Methods of irrigation is an important portion in hydraulics. There are mainly three methods- surface irrigation, subsurface irrigation and sprinkler irrigation. Subsurface irrigation is again divided into natural sub-irrigation and artificial sub-irrigation.
Before selecting a particular method, the irrigation engineer must evaluate all the factors, and choose that method which is best suited to the local conditions.
Basic requirements for adaptation of irrigation methods
- The method should be such that uniform water distribution with as small as 6cm water depth applications can be made for light irrigation
- At the same time, it should afford a heavy uniform application of 15 to 20 cm water depth.
- It should allow the use of large concentrated water flows for reduction of conveyance losses, and labour cost.
- It should be suitable for use with economical conveyance structure.
- It should be such that mechanized farming is facilitated
Good irrigation method results in increased yield and conservation of resources with soil productivity maintained and water utilised economically. Over irrigation results in soil erosion, leached fertilizers, drainage troubles and salt accumulation.
Basic methods of Irrigation
Water may be applied to the crops by through three basic methods of irrigation.
- Surface irrigation method
- Subsurface irrigation method
- Sprinkler irrigation method
Let’s dive into through each of them now.
Surface irrigation method- Largest among methods of irrigation
Surface irrigation is a method of irrigation where water is applied and distributed over the soil surface due to gravity. It is the most common form of irrigation throughout the world and has been practised in many areas.
Surface irrigation is also known as flood irrigation, which means that water distribution is uncontrolled. So, it will be inefficient. Some of the irrigation practices grouped under this name involve a large degree of management. Surface irrigation is mainly of three types.
- Flooding method
- Furrow method
- Contour farming
We shall discuss about each of the subdivisions in another blog. Now, come with me to shake hands with subsurface irrigation.
Subsurface irrigation method
The sub surface irrigation method consists of supplying water firectly to the root zone of the crop. The favourable conditions for the sub surfacr irrigation practice are
- Impervious sub soil at reasonable depth (2 to 3m) or existence of high water table
- Permeable soil such as loam or sandy loam in the root zone of the soil
- Uniform topographic conditions
- Moderate slopes
- Good quality irrigation water
If all these favourable conditions are fulfilled and if proper precautions are taken to prevent alkali accumulation or excess water logging, the method results in exonomical use of water, high crop yield and low labour cost in preparing the irrigation plots.
Subsurface irrigation may be of two classes
- Naural sub irrigation
- Artificial sub irrigation
Next, let’s know more details about these methods of irrigation shown in the diagram.
1. Natural sub irrigation
In natural sub irrigation, water is supplied to the root zone of the plants by controlling the level of local water table, such a high level of water table in the area may be available due to water seeping from earthen canals, drains, rivers, etc.
The main points in natural sub irrigation are,
- In order to ensure the requisite supply of water to the root zone, its is essential to maintain the desired water level by artificial means.
- For this purpose, water is supplied to a series of ditches half to one metre deep and 25 to 50cm wide having vertical sides.
- These ditches are spaced from 15 to 100m apart depending upon the Permeability_of_sub soil and topography of land.
- The depth of ditches may vary from 0.3 to 0.5m These channels have relatively flat slopes.
- Water flows at a slow rate and seeps into the ground to maintain the water table at a height such that water from the capiliary fringe is available to the vrops.
- Proper drainage of excess water is permitted, either naturally or with the other drainage works to prevent water logging of the fields.
- Sometimes the upward capiliary water flow from shallow water table may produce saline and alkali conditions and may make the land less productive.
- Under such circumstances, the subsurface irrigation method has to be discontinued and irrigation has to be resorted by sprinkling method.
Next member is artificial sub irrigation method. What are we waiting for? Let me give you more details on that.
2. Artificial sub irrigation
The artificial sub irrigation method consists of supplying water diretly to the root zone of crops through a network of buried perforated pipes. Water is made to pass under pressure, through these underground perforated pipes.
This method is suitable only for those soils formations which have high horizontal permeability to permit free lateral movement though the root zone of the crops and low vertical permeability so that deep percolation losses are minimised.
The pipe are buried 0.3 to 0.4m deep, so that cultivation operations are not hindered, an are spaced 0.4 to 0.5m horizontally, for uniform distribution of water.
Its time to meet the last member, sprinkler irrigation.
The sprinkler irrigation method consists of applying the water in the form of a spray, somewhat as in ordinary rain, as is done in the garden lawn sprinkling.
The greatest advantage of sprinkler irrigation is its adaptabilities to use under conditions where surface irrigatin methods are not efficient. The method is more useful where,
- The land cannot be prepared for surface methods
- Slopes are excessive
- Topography is irregular
- Soil is erosive
- Soil is excessively permeable or impermeable
- Depth of soil is hallow over gravel or sand
In this system, the cost of land preparations and permanent water delivery system of channels or conduits is less. However, there is large initaial investment in the purchace of the pumping and sprinkling equipment.
Sprinkler system can be classified under 3 heads.
- Permanent system
- Semi-permanent system
- Portable system
Earlier, stationary overhead perforated pipe installations were used. However, with the introduction of lightweight steel pipes and quick couplers, a portable sprinkler system was developed.
In the permanent system, pipes are permanently buried in such a way that they do not interfere with tillage operations.
In the semi-permanent system, the main lines are buried while the laterals are portable. A portable system has both portable mains lines and laterals. These systems are designed to be moved from around the farm from field to field.
A pump usually lifts the water from the source, pushes it through the distribution system and through the sprinkler nozzle on the sprinkler heads mounted on rising pipes attached to the laterals. Turbine and horizontal centrifugal pumps are used.
So, that’s it about methods of irrigation. Was that helpful to the knowledge seeker in you?