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CN ratio: Importance and its fuctions in soil


C:N ratio, its functions and importance

List of contents
(01). What is C:N ratio in soil?
(02). Breaking down of organic matters
(03). Important questions

Also read: Soil Science MCQ: Multiple Choice Questions

(01). What is C:N ratio in soil?

C:N ratio is the ratio of the weight of organic C to the weight of total N in a soil or organic matter.

The C:N ratio shows the relationship between carbon and nitrogen present in the soil. There are different types of soil, the carbon and nitrogen ratio of the soil may be different according to the location.

For example, this ratio is very low in dry area soils, whereas the ratio of carbon and nitrogen in average soil is 20:1.

In C:N ratio stands for ratio of carbon and nitrogen.

  • C= Carbon
  • N= Nitrogen

The more organic matter in the soil, the higher the CN ratio but it varies with soil.

The activity of micro-organisms increases greatly in the soil where the ratio of carbon and nitrogen is high.

Also read: 5 Ways to Increase Soil Fertility

(02). Breaking down of organic matters

These microbes break down organic matter into CO2 and energy. It is beneficial for the soil and the plants.

Therefore, the amount of organic matter in the soil decreases. At the same time, these soil organisms require more nitrogen to make new tissue due to this the CN ratio in the soil decreases.

Also read: Which is the most fertile soil?

(03). Important questions

Questions 3.1: What is the reason of low organic nitrogen ?

When the ratio of carbon and nitrogen is 20:1 or 25:1 or more, the process of decomposition of organic matter increases. The activity of micro-organisms increases, and due to increased demand and greater utilization of organic nitrogen, organic nitrogen in the soil decreases.

Question 3.2: Why does the competition between microbes and soil increase for inorganic nitrogen?

Decreased organic nitrogen in the soil increases the competition for inorganic nitrogen in micro-organisms and plants.

Question 3.3: What is the advantage of competition between micro-organisms and plants for inorganic nitrogen in the soil?

The competition between micro-organisms and plants for inorganic nitrogen in the soil has the following advantages:

The number of host bacteria decreases.
The ammonium ions are converted into nitrates by the process of nitrification.

These nitrates are destroyed by drainage, but are converted into compounds by soil organisms. In this way they remain permanently in the soil.

Whenever the CN ratio in the soil decreases, then this nitrate/nitrogen is received by micro-organisms and plants.

Question 04: What the importance of CN ratio?

Importance of C:N ratio

Controlling decomposition rate in soil.

Wide C and N ratio

  • The wide C:N ratio means slow decomposition rate.
  • Nutrient immobilization.
  • Wastage of carbon and energyin large quantities.
  • Restricted microorganisms activity.
  • Limited amount of N.

Narrow C and N ratio

  • Carbon and energy starvation.
  • Quick decomposition of plant materials. Helps in determining the rate of decay.

Question 05: What are the C and N ration of some important OM?

Carbon and Nitrogen ratio of some organic materials

Alfalfa20:1
Microbial population10:1
Soil organic matter10-12:1
Maize stalk40:1
Rice straw100:1
Rye straw200:1

Also read: Soils of India, Their Types and Characteristics


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