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Suggested Learning activities
1.Visit a mixed farm where various soil conservation measures can be observed.
2.Make models of soil erosion control measures.
3.Survey and identify the various water harvesting methods used in the local environment.
4.Learners to carry out soil and water conservation work in and out of school.
Before you begin this lesson, you should have covered soil fertility ,which is the ability of the soil to provide nutrients in their proper proportions. Soil fertility can however be lost through;
2.Burning the land
3.Accumulation of salts
4.Unfavourable changes in soil pH.
5. Soil erosion
Ag3-0500001B Photo- showing gully erosion
Maintenance of soil fertility
Soil is very important in agricultural production since it is a source of water, minerals and provides anchorage to plants which livestock depends on. Farmers must therefore strive to apply all the available principles to the solution of water and soil management problems.
Ag3-0500002B Photo-of a fertile land having healthy growing maize crop at silking stage.
Bunds-these are heaps of soil along the contour constructed to facilitate better erosion control. Contour farming-this is where tillage and planting are done across the hill to create ridge of earth which hold up water and reduce water run-off. Filter strips-these are uncultivated strips measuring at least 1-2 meter wide and are normally of grass. Gully erosion-a type of erosion in an advanced stage of rill erosion where channels becomes deeper and wider. Land slide-group name for several types of mass movements of soft rock debris down slope or mountain side. Negarims-these are regular squares made of soil bunds 25cm high which concentrate run-off water at lower corner of the square. Rill erosion-removal of soil by water from small but well defined channels . Splash erosion-soil splash resulting from the impact of water drops directly on soil particles dispersing the particles by detaching them. Solifluction erosion-gravitational flow of surface materials saturated in water
By the end of the lesson you should be able to
i.Define soil erosion
ii.Explain the various factors that influence soil erosion
iii.List the agents of erosion
iv. Describe the various types of erosion
v.Describe the various methods of soil erosion control
vi Carry out soil erosion control measures
viiDescribe water harvesting and conservation techniques
viii Describe micro-catchment and their uses
ix Design and construct a micro-catchment.
Soil and Water Conservation
Soil and water conservation is the application of principles to the solution of soil and water management problems. In this topic, you are going to cover :
3.Methods of soil and water conservation
Ag3-0500000movie Insert a video clip showing a school teacher with student planting trees in a school compound.
Insert a video clip showing Government officials planting trees in Mau forest.
Soil erosion is the process by which soil is detached , removed and carried away from one place to another by erosive agents. Serious soil erosion leads to deterioration of soil surface through loss of large volumes of soil.
Ag3-0510001Anim(sketch given within the written script)
Moving water detaching soil particle, removing and carrying it away from point A to point B as illustrated below
Click the play button to see the video on effects of soil erosion by water
Factors influencing rate of erosion
Rate of soil erosion is never constant. It highly depends on land use, extent of ground coverage by vegetation, topography ,type of soil and rainfall intensity. For example , there is higher rate of soil erosion where the land is steep than on a flat land.
Effects of soil erosion
The effects of soil erosion include ;
1.Loss of top fertile soil
2. Loss of useful micro-organisms
3.Deposition of eroded materials in dams and other water reservoirs
4.Damage to infrastructures such as roads and water pipes.
Types of water erosion
Water erosion is the erosion caused by moving water. The types of water erosion include;
1 .Splash erosion 2.Sheet erosion 3.Rill erosion 4.Gully erosion 5.River bank erosion
Solifluction is the gravitational flow of surface materials saturated with water. It is a process through which the earth flows from steep slopes as a result of heavy rainfall. The factors that influence solifluction are ; 1. The slope of land 2. The nature of material 3. Climate 4. Vegetation cover 5. Human activities 6. Forces within the earth crust
Effects of solifluction erosion
Movement of materials during solifluction erosion present far reaching effects, especially along the slopes. Common effects of solifluction erosion include ; 1.Increase in soil fertility where eroded materials are deposited 2.Creation of lakes 3.Damage to property and infrastructures 4.Loss of lives 5.Permanent scars on the landscape 6.Creation of tourist attraction sites eg. Weeping Stones in Kakamega district
Landslide is a sudden rotational movement of a mass of soil or rock along a more or less semi-circular slip surface. It therefore refers to several types of mass movement of rock debris down a slope or mountain side. Types of landslides include; 1.Slump 2.Debris slide 3.Debris fall 4. Rock fall 5.Rock slide
Wind erosion is the result of material movement by wind.It occurs when wind is travelling through the air, and it picks objects and materials including soil up. In wind erosion , movement of soil particles is of great distance especially in places where there are no barriers. Apart from causing erosion, strong wind also damages farm crops and farm buildings.
Erosion caused by mans activities
Some mans activities facilitate soil erosion.
Some of these activities include deforestation, burning of land, quarrying, mining, and sale of soil. Keeping large herds of livestock leading to overgrazing is a major cause of erosion in arid areas.
Click the play button to see the video on mans activities
Soil erosion control
Soil erosion has adverse effects on farming and this has created great concern to the Kenyan government. The Government and some Non-Governmental Organizations ( NGOs) are creating awareness about soil erosion and identifying appropriate methods to be used in soil and water conservation which are effective and economical. The common soil conservation measures used in Kenya can be classified into two categories, namely; 1. Biological or cultural control methods 2. Physical or Structural control methods
Cultural methods of soil erosion control.
Cultural methods of soil erosion control include all recommended farming practices which help to minimize soil erosion. Examples of cultural methods of soil erosion control include grass strip, cover cropping, mulching, grassed waterways and contour farming.
Click the play button to see the video on soil and water conservation
Grass strip involves leaving uncultivated pieces of land along the contours between the cultivated strips, about 30meters wide
Cover cropping is the practice of establishing crops that spread and cover the ground well.Cover cropping controls erosion by trapping detached soil particles and reducing the speed of surface run-off.
Mulching is the covering of the soil surface with either organic materials or inorganic materials.Organic mulch increasing soil humus content upon decomposition there by increasing water holding capacity of the soil.
In grassed waterway, vegetation especially grasses is planted or allowed to grow in a depression which act as a passage for water.Vegetation waterways should not be used as a cattle track or grazing land.
Contour farming involves carrying out all farming activities e.g. planting along contour lines. Contour farming reduces rill erosion as a result of cultivating land up and down the slope.
Strip cropping is the planting of crops with poor ground cover e.g maize in alternate strips with crops having good ground cover e.g sweet potatoes.
A hilly area showing alternate strips of maize crop and napier grass.
Physical methods of controlling soil erosion .
Gabion erected across a gully
Physical method of controlling soil erosion involves mechanical construction of farm structures which help to control soil erosion. They are used in areas of moderate slope of between 13-55 %. These measures include trash lines , stone lines, bunds, cut- off drains and terraces.
Trash lines are heaps of crop residues e.g. wheat straws or maize stalks arranged along the contour lines. Trash lines trap detached soil particles and reduce speed of surface water flow thereby controlling soil erosion.
Stone lines are heaps of stones arranged along contour lines. The stones help to trap detached soil particles and reduce the speed of surface run-off thereby lowering rate of soil erosion.
Bunds are heaps of soil 1-2m wide at the base and about 60cm high at the centre, placed along the contour lines. Grass should be allowed to grow on the bunds in order to hold soil particles together. For effective control of excess water, farmers are advised to build tie bunds (i.e. off-shots of soil above the main bund).The bunds trap soil particles which have already been detached thereby reducing rate of erosion.
A gabion is a box of galvanized wire mesh filled with stones which are built across a slope or a gully. The gabion should be heavy enough to resist large volumes of flowing water . Gabions trap the detached soil particles and reduce the speed of water flow.
Use of dams and other water reservoirs .
A dam is a wall or a barrier built across a river or any other waterway to hold and store water. Water reservoirs reduce the amount of surface water flow by holding excess water thereby lowering the rate of erosion.
Use of terraces.
Common types of terraces
A terrace is a raised level space constructed along the contours to help control soil erosion. Terraces reduce the flow of water and channel away the excess water through the use of ditches. Common types of terraces used in Kenya include;
- Broad-based terrace
- Narrow- based terrace
- Fanya-juu terrace
- Fanya-chini terrace
Use of Cut-off drains
A cut- off drain is a channel, erected on the upper part of the farm, which collects and diverts water from other areas and discharges it into rivers ,artificial waterways or grounds resistant to soil erosion. A cut off drain should have an embarkment on the lower side of the excavated channel to hold excess water. A cut-off drain trap detached soil particles and reduce the amount and speed of surface water flow thereby lowering rate of soil erosion.
Water harvesting is the manipulation of sources of water in order to increase the retention of water. The need to store water arises when there are large quantities of water available ,which cannot be used immediately. Large amount of water is normally lost through evaporation , transpiration and majorly through surface run-off if not harvested. Common methods of water harvesting include ;
- Roof catchment
- Rock catchment
- Retention ditches
A micro-catchment is a rainwater harvesting system which involves collection of run-off water for productive use within the field (i.e seedbed ). Types of micro-catchment include ;
- Negarim micro-catchment
- Contour bunds
- Contour ridges
- Semi-circular bunds
- Trapezoidal bunds
- Contour stone bunds
- Permeable rock dams
- Water spreading bunds
The laying out and construction of micro-catchment involves drawing the required design, marking the area ,clearing vegetation ,availing the required materials and then constructing the micro-catchment as per the designed plan.
Uses of micro-catchment
Uses of micro- catchments in a farm include ; 1.Reducing the speed of surface water run-off in the field. 2.Improving the level of water table through increasing the rate of water percolation into the soil. 3.Reducing siltation in dams and other water reservoirs. 4.Improving water catchment areas. 5.Creating suitable micro-climate which improves the ecological conditions of an area. 6.Collecting run-off water for productive use in the farm eg. for irrigation and fish farming.
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