- Soil and water are two very important natural resources in farming.
- They should therefore be well maintained and used without wastage to sustain continuous production.
- Water loss during the rainy season should be prevented and excess water conserved for use during scarcity.
- Soil erosion must be controlled at whatever cost if soil is to be conserved.
- It is the removal and carrying away of the top soil by the action of water or wind.
Factors Influencing Soil Erosion
Amount and intensity of rainfall.
- The steeper the land the higher the velocity of surface runof
- The higher the velocity of surface runoff the greater is its erosive power/effect.
Type of soil for example sandy soils are more easily detached and carried away than clayey soil
- The deeper the soil, the longer it takes to be saturated with
- Overstocking leads to bareness of the land and looseness of the soil.
- Deforestation – indiscriminate removal of trees leads to exposure of soil to heavy rainfall and high te
- Indiscriminate burning of vegetation exposes the soil to erosive agents.
- Clean weeding leaves the soil bare.
- Ploughing along the slope.
- Monoculture or continuous cultivation.
- Trees act as windbreakers.
- Roots of vegetation cover hold the soil particles together.
- Leaf fall act as mulch which reduces erosion.
- Leaves of vegetation cover intercepts raindrops reducing their erosive power.
Agents of Erosion
- Water – moving water has erosive power.
- Wind – wind carries away soil.
- Human beings – through man’s activities such as cultivation and mining.
- Animals – through overgrazing and creating footpaths where soil erosion takes place.
Types of Erosion
- Raindrop (splash) – displacement of the soil caused by raindrops.
- Sheet – uniform removal of soil in thin layers from flat or gently sloping areas.
- Rill – removal of soil from small bur well defined channels or rills.
- Gulley – removal of soil from channels which become progressively deeper and wide
- Riverbank Erosion – removal of soil along river banks by the river water.
- Solifluction – gravitational flow of soil saturated with wa
- Land slides – mass movement of rock debris and soil down a slope,
- Slip movement of earth or rock masses for a short distance.
- Debris slide – materials move at a greater speed.
- Debris fall – movement of materials/debris along vertical cliff.
- Rock fall – movement of rock down a very steep slope.
- Rock slides – mass of rock materials that slide along a bedding plate, a joint or a fault face.
Soil Erosion Control Measures
Soil conservation measures can be classified into:
- Biological or cultural control
- Physical or structural control
Biological or Cultural Control Measures
These measures are applicable where land slope is between 2-12%.
Grass strips/filter strips; These are narrow uncultivated strips along the contour left between cultivated strips.
Cover cropping ;
- The establishment of a crop that spreads out over the surface of the soil to provide it with a cover.
Contour farming ;
- Carrying out all land operations along the contour.
- Covering of the soil with either organic or synthetic materials.
Proper cropping systems such as:
- Crop rotation
- Correct spacing
- Strip cropping
- Proper stocking rate, rotational grazing.
- Growing crops which give little ground cover in alternate strips with crops such as beans which have a good ground cover.
Afforestation – growing of trees where non-existed.
Re-afforestation – growing of trees where they have been cut down.
Agroforestry – land use that involves the growing of trees in combination with crops and pastures on the same piece of land.
Physical or Structural Control Measures
- These are soil and water conservation measures which involve mechanical constructions on the earth.
- They are used in areas of moderate slope between 13-55%.
Trash or stone lines;
- These are rows of heaped crop’ residues or stones made along the
- It involves the growing of an open crop in the upper side of the slope followed by a dense crop to reduce speed of wate
- This increases infiltration.
- Are structures constructed across a slope to reduce the length of a slope thus reducing run-off.
- Are constructed where the slope is 35-55%.
- Tree crops are suitable for such areas.
Importance of a Bench Terrace: –
- Reduces slope of the land.
- Conserves soil moisture.
- Better retention of soil fertility.
Narrow based terraces –Cannot allow cultivation by machines.
Broad based terraces – Is wide enough to allow cultivation by machines.
- Have a drainage channel to lead off excess water to a vegetated place
- They should be about 100m in length.
- Have no outlet channels,
- The aim is to have water infiltrating,
- Hence no water can flow from the ends of the terrain
- A ridge made by digging a channel and throwing the soil uphill.
- In this case the soil is heaped on the lower side of the channel.
Bunds: heaps of soil (earth) made along the contour.
- An open trench with an embankment on the lower side into which water from the farm dra
Water from the trench should be discharged into;
- Natural waterways,
- Artificial waterways,
- Rocky ground
- Galvanized wire mesh boxes filled with stones which are built across slopes and gullie
Dams and reservoirs ;
- Dams – barriers built across a river/waterway to hold and store water. It reduces speed of runoff.
- Reservoirs – these are large storage ta
Ridging – heaps of soil to reduce the speed of water,
They retain the water for some time.
Water Harvesting Methods
- Water harvesting and storage should be done during the rainy seasons to avoid wastage.
This should be done using the following methods:
- Roof catchment – trapping and collection of rain water from roof tops.
- Rock catchment – water is harvested by constructing a barrier on the lower side of a large impervious rock to trap surface runoff from the rock.
- Weirs and dams.
- Dam – a barrier constructed across a river or a dry valley so that it can hold water.
- Weirs – barriers constructed across a river or a stream to raise the water level and still allow water to flow over it.
- Ponds – water retention excavations‘ made to hold excess surface water.
- Retention ditches/level terraces.-These are terraces constructed with blocked ends to retain water.
- A system of harvesting limited rainfall and storing the water in the ground for use by the planted crops.
Types of Microcatchments;
- V-shaped bunds measuring 25cm
- Are built with soil from the excavated planting holes to direct runoff water towards the basin area around the base of each plant
- Formed around the growing plant to hold water around the plant.
- Trapezoidal shaped bunds, which enclose a large area where the crops are grown.
Contour bunds/furrows ;
- These are furrows made along the contours between the rows of crops where agroforestry trees are intercropped with annual cro
Planting holes/pits ;
- These are extra large planting holes made and filled with dry plant materials before filling in with soil.
Use of Micro-Catchments
- Slow down the speed of surface runoff.
- Used during landscaping of the compound, parks and roadside nest areas.
- Reclamation of land for food crop in dry areas.
- Water collected and stored can be used for irrigation
- Afforestation in dry areas.