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Agricultural Science Paper 2, May/June 2009  
Questions: 1 2 3 4 5 6 7 8 9 10   Main
General Comments

Question 4

(a) List four soil conservation practices that can be used to control erosion on  a gentle slope.       [4 marks]
(b) Explain how each of the practices you have listed in 4(a) can be used to  conserve the soil.      [12 marks]


This question was poorly attempted by the candidates.  In question 4(a), majority of the candidates could not list soil conservation practices that can be used to control erosion on a gently slope.  Also in question 4(b), many  candidates were unable to explain how the practices could be used to conserve the soil.
The expected answers include:
Soil conservation practices that can be used to control erosion on a gently slope
(a) Terracing
(b) Ridging across the slope
(c) Construction of drainage channels
(d) Cover cropping/Afforestation
(e) Strip cropping
(f) Mulching
(g) Contour ploughing

How each practice can be used to conserve the soil
A practice in which the slope is broken into series of steps
(b)Each step is constructed along a contour so that each of them is on uniform height, but different from those above or below it
(c)It is done to reduce the length and gradient of slope and hence reduce the speed of run-off
(d)Water collected on each gentle slope runs across the field rather than down
(e)Each has a drainage channel which empties into a grassed waterway which leads water down the slope to nearby channel.

Contour ploughing
-           The slope is first surveyed to locate contour points
-           Ploughing is now done along the contours joining all areas along each
-           These contours are running across the slope of the land
-           Plants are established along the contours and not across

Ridging across the slope
-           Flood water will normally run down along the slope of a land
-           Ridges constructed should be across the slope to block the run-off water
-           Such ridges will also help to trap the water into small reservoirs which will sink into the soil
-           Can be practised by every farmer without technical know-how. 
Construction of drainages
-           Drainages are means of getting rid of excess water in the field
-           Many types of drainages are available, they may be open channels or
underground channels
-           Pipes are laid along the slope to carry the water straight down into
            reservoirs below, thus preventing soil erosion.
Cover cropping/Afforestation
-           The principle is not to allow the surface to be exposed to agents of erosion e.g. wind, water
-           The slope planted with cover crops to trap any run-off water
-           They also promote the percolation of such water which has been retarded in its flow
-           The leaves decay and enhance soil fertility, thereby encouraging more growth of other species.

Strip Cropping
-           Planting of crops in rows along the contour interspersed by rows of uncultivated area to retard water run-off across the slope
-           Planting of different crops with different growth characteristics in alternate rows along the contour and across the slope to check run-off.

-  Mulching is the act of covering soil surface with such materials as dry grasses, crop residues and polyethylene sheets
-   Reduces the impact of rain drops on soil
-   Reduces the speed of run-off water
-   Decayed mulch improves soil structure and so help check soil erosion.

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