Introduction 

• 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. 

Soil Erosion 

• 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 runoff. 

- 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 soils. 

• Soil depth;

- The deeper the soil, the longer it takes to be saturated with water. 

• Land use: 

- 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 temperatures. 

- Indiscriminate burning of vegetation exposes the soil to erosive agents.

- Clean weeding leaves the soil bare. 

- Ploughing along the slope. 

- Monoculture or continuous cultivation. 

• Ground cover 

- 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 wider. 

• Riverbank Erosion - removal of soil along river banks by the river water. 

• Solifluction - gravitational flow of soil saturated with water. 

• Land slides - mass movement of rock debris and soil down a slope, 

                   For example; 

- 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. 

• Mulching ;

- Covering of the soil with either organic or synthetic materials. 

• Proper cropping systems such as: 

- Crop rotation 

- Correct spacing 

- Inter-cropping 

- Ridging/furrowing 

- Strip cropping  

• Controlled grazing;

- Proper stocking rate, rotational grazing. 

• Strip cropping;

- Growing crops which give little ground cover in alternate strips with crops such as beans which have a good ground cover. 

• Afforestation/re-afforestation. 

- 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%.

They include: 

• Trash or stone lines;

- These are rows of heaped crop' residues or stones made along the contours. 

• Filter strips;

- It involves the growing of an open crop in the upper side of the slope followed by a dense crop to reduce speed of water. 

- This increases infiltration. 

• Terraces;

- Are structures constructed across a slope to reduce the length of a slope thus reducing run-off. 

• Bench terraces;

- 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. 

• Graded terraces: 

- Have a drainage channel to lead off excess water to a vegetated place. 

- They should be about 100m in length. 

• Level terraces: 

- Have no outlet channels, 

- The aim is to have water infiltrating, 

- Hence no water can flow from the ends of the terrace. 

• Fanya juu: 

- A ridge made by digging a channel and throwing the soil uphill. 

• Fanya chini:

- In this case the soil is heaped on the lower side of the channel. 

• Bunds: heaps of soil (earth) made along the contour. 

• Cutoff drains: 

- An open trench with an embankment on the lower side into which water from     the farm drains. 

Water from the trench should be discharged into; 

- Natural waterways, 

- Artificial waterways, 

- Rocky ground 

- Grassland 

• Gabion/Porous dams: 

- Galvanized wire mesh boxes filled with stones which are built across slopes and gullies. 

• 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 tanks. 

• 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. 

            Micro-Catchments 

• A system of harvesting limited rainfall and storing the water in the ground for use by the planted crops. 

              Types of Microcatchments; 

• Triangular/V-shaped/Negarims; 

- 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 

• Semi-circular bunds;

- Formed around the growing plant to hold water around the plant. 

• Trapezoidal bunds;

- 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 agro-forestry trees are intercropped with   annual crops. 

• 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.