Factors that affect the rate of decomposition of organic matter

Factors that affect the rate of decomposition

Plant factors

Age; young plants decompose faster than older ones because of high moisture content, they are less fibrous.

Moisture content: Succulent plants decompose faster than those which are less succulent.

Carbon: nitrogen ratio: legumes which have narrow C:N ratio decompose faster than cereals.

pH of the material: plants e.g. pine give acidic residues which are very difficult to break down.

Climatic factors:

Temperature: with in a given temperature range, the higher the temperature, the faster the rate of organic matter decomposition.

Rainfall: this influences the activity o soil living organisms and speed of chemical reactions.

Soil factors:

Soil moisture: influences activity of soil living organisms.

Soil structure: influences aeration.

Soil temperature.

Mineral content: Influences activities of soil living organisms that break down organic matter.

Presence of living organisms:

The more the living organisms present, the higher the rate of organic matter decomposition.

How organic matter level can be increased

Application of organic manures e.g. compost, FYM, green manure.

Minimum tillage or zero tillage


Ploughing back crop residues in the soil.

Liming to increase the living organisms which decompose the organic materials.

Proper drainage to encourage the soil micro organisms.

Expriment to determine the percentage of humas in the soil


  • Oven dried soil
  • Evaporating dish
  • Weighing scale
  • Source of heat
  • Stirring rod


  • Oven dried soil is weighed
  • The soil is heated strongly in an evaporating dish upto a temperature of 105oc
  • Stir while heating the soil
  • Note the colour change during heating
  • Repeat the heating until a constant weight/mass is got
  • Cool the dish and the contents in a desiccator


  • Smoke is given off
  • The soil changes colour to brown


  • Weight of oven dried soil      = (a) g
  • Weight of heated soil  = (b )g
  • Weight of humus                   = (a-b)g
  • %age of humus                   = weight of humus   *  100

Weight of oven dried soil

= (a-b)   * 100