The key project activities including drip irrigation, sprinkler irrigation, laser land leveling, and water course improvement are introduced below.
Drip irrigation is sometimes called trickle irrigation and involves dripping water onto the soil at very low rates (2-20 liters/hour) from a system of small diameter plastic pipes fitted with outlets called emitters or drippers. Water is applied close to plants so that only part of the soil in which the roots grow is wetted, unlike surface and sprinkler irrigation, which involves wetting the whole soil profile. With drip irrigation water, applications are more frequent (usually every 1-3 days) than with other methods and this provides a very favorable high moisture level in the soil in which plants can flourish.
Drip irrigation is most suitable for row crops (vegetables, soft fruit), tree and vine crops where one or more emitters can be provided for each plant. Generally only high value crops are considered because of the high capital costs of installing a drip system.
Drip irrigation is adaptable to any farmable slope. Normally the crop would be planted along contour lines and the water supply pipes (laterals) would be laid along the contour also. This is done to minimize changes in emitter discharge as a result of land elevation changes.
Drip irrigation is suitable for most soils. On clayey soils water must be applied slowly to avoid surface water ponding and runoff. On sandy soils higher emitter discharge rates will be needed to ensure adequate lateral wetting of the soil.
One of the main problems with drip irrigation is blockage of the emitters. All emitters have very small waterways ranging from 0.2-2.0 mm in diameter and these can become blocked if the water is not clean. Thus it is essential for irrigation water to be free of sediments. If this is not so then filtration of the irrigation water will be needed.
Blockage may also occur if the water contains algae, fertilizer deposits and dissolved chemicals which precipitate such as calcium and iron. Filtration may remove some of the materials but the problem may be complex to solve and requires an experienced engineer or consultation with the equipment dealer.
Drip irrigation is particularly suitable for water of poor quality (saline water). Dripping water to individual plants also means that the method can be very efficient in water use. For this reason it is most suitable when water is scarce.
c.6.2Sprinkler Irrigation 19
Sprinkler irrigation is a method of applying irrigation water which is similar to natural rainfall. Water is distributed through a system of pipes usually by pumping. It is then sprayed into the air through sprinklers so that it breaks up into small water drops which fall to the ground. The pump supply system, sprinklers and operating conditions must be designed to enable a uniform application of water.
Sprinkler irrigation is suited for most row, field and tree crops and water can be sprayed over or under the crop canopy. However, large sprinklers are not recommended for irrigation of delicate crops such as lettuce because the large water drops produced by the sprinklers may damage the crop.
Sprinkler irrigation is adaptable to any farmable slope, whether uniform or undulating. The lateral pipes supplying water to the sprinklers should always be laid out along the land contour whenever possible. This will minimize the pressure changes at the sprinklers and provide a uniform irrigation.
Sprinklers are best suited to sandy soils with high infiltration rates although they are adaptable to most soils. The average application rate from the sprinklers (in mm/hour) is always chosen to be less than the basic infiltration rate of the soil so that surface ponding and runoff can be avoided. Sprinklers are not suitable for soils which easily form a crust. If sprinkler irrigation is the only method available, then light fine sprays should be used. The larger sprinklers producing larger water droplets are to be avoided.
A good clean supply of water, free of suspended sediments, is required to avoid problems of sprinkler nozzle blockage and spoiling the crop by coating it with sediment.
Laser leveling is a process of smoothing the land surface (± 2 cm) from its average elevation using laser-equipped drag buckets. This practice uses large horsepower tractors and soil movers that are equipped with global positioning systems (GPS) and/or laser-guided instrumentation so that the soil can be moved either by cutting or filling to create the desired slope/level. This technique is well known for achieving higher levels of accuracy in land leveling and offers great potential for water savings and higher grain yields.
A laser transmitter transmits a laser beam, which is intercepted by the laser receiver mounted on the leveling bucket. The control panel mounted on the tractor interprets the signal from the receiver and opens or closes the hydraulic control valve, which raises or lowers the bucket. Loose soils are picked up by the bucket and released lower in the field.
A precisely leveled surface leads to uniform soil moisture distribution, resulting in good germination, enhanced input use efficiency and improved crop stand and yield.
Laser leveling allows for control of water distribution with negligible water losses.
Laser leveling improves irrigation efficiency and reduces the potential for nutrient loss through better irrigation and runoff control.
It facilitates uniformity in the placement of seedlings, helping to achieve higher yields.
Land leveling reduces weed (improved water coverage reduces weeds up to 40%), pest, and disease problems.
It results in 3 to 4 percent additional land recovery and improves operational efficiency (reducing operating time by 10 percent to 15 percent).
Leads to reduced consumption of seeds, fertilizers, chemicals and fuel
Facilitates movement of agricultural machinery through the fields.
c.6.4Water Course Improvement
Tertiary irrigation conveyance network in Pakistan is called watercourses. These are community channels off-taking from government controlled irrigation system. The watercourses are operated and maintained by the shareholders receiving water through these channels. A watercourse commands an area of about 150-250 hectares (375-625 acres) and is shared by 40 to 50 farm families. Studies have indicated that about 40 percent of irrigation water is lost during its conveyance through nation’s about 140,000 watercourses because of their aging and deteriorated conditions. Previous experience of watercourse improvement has shown that on an average, annual water saving in an improved watercourse is about 100 Acre Feet besides other socio-economic benefits.
The water course improvement consists of complete demolition of community channel and its re-building and re-alignment according to the proper engineering design with clean compacted soil. Parts of the constructed watercourse are brick-lined and necessary water control structures are installed to improve water conveyance.
Precast naccas (control structures) are installed at all junctions and authorized outlets in the water course to reduce the channel deterioration, seepage losses and to improve water control. Moreover culverts are installed at major crossings as well as check/drop structures, animal wallows, and clothes-washing sites for the communities.