irrigation system 2 Flashcards
- Components of irrigation systems
2. typical irrigation in Bhutan
source
storage
conveyance -irrgation channel, pipe,tunnel
irrigation methods- topography, soil type, availabiltiy of water resource,
2.source
conveyance
irrigation methods- furrow or surface irrigation in paddy field
components details
1.Source-Precipitation,Rainfall,Snow
Seasonal- Spring water, Small ,stream,Ponds,
Perennial Spring water, Stream, Rivers, Lakes,
- storage
a. Natural -soil water, ponds, lakes, underground water
b. Man made- big and small dams, ponds
- conveyance-
natural-natural drainage lines
manmade- open irrigation channels, covered irrigation channels, tunnels and pipelines - irrigation methods
surface irrigation, basin irrigation, overhead irrigation, drip irrigation, sprinkler
Field application system-
1.furrow irrigation (surface irrigation)
a. When to use
b. Suitable crops
c. suitable slopes
d. Suitable soil
e. Furrow shape
Furrows are narrow parallel ditches dug on the field between the row of crop
The water runs along them and irrigates the crops as it moves down the slope
a. suitable for wide range of soil types, crops and land uses
b.Suitable for many crops ( wheat, maize, sunflower, sugarcane, soybean, citrus and grapes)
c.Uniform flat or gentle slopes are preferred
Should not exceed 0.5%
Gentle slope of 0.05% to assist drainage following irrigation or excessive rainfall
d. Suitable soil
Most soil types except very course sands
Very coarse sands - high percolation loss
Easily crust soil is suited because the water does not flow over the ridge. So the soil in which the plant grows remains friable
e.
Furrow shape
Influenced by soil type and steam size
Sandy soils, water moves faster vertically than side ways
Narrow, deep V-shaped furrows are desirable to reduce the soil area through which water percolates
In clay soil, there is much more lateral movement of water and the infiltration rate is less than sand
Thus a wide, shallow furrow is desirable to obtain large wetted area to encourage infiltration
#A narrow deep furrow for sandy soil. #A wide shallow furrow for clay soil
Furrow spacing
As a rule
The spacing should be narrow (between 30-60 cm for sandy soil, 30 cm for coarse sand & 60 cm for fine sand)
Clay soils spacing between two adjacent furrows should be more (75-150 cm)
- Advantages of furrow irrigation
2. Disadvantages
1.Reduces the puddling & crusting of the soils and evaporation loss since the water in the furrow contacts only limited portion of the land (1/5 to ½) surface
Carry out on a wide range of slope without any soil erosion by constructing furrow across the slope
Suitable for crops which cannot withstand or are injured by contact with water
2.High amount of water needed
Suitable only in place with high water reserve
Basin irrigation
Basins are flat of land surrounded by low bunds.
The bunds prevent the water from flowing to the adjacent fields
Commonly used for river grown on flat land or in terraces on hillside
Trees can be grown in basin
In general, the basin method is suitable for crops that are unaffected by standing water for long periods
- Basin or ring irrigation
- Suitable crops
- Suitable soils
Basin and Ring Irrigation: Fruit crops in orchards are irrigated by constructing basins or rings around trees. Basins are usually for small trees, while rings are used in bigger trees which are widely spaced.
2.Paddy grows best when its roots are submerged in water so basin irrigation is best method
Eg citrus, banana, cereals
Not suited to crops which cannot stand in wet or waterlogged conditions for periods longer than 24 hrs.
3.Depends on crop grown
Paddy is best grown on clayey soils which are almost impermeable as percolation losses are low.
Rice could also be grown in sandy soils but percolation losses will be high unless a high water table can be maintained.
Coarse sand is not recommended due to high infiltration rate, percolation losses can be high
Loamy soil is preferred so that water logging can be avoided.
Also soil which forms a hard crust when dry, is not suitable
Suitable slope
The flatter the land surface, the easier it is to construct basin.
On flat land, only minor leveling may be required to obtain level basin
Possible to construct basin on sloping land even when the slope is quite steep
Level basins can be constructed like steps of a staircase and are called terraces
Irrigating basins
Direct method and Cascade method
In direct, irrigation water is led directly from the field channel into the basin through bundbreaks
Cascade- practice on sloping land where terraces are used. Water supplies to highest terrace then to lower terrace until the last terrace is filled
Drip Irrigation (trickle irrigation)
- Suitable crops
- Suitable slope
- Suitable soils
- Suitable irrigation water
Involves dripping of water onto the soil at a very low rate (2-20 liter/hr) from a system of small diameter plastic pipes fitted with outlets called emitter /drippers
Water is applied close to plants so that only part of wetting the whole soil profile
More frequent and favorable high moisture level in the soil in which plants can flourish
1.Suitable for row crops, trees and vine crops where one or more emitters can be provided for each plant
Generally high value crops are considered (due the high capital cost of installing)
- Adaptable to any farmable slope
In contour lines, water supply pipes would be laid along the contour
Done to minimize changes in emitter discharge as a result of land elevation changes
3.Suitable for most soils
On clay soil, water must be applied slowly to avoid surface water ponding and runoff
On sandy soil high emitter discharge rates will be needed to ensure adequate later wetting of the soil
4.Problem - blockage of emitter
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
It is essential for irrigation water to be free of sediments (filtration is needed)
Drip system layout
2.Advantages
Pump unit Control head Main and sub main line Laterals Emitter or drippers
2.Water saving to the extent of 30-50%
Reduced weed growth
Reduced labor cost
Constant supply of moisture to the crop (increase yield due to absence of spoil moisture stress)
Possible to combine irrigation with fertilizer and pesticide application
Wider applicability: flat to sloppy and windy area
- Sprinkler irrigation (overhead irrigation)
- Suitable crops
- Suitable slopes
- Suitable soils
- suitable water
Water is made to spray through nozzles fitted in the stand of water conveying pipes over the foliage of crops as artificial rains
Water is distributed though a system of pipes usually by pumping
It is then sprayed into the air though sprinklers so that it breaks up into small water drops which fall to the ground
2.Suited for most row, field, trees crops and water can be sprayed over
Large sprinklers are not recommended for delicate crops (Eg:lettuce because the large water drops produced by the sprinkler may damage the crop)
Adaptable to any farmable slope whether uniform or undulating
The lateral pipes supplying water to the spinklers should be always laid out along the land contour
This will minimize the pressure change at the sprinkler and provide a uniform irrigation
4.Best suited to sandy soils with high infiltration rates although they are adapted to most soils
The average application rate from the sprinkler is always chosen to be less than the basic infiltration rate of the soil (various discharge rate nozzles) so that surface ponding and runoff can be avoided
Not suitable for soils which easily form a crust
5.A good clean water, free of suspended sediment is required
to avoid problems of sprinkler nozzle blockage
- spoiling the crop by coating it with sediment
Advantages
On steep where leveling for surface irrigation is not feasible, sprinkler offers the only method of obtaining adequate distribution of water
Suitable where the depth of soil is limited by a high water table or underlain with a hardpan or other restrict in layers
Good for porous soil where the water penetrates so rapidly that irrigation by other method give excessive losses by deep percolation
Adapts to light application of water for shallow rooted crops, germination of seed and at seedling stage
Provides efficient use of water
Causes reduction in temp during hot periods
Fields ditches are eliminated and the area is available for cultivation
disadvantages of springklers
Involves high initial cost in the form of pipes and pump sets
Operation cost is higher
The movement of portable pipes across muddy field is hard and dirty work.
Fungicide & insecticides applied to the plants wash off
Under certain climatic condition foliage disease may be encouraged
Encouraged weed growth
Wind disturbs the sprinkler pattern, giving unequal distribution of irrigation water
Sprinkling with water may contain some amount of salts and may result in burning of plant leaves
