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.