As irrigation accounts for maximum consumption of fresh water resources, therefore proper attention is required to conserve this water.  Since surface method of irrigation is most commonly practiced which contribute major portion of it to evaporation and seepage losses. This method of irrigation should be avoided and method like sprinkler irrigation method should be used to have maximum irrigation efficiency.

Sprinkler Irrigation System:

            In the sprinkler method of irrigation, water is sprayed into the air and allowed to fall on the ground surface somewhat resembling rainfall.  The spray is developed by the flow of water under pressure through small orifices or nozzles.  

 
Design of the system:

            The system is designed after considering the agro-climatic like soil, plant, root-depth and climate etc.  These factors enable one to develop a clear understanding of
      (a)   Water application rate.  
     (b)   Depth of application.
      (c)   Period of application. 
Suggested maximum application-rates for sprinklers for average soil, slope and tilth.  

Source: Adopted from Hurd (1969)

Adaptability of Sprinkler system:

§     Sprinkler irrigation can be used for almost all crops (except rice and jute) and on most soils.  It is however, not usually suitable in very fine textured soil (heavy clay soils) where the infiltration rates are less than about 4 mm per hour.

§     The flexibility of the sprinkler equipment and its efficient control of water application make this method adaptable to most topographic conditions without extensive land preparation and leveling.  This saves considerable cost and does not disturb the soil.

§      Saves water thus irrigating more land.  Approximately 54% to 71% of water applied by surface irrigation is lost through deep seepage and evaporation.  The sprinkler system supplies only the required amount of water for crop root zone.  The saved water can irrigate 25% to 33% additional area.

§      Helps to grow more crops per year as three or even four crops per year can be grown.  Crops can be planted at the right time without waiting for seasonal rains to achieve maximum growth.

§     Helps in saving of land as there is no need to contract bunds or water channels hence more land under crops.

§      Reduce pests as it sweeps away all pests present on the surface of leaves.

§  Easier harvesting of root crops because the soil remains friable and uncompacted.

§      Low running cost as compared to that of other lift irrigation system.

§      Well suited for sports grounds, parks and gardens.
 

Disadvantages of the Sprinkler System:

§      Higher initial cost.

§      High power requirement

§    Not usually suitable in very fine textured soil (heavy clay soils) where the irrigation rates are less than about 4 mm per hour.
 

Area covered = 15 feet on both sides of the lateral lines.

Total time to cover an area of one acre = 12 hours excluding shifting time.

With each set one can cover maximum area = 10 acres
 

Proper design of a sprinkler system does not in itself ensure success. The System should be operated in keeping with good irrigation practice.  It should be ensured that the prime mover and the pump are in alignment, particularly in the case of tractor-driven pumps.  For these the drive shaft as well as the pump shaft should lie at nearly the same height to prevent too great an angle on the universal shaft.  Service and installation procedures in respect of the pump and power units should be strictly observed.      

Maintenance:

            A sprinkler system, like any other farm equipment, needs maintenance to keep it operating at peak efficiency.  Parts of the system subject to the most wear are in rotating sprinkler heads, the pumping set, the couplers and the pipeline.  Details regarding the maintenance of the pumping unit are given in Chapter 3. General principles regarding the maintenance of the pipes and fittings and sprinkler heads are given below: 

1. Pipes and fittings

The pipes and fittings require virtually no maintenance but attention must be given to the following procedures:

(a) Occasionally clean any dirt or sand out of the groove in the coupler in which the rubber sealing ring fits.   Any accumulation of dirt or sand will affect the performance of the rubber sealing ring.

(b)  Keep all nuts and bolts tight.

(c) Do not lay pipes on new damp concrete or on piles of fertilizer.  Do not lay fertilizer sacks on the pipe.

(b) Do not apply oil, grease or any lubricant to the sprinklers.  They are water lubricated and using oil, grease or any other lubricant may stop them from working.  

(c) Sprinklers usually have a sealed bearing and at the bottom of the bearing there are washers.  Usually it is the washers that wear and not the more expensive metal parts.  Check the washers for wear once a season or every six months-this is especially important where water is sandy.  Replace the washers if worn.

(d) After several season’s operation the swing arm spring may need tightening.  This is done by pulling out the spring end at the top and rebending it.  This will increase the spring tension.

In general, check all equipment at the end of the season and make any repairs and adjustments and order the spare parts immediately so that the equipment is in perfect condition to start in the next season.
 

The following points are to be observed while storing the sprinkler equipment during the off season:

(a) Remove the sprinklers and store in a cool, dry place.

(b) Remove the rubber sealing rings from the couplers and fittings and store them in a cool, dark place.

(c) The pipes can be stored outdoors in which case they should be placed in racks  with one end higher than the other.  Do not store pipes along with fertilizer.

(d) Disconnect the suction and delivery pipe-work from the pump and pour in a small quantity of medium grade oil.  Rotate the pump for a few minutes.  Blank off the suction and delivery branches.  This will prevent the pump from rusting.  Grease the shaft.

Protect the electric motor from the ingress of dust, dampness and rodents.
 

The following are the general guidelines to identify and remove the common troubles in the sprinkler systems:

1. Pump does not prime or develop pressure

(a) Check that the suction lift is within the limits.  If not get the pump closer to the water.

(b) Check the suction pipeline and all connections for air leaks.  All connections and flanges should be airtight.

(c)  Check that the strainer on the foot valve is not blocked,

(d)  Check that the flap in the foot valve is free to open fully.

(e) Check the pump gland (s) for air leaks.  If air leaks are suspected tighten the gland (s) gently.  If necessary repack the gland (s) using a thick grease to seal the gland satisfactorily.

(f) Check that the gate valve on the delivery pipe is fully closed during priming and opens fully when the pump is running.

(g)  Check that the direction of rotation of the pump is correct.

2. Sprinkler do not turn

(a)  Check pressure

(b) Check that the nozzle is not blocked.  Preferably unscrew the nozzle or use a small soft piece of wood to clear the blockage.  Do not use a piece of wire or metal as this may damage the nozzle.

(c) Check that the sprinkler bearing is quite free and smooth. During operation, the sprinkler can usually be pushed down towards the riser pipes so that the water pressure flushes out the bearing.  If the bearing is still stiff dismantle and then clean it.  Do not use oil, grease or any lubricant.

(d) Check the condition of washers at the bottom of the bearing and replace them if worn or damaged.

(e) Check that the swing arm moves freely and that the spoon which moves into the water stream is not bent by comparing it with a sprinkler that is operating correctly.  If it is bent then carefully bend it back into position.

(f) Adjust the swing arm spring tension.  Usually it should not be necessary to pull up the spring by more than about 6 mm.

3. Leakage from coupler or fittings

The sealing rings in the couplers and fittings are usually designed to drain the water from the pipes when the pressure is turned off.  This ensures that the pipes are automatically emptied and ready to be moved.  When the pump is first started and before the pressure has built up in the system the seals may give a little leakage.  With full pressure in the system the couplers and fittings will be effectively leak-free.  If, however, there is a leakage, check the following:

(a) There is no accumulation of dirt or sand in the groove in the coupler in which the sealing ring fits.  Clean out any dirt or sand and refit the sealing ring.

(b) The end of the pipe going inside the coupler is smooth, clean and not distorted.

(c) In the case of fittings such as bends, tees and reducers ensure that the fitting has been properly connected into the coupler.

        In addition to water conservation the use of sprinkler irrigation reduces the runoff of soil and may reduce the runoff of pesticides and nutrients from irrigated cropland and their transport to surface waters and hence its use should be promoted as much as possible.