Irrigation is defined as the artificial application of water to soil or land for farming puposes.  In other words, irrigation is the artificial application of water to the soil to supplement insufficient rainfall.  Irrigation is mainly practiced in areas where there is insufficient rainfall. Water is the most important determinant in the growth of crops. 

The choice of irrigation system depends on: (i) availability of water  (ii) slope of land  (iii) soil type  (iv) typees of crops and  (v) size of farmland

Aims of Irrigation

(i)            To add water to the soil to supply moisture for plant growth.

(ii)           To ensure the survival of crops during droughts.

(iii)          To cool the soil and the atmosphere, thereby making the environment more favourable for plant growth.

(iv)         To make early planting possible.

Importance or effects of Irrigation on crop production

The effects of irrigation on crop production are:

1. Irrigation softens the soil for easy tillage operations
2. It provides moisture in the soil for root absorption
3. It reduces the amount of salts accumulated in the topsoil, which could be harmful to crop plants.
4. It also cools the soil by reducing the soil temperature during the dry season when the soil temperature is very high. Plant growth is thus improved.
5. Irrigation enables the crop to be well established even when rain is erratic.
6. It increases crop productivity or crop yield
7. Irrigation provides a humid environment for the breeding of pest and pathogens of crops.
8. It helps in the improvement of microbial decomposition of organic manure to release nutrients for crop plants.
9. Irrigation dissolves nutrients for root absorption.
10. It assists in facilitating crop production all year round.
11. Irrigation encourages the spread of weed seeds.

Irrigation Systems

Irrigation systems or types can be grouped into three main classes:  Surface irrigation, sub-surface irrigation, and Overhead irrigation.

In the system, water from rivers, dams, or streams flows along the surface of the land to farmland.  This can be in the form of channels, flooding, contour ditch, furrow, basin, border dyke, border ditch, etc. The most important condition for surface irrigation to be efficient is for the land to have a gentle slope towards the direction of the farmland.

Advantage

•  It removes excess water caused by heavy rainfall, especially in heavy soils.
• It is easier to construct.
• Irrigation is cheap to establish and maintain.
• It prevents the accumulation of alkalis.
• It increases the activities of microbes in top topsoil.
• It helps in the collection and disposal of surface run-off.

Factors to be considered in choosing a surface irrigation method

• The topography or sloppy land
• The soil type
• The type of crop to be grown
• The size of the farmland.

In this system, water is applied below the soil surface by maintaining an artificial water level at a certain depth.  This, however, depends on the type of crop and the nature of the soil.  In all cases, perforated pipes are used to deliver water within the soil, and this water gets to the roots of crops through capillary action.

Advantages:

• By irrigation, it is possible to maintain water at the optimum depth for the crop’s needs.
• In addition, water use efficiency is high.
• It also ensures
• low evaporation losses from soils.
• It does not create obstruction or obstacles when carrying out cultural practices

Disadvantages:

• Water that has a high salt content cannot be used.
• It requires some level of expertise or technical know-how.
• It is a bit expensive

Factors to be considered in choosing a sub-surface irrigation method

The permeability of sub stratum

The level of the water table

Soil texture or capillarity

Soil structure.

Overheard irrigation

In an overhead irrigation system, water is supplied to the farmland above the surface of the soil.  Overhead irrigation exists in two forms:  Sprinkler Irrigation and Drip Irrigation.

(a) Sprinkler Irrigation: In this system, water is sprayed from the air and allowed to fall on the ground surface, somewhat as rainfall, through nozzles under high pressure.  A pumping machine that operates under high pressure is needed to pump water into irrigation pipes, which are spaced to ensure even distribution of water.

Advantages of Sprinkler Irrigation

• The amount of water supplied is regulated.
• It economises the use of water.
• It is suitable for high arid lands with a high evapotranspiration rate
• Soluble fertilizers, herbicides, etc., can be applied through the irrigation water.
• It can be used for all crops except tree crops, like cocoa.

Disadvantages of Sprinkler Irrigation

• Sprinkler irrigation is costly to operate
• High wind velocity may prevent the distribution of water
• A stable water supply is required
• It requires high power to produce the high pressure needed to pump water into pipes.
• There is a lack of sufficient technical know-how on sprinkler irrigation operation.

(b)  Drip Irrigation:  Drip or trickle irrigation is a new method of irrigation where water is discharged through nozzles called emitters or drippers at selected spacing to deliver water to the soil surface near the base of the plant.  With this system, loss of water through deep percolation, run-off, and evaporation is greatly reduced.

Advantages of Drip Irrigation

• It is economical in the use of water
• It reduces salt concentration in the root zone.
• Fertilizers can be applied through this system
• It operates with slower line pressure
• It is the most appropriate system needed in arid and semi-arid areas.

Disadvantages of Drip Irrigation

• It is very expensive to set up and maintain
• Water cannot be distributed in a sloppy farmland evenly
• Water with high salt content cannot be used

Problems Associated with Irrigation

There are many problems associated with irrigation, and these include:

• Inadequate water supply for irrigation
• Irrigation equipment is expensive
• Pests from dry surroundings may invade and damage crops in irrigated land.
• Disease-causing organisms increase with increasing humidity
• Vectors of disease, like snails, tsetse flies, breed freely in irrigated areas.
• Irrigation equipment is expensive to maintain
• Lack of adequate technical know-how on irrigation on the establishment and operations of the irrigation scheme.
• Excessive dissolution of salt in irrigated water prevents proper growth of corps.
• It may lead to pollution. If it contains dangerous chemicals
• It disturbs the free movement of farm machinery

How to reduce disease buildup in irrigated farms

Reduction of disease build up in an irrigated farm may be achieved through:

• Use of disease resistant varieties
• Crop rotation
• Use of appropriate chemicals
• Use of clean tools
• Use of clean or healthy planting materials
• Destruction of disease crops to prevent its spread.
• Avoidance of excessive irrigation
• Weed control

Methods of Irrigation a small nursery

A small nursery can be irrigated through:

• Manual sprinkling e.g., hand, brooms, brush
• Use of a watering can
• Drip irrigation
• Channel irrigation
• Sprinkler Irrigation

Sources of water for irrigation include rivers, lakes, streams, ponds, dams, bereholes, wells and reservoirs.

DRAINAGE

Drainage is a process whereby excess water in the soil is removed artificially to promote good farming activities.  In other words, drainage is the withdrawal of excess water from the soil while at the same time retaining adequate reserves to carry the crops through the periods of scarcity.

Importance or the effects of Drainage

The reasons for draining agricultural land include the following:

1. Drainage helps in reclaiming waterlogged soil for crop production
2. Drainage improves the soil structure, thereby improving the water-holding capacity of the soil
3. It improves soil aeration for good root respiration
4. It gives suitable conditions for the growth of soil microbes responsible for the decomposition of soil organic matter, which provides nutrients for plant growth.
5. It helps to increase the soil temperature for the benefit of crop plants.
6. Draining also leaches excess salts from the soil, thereby preventing the death of plants arising from poisoning.
7. It makes tillage operations easier
8. It reduces the incidence of crop diseases
9. It enhances the harvesting of crops, especially swamp rice.
10. It enhances the early planting of crops
11. Drainage makes land preparation easier
12. It reduces soil acidity
13. It increases the soil temperature
14. It increases crop production
15. It makes the soil workable or light.
16. Drainage reduces soil salinity.

Drainage Systems

There are two major systems or types of drainage.  These are surface and subsurface (underground) drainage.

Surface Drainage

This involves the orderly removal of excess water artificially from the surface of the land, using constructed open ditches, fid drains, and land grading.  Open ditches ensure easy evacuation of excess water from farmland.

Advantages of surface drainage

(i)            it is relatively easy to construct

(ii)           it is cheaper than the subsurface drainage system.

Disadvantages of surface drainage

(i) It occupies good land (space) that could have been used for planting

(ii) They hinder the passage of machines like tractors

(iii) They are prone to gully erosion

(iv) It requires frequent maintenance

(v) it increases the cost of crop production

(vi) Farm mechanization is impaired

(vii) It is expensive and difficult to establish

(viii) It makes the farm more prone to hazards, e.g., falling into an open drain.

Sub-surface/Underground Drainage

This is the orderly removal of excess water from the land, using tiles or moles or perforated pipes dug under the ground.  These collect water and channel it away from the farmland.

Advantages of sub-surface drainage

• It does not pose any threat to machines
• High-value crops are grown
• It leaves the field free from surface obstructions
• Soil is hard in place so that it would not damage the drainage pipes.
• More land is made available for cultivation
• The cost of maintenance is low

Drainage is faster and more efficient

Disadvantages of sub-surface drainage

• It is very expensive to operate
• It cannot be easily constructed
• It is difficult to maintain
• It needs a very deep excavation of the soil.Questions:

1. What is irrigation
2. State five importance of irrigation
3. What is sub-surface irrigation
4. State two advantages of sub-surface irrigation