O Level Notes : Agriculture - Farm roads

Farm roads are pathways on which people and machinery use to move from one point to another around the farm. They are constructed by use of various materials.

The best roads should be wide enough to allow big and small machinery to move and have access to every corner of the farm. They should be constructed in such a way so as to be usable during rainy season. The roads should be maintained in order to keep them in good state all the time.

Materials required in road construction

The required materials include cement, gravel, quarry, water, drainage pipes, tar, bridge decks and steel rods.

Materials and their functions


It is mixed with quarry stones and rammed on top of gravel road in order to put tar on top. It is also used to mold concrete drainage pipes and for construction of slabs.


After levelling the road, gravel is put during road surfacing so as to improve drainage, increase strength, reduce slippery and also to reduce soil erosion.


It is mixed with cement to make a concrete mixture. This will be poured and rammed on the road surface to make a very strong hard surface.


It is usually mixed into concrete and poured on top of rammed gravel road. The resulting surface will be strong and dust free.

Bridge decks

These are slabs made of cement and concrete. They can be reinforced using steel rods at the centre. They are rectangular prisms in shape. They are put across the drainage trenches to allow the road to pass to the other side.

Steel rails

They can be put on the sides of bridges to guard vehicles from falling in the case of accidents. They can be put below the bridge to support the deck and make it strong.

Drainage pipes

They can be made of reinforced concrete and used to make culverts. A culvert is a structure whereby the concrete pipe is put below the road to allow water to drain from one side to another and the top is levelled and rammed as part of the road.


It is used when mixing cement and quarry to make concrete. Water can be poured on dust roads to suppress dust during dry season. Water can be fetched from dams, rivers, wells and boreholes.

Construction of farm roads

Farm roads are constructed using several equipment and machinery. The type of equipment and machinery to be used will depend on the availability and size of roads to be constructed. Road are normally constructed in winter when there are no rains. Rains will disturb by causing erosion on loose soil and the machinery will be sticking in clay soils during operations. Below are the steps to be followed when constructing farm roads.

  1. Siting

This is to locate the area on which the road is to be constructed. It is first done on the map. A plan is then drawn to scale on a piece of paper. This will guide the construction workers on the width, length and direction of the road. On the ground, the actual site is demarcated using pegs. During pegging, a dumpy level is used to calculate distance and gradient of different places.

  1. Clearance

This is to remove all the obstacles on the pegged area. All the vegetation is removed and big stones are also removed. This can be done manually using axes, shovels and mattocks. Machinery like caterpillars and bulldozers can be used when they are available.


  1. Ploughing

The purpose of ploughing is to loosen the soil so that it will be easily graded to fill the depressions and level the uneven areas. On large farms, tractor drawn ploughs are used.

  1. Grading

The reason is to fill the depressions and level the road so that a suitable gradient is achieved. A self-motorised or tractor drawn grader is used. It will be scrapping the soil from the road sides to fill all the uneven areas along the road and a cambered structure is made. Road should be cambered in order to drain the water to the sides which in turn will flow towards the mitre drains.

  1. Mitre drain construction

Mitre drains are drainage channels that are constructed on road sides to channel the water from the road sides to the water way. They are constructed at approximately 450 angle to the road. They should be relatively flat to reduce soil erosion and are also U- shaped to reduce runoff. They deposit water to the area covered with grass that is not prone to erosion. The spacing of mitre drains will depend on the soil type and road gradient. When the soil is loosely packed and the gradient is steep, mitre drains should be closely spaced to reduce the distance of water flow along the side of the road. When the soil is less prone to erosion, e.g. clay soils or when the gradient is gentle, then the spacing may be relatively wider.

  1. Road surfacing

This is done using gravel or laterite. Farm roads may not need tar as there are few traffic found on the farm and tar is relatively expensive as compared to gravel. Also other minor roads may not be surfaced using gravel as it require to be ferried from other places and there are costs involved. The gravel or laterite must be rammed to make the firm surface using tractor drawn rammers.

  1. Construction of culverts

Culverts are water drainage pipes that directs water through from one side of the road to the other. Usually the pipes are molded using concrete mixture and reinforcement steel in order to strengthen them. They are usually put in places where roads crosses water channels.

  1. Construction of inverts

Inverts are the road structures made up of strong concrete slabs. The slab can be cast on the area across the road to allow water to flow from one side to the other without eroding the soil. It is constructed wide enough to hold maximum amount of water that may flow across.

Maintenance of farm roads

The road require maintenance so as to keep them in good state for a long period of time. This can be done through the following activities;

  • Mitre drain clearance -This is done to remove all the blockages to allow free water movement.
  • Removal of soil and other wastes that were silted into the culverts and inverts.
  • Re-grading the road surface to fill the gulley, strips and holes caused by erosion and vehicle movement. Another purpose for re-grading is to reshape the road camper.
  • Road resurfacing can be done from time to time using gravel in order to improve drainage and reduce slippery surfaces. The gravel is rammed to become firm.
  • Clearance of trees, grass and shrubs. As time progresses, vegetation tend to encroach into the road thereby reducing the road width and disturbing the movement of vehicles and people. This should be cleared so that vehicles will move freely around the farm.
  • When they are bridges, the decks are checked for cracks and filled with mortar.
  • The bolts and nuts of the supporting beams are tightened or replaced when they are worn out.
  • Painting can be done on steel bars on the road sides to prevent rusting.


Here is what we discussed on this topic

  • Materials necessary for farm roads construction includes cement, gravel, quarry, water, drainage pipes, tar, bridge decks and rail steel roads.
  • When constructing farm roads, one can follow the steps below;
  • Siting and pegging- this is to locate the area on which the road is to be constructed and pegs are used to mark it.
  • Clearance- all the vegetation and unwanted material are removed to leave a bare surface.
  • Ripping and ploughing- this is done in order to make loose the soil along the pegged area. This can be done using a tractor drawn plough.
  • Grading – it is done in order to fill up the depressions with soil and to make a camper shape on the road.
  • Mitre drains are drainage channels that are constructed on road sides to channel the water towards the waterways. They should be flat to reduce soil erosion.
  • Road surfacing is done using gravel or laterite. Minor roads may not be surfaced because they are not always in use.
  • Culverts and inverts are constructed to allow water drainage from one side of the road to the other.
  • Farm roads can be maintained by resurfacing, re-grading, clearing the silt from inverts and culverts and also by cutting trees and shrubs along the roads.



Definition of terms used in this topic

  • Quarry – these are stones that are broken into smaller pieces of about 1-3cm diameter.
  • Reinforce- is to strengthen using steel rods that are put at the middle when moulding concrete slabs.
  • Depression – is a low lying area surrounded by a raised area.
  • Camber – is a dome shape on the road surface that allows it to drain water to the road sides.
  • Self-motorised- having the mechanism of driving itself.
  • A mitre drain – is a structure at the edge of the road that carries water from road surface to the waterway.
  • Culvert – it is a concrete reinforced pipe that is placed below the road to drain water across it.
  • Invert – is the slab that is set on the road surface to allow water passage from oneside to the other.