Loam soil. Image credit betterground.org

Loam soil. Image credit betterground.org

ZIMSEC O Level Combined Science Notes: The physical components of the soil

 

  • Soil is made up of rock/soil particles
  • Some soils are easy to compress because they have air in them
  • Soils are usually moist
  • Soils also have dissolved minerals in them

Sand, Loam and Clay soils

  • Different types of soil have different characteristics
  • For example sandy soils are different from clay soils
  • Sand soil is light and composed loose particles
  • Sand soils also have larger particles and there is more air spaces between the particles
  • They thus drain more quickly and do not retain water
  • Clay soil is darker, heavier and more compact
  • Clay soils have small particles and there is little air between these particles
  • They retain water because they drain much more slowly
  • Loam soils have properties that are between those of sand and clay soils
  • Loam soils also contain rotted plant matter

Minerals in the soil

  • All soils contain mineral salts
  • These salts are dissolved in the soil water or they may be combined with the clay particles
  • When soil water drains through the soil it carries the minerals with it
  • This is called leaching
  • Leaching-is when water dissolves and carries minerals through the soil.
  • Sand soil leaches easily as it drains much more easily
  • Leaching takes away all the vital elements that plants need for growth
  • Farmers need to reduce leaching by maintaining a healthy soil structure
  • This can be done by adding manure and compost to the soil on a regular basis
  • Whenever rain occurs there is run off and infiltration
  • Run off-this is when water flows away
  • Infiltration-this is when water filters into the soil
  • Infiltration is reduced when the soil is hardened for example as a result of animal hooves beating the soil or as result of erosion
  • Water must penetrate the ground to maintain underground reserves
  • This can be done by ploughing and
  • ity/alkalinity of the soil
  • If soils are too acidic lime can be added to reduce its acidity
  • digging the soil
  • This ensures not too much water is lost via run off and more of it penetrates the soil

Soil PH

  • Plant roots and organisms are also affected by the acid
  • If the soil is too alkaline manure/compost can be added
  • Farmers find it beneficial to know the PH of the soil and to keep it at optimum levels
  • Most soils have a PH of around 6-7
  • They should have their soils tested regularly at soil laboratories or use portable test kits
  • They can therefore find out which crops best grow in their types of soil
  • Different crops favour different types of soil
  • For example cotton prefers dark clay soils
  • Maize grows in a wide variety of soils
  • Tobacco grows in light sandy soils with good drainage
  • Climatic conditions also need to be taken into consideration when choosing the crops to grow

To access more topics go to the Combined Science Notes page.


Quick NetOne, Telecel, Africom, And Econet Airtime Recharge

If anything goes wrong, chat with us using the chat feature at the bottom right of this screen