2.4 Modern methods of Irrigation

1. Sprinkler irrigation method

Sprinklers provide efficient coverage for small to large areas and are suitable for use on all types of properties In this method water is applied to the soil in the form of spray through a network of pipes & pumps. As is a kind of rain gives very good results.

Sprinkler Irrigation is a method of applying irrigation water which is similar to rainfall.

Sprinkler irrigation is more useful when

• · Land cannot be prepared for surface methods
• · Slopes are excessive
• · Topography is irregular
• · Soil is erosive
• · Soil is excessively permeable or impermeable
• · Depth of soil is shallow over gravel or sand

Sprinkler system can be classified into three types.

1. · Permanent system
2. · Semi permanent system
3. · Portable system

Types of sprinklers

• · Lawn sprinklers & garden popups
• · Raingun
• · Pop up
• · Corporate
• · Automated
• · Micro
• · Macro
• · Small area
• · Large area coverage

In the permanent systems, pipes are permanently buried in such a way that they do not interfere tillage operations. In the semi permanent system the main lines are buried while the laterals are portable. Portable system has both portable mains lines and laterals. These systems are designed to be moved from around the farm from field to field.

Components of Sprinkler system-

1. · Spray nozzles
2. · Controllers
3. · Valves
4. · Backflow preventers
5. · Fertilizer systems
6. · Rain & freeze sensors
7. · Irrigation tools & parts
8. · pipes & fittings (Generally PVC these days)

Working of sprinkler system – A pump usually lifts the water from the source, pushes it through the sprinkler nozzle on the sprinkler heads mounted on rising pipes attached to the laterals. It is then sprayed into the air and irrigated entire soil surface through spray heads so that it breaks up into small water drops which fall to the ground.

Turbine and horizontal centrifugal pumps are used. Sprinkler system usually is composed of perforated pipes or revolving head sprinklers and may be high pressure ( 2.1 kg/cm²) or low pressure ( 1.4 kg/ cm²) system. Generally a perforated pipe system operates on low pressure where as the revolving head sprinklers operate in both ranges depending upon the type of rotary head used.

Advantages of sprinkler system

• · Erosion can be controlled
• · Uniform application of water is possible
• · Small streams of irrigation water can be used efficiently.
• · Time and amount of fertilizers can be controlled.

Limitations

• · Wind may distort sprinkler pattern.
• · A constant water supply is needed for commercial use of equipments.
• · Water must be clean, free from floating, suspended matter as it is likely to get trapped in perforations.
• · Power requirement is high.
• · Heavy soil with poor intake cannot be irrigated efficiently.

2. Drip irrigation method

Drip irrigation, also known as trickle irrigation or micro irrigation, is an irrigation method in which, water is applied in form of drops directly near the base of plant. Drip irrigation limits the water supplied for consumptive use of plant by maintaining minimum soil moisture, equal to field capacity, thereby maximizing saving. This system minimizes evaporation and percolation losses.

Along with irrigation water, nutrients (fertilisers) are also fed to the system by allowing water to drip slowly to the roots of plants, either onto the soil surface or directly onto the root zone, through a network of valves, pipes, tubing, and emitters. Because of the way the water is applied in a drip system, traditional surface applications of timed-release fertilizers are sometimes ineffective, so drip systems often mix liquid fertilizer with the irrigation water. This is called fertigation ; fertigation and chemigation pesticide and other chemicals to periodically clean out the system, such as chlorine or sulphuric acid use chemical injectors such as diaphragm pumps, piston pump, or venturi pump. The chemicals may be added constantly whenever the system is irrigating or at intervals. Fertilizer savings of up to 95% are being reported from recent university field tests using drip fertigation and slow water delivery as compared to timed-release and irrigation by micro spray heads.

Drip and subsurface drip irrigation is used almost exclusively when using recycled municipal waste water. Regulations typically do not permit spraying water through the air that has not been fully treated to potable water standards.

Drip irrigation is used by farms, commercial greenhouses, and residential gardner.

Drip irrigation is adopted extensively in areas of acute water scarcity and especially for crops such as coconut, containerized landscape trees, grapes, banana, Ber, Brinjal, citrus, strawberries, sugarcane, cotton, maize, and tomatoes.

Components and operation

• Pump – to lift water
• A head tank to store the water and to maintain a pressure head of 5 to 7 m
• Central distribution system which filters the water, adds nutrients ( fertiliser solution) and regulates the pressure and amount of water to be applied.
• Mains and secondary lines made of polyethelene or PVC material. The diameter of the piping may vary from 20 mm to 40 mm. A water may be fixed at the beginning of the mains.
• Trickle lines – consisting of 10 to 20mm dia. PVC pipes with perforations at a distance equal to the spacing of the crops. The trickle lines are fitted to the secondary lines at a distance equal to row to row spacing of crop. Varies from 60cm to 90cm. Spacing of nozzles to be fitted in the perforations of the trickle lines, depends upon the planting distance along row. Varies from 30 to 50cm.
• Plastic nozzles - having perforations attached to the trickle line. The perforations are so designed that water leaves the nozzle at a very slow rate, usually 2 to 10 lit per hour depending upon crop requirement.

The drip irrigation system is suitable for almost all types of crop except paddy, which requires standing water. Like sprinkler system this system also requires specialised knowledge. Widely known commercial Indian company is Jain irrigation systems ltd, Jalgaon.

Drip irrigation system layout and its parts

Components (listed in order from water source)

• · Pumpor pressurized water source
• · Water Filter(s) - Filtration Systems: Sand Separator like Hydro-Cyclone, Screen Filter, Media Filters
• · Fertigation Systems, venturi injector and Chemigation Equipment (optional)
• · Backwash Controller (Backflow Preventer)
• · Main Line (larger diameter Pipe and Pipe Fittings)
• · Hand-operated, electronic, or hydraulic Control Valves and Safety Valves
• · Smaller diameter poly tube (often referred to as "laterals")
• · Poly fittings and Accessories (to make connections)
• · Emitting Devices at plants (ex. Emitter or Drippers, micro spray heads, inline drippers, trickle ring

· Note that in Drip irrigation systems Pump and valve may be manually or automatically operated by a controller

Banana plants with drip irrigation in Maharashtra, India

The advantages of drip irrigation are:

• Less requirement if irrigation water – evaporation and percolation losses commonly associated with surface irrigation are reduced.
• Minimized fertilizer/nutrient loss due to localized application and reduced leaching.
• High water application efficiency – Optimum water level equal to field capacity can always be maintained. Soil is maintained in most congenial form.
• Water logging avoided- due to check on over irrigation water logging chances are nil.
• High yield- High yield is obtained because of control over factors governing soil-water-crop relationships.
• Cultivation of cash crops – this method is suited to cash crops
• No over irrigation- over irrigation is avoided as water is applied directly at root zone.
• Control over water application rate- It is possible to vary the application rate, throughout the crop period as per growth and requirement of crop.
• Weed control – The nuisance of weed is commonly associated with surface application methods, is minimum in this method in turn increasing crop production.
• Increase in net irrigable area – A lot of area wasted in construction of field channels etc can be used for cultivation.
• Nutrients preservation – Soil nutrients which may be wasted due to deep percolation of water can be avoided.
• Effective pest control – Insect & pest combating chemicals can be directly reached to root zone.
• Reduced labor cost – Labor cost associated with construction and maintenance of furrows, bunds etc can be reduced.
• No soil erosion – Problems of surface soil erosion associated with surface application method are absent.
• Suitability for saline soils – Saline, alkaline or brakish soils otherwise unsuitable, can be utilised by cultivation by drip irrigation method.
• Maintenance of high surface temperature – In this method as entire surface is not wetted hence is not lowered as in surface application methods, which is useful in hastening the ropening of crop.
• Suitability for any topography – No land leveling is required and is suitable even for sloping and undulating land and irregular shaped fields
• Allows safe use of recycled water.
• Highly uniform distribution of water i.e., controlled by output of each nozzle.
• Fertigation can easily be included with minimal waste of fertilizers.
• Foliage remains dry thus reducing the risk of disease.
• Usually operated at lower pressure than other types of pressurized irrigation, reducing energy costs.

The disadvantages of drip irrigation are:

• · High inintial cost - Initial cost of various components such as pumping unit, filter units, pipe lines, nozzles etc is very high.can be more than overhead systems.
• · Wasteage of material - The sun can affect the tubes used for drip irrigation, shortening their usable life. Longevity is variable.
• · Clogging/blockade of nozzles- Nozzle holes are very small in size (0.5 to 1 mm dia) If the water is not properly filtered and the equipment not properly maintained, it can result in clogging. Also there is danger of blockage due to high degree of dissolved salts.
• · Change in spacing of nozzles due to change in crops may result in frequent replacement of trickle lines
• · Drip irrigation might be unsatisfactory if herbicides or top dressed fertilizers need sprinkler irrigation for activation.
• · Drip tape causes extra cleanup costs after harvest. You'll need to plan for drip tape winding, disposal, recycling or reuse.
• · Waste of water, time & harvest, if not installed properly. These systems require careful study of all the relevant factors like land topography, soil, water, crop and agro-climatic conditions, and suitability of drip irrigation system and its components.
• · Germination Problems. In lighter soils subsurface drip may be unable to wet the soil surface for germination. Requires careful consideration of the installation depth.
• · Salinity. Most drip systems are designed for high efficiency, meaning little or no leaching fraction. Without sufficient leaching, salts applied with the irrigation water may build up in the root zone, usually at the edge of the wetting pattern.