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SOIL AND WATER CONSERVATION

A paper presented to participants at 31st KIOF workshop.

Presented by:KIMOLE STEPHEN.


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Objectives:

To discuss importance of soil and waterprotection.

To discuss the factors that contribute to soilfertility and how the fertility is lost from thesoil.

To develop skills for measuring out contours.

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Definitions

Soil and water conservationrefers to the practicesthat are carried out to prevent loss of the tworesources. These practices maintain the soil fertility.

Soil fertilityis the ability of a soil to supply thenutrient elements in the amounts, forms andproportions needed for the growth of specifiedplants when temperature and other factors arefavorable.

Soil productivity refers to the capacity of a soil toproduce a given yield of crops under a specifiedsystem of management.

Therefore for a soil to productive it must be fertile.

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Main factors contributing

towards soil fertility Soil depth.

Drainage.

Good aeration. High water holding capacity.

High levels of nutrients.

Freedom from pests and diseases.

High levels of micro-organisms.

Optimum Ph.

ORGANIC MATTER.

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Cont.

Soil texture and structure play a vital role indetermining the ability of the soil to producehigh crops through their influence on some ofthese factors e.g. moisture holding capacityand drainage.

Organic matter is another component which

influences most of the factors that contributeto soil fertility.

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Influence of pH on Nutrient Availability


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Soil fertility may be lost

through: Soil erosion - wind or water.

Leaching.

Weeds.

Monocropping.

Loss of nutrients through sale of farm

produces off the land. Unduly too frequent cultivation's.

Change of soil pH.

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Cont.

Compaction- hardpan impeding infiltration ofwater and root penetration.

Rainfall amount and intensity. Sun / heat.

Fires.

Wind. Mining.

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Methods of maintaining and / or

improving soil fertility Improving soil moisture characteristics.

Good cropping system.

Minimum soil disturbance.

Soil pH control.

Addition of organic matter.

Erosion control.

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Soil erosion control.

The first aim oftropical soilmanagement is tocontrol erosion sinceit contributes tomost of fertility loss.

Factors influencingwater erosion

Rainfall Intensity and

Runoff

Soil erodibility.

Slope Gradient andLength.

Vegetation.

Land use.

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Principles of soil erosion

control De-energise raindrop.

Stop or Slow down water flow across land.

Increase porosity of the soil.

Do something about small channels (rillerosion), which may wash out. Cover cropsmay be planted etc.

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Types of conservation

measures: Overall management: such as area closures,

selective clearing, control livestock numbers.

Agronomic: such as plant / soil cover,conservation farming methods, contourfarming

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Covercropping.

Dolichos used as a cover crop.

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Structural: such as Fanya Juus,

terraces, banks , bunds, cutoff drains, barriers

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Structural.

Fanya juu.

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Structural:

A newly constructed fanya juu An old fanya juu.

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Vegetative: such as planting

barriers (vegetative strips),

live fences, windbreaks

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Contour farming

Contour farming involves ploughing, planting andweeding along the contour, i.e., across the sloperather than up and down. Contour lines are lines thatrun across a (hill) slope such that the line stays at the

same height and does not run uphill or downhill. Ascontour lines travel across a hillside, they will beclose together on the steeper parts of the hill andfurther apart on the gentle parts of the slope.

Experiments show that contour farming alone canreduce soil erosion by as much as 50% on moderateslopes. However, for slopes steeper than 10%, othermeasures should be combined with contour farmingto enhance its effectiveness.

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Measuring out

contours.Spirit level.

The tube level.A-frame.

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A- frame.

Materials.

Three poles-of 2.5m length

Handful of nails 1m 2m strong string

A piece of rock (stone)

Two pegs

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Procedure.

Use the poles and nails to make a frame inthe shape of an "A" (Picture 1)

2. Tie one end of the string to the top of the"A

Tie the stone to the other end of the string, so

it hangs down just below the horizontalcrossbar of the "A"

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Calibrating the A-frame

Stand the A-frame upright on reasonably level ground. Mark onthe ground where the two legs stand.

5. Hold the A-frame still, and use the pencil to mark lightly on thecrossbar where the string crosses it (Picture 2).

Turn the A-frame round, so that each leg stands exactly wherethe other had stood.

7. Make a second light mark on the crossbar where the stringcrosses it.

8. The two marks on the crossbar should be fairly close together.Halfway between them shows where the string would cross if theA-frame were standing on exactly level ground. Make a heavypencil mark or notch the bar with a knife at this point (Picture 3).

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Figures

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Cont.

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Locate the contour lines using

the A-Frame 1. Choose a place on the slope to begin. Stand the A-frame up

and mark where the first leg stands with a peg or large stone.

2. Keeping the A-frame upright, and without moving the first leg,swing the second leg up or down the slope until the string crosses

the crossbar exactly at the heavy pencil mark (Picture 4).3. Mark where the second leg stands with another peg or stone.

4. Keeping the second leg in the same place, lift the first leg upand pivot it around. Move it up and down the slope until you findthe place where the string crosses the crossbar at the heavy

pencil mark.

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Cont..

5. Mark where the first leg is now standing with anotherpeg or stone.

6. Continue in this manner to the end of the field.

7. The line of pegs or stones will mark a contour line: theywill all be at the same height on the slope. The pegs areusually not in a straight line. If necessary, make a smoothcurve by moving them a little up or down.

9. To mark another contour line, move up or down the slopea certain distance - usually about 20 m (20 paces) on agentle slope, or a drop of 1.5 m on steeper slopes. Repeatthe process from Step 9 above onwards.

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