Three basic demands of agricultural production are seed, soil and water. Besides, insecticides, fertilizers, sunshine, appropriate atmospherical temperature and human labour are also needed. Of all these, water seems to be the most important requirement of agricultural production.
In several parts of the world, the moisture accessible within the root-zone soil, either from rain or from underground waters, might not be adequate for the wants of the plant life.
The deficiency may be either for the entire crop season or only part of the crop season.
For the proper growth of plants/crops, water within the root-zone soil is maintained through irrigation.
Irrigation may be defined as the science of the artificial application of water to the land following the crop water requirements throughout the crop period for the full-fledge nourishment of the crops.
1.1. Necessity of Irrigation
Rainfall varies considerably in place, time and amount. The intensity of rainfall is very high during the monsoon season and less during other seasons.
So crop can not be raised effectively over the complete land without supplying synthetic irrigation of fields.
The necessity of irrigation is as follows:
a. Non-uniform rainfall throughout the year.
b. Less rainfall than the requirement
c. Increasing food demand
d. Controlled water supply
1.2. Advantages of Irrigation
Every irrigation project is designed based on the economical view. So any irrigation project should be economically feasible.
Generally, a project giving benefit at least about 8% interest of the capital outlay is implemented.
Sometimes unproductive projects are also implemented because of the general public benefits.
The advantages of irrigation are as follows:
a. Increase in food production.
b. Hydropower generation.
c. Elimination of mixed cropping.
d. Flood control.
e. Insurance against drought.
h. Facility of communication.
i. Prosperity of the nation.
j. Optimum benefits.
k. Domestic water supply.
l. Quality of life.
1.3. Disadvantages of Irrigation
The disadvantages of irrigation are as follows:
a. Creation of damp climate.
b. Formation of water-logged area.
c. Requirement of crossing structures.
d. Creation of damp climate, marshy lands and breeding place for mosquitoes causing the outbreak of a disease like malaria and dengue.
e. Water pollution problem: Seepage of nitrate applied in the soil as fertilizer may pollute underground water.
f. Raising of the water table.
g. Loss of soil fertility.
h. Soil erosion.
i. Loss of valuable land.
1.4. Source of water for irrigation
As we know every water is not suitable for human beings in the same way every water is not suitable for plant life.
Water containing impurities are injurious to plant health is not satisfactory for irrigation.
Selection of sources of water for irrigation depends upon the following factors:
a. Quantity needs
b. Quality factors
d. Conflict and competition for water
a. Quantity needs:
The source selected for irrigation should have adequate quantity of water to fulfil the water requirements of the command area.
If water is not available in adequate quantity, there will not be desirable yield of the crops in one hand and conflict between farmers in another hand.
b. Quality factors:
The concentration and composition of dissolved constituents in water determines the quality of irrigation use.
The various impurities which make the water unfit for irrigation are as follows:
i. Sediment concentration in water
ii. Total concentration of soluble salts
iii. Potentially toxic elements
iv. Bacterial contamination
i. Sediment concentration in water
The effect of sediment present in the irrigation water depends upon the type of irrigated land.
When the sediment from water is deposited on sandy soil the fertility is improved but if the sediment has been derived from the eroded areas it may reduce the fertility or decreases the soil permeability.
Sedimented water creates troubles in irrigation canals by causing canal siltation & by increasing maintenance costs.
So from the sediment concentration viewpoint groundwater and surface water from reservoir don’t have sufficient sediment to cause serious problems in irrigation.
ii. Total concentration of soluble salts
Salts of Calcium, Magnesium Sodium & Potassium present in irrigation water may prove injurious to plants.
When these salts are present in the excessive amount they reduce the osmotic activities of plants and may cause injury to plant growth.
At the initial phase of irrigation, no harm may be evident but over time, the salt concentration in the soil will reach a harmful level.
iii. Potentially toxic elements
Several elements like Boron, Selenium etc. may be toxic to the plant’s health.
Traces of Boron are vital for plant growth but its concentration above 0.3 ppm is considered as toxic.
Presence of selenium even in low concentration is toxic and must be avoided.
Boron is commonly present in various soaps. Therefore soap water should be used in irrigation with great care.
c. Location of sources:
Source of irrigation canal should be as near as possible to the command area. Nearer the source lesser the losses, construction cost and maintenance cost.
Source of water selected should be free from conflict or dispute or the dispute should be managed.
1.5. Methods of Irrigation
Water can be applied to the land for irrigation by various methods. The choice of the method application of water depends upon several factors. They are
i. Topography of the land
ii. Types of crop
iii. Soil type
iv. Quantity and quality of available water
v. Ability of farmer to afford the installation
vi. Cultural practices
vii. Crop water requirement
viii. Net effective rainfall in that locality
ix. Initial development costs and availability of funds,
x. Preferences and experience of the farmer.
There are many methods of irrigation. They are
a. Surface irrigation
b. Subsurface irrigation
c. Overhead or sprinkler irrigation
d. Buried irrigation
e. Seepage line irrigation
f. Suction line irrigation
1.5.1. Sub-surface irrigation
In sub-surface irrigation, water is applied below the surface. It means water does not wet the soil surface. The underground water nourishes the plant roots by the capillary. The artificial water table is created and maintained at some depth, usually 30 – 75 cm below the ground surface.
Subsurface irrigation can be classified into the following two categories. They are:
188.8.131.52. Natural Subsurface Irrigation
In this type of irrigation water reaches below the land surface from natural sources of water, such as streams, lakes, ponds etc. The process of irritating land by natural process without any additional extra efforts, it is called natural sub-surface irrigation.
184.108.40.206. Artificial sub-surface irrigation
In this 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.
Merits and Demerits of sub-surface irrigation
|1. Reduction in evaporation & percolation loss.||1. Initial cost is more.|
|2. No wastage of water.||2. Quality of water should be good.|
|3. No wastage of land.||3. Difficult to supervise.|
|4. Reduction in soil erosion.||4. Highly skilled technology and manpower are required.|
|5. Minimum water requirement for raising crops.||5. Possibility of choking of pipes.|
~ Soil having uniform texture and Permeability (sand, loam).
~ Land having uniform topography and moderate slope.
~ Good quality irrigation water.
Proper drainage arrangements are done to drain excess water for avoiding water-logging of the field.
1.5.2. 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 floe irrigation. The efficiency of surface irrigation depends upon proper land preparation and distribution system.
Types of surface irrigation
220.127.116.11. According to the system of supply of irrigation water
According to the system of supply of irrigation water, Surface irrigation is classified as:
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 called lift irrigation.
18.104.22.168. According to the method of distribution of irrigation water
According to the method of distribution of irrigation water, Surface irrigation is classified as:
a. Flooding method
b. Contour farming
c. Furrow methods
1. Flooding methods
In this type of surface, irrigation soil is kept submerged & thoroughly flooded with water. It may be classified as:
a. Wild/ uncontrolled flooding
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.
~ Inefficient use of water
~ Uneven distribution of water
~ Over irrigation
~ Large percolation loss
b. 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 the quantity of water.
Types of controlled flooding
Controlled flooding is classified into the following types:
i. Free flooding
ii. Boarder flooding
iii. check flooding
iv. basin flooding
v. Contour laterals
vi. Zigzag method
i. Free flooding
Free flooding method is also known as irrigation by plots. The field is divided into several 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.
~ Initial cost of land preparation is less.
~ Labor requirements are high.
~ Water application efficiency low.
ii. Boarder strip method or boarder flooding
The agricultural farm is divided into a series of strips. Strips are about 10-20 m wide and 100-400 m long.
Water flows from supply ditch to the strip’s water flows from 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 except 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 labour 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 labour.
~ Less maintenance cost.
~ Provide efficient use of water.
~ High initial cost.
~ Large quantity of water needed.
~ Requires levelling.
v. Contour Laterals
This method is best suited in steeper terrain. The field is cut by a relatively dense network of contour laterals.
The spacing of laterals depends upon the grade of land, uniformity of slope & types of soil.
~ For close-growing crops on sloping land.
~ It can be used in all types of soils.
~ Low cost.
~ Inefficient use of water.
~ Uneven distribution of land.
~ Over irrigation.
~ Large percolation.
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 circuitous 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.
2. 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.
3. 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
~ 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, the number of simultaneously supplied furrows can be easily changed. In this manner, very high irrigation efficiency can be achieved.
~ Cheap to construct & maintain.
~ Evaporation loss is small.
~ Furrows also serve as drainage.
~ Less wastage of land to make a furrow.
~ Only one-fifth to one-half of the land is wetted by the water.
~ Permits cultivation sooner after irrigation.
~ Less loss.
The following are the disadvantages of furrow irrigation:
~ Furrow making skills is required.
~ Silts from furrows should be regularly removed.
~ Possibility of increased salinity between furrows.
~ Loss of water at the downstream end unless end dikes are used.
~ The necessity of one extra tillage work, viz., furrow construction.
~ Possibility of increased erosion
~ Furrow irrigation requires more labour than any other surface irrigation method.
Furrow irrigation is suitable in the following conditions:
~ In the relatively flat ground.
~ In flat land furrows are straight but in the sloping ground, furrows are constructed in the contour line.
|Read Also: Complete Detail of Furrow Irrigation|
1.5.3. 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 the 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.
~ Reduction in labour cost.
~ No over-irrigation.
~ Initial cost is high.
~ Problem of clogging of nozzles.
|Read Also: Complete Detail of Drip Irrigation|
1.5.4. 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 than area to the irrigated.
1.5.5. Seepage Line Irrigation
A relatively new concept of irrigation is seepage line irrigation which can provide limited but assured irrigation facilitated to crops during the critical time.
Numbers 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 the individual from this tank at a nominal cost.
1.5.6. 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 the sprinkler method of irrigation, 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 in the pipeline 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.
Conditions favourable for sprinkler irrigation.
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.
~ If the soil is very pervious, 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.
~ The sprinkler irrigation can be used even for the lands having a steep slope or having an easily-erodible soil for which surface irrigation is not possible.
~ The sprinkler irrigation can be used when the irrigation stream is too small to distribute water efficiently by surface irrigation.
~ The sprinkler irrigation 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%.
~ More land can be irrigated by less water.
~ Protects soil & crops from extreme weather conditions such as frost.
~ Uniform application of water.
~ Prevention of soil erosion.
~ Application of fertilizer can be done along with irrigation water.
~ Elimination of the channels for conveyance, therefore no conveyance loss.
~ Suitable to all types of soil except heavy clay.
~ Suitable for irrigating crops where the plant population per unit area is very high.
~ It is most suitable for oilseeds and other cereal and vegetable crops.
~ Water saving.
~ Closer control of water application convenient for giving light and frequent irrigation and higher water application efficiency.
~ Increase in yield.
~ Mobility of system.
~ May also be used for the undulating area.
~ Saves land as no bunds etc. are required.
~ Influences greater conductive 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.
~ Initial cost is high.
~ There is the effect of pressure, during application.
~ Not suitable for crops requiring a large depth of water.
~ Power is required for running pump.
~ Effect of wind.
~ 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
i. Permanent system: It is a system in which both the mains & laterals are fixed.
ii. Semi-permanent system: Mains are permanently fixed and laterals are portable.
iii. Portable system: The system in which mains and laterals are both portables.
Components of the sprinkler irrigation system
Sprinkler system usually consists of the following components:
~ A pump unit
~ Tubings-main/ sub mains and laterals.
~ Sprinkler head
~ Other accessories such as valves, bends, plugs and risers.
|Read Also: Duty in Irrigation|