Properties of Soil

12 Grade 10 Agriculture questions on Properties of Soil, with worked marking schemes. 12 questions are available on this topic in full.

1. Question 1

   1 mark

   Which statement best explains why loam soil is recommended for growing most crops?

   A. It is always dark in colour

   B. It contains the highest proportion of clay particles

   C. It combines good drainage with good water and nutrient retention

   D. It does not require any fertiliser application

   (1 mark)

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2. Question 2

   4 marks

   State four physical properties of soil that a farmer should assess before deciding which crop to grow on a field.

   (4 marks)

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3. Question 3

   3 marks

   State three ways in which living organisms in the soil improve its productivity.

   (3 marks)

   Marking scheme

   Award 1 mark for each of any THREE ways (max 3): - Earthworms and termites burrow through the soil, improving aeration and drainage. - Bacteria and fungi decompose organic matter, releasing nutrients and forming humus. - Rhizobia bacteria in legume root nodules fix atmospheric nitrogen into a form crops can use. - Mycorrhizal fungi extend the root system and increase uptake of phosphorus and water. - Organisms secrete substances that bind particles into stable crumbs, improving soil structure. - Burrowing organisms mix topsoil and subsoil, spreading nutrients through the rooting zone.

4. Question 4

   2 marks

   Distinguish between soil texture and soil structure.

   (2 marks)

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5. Question 5

   1 mark

   A farmer in Bungoma observes that rain water stands on his plot for several hours after a storm, and that the same plot develops wide cracks in the dry season. The soil on this plot is most likely

   A. clay soil

   B. sandy loam soil

   C. loam soil

   D. sandy soil

   (1 mark)

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6. Question 6

   4 marks

   Outline four ways in which a farmer can improve the water-holding capacity of a sandy soil.

   (4 marks)

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7. Question 7

   1 mark

   Maize on a farm in Kisii is stunted and pale despite heavy application of manure. A soil test gives a pH of 4.5. The most appropriate corrective measure is to apply

   A. agricultural lime

   B. more farmyard manure

   C. more calcium ammonium nitrate

   D. sulphur dust

   (1 mark)

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8. Question 8

   1 mark

   Which soil structure is the most suitable for the growth of most crops?

   A. Platy

   B. Single grain

   C. Columnar

   D. Crumb

   (1 mark)

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9. Question 9

   6 marks

   Explain three ways in which a heavy clay soil can limit the growth of a root crop such as carrots.

   (6 marks)

   Marking scheme

   Award 1 mark for each correct point and 1 mark for the explanation (max 3 points, 6 marks): - The soil holds water and drains poorly (1); the roots lack oxygen and rot or fail to enlarge (1). - The soil is dense and compacts easily (1); the swelling root cannot push the particles aside, giving short, forked or twisted carrots (1). - The soil is sticky when wet and sets hard when dry (1); seedbed preparation and lifting of the crop are difficult and many roots break during harvesting (1). - Wet clay warms up slowly (1); germination and early growth are delayed, lengthening the time to maturity (1). - The surface crusts and cracks on drying (1); emerging seedlings are held back and exposed roots turn green (1).

10. Question 10

    1 mark

    Nitrogenous fertiliser top-dressed on a sandy soil in Kilifi County is often lost before the crop can use it. The property of the soil responsible for this loss is

    A. its poor aeration and lack of oxygen

    B. its low temperature during the dry season

    C. the rapid movement of water through its large pores

    D. its high content of clay particles

    (1 mark)

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11. Question 11

    1 mark

    Soil collected from the edge of a forest in Nyeri County is very dark in colour. This dark colour is mainly an indication of

    A. a high clay content

    B. a high iron content

    C. permanent waterlogging

    D. a high organic matter content

    (1 mark)

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12. Question 12

    6 marks

    Explain three effects of a strongly acidic soil, of pH about 4.5, on crop production.

    (6 marks)

    Marking scheme

    Award 1 mark for each correct effect and 1 mark for the explanation (max 3 effects, 6 marks): - Phosphorus becomes fixed by iron and aluminium compounds (1); it is no longer available to the crop, so root development and grain filling are poor (1). - Aluminium and manganese become highly soluble (1); at toxic levels they damage root tips, so the crop is stunted and wilts easily (1). - Activity of nitrogen-fixing and decomposing bacteria is reduced (1); less nitrogen is fixed and less organic matter is broken down, so nutrient supply falls (1). - Calcium and magnesium are depleted (1); the crop shows deficiency symptoms and yields fall (1). - The range of crops that can be grown narrows (1); acid-sensitive crops such as beans perform poorly and only tolerant crops such as tea do well (1).

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