Drainage Is the removal of excess water from the soil.Excess water may be as a result of flooding,excess application of irrigation HO2 or even natural precipitation (rain)
Types of drainage
(i) surface drainage
(ii) Sub surface drainage
(iii) Sub soiling
(iv) Use of deep rooted crops.
Here water is led away by channels constructed on the soil surface.
The water then flows down the slope due to the pull of gravity.
ADVANTAGES OF SURFACE DRAINAGE
- It is cheap to install
- It is relatively easy to maintain
- It is highly effective because of large surface area that they provide for seepage of water into the ground.
DISADVANTAGES OF SURFACE DRAINAGE
- The ditches occupy space that would be used for growing crops.
- Ditches may lead to excessive depressions of HO2 table which may lead to complete drying of soil.
- Ditches/channels interferes with agriculture operations, Livestock since animals may drop in the ditches.
- Channels are very prone to soil erosion and may develop into gullys.
SUB SURFACE DRAINAGE
Here drainage channels are constructed below the ground surface. Excess water in the soil moves under the influence of gravity from the soil and enters the drains.
Forms of subsurface drainage;
(i) Tile and pipe drainage; here perforated plastic pipes are used, they are buried 50 – 60cm below the ground.
(ii) Stone drainage/use of Rubbles
Here channels are constructed on certain areas in the field; filled with stones, followed by covering soil.Water slowly drains into these channels and then flows away.
ADVANTAGES OF SUB SURFACE DRAINAGE
- The system does not interfere with farm operations
- There’s no wastage of land since the drains are below the ground.
- Once installed, there’s no maintenance costs incurred
- There’s less risk of gully erosion than in the surface drainage
- It removes only excess HO2 but not the water required by plants.
DISADVANTAGES OF SUB SURFACE DRAINAGE
- It is very expensive to install
- Requires skilled labour
- Once it is damage, it is difficult to maintain, to locate the blocked part of the pipes.