METHODS OF IRRIGATION
• Sprinkler irrigation is adopted where land leveling is uneconomical or impractical.
• Drip irrigation is used where water is scarce.
• Flood method of irrigation is exclusive for lowland rice.
• Labour requirement for irrigation is minimum in flooding.
• Check basin method of irrigation is the most common method among surface methods of irrigation.
• Check basin method is suitable for close growing crops like groundnut, wheat, finger millet, pearl millet, para grass etc.
• In check basin method water can be applied uniformly.
• In check basin method more land is wasted under channels and bunds and intercultivation is difficult.
• Basin method is suitable for fruit crops.
• In border strip method of irrigation, field is laid out into long, narrow strips, bordering with small bunds.
• Length of border strips ranges from 30 to 300m and width from 3 to 15m.
• Border strip method is suitable for close growing crops and medium to heavy textured soils, but not suitable for sandy soils.
• Size of border strips depends on stream size and soil texture.
• For larger size streams and heavy soils, longer strips are made.
• Furrow method of irrigation is adopted to crops grown with ridges and furrows.
• Furrow irrigation is suitable for crops like sorghum, maize, cotton, tobacco, brinjal, tomato, potato, Napier grass, sugarcane etc.
• Length of furrow ranges from 30 to 300m.
• Close growing crops like wheat, setaria, groundnut etc. are occasionally given supplemental irrigation though they are originally planned as rainfed crops.
• Intercultivation is done so as to make shallow furrows. Applying irrigation through these shallow furrows is called corrugation irrigation.
• Water in the furrows contacts only one-half to one-fourth of the land surface, thereby reducing evaporation losses.
• Crust problem is avoided in furrow irrigation.
• Surge irrigation is defined as the intermittent application of water to the field surface under gravity flow which results in a series of ‘on’ and ‘off’ modes of constant or variable time spans.
• In surge irrigation large intermittent flows rather than a continuous one are used with two sets of furrows and gated pipes laid in the ‘Tee” configuration.
• Cablegation is an automated method of surface irrigation.
• Cablegation is a form of gated pipe system.
• Subsurface irrigation through trenches causes deep percolation losses.
• Subsurface irrigation method is suitable where water table is shallow.
• Subsurface irrigation is practiced in a few places in Kerala for coconut gardens and in Kashmir for vegetables.
• Rotational irrigation is a system of rotational supply of irrigation water to ensure equitable supply to all the farmers in the realized area of an irrigation system, irrespective of the location of the field.
• Rotational irrigation is also known as warabandi irrigation.
• Flood recession farming is the practice of growing crops on land that is flooded annually and crops are grown during the recession period. By way of sediment deposits soil fertility is improved.
• Deficit irrigation is an irrigation water management alternative where the soil in the plant root zone is not refilled to field capacity in all or part of the field.
• In sprinkler irrigation height of riser pipes depends on the height of the crop. It should be equal to maximum height of the crop.
• To achieve uniform sprinkling of water, it is necessary to overlap the area of influence of each of the sprinklers.
• Conveyance losses with surface irrigation ranges from 15 to 20% in well irrigated areas and 30-50% in canal and tank irrigated areas.
• In sprinkler irrigation saving of water ranges from 25 to 50% for different crops.
• It is difficult to irrigate sandy soils with surface irrigation and it is easy with sprinkler irrigation.
• Sprinkler irrigation does not work well under high wind velocity.
• Sprinkler irrigation is not suitable for areas with hot dry winds.
• Power requirements are usually high since sprinklers operate at a pressure.
• Christensen developed uniformity coefficient to measure the uniformity of sprinkler systems, and it is most often applied in sprinkler irrigation situation. It is seldom used in other types of irrigation.
• Uniformity coefficient is defined as the ratio of the difference between the average infiltrated amount and the average deviation from the infiltrated amount, to the average infiltrated amount.
• Values of Uniformity coefficient varies from 0.6 to 0.9.
• Drip irrigation is defined as the precise, slow application of water in the form of discrete or continuous or tiny streams or miniature sprays through mechanical devices called emitters or applicators located at selected points along water delivery lines.
• The terms trickle or drip irrigation are used synonymously.
• In 1964 Symcha Blasé, an Israeli engineer developed the first patented drip irrigation system.
• Screen (mesh) filter is primarily useful for removing suspended organic particles in water containing sufficient amounts of organic matter.
• Screen filters of 100-200 mesh remove particles of size range > 100-150 µm.
• Sand filter is most effective in the removal of inorganic and organic particles from water.
• Sand filters remove suspended particles of size range > 20 µm to 100 µm.
• Sand filter is provided with a back flushing arrangement.
• Point source drippers or emitters discharge water from individual or multiple outlets that are spaced at least 1m apart.
• Point source systems are used for widely spaced crops.
• Line source emitters or drippers have perforations, holes or porous walls in the irrigation tubing that discharge water at close spacing or even continuously along a lateral line.
• Line source emitters or drippers are used for close growing crops.
• Water discharge rate per dripper is normally between 1 to 4 l/h though the discharge rate of emitters is up to 15 to 20 l/h.
• Rate of application of water through dripper has to be less than the infiltration rate of the soil.
• Chlorine in the form of bleaching powder is used to control algae and bacterial slimes.
• HCl (36%) of 0.5-2.0% concentration removes precipitates in drip system.
• Sulphuric and hydrochloric acids can be used to remove chemical precipitates.
• Acid treatment is given when Ca and Mg in irrigation water exceeds 50 ppm of each.
• Sodium hypochlorite at 500 ppm helps to remove clogging of drippers.
• In drip irrigation saving in irrigation water compared to conventional method of irrigation was 40-70%.
• Disadvantages of drip irrigation
1) High initial cost
2) High energy consumption to pump water with pressure for distribution
3) Restricted area of root growth
4) Requirement of higher level of design, management and maintenance
5) Clogging of emitters
• In sugarcane an efficient irrigation system known as Typhoon system has been developed.
• Bubbler irrigation is designed to reduce energy requirements through inexpensive, thin walled, corrugated plastic pipe with a diameter that even the low pressure head from a surface ditch might suffice.
• Siphon tubes are curved pipes which are used to take water from supply channel into the field.
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