Irrigation Methods

By

Dr. Dipankar Roy

What is Irrigation?

Irrigation may be defined as the process of supplying water by artificial means to agricultural fields for crop production. If water available to the plants from rainfall is not sufficient, it is supplemented by irrigation water.

In order to achieve this objective, an irrigation system is required to be developed that involves planning, design, construction, operation and maintenance of various irrigation works

Necessity

• Insufficient rainfall
• Uneven distribution of rainfall
• Improvement of perennial crop
• Development of agriculture in desert area

Benefits

• Increase in crop yield
• Protection from famine
• Cultivation of superior crops
• Elimination of mixed cropping
• Economic development
• Hydro power generation
• Domestic and industrial water supply

Ill effects of irrigation

• Rising of water table
• Formation of marshy land
• Dampness in weather
• Loss of valuable lands

Types of Irrigation

• Surface Irrigation
• Sub-surface Irrigation
• Sprinkler Irrigation
• Drip Irrigation

Surface irrigation

It is defined as the group of application techniques where water is applied and distributed over the soil surface by gravity.

It is by far the most common form of irrigation throughout the world

Types of Surface Irrigation

• Basin Irrigation
• Border Irrigation
• Furrow Irrigation

Basin Irrigation

It is the most common form of surface irrigation, particularly in regions with layouts of small fields.

If a field is level in all directions, is encompassed by a dyke to prevent runoff, and provides an undirected flow of water onto the field, it is herein called a basin.

A basin is typically square in shape but exists in all sorts of irregular and rectangular configurations.

Suitable Crops for Basin Irrigation

• Paddy rice grows best when its roots are submerged in water and so basin irrigation is the best method to use for this crop.
• Not suited to crops which cannot stand in wet or waterlogged conditions for longer than 24 h periods (eg. Potatoes, beet and carrots etc.

Suitable Land Slopes for Basin Irrigation

• The flatter the land surface, the easier it is to construct
  basins.
• On flat land only minor levelling may be required to
  obtain level basins.

Suitable Soil for Basin Irrigation

• Loamy soils are preferred for basin irrigation so that waterlogging (permanent saturation of the soil) can be avoided (which can occur on clayey soils).
• Coarse sands are not recommended for basin irrigation. Due to the high infiltration rate, percolation losses can be high.
  

Surface irrigation can be further classified into

Flow irrigation

Process of irrigation in which water flows from its source to the field by gravity. It is also known as canal irrigation. It may further be classified as given below.

• Perennial Irrigation.
• Non-perennial Irrigation

Lift irrigation

Process of supplying water to the field by lifting it from its sources of supply. The sources may be tube well or well in which water comes from underground water resources. Example: Tube well irrigation, Submersible pump

Water Application Methods

• Direct Method
• Cascade Method

Direct Method

• Irrigation water is led directly from the field channel into the basin through bundbreaks.
• In the following figure "Basin a" is irrigated first, then "Basin b" is irrigated and so on.
• This method can be used for most crop types and is suitable for most soils.
  

Cascade Method

• In the following figure the water is supplied to the highest terrace (a.1) and is allowed to flow through terrace a.2 until the lowest terrace
  (a.3) is filled.
• The intake of terrace a.1 is then closed and the irrigation water is diverted to terrace b.1 until b.1, b.2 and b.3 are filled, and so on.
  

Border irrigation

It can be viewed as an extension of basin irrigation to sloping, long rectangular or contoured field shapes, with free draining conditions at the lower end.

Field is divided into sloping borders.

• Water is applied to individual borders from small hand-dug checks from the field head ditch.
• When the water is shut off, it recedes from the upper end to the lower end.

Border Irrigation

Furrow irrigation

Avoids flooding the entire field surface by channeling the flow along the primary direction of the field using ‘furrows,’ ‘creases,’ or ‘corrugations’. Water infiltrates through the wetted perimeter and spreads vertically and horizontally to refill the soil reservoir.

Furrow Irrigation

Sub-surface irrigation

Subsurface irrigation (or simply sub irrigation) is the practice of applying water to soils directly under the surface. Moisture reaches the plant roots through capillary action. The conditions which favor sub irrigation are as follows:

• Impervious subsoil at a depth of 2 meters or more,
• A very permeable subsoil
• A permeable loam or sandy loam surface soil,
• Uniform topographic conditions, and
• Moderate ground slopes

Sub-surface Irrigation

Sprinkler irrigation

it 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.

Sprinkling is the method of applying water to the soil surface in the form of a spray which is somewhat similar to rain.

Rotating sprinkler-head systems are commonly used for sprinkler irrigation.

Each rotating sprinkler head applies water to a given area, size of which is governed by the nozzle size and the water pressure. Alternatively, perforated pipe can be used to deliver water through very small holes which are drilled at close intervals along a segment of the circumference of a pipe

Sprinkler irrigation

Sprinklers have been used on all types of soils on lands of different topography and slopes, and for many crops.

The following conditions are favorable for sprinkler irrigation:

• Very previous soils which do not permit good distribution of water by surface methods,
• Lands which have steep slopes and easily erodible soils,
• Irrigation channels which are too small to distribute water efficiently by surface irrigation, and
• Lands with shallow soils and undulating lands which prevent proper leveling required for surface methods of irrigation

Pop-up Sprinkler

Pop-up Sprinkler

Portable Sprinkler

Advantages of Sprinkler

• Low water loss (efficiency up to 80%)
• Saving in fertilizer
• Suitable for any topography
• No soil erosion
• Better seed germination, free aeration of root zone
• Uniform application of water

Disadvantages Sprinkler

• High initial cost, cannot be adopted by ordinary farmers
• Poor application efficiency in windy weather and high temperature
• High evaporation losses
• Physical damage to crops by application of high intensity spray
• Water should be free of debris

Drip irrigation

It is sometimes called trickle irrigation and involves dripping water onto the soil at very low rates (2-20 litres/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.
• Suitable for high value row crops.

Drip Irrigation System

Drip Irrigation - Emitters

Advantages

• Low water loss and hence saves water
• Enhances plant growth and plant yield
• Saves labor and energy
• Control weed growth
• No soil erosion
• Improves fertilizer application efficiency

Disadvantages

• High skill in design, installation, and subsequent
• operation
• Clogging of small conduits and openings in emitters due to sand, clay particles, debris, chemical precipitates and organic growth
• Not suitable for closely planted crops such as wheat and other cereal grains

The End