Irrigation And Drainage SS2 Agricultural Science Lesson Note

IRRIGATION

Irrigation is the artificial application of water to soil or land for farming purposes.

FACTORS THAT DETERMINES IRRIGATION SYSTEM

1. Availability of water.
2. Slope of the land.
3. Soil type.
4. Type of crop.
5. Size of the farmland.

IMPORTANCE OF IRRIGATION IN CROP PRODUCTION

1. Irrigation softens the soil for tillage operations.
2. It provides moisture in the soil for root absorption.
3. It reduces the amount of salt accumulated in the topsoil which could be injurious to the crops.
4. It cools the soil, thereby reducing soil, theoretically reducing soil temperature.
5. It enables crops to do well.
6. It increases crop productivity and yields.
7. It assists in the production of crops all around the year.
8. It helps in microbial decomposition and nutrient release to the soil.
9. It dissolves soil nutrients for root absorption.

NEGATIVE EFFECTS OF IRRIGATION

1. It provides a humid environment which favours the buildup of pests and diseases. 
2. It encourages the spread of weed seeds.

TYPES OF IRRIGATION SYSTEMS   

The three types of irrigation systems are:

1. Surface irrigation 
2. Sub-surface irrigation 
3. Overhead irrigation

i. SURFACE IRRIGATION

In this system, water from rivers, dams or streams flows along the surface of the land to the farmland. This can be in the form of channels, flooding, contour ditches, furrows, basins etc. This type of irrigation requires a gentle slope to be successful.

Advantages Of Surface Irrigation

1. It removes excess water caused by heavy rainfall.
2. It is easier to establish or set up.
3.  It is cheap to maintain.
4. It prevents the accumulation of alkali.
5. It increases the activities of microbes in the soil too.

Disadvantages Of Surface Irrigation

1. It cannot be practised where land is hilly. 
2. It cannot be successful in sandy soil. 
3. The volume of water, especially in flooding, may be difficult to control.
4. Some crops may not tolerate heavy flooding.

2. SUBSURFACE IRRIGATION

In this system, water is applied below the soil surface. It involves the use of perforated pipes to deliver the water within the soil. This water gets to the root through capillary action.

Advantages Of Subsurface Irrigation

1. It is possible to maintain water at optimum depth for crop needs.
2. Water used efficiently.
3.  It ensures low evaporation losses from the soil.
4. It does not create obstruction when carrying out cultural practices.

Disadvantages Of Subsurface Irrigation

1. Water with high salt content cannot be used.
2. It requires some level of expertise or technical know-how.
3. It is a bit expensive.

3. OVERHEAD IRRIGATION

In this system, water is supplied to the farmland above the surface of the soil.

Problems Associated With Overhead Irrigation

1. Wind can cause uneven distribution of water by distorting the sprinkler pattern.
2. The spray force can damage the ripening of soft fruits.
3. A stable water supply is needed for the economic use of the equipment.
4. The initial investment is usually high.
5. Power requirement for pumping water is high.
6. Requires technical know-how.
7. It can spread diseases.
8. Lateral pipes hinder the movement of farm machines.
9. High cost of maintenance, repair and spare parts.

There are two types of overhead irrigation:

a) Drip irrigation

b) Sprinkler irrigation 

a) Sprinkler Irrigation

In this system, water is sprayed from the air and allowed to fall on the ground like rain through a nozzle under pressure.

Advantages Of Sprinkler Irrigation

1. The amount of water supplied is regulated.
2. It economizes the use of water.
3. It is suitable for arid lands with a high evapotranspiration rate.
4. It can be used for all crops except tree crops.  
5. Soluble fertilizers and herbicides can be applied through the irrigation water.

Disadvantages Of Sprinkler Irrigation

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

b) Drip Irrigation

Drip irrigation is a method whereby water is discharged through nozzles called emitters or drippers at a selected spacing to deliver water to the soil surface near the best of the plant.

Advantages Of Drip Irrigation

1. It is economical in the use of water.
2. It reduces salt concentration in the root zone.
3.  Fertilizers can be applied through the system.
4. It operates in slower and arid areas.

Disadvantages Of Drip Irrigation

1. It is very expensive to set up and maintain.
2. Water cannot be distributed in sloppy farmland evenly.
3. Water with high salt content can be used.

PROBLEMS ASSOCIATED WITH IRRIGATION

1. Inadequate water supply for irrigation.
2. Irrigation equipment is expensive.
3. Pests from the surrounding area may invade irrigated areas and damage crops.
4. Disease-causing organisms increase with increased humidity.
5. Vectors eg. Snails and tsetse flies breed freely in irrigation areas.
6. Lack of technical-know-how.
7. Excessive dissolution of salt affects crops.
8. It disturbs the free movement of farm machinery. 

HOW TO REDUCE DISEASE BUMPS IN IRRIGATION FARM

1. Use of disease-resistant varieties.
2. Crop rotation.
3. Use of appropriate chemicals.
4. Use of clean tools.
5. Use of clean or healthy planting materials. 
6. Destruction of infected crops to prevent the spread of diseases.
7. Avoidance of excessive irrigation.
8. Weed control.

DRAINAGE

Drainage is the process whereby excess water in the soil is removed artificially to promote good farming activities.

IMPORTANCE OR EFFECTS OF DRAINAGE

1. It helps in regaining water-logged soil for crop production.
2. It improves soil structure and water-holding capacity of the soil.
3. It improves soil aeration for good root respiration.
4. It gives suitable conditions for the growth of microbes which helps in decomposition.
5. It helps to increase soil temperature.
6. Drainage leaches excess salt from the soil which prevents poisoning and death of the plants.
7. It makes tillage operations easier.
8. It reduces the incidence of crop diseases. 
9. It enhances the harvest of crops e.g. swamp rice.
10. It enhances the early planting of crops.
11. It makes land preparation easier.
12. It reduces soil acidity.
13. It increases soil temperature.
14. It increases crop production. 
15. It makes soil workable and light.
16. It reduces soil salinity.

TYPES OF DRAINAGE

1. Surface drainage
2. Subsurface drainage

1. SURFACE DRAINAGE

This involves the orderly removal of excess water artificially from the surface of the land using constructed open ditches, field drains and land grading.

Advantages Of Surface Drainage

1. It is relatively easy to construct.
2. It is cheaper than the subsurface drainage system.

Disadvantages Of Surface Drainage

1. It occupies good land (space) that could have been used for planting. 
2. It hinders the passage of machines like tractors.
3.  It is prone to gully erosion.
4. It requires frequent maintenance.
5. It increases the cost of production. 
6. Farm mechanization is impaired.
7.  It is expensive and difficult to establish.

2. SUBSURFACE DRAINAGE

This is the orderly removal of excess water from the land using tiles moles or perforated pipes dug under the ground, it is also called underground drainage.

Advantages Of Surface Drainage

1. It does not pose any threat to machines.
2. High values of crops are grown.
3.  It leaves the field free from surface obstruction.
4. More land is made available for cultivation.
5. Cost of maintenance is low.
6. Drainage is faster and more efficient.

Disadvantages Of Subsurface Drainage

1. It is very expensive to operate.
2. It cannot easily be constructed.
3. It is difficult to maintain.
4. It needs very deep excavation of the soil.