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Satish Lele

Drip Irrigation for Pongamia Pinnata

In this system water is fed drop by drop near the root of plant. Pongamia Pinnata needs 1 liter of water in 8 hours every day. This is effective in both dry and humid atmospheres. 1.5 to 2.5 times more soil can be provided with water, using this system, compared to conventional irrigation. The daily need of water varies with the location and the age of plant.

    Advantages of Drip System:
  1. Every drop of water is used effectively for the growth of plants.

  2. The quantity of water can be accurately provided using this system.

  3. Each plant gets equal quantity of water.

  4. Exact quantity of fertilizer can be added to water and supplied to plants. This reduces loss of fertilizer with the drained water.

  5. The area around the stem is maintained wet, where the lateral roots are present. This helps in better absorption of nutrients by roots. It also reduces growth of weeds in other area.

  6. Since supply of water and fertilizer is controlled, productivity increases by 20 to 30%.

  7. Crops grow faster and mature on time.

  8. The amount of electrical power required for conventional and drip system is same, but drip is 20 to 30% more effective.

  9. Less manpower is required, as compared to that required for conventional system.

  10. It can be used in day time or even at night.

  11. Water with lower quality can be used in drip system.

    Problems of Drip System:
  1. Initial investment is much higher than conventional system. Dripper can get choked due to mud in the water. If not designed properly, it may have adverse effect on crop.

  2. Lateral pipe, drippers and water purification equipment are the most capital intensive parts of the system. The price of system depends on gradient of land, type of crop and availability of water. Price of drip is much higher than sprinkler system. Drip system should be carefully designed to reduce cost of system.

  3. Drippers are very cheap but the system providing water to dripper is much more expensive.

  4. Water filtration unit is heart of the system. It should not get choked. It is back washed and cleaned from time to time.

  5. If the land is uneven, some plants may get more water and some may get less water, as compared to design flow.

  6. If the system breaks down for a long time, it may affect the crop badly.

  7. Rodents can destroy lateral pipes. Rodent control is also essential.

Components of Drip Irrigation System and their Function: The size of plantation grown on water supply from one well, depends on the filling rate of the well. The main components of drip irrigation system are Electric Pump Set, Non-Return Valve, Fertilizer Feed Tank, Flow Control Valve, Ventury Injection System or Pressure Pump Ejection System, Block Valve, Sand Filter, Mesh Filter, Pressure Gauge, Main Pipe Line, Secondary Pipe Lines, Manifolds, Laterals, Dripper etc.

    This can be divided into 3 sections. Electric Pump Set, Pipelines and Emitter or Dripper.
  1. Electric Pump Set: This consists of fuse box, pump set, non-return valve, fertilizer feed tank, flow control valve, ventury injection system, pressure pump ejection system or pressure differential injection system and a block valve. A centrifugal pump, running at 2,880 RPM or submersible multistage pump or vertical turbine pump is used depending on requirement. The pump should be selected based on discharge head and flow rate of water required. Multistage submersible pump is used when higher head and lower flow rate is required. For large scale drip irrigation, turbine pump set should be selected. As far as possible, it should have single stage pumping. A non-return valve is installed in discharge pipe, to avoid water hammering. By ventury injection system, fertilizers and other chemicals are sucked in pipeline, due to sudden rise in velocity of flow of water. This is not useful in systems with low discharge head. It works well if discharge pressure is more than 2 kg/cm2. In case of pressure pump ejection system, fertilizers and other chemicals are pumped into the line, from a tank using a small pump having head higher than that of main pump. In pressure differential injection system, a closed tank is used. The inlet and outlet of the tank are connected to main pipe. A valve is placed in main line, between these inlet and outlet lines. To avoid choking of dripper, water should be filtered in a filter. Filter can be disc filter, sand filter or mesh filter. A pressure gauge is installed to indicate discharge pressure. A block valve is installed after all these systems to start or stop flow of water.

  2. Pipelines: These include main pipeline, side pipelines, manifold and laterals. Main pipe carries water to the highest point in the field. Depending on the size of the plantation, sub pipelines, side branching and manifolds should be designed. Manifolds should be along the slope of the land, and laterals should be perpendicular to manifolds and parallel to contours. Main pipe, Side pipelines and manifold should be made of PVC, HDPE, LDPE or LLDPE. PVC pipe can be used for laterals. One lateral is provided for each plant. It is placed close to roots of plant. A micro tube is used to fix multi emitter dripper.

  3. Emitter or Dripper: The emitters are tubes. A small tube is inserted 50 mm inside the lateral which can be 300 mm to 1 meter long outside. It is used for flat land but the lateral should be placed around contour and its length should be less than 50 meters. Drippers are of two types. One is clip on and the other one is pressure compensating. Clip on is used for flat land and pressure compensating for sloping lands.

    1. Self Cleaning Drippers: These fit on lateral, and clean by themselves. The flow is equal in all drippers. These are sleek and cheap. These are strong and can be used for all types of waters and chemicals. 9.8 mm to 17.4 mm diameter pipes are used as laterals. Flow rate achieved is 2.3 to 3.75 liters per hour. It works well at a pressure of 0.6 to 3.5 kg/cm2.

    2. Button Drippers: These fit on lateral like a button. It is useful for pot drip and for green house. These can be under the soil. Flow rate achieved is 2, 4 or 8 liters per hour. It works well at a pressure of 0.7 to 1.5 kg/cm2. To provide water at a constant rate, some valves are important. These work on water pressure.

    3. Pressure Regulating Valve: To get equal discharge of water, water supply to all laterals should be equal. To get equal flow at start and end of manifold, pressure regulating valve is used. Rolling diaphragm is used to control the flow.

    4. Air Release Valve: This is used at the end of lateral to release air in the pipe.

    5. Filter Backwash Valve: These are used to clean up filters automatically.

    6. Water Quantifier Valve: This shuts off automatically, when required quantity of water, is supplied to plants.

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