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 EFFECTS OF DRAINAGE
The reasons for draining agricultural land include the following:
- Drainage helps in reclaiming waterlogged soil for crop production.
- Drainage improves the soil structure, thereby improving the water-holding capacity of the soil.
- It improves soil aeration for good root respiration.
- It gives suitable conditions for the growth of soil microbes responsible for the decomposition of soil organic matter which provides nutrients for plant growth.
- It helps to increase the soil temperature for the benefit of crop plants.
- Drainage also leaches excess salts from soil, thereby preventing the death of plants arising from poisoning.
- It makes tillage operations easier.
- It reduces the incidence of crop diseases.
- It enhances harvesting of crops, especially swamp rice.
- It enhances early planting of crops.
- Drainage makes land preparation easier.
- It reduces soil acidity.
- It increases the soil temperature.
- It increases crop production.
- It makes the soil workable or light.
- Drainage reduces soil salinity.
TYPES OF DRAINAGE SYSTEMS
There are two major systems or types of drainage.” These are surface and subsurface (underground) drainage.
a) 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. Open ditches ensure easy evacuation of excess water from farmland.
Advantages of Surface Drainage
- It is relatively easy to construct.
- It is cheaper than the subsurface drainage system.
Disadvantages of Surface Drainage
- It occupies good land (space) that could have been used for planting.
- They hinder the passage of machines like tractors.
- They are prone to gully erosion.
- It requires frequent maintenance.
- It increases the cost of crop production.
- Farm mechanisation is impaired.
- It is expensive and difficult to establish.
- It makes the farm more prone to hazards, e.g. falling into an open drain.
b) 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 drainage pipes.
- More land is made available for cultivation.
- 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 very deep excavation of the soil.