Irrigation is the process of providing a controlled amount of water to the plants. It plays a vital role in crop production. If there is a good irrigation system there will be high crop production and vice versa. Mainly surface and sub-surface types of irrigation are used. The choice of the method of application of water depends upon several factors. They are:
1. The topography of the land
2. Types of crop
3. Soil type
4. Quality & quality of available water.
5. The ability of the farmer to afford to installation
6. Cultural practices
7. Crop water requirement
8. Net effective rainfall in that locality
9. Initial development costs and availability of funds.
Types of Irrigation
1.2 Sub-surface irrigation
In this method, water is applied below the soil surface. It means water does not wet the soil surface. The underground water nourishes the plant roots by the capillary action artificially-75 cm below the ground surface.
1. Natural sub-surface irrigation
In this type, water reaches below the land surface from natural sources of water, such as streams, lakes ponds etc. The process of irrigating the land by a natural process without any additional extra efforts it is called natural subsurface irrigation.
2.Artificial sub-surface irrigation
In the method, water is provided to crops by capillarity through a network of buried perforated pipes which carry water under pressure that percolates through perforations.
The depth of the pipe should not be less than 40 cm so that there will not be any interference to the cultivation.
1. Soil having uniform texture and permeability (sand, Loam).
2. Land having uniform topography and moderate slope.
3.Good quality of irrigation water.
Proper drainage arrangements are done to drain excess water for avoiding water-logging of the field.
1.3 Surface irrigation
It is the most common type of irrigation in which water is directly applied on the surface of the field. It is also called flow irrigation. The efficiency of surface irrigation depends upon proper land preparation and distribution system.
1.3.1 Types of surface irrigation
A. According to the system of supply of water
a. Flow irrigation
When irrigation water available at a higher level is supplied to the lower level by the action of gravity, this type of irrigation is called flow irrigation.
b. Lift irrigation
If the irrigation water is lifted by mechanical or manual means then it is called lift irrigation.
B. According to the method of distribution of water
In this type, the soil is kept submerged & is thoroughly flooded with water. It may be classified as:
It is one of the most primitive and insufficient methods of irrigation. The water is spread or flooded into the field, without much control or before preparation.
This method is suitable for inundation irrigation systems, pastures & forage crops which is inexpensive.
1. Inefficient use of water
2.uneven distribution of water
4.Large percolation loss
2. Controlled flooding
In this type of flooding, water is applied to the land in a controlled manner. There is proper control in the flow as well in quantity of water.
Types of controlled flooding
Controlled flooding is classified into the following types:
i. Free flooding
ii. Border flooding
iii. Check flooding
iv. Basin flooding
v. Contour laterals
vi. The ZigZag method
i. Free flooding
Free flooding method is also known as irrigation by plots. The field is divided into several plots of nearly equal levels and water is admitted to these plots at the higher end. The size of the plot depends upon the porosity of the soil.
-In the area having sufficient amount of cheap water.
-Relatively flat field
-The initial cost of land preparation is less.
-High labour requirement
-Water application efficiency low
ii. Border strip method or border flooding
The agricultural farm is divided into a series of strips. Strips are about 10-20m wide and 100-400m long. water flows from supply ditch to the strip’s water flows from the upper end to lower end of the ditch.
-Suitable for all close-growing crops
-Suitable for row crops & orchards.
-Requires less labour & time.
-Low maintenance cost.
-Utilizes a large volume of water from the stream to the irrigation field safely.
-High initial cost
-Requires proper levelling
-Requires a huge amount of water
iii. Check flooding
Check flooding is similar to ordinary flooding or free flooding expect that water is controlled by surrounding the check area with flat & low levees. If the ground has some initial slope, levees may follow the contour. It is suitable to irrigate food & grain crops in heavy soil.
-This method is suitable for both permeable and impermeable soil.
-If soil is permeable, water can be spread easily without any percolation losses.
-If the soil is impermeable, water can be held for a long time.
-High irrigation efficiency can be achieved.
-Unskilled labour can be employed.
-Large numbers of labours are required.
-Levees restrict the use of modern machinery.
iv. Basin flooding
It is a special type of check flooding. This method of irrigation is used to irrigate orchards & large trees. One or more trees are generally placed in the basin & the surface is flooded as in check method.
-It is suitable for orchards and trees.
-Less maintenance cost.
-Provide efficient use of water.
-High initial cost.
-A large quantity of water needed.
v. Contour laterals
This method is best suited in steeper terrain. The field is cut by a relatively dense network of contour laterals of laterals depends upon the grade of land, uniformity of slope & type of soil.
For close-growing crops on slopy land.
-It can be used in all types of soils
-Inefficient use of water.
-Uneven distribution of land
vi. Zigzag method
The Zigzag method is a special method of controlled flooding where water applied to the land takes a circuitous route, starting from the field channel and reaching the dead end of each plot. For this purpose, the whole farm is divided into several squares (or rectangular) plots. Each plot is provided with levees ( or small bunds ) such that the water takes the circulations path covering the entire plot. The Zigzag method is quite suitable for relatively level plots. However, the method is not suitable when the farming operations are to be done with modern farm machinery.
b. Contour farming
It is adopted in hilly areas with a steep slope and quickly falling contours. The land is divided into longitudinal curves into a series of strips and the cultivation of the crop is done along the contour lines instead of the usual downslope. Contour cultivation reduces runoff and soil loss. This method is suitable in hilly regions having a steep slope.
c. Furrow irrigation
This is an excellent method of irrigation for row crops like potatoes, cauliflowers etc.
Furrows are a series of long narrow channels constructed in the field. Furrows vary from 8 to 30 cm deep and maybe as much as 400 meters long. Excessive long furrows lead to excessive percolation at the upper end and too little water near the downslope end. Deep furrows are widely used for row crops. Small shallow furrows called corrugations are particularly suited for meadows and small grains. Crops are usually planted on the top or sides of ridge or furrows. Water applied in the field gets soaked into the soil & spreads into the Root Zone.
Furrows are of two types. They are:
a. Straight furrows
b. Contour furrows
1. Water efficiency is high puddling of heavy soils is also lessened and it is possible to start cultivation soon after irrigation with the change in supply conditions, numbers of simultaneously supplied furrows can be easily changed. In this manner, very high irrigation efficiency can be achieved.
2.Cheap to construct & maintain.
3. Evaporation loss is small.
4. Furrows also serve as drainage.
5.Less wastage of land to make a furrow.
6. Only one-fifth to one-half of the land is wetted by the water.
7.Permits cultivation sooner after irrigation.
1. Furrow making skills are required.
2. Silts from furrows should be regularly removed.
3. Possibility of increased salinity between furrows.
4. Loss of water at the downstream end unless end dykes are used,
5. The necessity of one extra tillage work, VIZ, furrow construction,
6. Possibility of increased erosion, and
7. Furrow irrigation requires more labour than any other surface irrigation method.
-Furrow irrigation is suitable in the following:
-In the relatively flat ground.
-In flat land furrows are straight but in the sloping ground, furrows are constructed in the contour line.
1.4 Drip irrigation
It is a special type of subsurface irrigation. It is also called trickle irrigation. It is the latest field irrigation technique where there is a scarcity of irrigation with salt problems. In this method, water is slowly and directly applied to the root Zones of the plants.
-Head tank maintains the pressure.
-Main & secondary line: black PVC.
-Lateral lines: 10-20 mm in diameter.
-Discharge through the nozzle is 2 to 10 lit#hr.
This method is suitable for any topography.
-Less amount of irrigation water.
-Water-logging is avoided.
-Less loss of water.
-High crop yield.
-Reduce labour cost.
-The initial cost is high
-The problem of clogging of nozzles.
1.5 Buried irrigation
It is a substitute of canals by pipelines. In this system, water is delivered by a canal from the source of water supply to irrigation area & inside area. It is distributed by gravity pressure. The distributing pipeline receives water from the farm pipeline or open canal along the contour lines. Water runs to field pipelines which in turn discharge into flexible irrigation pipeline. Water is lifted mechanically to the buried networks when the level of source of supply is below that area to be irrigated.
1.6 Seepage Line irrigation
A relatively new concept of irrigation is seepage line irrigation which can provide limited but assured irrigation facilitated to crops during a critical time. No of the well can be developed at a different point in and around the area where big water seepage is observed. These wells are connected by pipelines to a central point in the command area which is dug as a water tank. Water is supplied to an individual from this tank at a nominal cost.
1.7 Sprinkler irrigation
This irrigation is also called overhead irrigation. In this method of irrigation water is applied in the form of a spray or artificial rain. In this method, water is sprayed into the air and allowed to fall on the ground surface somewhat resembling rainfall. The spray is developed by the flow of water under pressure through small orifices or nozzles. The pressure is usually obtained by pumping. With careful selection of nozzle sizes, operating pressure and sprinkler spacing the amount of irrigation water required to refill the crop root zone can be applied nearly uniform at the rate to suit the infiltration rate of the soil.
The following conditions are favourable for the sprinkler irrigation.
-If the land is undulated, the sprinkler irrigation can be used, because it will be costly to level the land for the surface irrigation.
-If the soil is very previous, the sprinkler irrigation can be used, because it will be difficult to achieve good water distribution by the surface irrigation.
-If the soil depth is shallow, the sprinkler may be used, because it would be difficult to properly level the land for surface irrigation.
-It can be used even for the lands having a steep slope or having an easily-erodible soil for which surface irrigation is not possible.
-It can be used when the irrigation stream is too small to distribute water efficiently by surface irrigation.
-It can be used when the land is to be brought into use in a short period.
-It is suitable when the soil requires a light application of water at frequent intervals.
-It is suitable for regions with a high water table where percolation losses will be high if the surface irrigation is done.
-It is suitable for shallow-rooted crops.
-It is suitable for effective fertilizer application and soil improvement.
-It is suitable where well-trained and reliable labour is not available for surface irrigation.
-Land preparation not required.
-Water efficiency is very high i.e. about 80%.
-Moreland can be irrigated by less water.
-Protects soil & crops from extreme weather conditions such as frost.
-Uniform application of water.
-Preservation of soil erosion.
-Application of fertilizer can be done along with water.
-Elimination of the channels for conveyance, therefore no conveyance loss.
-Suitable to all types of soil except heavy clay.
-Suitable for irrigation crops where the plant population per unit area is very high.
-It is most suitable for oilseeds and other cereal and vegetable crops.
-Closer control of water application convenient for giving light and frequent irrigation and higher water application efficiency.
-Increase in yield.
-Mobility of the system.
-May also be used for the undulating area.
-Saves land as no bunds etc. are required.
-Influences greater conducive micro-climate.
-Areas located at a higher elevation than the source can be irrigated.
-Possibility of using soluble fertilizers and chemicals.
-Less problem of clogging of sprinkler nozzles due to sediment-laden water.
-The initial cost is high.
-There is an effect of pressure, during application
-Not suitable for crops requiring a large depth of water.
-Power is required for running pump.
-Effect of wind.
-The problem of clogging of the nozzle.
-Good quality if the water is necessary.
-Requires frequent supervision.
-Requires continuous supply of water.
-Not suitable for heavy soils.
-Evaporation losses will be high in a place having high temperature and high wind speed
Classification of Sprinkler System
1. Permanent system:
It is a system in which both the mains & laterals are fixed
Mains are permanently fixed and laterals are portable.
3. Portable system
The system in which main and laterals are both portables.
Sprinkler system usually consists of the following components
i. A pump unit
ii. Tubings- main/sub mains and laterals
iv. Sprinkler head
v. Other accessories such as valves, bends, plugs and risers.