Irrigation Systems

IRRIGATION

Irrigation is the bringing of water unto the land or to crops from a major source by some means e.g. a drain or canal.

Benefits of Irrigation

Steady yield from crops
Better quality products
Better use of inputs/resources
Better land use
Provide the optimum condition for reaping certain crops

Methods of Irrigation

There are several methods of irrigation. The more commonly known ones are:

Surface Irrigation
Overhead irrigation
Drip Irrigation

Surface Irrigation

Surface irrigation is an effective method of applying rain and/or surface water to irrigate crops by taking advantage of gravity and the shape of the land to either partially or completely “flood” the soil.

It is the easiest and cheapest method requiring the least technical knowledge, equipment, setup and maintenance.

However, it is heavily dependent on terrain to be successful and can lead to waterlogging if care is the correct preventative measures are not taken.

Surface Irrigation comprises:

1. Channel Irrigation
2. Furrow Irrigation
3. Flooding

Channel and Furrow Irrigation

Using siphons to support furrow irrigation.

Channel Irrigation

Water from a source or reservoir is pumped into the main channel and will flow into smaller channels.

Furrow Irrigation

Water flows from a source into the furrows.

Furrows are small, parallel channels, made to carry water in order to irrigate the crops grown on the ridges between the furrows.

The following crops can be irrigated by furrow irrigation:

- row crops such as maize, sunflower, sugarcane, soybean;

- crops that would be damaged by inundation, such as tomatoes, vegetables, potatoes, beans;

- fruit trees such as citrus, grape;

- broadcast crops (corrugation method) such as wheat.

Practical Activity: Research the corrugation method. Make summarized notes in your portfolio.

Uniform, flat or gentle slopes are preferred for this type of irrigation although it can be done on undulating land if the furrows follow the land contours.

Soils that crust easily are especially suited to furrow irrigation because the water does not flow over the ridge, and so the soil in which the plants grow remains friable. Very coarse sands are not recommended as percolation losses can be high.

Runoff at the ends of furrows can be a problem on sloping land, therefore a shallow drain should always be made at the end of the field, to remove excess water and prevent waterlogging.

Light vegetation can be allowed to grow in the drain to prevent erosion. Excessive runoff can be prevented by reducing the inflow once the irrigation water has reached the end of the furrows. This is called cut-back irrigation.

Consider the ideal method for constructing an irrigation channel (canal) in the diagram below:

Construction of Irrigation Canals

Consider the irrigation canals in Guyana...

What are the differences between canals in Guyana and the ones shown in the picture?

Which canal do you think would be better at reducing overtopping (water flowing over the banks of the canal)?

Which canal do you think would be better at preventing erosion of the banks?

Which would be more costly?

Which would require more effort to construct?

Would it be better for the irrigation canals in Guyana to be constructed after this fashion?

Flooding (Basin Irrigation)

This method is necessary for some crops such as rice and sugar cane cultivation. It is done on low lying areas or on slopes using terraces.

Bunds (a.k.a. ridges, dykes or levees) are small earth embankments used to contain irrigation water within basins.

Basin irrigation is suitable for many field crops, especially those that grow best when their roots are submerged in water.

Other crops which are suited to basin irrigation include:

- pastures, e.g. alfalfa, clover;

- trees, e.g. citrus, banana;

- crops which are broadcast, such as cereals;

- to some extent row crops such as tobacco.

Basin irrigation is generally not suited to crops, such as root and tuber crops, which cannot stand in wet or waterlogged conditions for periods longer than 24 hours.

The size of the basin depends on several factors. Basins should be small if the:

1. slope of the land is steep;

2. soil is sandy;

3. stream size to the basin is small;

4. required depth of the irrigation application is small; and/or

5. field preparation is done by hand or animal traction.

Basins can be large if the

1. slope of the land is gentle or flat;

2. soil is clay;

3. stream size to the basin is large;

4. required depth of the irrigation application is large;

5. field preparation is mechanized.

There are two methods to supply irrigation water to basins: the direct method and the cascade method.

In the direct method, irrigation water is led directly from the field channel into the basin through siphons, spiles or bundbreaks. The cascade method is used on sloping land, where terraces are used; the irrigation water is supplied to the highest terrace, and then allowed to flow to a lower terrace and so on .

Terrace Flooding

Water enters the basin through bundbreaks

Bundbreaks

Siphons

Spiles

Overhead (Sprinkler) Irrigation

In this method, water is applied to crops through sprinklers and jet sprays. 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.

The main objective of a sprinkler system is to apply water as uniformly as possible to fill the root zone of the crop with water.

The uniformity of sprinkler applications can be affected by wind and water pressure. Wind can blow water droplets away and too low or too high a water pressure can cause water to be distributed poorly among the crops.

This system comprises of a:

Water source
Pump
Distribution lines
Sprinklers

Sprinkler irrigation is suited for most row, field and tree crops and water can be sprayed over or under the crop canopy. However, large sprinklers are not recommended for irrigation of delicate crops such as lettuce because the large water drops produced by the sprinklers may damage the crop. Sprinkler heads may be rotary sprinklers or spray sprinklers.

The rotary sprinkler system rotates by force of water action usually against a spring loaded lever. The stream of the water form an outlet deflects the lever which then returns to its original position by spring tension. As this action is repeated, the sprinkler continues to turn, thereby making a complete rotation. This system spreads water over a wider area.

In the spray sprinkler system, water flows through a perforated head. It is used when applying water over a smaller distance.

Sprinkler irrigation is adaptable to any farmable slope.

Sprinklers are best suited to sandy soils with high infiltration rates although they are adaptable to most soils. Sprinklers are not suitable for soils which easily form a crust.

It is the most versatile system of irrigation and is the most cost-effective way or irrigating last tracts of land.

A good clean supply of water, free of suspended sediments, is required to avoid problems of sprinkler nozzle blockage and spoiling the crop by coating it with sediment.

Setting up and maintaining a sprinkler irrigation system can be very costly.

A Sprinkler Irrigation System Layout

Types of Sprinkler Heads

Drip Irrigation

Drip or trickle irrigation, in a nutshell, is the process of lacing your garden area with irrigation lines that feed directly into the root systems of your plants, “dripping” water into them gradually. This is the most popular and most efficient system because it allows you to directly hydrate your plants without having to water the surface.

Drip systems are much more efficient in their net water usage than surface watering systems where much more water is used and most of the water used doesn’t even make it to the soil. Water emitted is less prone to evaporation or loss by wind. As such this system is most suitable when water is scarce and of poor quality (saline

A drip system is usually permanent and can easily be automated. This is very useful when labour is scarce or expensive to hire. However, setup, automation and maintenance requires specialist skills to make the system most effective and so this approach is unsuitable if such skills are not available.

It is also prone to problems. One of the main problems occurs due to blockage of the emitters which have very small waterways ranging from 0.2-2.0 mm in diameter. Sediments can block the emitters and so the irrigation water should be completely free of sediments or thoroughly filtered before entering the pipes. Blockage may also occur if the water contains algae, fertilizer deposits and dissolved chemicals which precipitate such as calcium and iron.

Drip irrigation is most suitable for row crops (vegetables, soft fruit), tree and vine crops. Generally only high value crops are considered because of the high capital costs of installing a drip system. Water can be applied frequently (every day if required) with drip irrigation and this provides very favourable conditions for crop growth. However, if crops are used to being watered each day they may only develop shallow roots and If the system breaks down, the crop may begin to suffer very quickly.

Also, since water spread is restricted to plant roots, weed growth is reduced due to the lack of water.

Drip irrigation is adaptable to any farmable slope.

Drip irrigation is suitable for most soils. Water must be applied slowly on clay soils to avoid surface water ponding and runoff and more rapidly on sandy soils to ensure adequate lateral wetting of the soil.

Components and Layout of a Drip Irrigation System

Dripline Components

Considerations when establishing Drip Irrigation

Irrigation Methods Overview

Transcript for Video

Modern Irrigation.

We have different modern techniques of irrigation. Let us learn about this one-by-one.

Furrow irrigation: water is allowed to enter the field through channels or furrows that are made between two rows of crops crops such as tomatoes leafy vegetables and grapes are grown using this method of irrigation.

Basin irrigation: a basin is formed by surrounding a flat piece of land with low walls made of mud it is then flooded with water so that the roots of the crops are submerged in the water paddy, for example, grows best when its roots are completely under water.

Sprinkler irrigation: the water is dispersed through sprinklers which have perpendicular pipes with rotating nozzles on top the pipes are joined to the main pipeline at regular intervals when water is pumped through the main pipe under pressure it escapes out from the rotating nozzles in the form of rain.

Drip irrigation: in this type of irrigation the water is made to trickle or fall down drop by drop near the roots of the plants this method ensures a minimum wastage of water it is useful in places where water is not easily available

Choice of Irrigation System

The choice of irrigation system depends on the following:

Soil type
Crops grown (whether shallow or deep rooted)
Stage of growth of crops (whether early or late stage)
Availability of water
Topography
The economics of the venture
The labour force available

Irrigation in Guyana

The National Drainage and Irrigation Authority (NDIA) is responsible for maintaining the drainage and irrigation systems within Guyana.

Learn more about the NDIA through this Practical Activity.

Generally, in Guyana, we use surface irrigation where water is allowed to flow from nearby water conservancies into canals and then into drains and other waterways.

The flow of this water is controlled naturally or artificially by kokers.

Water can also be pumped from canals into furrows, fields, drains and reservoirs using mechanical pumps.

This system has its disadvantages as water can be contaminated and the entire field of crops can be destroyed as a result of the use of contaminated water.

Sprinkler Systems and Drip Irrigation Systems are also used to a lesser extent.

In smaller, intensive farming or kitchen gardens , water is obtained from the national potable water supply grid supplied by the Guyana Water Incorporation.gardens.

Irrigation by watering cans with fine roses is effectively used in small nurseries, kitchen gardens and small farm plots. This allows the farmer to cultivate a large variety of crops independent of rain fall pattern. However, this source of water can be limited and farmer have to be careful not to waste it

Koker

Mechanical pumps

Watering Cans

Irrigation Systems Quiz

1. Which definition is MOST accurate?

a. Irrigation refers to the removal of water from the land.

b. Irrigation generally refers to bringing water unto the land.

c. Irrigation refers to the provision of water to crops by different means.

d. Irrigation refers to providing water for plants through drains and canals only.

2. Which of the following is NOT a reason for irrigation?

a. To provide the optimum conditions for growing certain crops.

b. To prevent the waterlogging of soils.

c. To improve the quality of crops.

d. To allow for the growth of crops in times of water shortage.

3. What are the three main methods of irrigation?

a. channel, furrow, drip

b. surface, overhead, drip

c. channel, furrow, flooding

d. surface, channel, drip

4. What are the three methods of surface irrigation given in the notes?

a. channel, furrow, drip

b. surface, overhead, drip

c. channel, furrow, flooding

d. surface, channel, drip

5. Which is the definition for surface irrigation?

a. Applying water to crops using gravity and the shape of the land.

b. Applying water in the form of droplets released through sprinklers or jet sprays.

c. Submerging crops in water on land surrounded by earth bunds.