soil

• what are the components of soil?


  -rock particles: hold clay and sand particles together, increase air pores, draining water.

  -organic matter (humus): holds water in soil, makes texture lighter and easier to dig and adds nutrients to soil.

  -pore spaces: the spaces trap air in the soil.

  -soil water: soil particles become surrounded by a thin film of water by capillary attraction. (depends on the size of particles)

  -mineral salts: salts of potassium, iron, magnesium, phosphates, sulphates and nitrates. come from rock particles and from the action of bacteria on the organic matter of the soil
• what are the different kinds of soil?


  -sandy soil

  -loam soil

  -clay soil
• describe the characteristics of sandy soil.

  -loose, light and easy to dig.

  -contains a lot of air and drains well

  -cold type of soil = it loses heat.

  -dries up quickly in hot weather.

  -not very fertile = useful chemicals wash out of it in case of rain
• describe the characteristics of clay soil.


  -holds on to water and nutrients very well = rich in plant food

  -heavy and difficult to dig

  -sticky when wet and hard when dry

  -rain runs off the top layer of the soil
• define mulching in sandy soil.


  spreading a layer of peat or manure over the surface of the soil. keeps the soil warm.
• define flocculation in clay soil.


  adding lime to clay soil which causes the particles of clay to clump together into soil crumbs.

  -breaks up the soil, getting air into it and draining it.
• describe the characteristics of loam soil.


  -neutral pH

  -fairly loose texture

  -soil particles form readily and the particles are of a size which keep the soil well aerated and allows it to drain easily.
• describe the ideal conditions of soil.

  The best soil is a balanced mixture of sand, clay, humus, and lime.

  • 50 per cent sand, 30 per cent clay, 12 per cent humus, and 8 per cent lime.
• what are some organisms living in soil?

  -the mole: lives underground since it is blind, has short forelegs for digging. its burrows serve as irrigation channels, eats soil pests and earthworms.

  -soil micro organisms: bacteria, fungi. they secrete digestive enzymes into the organic matter of the soil and absorb the soluble products into their cells or hyphae.
• describe the beneficial effect of plants on the soil.


  the main effect which plants have on the soil is to hold it together.
• describe soil erosion.


  The soil, no longer bound together by the roots, starts getting loose. Rain and wind then wear it away, and soon the area becomes bare and incapable of supporting life. This is called erosion, and one of its main causes is over-grazing.
• how do earthworms help the soil?


  -improve soil fertility:

  • making burrows in the soil partly by pushing between particles and partly by swallowing the soil. help in mixing the soil, taking organic matter to deeper layers
  • earthworm burrows improve the drainage and aeration of the soil
  • As soil passes through the earthworm's intestine, the material is finely ground and made more alkaline. Secretions from the intestine help to bind the organic and mineral particles together. The raised pH favours the growth of soil bacteria; the grinding of coarse humus makes a good crumb structure.
• describe examples of harmful soil organisms.


  -nematodes: live in the pore spaces, feeding on bacteria, algae, protozoa and other nematodes. Some nematodes are ectoparasites, piercing the roots of plants and absorbing the cell contents. Others are endoparasites of plant roots and cause serious damage to crops.

  -arthropods: insect larvae, centipedes, millipedes and mites. Some feed on living and dead plant material, faeces, fungi, nematodes, small worms and each other. Some of the insect larvae, such as the 'wireworms', can become agricultural pests by eating the roots of crop plants.