Soil and Water Conservation - Agriculture Form 3 Notes

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.

It is the removal and carrying away of the top soil by the action of water or wind.

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 soils
Soil depth;
- The deeper the soil, the longer it takes to be saturated with
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 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.
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.

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.

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,
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 conservation measures can be classified into:

- 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.

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
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 wate
- 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 plac
- 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 terr
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 dra
- 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 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 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.

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 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.