IRRIGATION

1. 5. Irrigation

2. • Water is a critical requirement for crop production.
• For optimum crop production, moisture must be supplied in right
amounts and at right times. In certain regions, crops are entirely rain-fed,
and so they need no supplemental moisture supply for their growth and
development.
• However, summer crops require additional water supply for commercial
production.
• Many horticultural crops and ornamentals require a good supply of water
for high yield and superior quality.
• High-value crop production often relies on artificial moisture
supplementation.
• For small gardens, additional moisture may be delivered by using
buckets and watering cans. A garden hose may also be used for
watering garden crops.
• A continuous moisture supply for a given period is provided by a variety
of methods. Some of such methods are employed for large-scale
production and the others for small-scale production.

3. Methods of irrigation
• The method of irrigation, employed in a particular situation, depends on
several factors, such as the nature of the crop, source of water, slope of
the land, rainfall regime of the region, crop rotation, surface of the land,
etc.
• There are three general methods for supplying supplemental moisture to
plants, namely drip irrigation or trickle irrigation, sprinkler irrigation, and
gravity irrigation or surface irrigation.
• In sprinkler and drip irrigations, a pump may be required to move water
through pipes.
• But, gravity systems depend on the slope of the land to move water.
• G irrigation requires initial land preparation, such as leveling of the land
(in fi irrigation) or digging of ditches (in furrow irrigation).

4. (i) Drip irrigation or trickle irrigation

5. • This is the spot irrigation system in which minute amounts of water may be
sun. plied to plants almost continuously throughout the growing period.
• It is economical and highly desirable in areas where water availability is
limited.
• Plastic pipes with emitters are used to deliver water.
• Drip irrigation is especially desirable for high value crops that require uniform
soil moisture for good development.
• For example, when tuber crops, such as potatoes, are grown under conditions
of fluctuating moisture levels, tuber formation will be irregular, leading to low
market value.

6. Merits of drip irrigation
1. Saves water to the extent of 30 to 50 percent.
2. Increases the yield.
3. Reduces weed growth.
4. Lowers labour cost.
5. Causes the early maturing of crop due to the absence of moisture
stress.
6. Improves the quality of the produce.

7. (ii) Sprinkler irrigation

8. • Sprinkler irrigation is a method of irrigation that mimics rainfall by supplying
moisture from above.
• Its equipment may be as simple as a lawn sprinkler or garden sprinkler, or may
be a self-propelled system used in large commercial farms.
• The sprinkler system consists of portable or fixed pipes.
• Sprinklers are desirable in soils with high infiltration rates or uneven surfaces.
• Sprinklers are also used where irrigation is not the primary source of moisture
for crop growth.
• In this case, a portable irrigation system may be transported to the area when
needed.

9. (iii) Surface irrigation or gravity irrigation

10. • This is the irrigation in which water is distributed over the soil surface by
gravity.
• It is the commonest form of irrigation and it has been in practice over
thousands of years in many parts of the world.
• Surface irrigation is often referred to as flood irrigation, implying that water
distribution is not under control and hence inefficient.
• In reality, some of the irrigation practices grouped under this category involve
a significant degree of management.
• Surface irrigation is of three major types, namely level basin flood irrigation,
furrow irrigation and border strip irrigation or bay irrigation.
• These methods are not ideal for sandy soils or the soils that have high
infiltration rate, especially if water is to be moved over long distances.
• Flood irrigation is commonly used in orchards.
• Furrow irrigation is a version of flood irrigation in which the surface low is
limited to channels between ridges.
• Vegetable gardens may be irrigated in this way.

11. a) Level basin flood irrigation

12. • Level basin irrigation has been conventionally used in small areas having to
surface that are surrounded by earth banks.
• Water is applied rapidly to the entire basin and is allowed to infiltrate.
• Basins may be linked sequentially so that drainage from one basin is diverted
into the next, until the desired soil water deficit is satisfied.
• From a "closed" type of basin, no water normally drains out.
• Basin irrigation is favored in soils with relatively low infiltration rates.

13. b) Furrow irrigation

14. • Furrow irrigation involves making small parallel channels along the field length
in the direction of predominant slope.
• Water is applied to the top end of each furrow and allowed to flow down the
field under the influence of gravity.
• Water may be supplied using gated pipe or siphon.
• The speed of water movement is determined by many factors such as slope,
surface roughness, furrow shape, and most importantly the inflow rate and soil
infiltration rate.
• The spacing between adjacent furrows depends on crop species.
• Common spacing typically ranges from 0.75 to 2 metres.
• The crop is planted on the ridge between furrows either in a single row, or in
several rows.
• Furrows may range from 100 m to 2000 m in length, depending on the soil
type, location, and crop type.

15. • Furrow irrigation is particularly suited for raw crops, such as cotton, maize and
sugarcane.
• It is also practiced in the horticultural fields of citrus, stone-fruit and tomato.
• In furrow irrigation, water may take a considerable period of time to reach the
other end.
• So, water may infiltrate for a longer period of time at the top end of the field.
• This causes less uniformity, with high application of water at the top end and low
application at the bottom end.
• In most cases, the performance of furrow irrigation can be improved through
increasing the speed (the advance rate) at which water moves along the field.
• This can be achieved either through increasing the flow rate or through adopting
surge irrigation.

16. • Increasing the advance rate not only improves the uniformity, but also reduces
the total volume of water required to complete the irrigation.
• Surge irrigation is a variant of furrow irrigation.
• In this case, water supply is pulsed on and off in planned time periods (e.g., on
for 12 hour, and off for 2 hour)
• The wetting and drying cycles reduce infiltration rates resulting in faster
advance rates and higher uniformities than continuous flow.
• The reduction in infiltration results from surface consolidation, filling of cracks
and micropores, disintegration of soil particles during rapid wetting, and the
consequent surface sealing during the drying phase.
• The effectiveness of surge irrigation depends on soil type.
• For example, many clayey soils experience a rapid sealing behaviour under
continuous flow so that surge offers little or no benefit.

17. c) Border strip irrigation

18. • Border strip irrigation, or bay irrigation, could be considered as a hybrid of
level basin irrigation and furrow irrigation.
• The borders of the irrigated strips are longer and the strips are narrower than
in basin irrigation.
• Also, they are oriented lengthwise to align with the slope of the field.
• Water is applied to the top end of the bay, which is usually constructed to
facilitate free-flowing conditions at the downstream end.
• The common use of this technique is the irrigation of pastures for dairy
production.

19. Issues associated with surface irrigation
• Surface irrigation can be carried out effectively using the right management
under the right conditions.
• Still, it is often associated with a number of issues which undermine
productivity and environmental sustainability.
• Some of such issues are the following:
1. Waterlogging delays the further growth of plants, until sufficient water drains
from the root zone. Waterlogging may be countered by drainage.
2. Overirrigation may cause water to move below the root zone resulting in the
rising of the water table. In regions with naturally occurring saline soil layers,
the rising water table may bring salt to the root zone, leading to problems of
irrigation salinity.
3. Irrigation water may add significant amounts of salts to the soil profile. Lack
of subsurface drainage may restrict the leaching of these salts from the soil.
This can be solved by proper drainage and soil salinity control.