Drip irrigation systems deliver water and agrochemicals (e.g., fertilizers and pesticides) directly to the root zones of the irri-gated plants at a rate best suited to meet the needs of the plants being irrigated.
Drip irrigation equipment consists of a network of pipes, which is laid on the fields. The pipes have small holes at regular inter-vals for water to trickle down to the plants.
Drip irrigation equipment consist of a network of pipes with small holes at regular intervals for water to trickle down to the plants root.
The network of pipes is fed to tank sited to supply a head of 2.5-3 m to the network for irrigating about 0.25 hectare of land.
This system helps in generating proper pressure for water to flow around the grid
The pipes are made from flexible vinyl or polyethylene and are hidden with a layer of mulch or soil, but the part that emits water should be remain uncovered. As the plants grow, less and less of the network of pipes will be visible.
The drip is to be kept at a steady water pressure level because an open spray will redistribute the soil and destroy the purpose of the drip system. The space/time between each drip is crucial for the proper distribution of water.
The capital costs involved in the establishment of a drip irrigation system are high compared to the costs of establishing conventional irrigation systems. However, the labor requirements and operational costs are low.
The principle operation and maintenance requirements include the need for regular cleaning of the system and careful monitoring of the quality of the source water, as the drip irrigation systems are very sensitive to the clogging of the drippers.
The systems also require a relatively high degree of skill to design, install and operate, and are susceptible to theft, damage and disruption by rodents that destroy the drip pipes and drippers.
Drip irrigation systems make efficient use of water, especially when compared to traditional methods of irrigation such as furrow, border, basin and sprinkler irrigation systems, which, under arid and drought conditions, suffer from a high rate of water loss and have a low degree of water use efficiency.
Drip irrigation nourishes plants at the correct water level without supervision. Water and agrochemicals are delivered to plants at a rate, which is best suited to meet the needs of the plants being irrigated. These techniques are highly effi-cient water saving devices and can cut down water requirements by about 50%.
Sprinkler irrigation is a method in which sprinkler device is used to irrigate the fields.
This method of irrigation serves dual purpose of cooling and controlling air dust along with appropriate field irrigation.
The system can be of two types: one is a wholly above the ground type, where the pipes are fitted on the surface with sprinklers at regular intervals; an alternative is where the pipes are fitted below the ground and only the sprinkler nozzle is present above the ground for delivering water.
A typical sprinkler irrigation system consists of the following components: Pump unit, Mainline and sometimes sub mainlines, Laterals, Sprinklers.
The mainline - and sub mainlines - are pipes which deliver water from the pump to the laterals. In some cases these pipelines are permanent and are laid on the soil surface or buried below ground.
The water is distributed through a stationary sprinkler system, which evenly sprays water over crops and plants.
In other cases when fields may be too large for stationary sprinklers; they are temporary, supported by mov-able trusses running across the fields.
The main pipe materials used include asbestos cement, plastic or aluminum alloy.
The laterals deliver water from the mainline or sub mainlines to the sprinklers.They can be permanent but more often they are portable and made of aluminum alloy or plastic so that they can be moved easily.
The main objective of a sprinkler system is to apply water as uniformly as possible to fill the root zone of the crop with water.
Wetting patterns -The wetting pattern from a single rotary sprinkler is not very uniform. Normally the area wetted is circular.
The heaviest wetting is close to the sprinkler. For good uniformity several sprinklers must be operated close together so that their patterns overlap to the extent of at least 65% of the wetted diameter.
This determines the maximum spacing between sprinklers.
The uniformity of sprinkler applications can be affected by wind and water pressure. Spray from sprinklers is easily blown about by even a gentle breeze and this can seriously reduce uniformity.To reduce the effects of wind the sprinklers can be positioned more closely together.
Sprinklers will only work well at the right operating pressure recommended by the manufacturer. If the pressure is above or below this then the distribution will be affected.
The most common problem is when the pressure is too low. This happens when pumps and pipes wear. Friction increases and so pressure at the sprinkler reduces. The result is that the water jet does not break up and all the water tends to fall in one area towards the outside of the wetted circle. If the pressure is too high then the distribution will also be poor. A fine spray develops which falls close to the sprinkler.
The sprinkler system irrigates the field drop by drop and thus it is widely used in sandy areas as it checks the wastage of water through seepage and evaporation.
Sprinkler irrigation has less interference with cultivation and less land loss, coupled with higher application efficiency. Sprinkler irrigation makes for easy mechanization and automation where high and frequent application can be effectively accomplished.
Deficit irrigation is a water management strategy that focuses on allocating limited seasonal water supplies to the critical growth stages of crops and reducing irrigation during specific periods that have little impact on yield. A clear understanding of the water requirement across various growth stages of the specific crop and variation of crop yield due to water stress is needed for adopting this practice.
It is not an irrigation system but an irrigation strategy.
The technique/strategy consists of applying small quantities of water during critical periods to improve and stabilize yields, save water and balance low water availability with a sustainable production level.
Alternate wetting and drying (AWD) is an irrigation management practice for lowland paddy cultivation that saves water and reduces greenhouse gas (GHG) emissions while maintaining yields. It involves periodic drying and re-flooding of the paddy field.
A practical way to implement AWD is by using a ‘field water tube’ to monitor the water depth on the field. A 30 cm long plastic pipe or bamboo having a diameter of 10−15 cm is used so that the water level is easily visible, and it is easy to remove soil inside. The tube is perforated with holes on all sides, so that water can flow readily in and out of the tube. It is put into the soil with about 15 cm protruding out. Soil from inside the tube is removed, so that the bottom of the tube is visible.
When the field is flooded, the water level inside the tube is the same as outside the tube. After irrigation, the water depth will gradually decrease.
When the water level has dropped to about 15 cm below the surface of the soil (i.e. end of the tube), irrigation should be applied to re-flood the field to a depth of about 3-5 cm. This is repeated except during flowering time.
From one week before to a week after flowering, the field should be kept flooded, topping up to a depth of 5 cm as needed. After flowering, during grain filling and ripening, the water level can be allowed to drop again to 15 cm below the soil surface before re-irrigation.
The tube should be placed in a readily accessible part of the field close to a bund, so that it is easy to monitor. The location should be representative of the average slope of the field (i.e. it should not be on a high ground or a depression).
Proper levelling of paddy fields is necessary to ensure that no areas are excessively dry or wet, which could adversely affect yields.
Weed management is important, as periods of drying can encourage weed growth.
Take care not to damage the tube while ploughing or weeding.
When the field is flooded, the water level inside the tube should be the same as outside the tube. If it is not the same after a few hours, the holes are probably blocked. The tube needs to be carefully cleaned and re-installed.
Sub-surface Drip Irrigation (SDI) is a highly efficient irrigation system of applying water from beneath the soil surface directly to the root zone. It uses buried perforated drip tubes to meet crop water needs. This is suitable for arid, semi-arid lands, areas with limited water supply or with sandy, porous soil having low water retention capacity. It is commonly used for high value vegetable crops.
Sub-surface Drip Irrigation (SDI) uses underground perforated pipes from which water trickles out through perforations along the pipes.
Water moves laterally and upward to the root zone soil due to capillary action.
The pipes are placed 10 to 60 cm below the ground, depending on crop being cultivated and the soil properties.
SDI generally does not require high water pressure. However, if the water source is not higher up from the field, a pump might need to be used to direct water to the irrigation pipes. A filter system is installed to remove particles that may block the pores or emitters.
Backflow preventer and regulator valves are added to regulate the water flow if needed. Connectors are used to attach drip lines to the main lines or sub-mains.
Pipelines should remain filled with water during the period of irrigation. The upper layers of soil would appear relatively dry while lower layers closer to root zones would remain moist.
A subsurface drip system may require higher initial investment than a furrow system and cost will vary based on distance of water source, filtration needs, soil characteristics.
The performance and durability of the system depends on how well it is operated and maintained.
Systems must be designed with flushing valves/ball valves at regular intervals such that mainlines, sub-main drip lines and laterals can all be flushed as needed.
It is essential to install a filtration unit for the drip system.
Adequate water supply must be available throughout the growing season. An outlet for drainage is needed, particularly in high rainfall areas.
Since the soil surface appears dry, soil moisture monitoring is required to determine when irrigation should be applied next.
Use of filters is advised to reduce the risk of clogging the pores.
Periodic inspection is necessary to check if the roots are damaging the drip pipes or blocking the pores. Field machinery and rodents can also damage the pipe. Do not use a buried system where rodents are common.
A bubbler irrigation system is a combination of a drip irrigation and sprinkler system. The bubblers are also known as mushroom bubblers and can emit a large volume of water from about six inches above the ground. These are used in farm fields with level or mild slopes, usually with raised plant beds, and are useful for watering perennial trees and shrubs.
Low-head bubbler systems are based on gravity flow. The water source should be located at least 1 meter above the farmland for a bubbler system to work.
Bubblers can be attached to 0.25-inch micro tubes or 0.5 inches drip tubes.
The drip tubes are laid out as per watering requirement and buried under soil to keep them secure.
The bubblers are installed along the line near the trees to be watered.
The water from the bubbler floods the ground surface around the tree. Because the application rates generally exceed the soil infiltration rates, a small earthen mound or ridge need to be created around the tree to contain this water and allow for infiltration.
The flow rates of the bubblers can be adjusted as per need.
A ratchet mechanism on the cap and a notch or srew at the base allows for control of flow, pattern and diameter of throw as required. A bubbler can typically serve an area of 3 ft diameter.
Trees that are susceptible to damage by waterlogging next to the trunk (rot/ fungal attack), should be planted in the middle of a basin with a raised centre, with a circular trough surrounding it, to prevent water accumulating next to the tree trunk.
As a tree grows, the bubbler needs to be moved away from the base of the trunk. As the root system develops and expands, the watering zone should be extended to cover the entire area under the canopy. The earthen basin/mound around the tree should be adjusted accordingly.
The bubblers can of different types. Flood bubblers operate by flooding the area around them with water. Stream bubblers can spray the water 2-5 feet from the bubbler. Micro bubblers have lower flow rates.
Periodic checks are needed to identify and repair leaks in the drip lines.
The earthen basins and ridges are usually unstable and require periodic maintenance.
Energy requirements are low due to use of gravity flow. Hence Operating costs also remain low.
Maintenance cost is low as it does not require to many accessories (e.g. filters, pumps etc) and do not get clogged easily. The bubblers are quite durable.
Duration of an irrigation event is short because the large discharge rates.
The bubblers are water efficient. They provide water directly where it is needed, and thereby save water by upto 70%.
Bubbler systems are ideal for larger plants, or those that require more water than a drip system can provide. Water emitted from bubblers penetrates deep into the soil to produce longer root hairs to improve plant health.
The technology is simple and no sophisticated equipment is needed