Measuring Devices
Ø Electrical Timers
4.1 PRESSURE REGULATORS
Pressure regulators,installed in-line with the system, regulate water pressure at a given water flow there by helping to protect system components against damaging surges in water pressure. Pressure surges may occur when the water in the pipe has a velocity >5 feet /second ("water hammer") or when water flowing in the pipe has no avenue for release due to a closed valve or a clog inthe pipe.
4.2 WATER METERS
Water meters monitor and record the amount of water moving through a pipe where the water meter is installed. When a stopwatch is used together with a water meter, it is possible to determine the water flow in the system in terms of gallons-per-minute.
4.3 PRESSURE GAUGES
Pressure gauges monitor water pressure in the system and ensure operating pressure remains close to the recommended or benchmark values. Based on where the pressure gauge is installed, it will measure water pressure in a various ranges, from 0-100 psi near the pump to 0-20 psi at the end of drip tape.Pressure gauges may be installed at set points (near the pump, before and after the filter, near the Field.They can also be mounted as portable devices and installed temporarily at the end.
4.4 SOIL MOISTURE MEASURING DEVICES
Soil-moisture-measuring devices (such as tensiometers, capacitance probes or Time Domain Reflectometry probes) are used to measure soil moisture in the root zone of the crop.
4.5 ELECTRICAL TIMERS
Electrical timers connected to solenoid valves may be used to automatically operate a drip-irrigation system at pre-set starting and ending operating times of day.
Fig 4.3 Portable Pressure Gauge (Credits:Eric Simonne)
Fig 4.4 Electrical Timer (Credits:Eric Simonne)
The goal of drip-irrigation maintenance is to preserve the high uniformity of water application allowed by drip irrigation. A successful program of maintenance for a drip-irrigation system is based on the prevention-is-the-best-medicine approach. It is
easier to prevent a drip tape from clogging than to"unclog" it or replace it.
5.1 WATER SAMPLING
An essential part of drip-irrigation management is determining water quality through water testing. Water testing will help determine water chemical composition, pH, and hardness.These parameters have direct implications on chlorination, acidification and filtration needs for irrigation water.
Table 5.1 Water quality parameter levels for emitter plugging potential of
Drip irrigation systems
5.2 THE PREVENTION IS THE BEST MEDICINE MAINTENANCE PROGRAM
This maintenance program is based on filtration, chlorination/acidification, flushing and observation.
Table 5.2 Components of the “prevention is the best medicine” maintanence plan
5.3 WATCH FOR LEAKS
Leaks can occur unexpectedly as a result of damage by insects, animals, or farming tools. Systematically monitor the lines for physical damage. It is important to fix holes as soon as possible to prevent uneven irrigation.
5.4 CHLORINE CLEARS CLOGGED EMITTERS
5.4 CHLORINE CLEARS CLOGGED EMITTERS
If the rate of water flow progressively declines during the season, the tubes or tape may be slowly plugging, resulting in severe damage to the crop. In addition to maintaining the filtering stations, regular flushing of the drip tube and application of chlorine through the drip tube will help minimize clogs. Once a month, flush the drip lines by opening the far ends of a portion of the tubes at a time and allowing the higher velocity water to rush out the sediment.Because algae growth and biological activity in the tube or tape are especially high during warmer months,chlorine usually is applied at 2-week intervals during these months.
Manage irrigation and fertilization together to optimize efficiency. Chemigation through drip systems efficiently delivers chemicals in the root zone of the receiving plants. Because of the precision of application, chemigation can be safer and use less material.
Soil microorganisms convert nitrogen (N) fertilizers to nitrate. Nitrate is water soluble, available to plants, and subject to leaching loss.Fertilizer can be injected through the drip system. Fertilizer usually is introduced into the irrigation system in front of the filter station so the filters can remove any precipitates that occur in the solution Fertilizers containing sulfate, phosphate, calcium, or anhydrous or aqua ammonium can lead to solid chemical precipitation inside the drip lines, which can block emitters.
5.6 PLACEMENT OF TAPE
The drip tape must be close enough to the surface to germinate the seed if necessary, or a portable sprinkler system should be available. For example, a tape tube 4 to 5 inches deep has successfully germinated onion seeds in silt loam soil. Tape at 12 inches failed to uniformly germinate onions.
5.8 TIMING AND RATES
The total irrigation water requirements for crops grown with a drip system is greatly reduced compared to a surface flood system because water can be applied much more efficiently with drip irrigation. For example, with furrow irrigation, typically at least 4 acre-feet/acre/year of water is applied to onion fields in the Treasure Valley of eastern Oregon and southwestern Idaho. Depending on the year, summer rainfall, and the soil, 14 to 32 acre-inches/acre of water has been needed to raise onions under drip irrigation in the Treasure Valley.
5.9 STANDARD MAINTENANCE
Add chlorine or other chemicals to the drip line periodically to kill bacteria and algae. Acid might also be needed to dissolve calcium carbonates. Filters must be managed and changed as needed. Even with filtration, however, drip tape must be flushed regularly. The frequency of flushing depends on the amount and kinds of sedimentation in the tape.
ADVANTAGES AND DISADVANTAGES OF DRIP IRRIGATION
6.1.1 Reduced water use
Because drip irrigation brings the water to the plant root zone and does not wet the entire field, drip irrigation typically requires half to a quarter of the volume of water required by comparable overhead-irrigation systems.
6.1.2 Joint management of irrigation and Fertilization
Drip irrigation can improve the efficiency of both water and fertilizer. Precise
application of nutrients is possible using drip irrigation. Hence, fertilizer costs and soluble nutrient losses may be reduced with drip irrigation. Nutrient applications may also be better timed to meet plant needs.
6.1.3 Reduced pest problems
Weed and diseaseproblems may be reduced because drip irrigation does not wet the row middles or the foliage of the crops as does overhead irrigation.
Polyvinyl chloride (pvc) andpolyethylene parts are widely available in several diameters and are easy to assemble. Many customized, easy-to-install connectors, endcaps, and couplers are available in different diameters. Cutting and gluing allows for timely repairs.
6.1.5 Low pumping needs
Drip systems require low operating pressure (20-25 psi at field entrance, 10-12 psi at the drip tape) compared to overhead systems (50-80 psi). Many existing small pumps and wells may be used to adequately irrigate small acreage using drip systems.
Drip-irrigation application may be simply managed and programmed with an AC- or battery-powered controller, thereby reducing labor cost.
Drip systems are adaptable to oddly shaped fields or those with uneven topography
or soil texture, thereby eliminating the underutilized or non-cropped corners and maximizing the use of available land.
6.1.8 Production advantages
Combined with raised beds, polyethylene mulch, and transplants, drip irrigation enhances earliness and crop uniformity. Using polyethylene mulch also increases the
cleanliness of harvested products and reduces the risk of contamination with soil-born pathogens. Reflective mulches further help reduce the incidence of viral diseases by affecting insect vectors, such as thrips, whiteflies or aphids.
6.2.1 Drip irrigation requires an economic Investment
Drip-irrigation systems typically cost $500 - $1,200 or more per acre (Table 1). Part of the cost is a capital investment useful for several years, and another part is due to the annual cost of disposable parts. Growers new to drip irrigation should start with a relatively simple system on a small acreage before moving to a larger system.
6.2.2 Drip irrigation requires maintenance and high-quality water
Once emitters are clogged or the tape is damaged, the tape must be replaced. Water
dripping from an emitter and the subsequent wetting pattern are hard to see, which makes it difficult to know if the system is working properly. Proper management of drip irrigation requires a learning period.
6.2.3 Water-application pattern must match planting pattern
If emitter spacing (too far apart) does not match the planting pattern, root development may be restricted and/or plants may die.
Drip tubing may be lifted by wind or may be displaced by animals unless the drip tape is covered with mulch, fastened with wire anchor pins,or lightly covered with soil.
6.2.5 Leak repair
Drip lines can be easily cut or damaged by other farming operations, such as tilling, transplanting, or manual weeding with a hoe. Damage to drip tape caused by insects, rodents or birds may create large leaks that also require repair.
6.2.6 Drip-tape disposal causes extra cleanup costs after harvest
Planning is needed for drip-tapedisposal, recycling or reuse.
APPLICATIONS OF DRIP IRRIGATION
- Drip irrigation is used by farms, commercial greenhouses and residential gardeners.
- In shopping malls and embankments
- In steep slopes
Drip irrigation is a latest sub-surface methods of irrigating water with higher water demands in arid region.It may not be applicable to all farms.Yet, when properly designed, installed and managed, drip irrigation may help achieve water conservation by reducing evaporation and deep drainage when compared to other types of irrigation such as flood or overhead sprinklers since water can be more precisely applied to the plant roots.In addition, drip can eliminate many diseases that are spread through water contact with the foliage.It also results reduced energy costs.
1. Eric Simonne, Robert Hochmuth, Jacque Breman, William Lamont, Danielle Treadwell and Aparna Gazula ( June 2008), Drip Irrigation System for Small Conventional Vegetable Farms and Organic Vegetable Farms, Horticultural Sciences Department, Florida Co-operative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, HS 1144.
2. Shock.C.C (August 2006, June 2001), Drip Irrigation: An Introduction, Malheur Experiment Station, Oregon State University, EM 8782.
3. Modi.P.N (2008), Irrigation Water Resources and Water Power Engineering, Standard Book House, Rajsons Publications Pvt.Ltd,1705-A, Nai Sarak, New Delhi-110 006.