Factors that influence the abundance of living organisms

Tillage practices: Tillage of the soil directly kills soil living organisms leading to a reduction in their numbers.

Soil depth: Deep soils favor abundance of soil living organisms because they provide space for soil living organisms. The deeper the soil down words, the less the number of soil living organisms.

Type of crop grown: Some organisms are only abundant in number when certain crops are grown. E.g. Blue green algae in rice fields.

Soil moisture content: Some organisms require some moisture to survive. However, high moisture favors less organisms

Soil aeration: Most organisms require oxygen for survival and absence of oxygen will reduce their population.

Soil temperature: Most organisms live with in a given temperature range.

Soil pH: Most bacteria and earthworms do well in slightly alkaline soil while fungi do well in acidic conditions.

Organic matter content: Many soil living organisms need organic matter for their nutrition. The higher the organic matter content, the higher the population of micro organisms.

Pollution: Use of agricultural chemicals e.g. pesticides, industrial wastes reduce the population of soil living organisms.

Expriment to investigate the presence of soil living organisms


  • Muslin bags
  • Lime water
  • Garden soil
  • Conical flasks
  • Cork


Put a handful of fresh garden soil in muslin bag A.

Put garden soil that has been heated strongly to kill living organisms in muslin bag B.

Suspend the muslin bags in different conical flasks containing lime water and cork the flasks.

Leave the apparatus to stand for about 4 hours.


The lime water in flask A will turn milky while that in flask B will remain clear.


  • Carbon dioxide produced during respiration of living organisms in fresh soil (A) turned lime water milky.
  • The lime water in flask B will remain clear since the organisms were killed by heating.


  • Fresh garden soil contains micro organisms which respire actively.