Drip Irrigation

DRIP IRRIGATION

 DRIP IRRIGATION SYSTEM

INTRODUCTION

Drip irrigation refers to application of water in small quantity at the rate of mostly less than 12 lph as drops to the zone of the plants through a network of plastic pipes fitted with emitters. Drip irrigation in its present form has become compatible with plastics that are durable and easily moulded into a variety and complexity of shapes required for pipe and emitters.

MERITS

1. Increased water use efficiency

 2. Better crop yield

3. Uniform and better quality of the produce

4. Efficient and economic use or fertiliser through fertigation

5. Less weed growth

 6. Minimum damage to the soil structure

7. Avoidance of leaf burn due to saline soil

8. Usage in undulating areas and slow permeable soil

9. Low energy requirement (i.e.) labour saving 

10. High uniformity suitable for automization

DEMERITS

1. Clogging of drippers

2. Chemical precipitation

3. Salt accumulation at wetting front

COMPONENTS AND ITS SELECTION FOR A TYPICAL DRIP IRRIGATION LAYOUT 

HEAD                               EQUIPMENTS

 a. Water source            - Subsurface tank

b. Pump             - Suction, monoblock pump, delivery non return valve, gate valve                    

c. Filter station  - Sand filter, screen filter, manifold and pressure  gauge

d. Fertiliser application  - Fertiliser tank and ventury assembly

DISTRIBUTION SYSTEM

e. Conveyance line - Main line, sub main, gromet take off assembly,  laterals, minor tubes and end caps.

 f. Drippers    - Pressure corresponding drippers (moulded/threaded  type)

g, Valves   - Non-return valve (NRV), Ball valves, Air release  valve (ARV), flush valves

h. Water meter - If necessary

 i. Water source  

a. WATER SOURCE SUBSURFACE TANK

                To minimise the energy requirement and also to get a uniform or constant level of water owing to the accumulation of bore wells in one pat1 of the irrigation regime; keeping in the effective hydraulic DIS design, it is necessary to construct a subsurface tank in an elevation point at the centre. The capacity of the tank is calculated from the water requirement of the crop, dripper capacity, type of soil etc.

b. PUMP

Pump/Overhead Tank: It is required to provide sufficient pressure in the system. Centrifugal pumps are generally used for low pressure trickle systems. Overhead tanks can be used for small areas or orchard crops with comparatively lesser water requirements.  1. Filters: The hazard of blocking or clogging necessitates the use of filters for efficient and trouble free operation of the microirrigation system. The different types of filters used in microirrigation system

a)      Gravel or Media Filter: Media filters consist of fine gravel or coarse quartz sand, of selected sizes (usually 1.5 – 4 mm in diameter) free of calcium carbonate placed in a cylindrical tank. These filters are effective in removing light suspended materials, such as algae and other organic materials, fine sand and silt particles. This type of filtration is essential for primary filtration of irrigation water from open water reservoirs, canals or reservoirs in which algae may develop. Water is introduced at the top, while a layer of coarse gravel is put near the outlet bottom. Reversing the direction of flow and opening the water drainage valve cleans the filter. Pressure gauges are placed at the inlet and at the outlet ends of the filter to measure the head loss across the filter. If the head loss exceeds more than 30 kPa, filter needs back washing.

b)     Screen Filters: Screen filters are always installed for final filtration as an additional safeguard against clogging. While majority of impurities are filtered by sand filter, minute sand particles and other small impurities pass through it. The screen filter, containing screen strainer, which filters physical impurities and allows only clean water to enter into the micro irrigation system  The screens are usually cylindrical and made of non-corrosive metal or plastic material. These are available in a wide variety of types and flow rate capacities with screen sizes ranging from 20 3 mesh to 200 mesh. The aperture size of the screen opening should be between one seventh and one tenth of the orifice size of emission devices used.

c)      Centrifugal Filters: Centrifugal filters are effective in filtering sand, fine gravel and other high density materials from well or river water. Water is introduced tangentially at the top of a cone and creates a circular motion resulting in a centrifugal force, which throws the heavy suspended particles against the walls. The separated particles are collected in the narrow collecting vessel at the bottom.

d)     Disk Filters: Disk filter contains stacks of grooved, ring shaped disks that capture debris and are very effective in the filtration of organic material and algae. During the filtration mode, the disks are pressed together. There is an angle in the alignment of two adjacent disks, resulting in cavities of varying size and partly turbulent flow. The sizes of the groove determine the filtration grade. Disk filters are available in a wide size range (25-400 microns). Back flushing can clean disk filters. However they require back flushing pressure as high as 2 to 3 kg/cm2.

                        4. Pressure relief valves, regulators or bye pass arrangement:

                    These valves may be installed at any point where possibility exists for excessively                                     high pressures, either static or surge pressures to occur. A bye pass arrangement is                                     simplest and cost effective means to avoid problems of high pressures instead of                                     using costly pressure relief valves. 

                        5. Check valves or non-return valves:

                    These valves are used to prevent unwanted flow reversal. They are used to prevent                                    damaging back flow from the system to avoid return flow of chemicals and                                            fertilizers from the system into the water source itself to avoid contamination of                                        water source.

INSTALLATION, OPERATION OF DRIP IRRIGATION SYSTEM:

 The installation of the drip system be divided into 3 stages.

1. Fitting of head equipments

2. Connecting mains and sub mains

3. Laying of lateral with drippers.

3.1. INSTALLATION OF HEAD EQUIPMENTS 

The following points should be considered for fixing the position of filter station.

1. Minimum use of fitting such as elbows and bends to be made

2. Whether the pump delivery can be connected to the sand / screen filter

3. Sand / screen filter can easily be connected to mainline

4. Arrangement of back-wash to be made as per the farmer's suitability

5. Arrangement of by-pass water to be made

6. Sufficient space to be provided for the easy operation of filter valves

7. Hard surface or cement concrete foundation to be made for sand filter so that it will not                         collapse due to vibration and load. For screen filter, provide strong support by using GI fittings              to avoid its vibrations due to load

8. Use hold-tight over the threads of GI fittings and apply proper mixture of M-seal over the                     joints uniformly to avoid leakage

9. Fix the pressure gauges in inlet and outlet of the filter

10. Avoid direct linking of oil pump delivery and filter. Instead connect the filter to the pump                 delivery using flanges or even the hose pipe can be used for this

3.2. CONNECTING MAINS AND SUB MAINS

1. It should be laid at a depth of more than 30 - 45 cm so as to avoid damages during                                 intercultivation

2. Remove mud, if any, in the pipes before fitting. These pipes can be fitted using solvent                         cement with the help of brush

3. A gunmetal gate valve / PP Ball valve is provided at the start of sub main with PVC MTA                     fittings for connecting the valve in the PVC sub main

4. Provide flush valve at the end of main and sub main such that it faces towards slope

5. Apply uniform pressure vertically over the drill while drilling in the sub main so that the hole             will be smooth and round.

6. Fix the rubber grommets in the holes made in the sub main in such a way that the groove in it             goes inside the pipe

7. Fix the take-off position such that its arrow or the chamber faces towards the gate valve of the             sub main for the easy flow of water. See that the take-off is fixed tightly in the grommet. The                 loose fitting of take-off indicates the breakage of grommet

8. Get the sub main flushed so that the PVC piece / mud fallen in the sub main while making                drill will get flushed. Otherwise this scrap will block the drippers through polytube

3.3. LAYING OF LATERALS AND DRIPPERS

1. Pass water through the poly tube and get it flushed so that it gets bulged and makes easy for                 punching

2. Punch the lateral sideway from the yellow strip

 3. The dripper position should be fixed according to design, soil and water report and water                     level in peak summer

4. If two drippers are to be provided such that all the drippers come in a straight line

5. Do not fix drippers unless a complete lateral line is punched. Otherwise the placement of                     drippers will be changed if moved

6. Punching should be done from the sub main

7. While fixing the dripper, push it inside the lateral and pull it slightly

8. Close the end of lateral by fitting end cap

4. STANDARD PROCEDURE FOR ASSESSING DIS PERFORMANCE

1. Check installation according to approved design layout

2. Start the pump

3. Flush the filters

4. Allow the drip system to be loaded with water for 10 min.

5. Note the pressure from the pressure gauge at the inlet and outlet of sand and screen filters

6. Record the dripper discharge as per the format

7. The discharge and pressure readings have to be taken in the below mentioned locations a.                     First, Middle and Last Dripper of a lateral b. For laterals at beginning, ¼, ½, ¾ and end of sub                 main

8. Laterals on anyone side of the sub main can be selected in case of plain land or alternative                 laterals on either side in case of slight slope in the direction along the lateral

9. Measure the volume of water collected for 36 seconds

10. Measure the pressure at start and end of laterals

 11. If the Emission Uniformity is less than 85 % then the issue has to be taken up with the Drip              Irrigation System Designer

12. Modifications have to be taken accordingly