Microbial decomposition of the Organic matter, C:N ratio

Microbial decomposition of the Organic matter

When an organism dies, the death of the organism result in the rupture of the cell membrane and the dissolution of much of the soluble cell substance takes place then it moves to the soil. The organic solids are slowly decomposed by the microorganisms. The bacteria, fungi, and the other microorganisms excrete the varieties of the enzymes for breaking of the each kind of the bond.

The decomposition in the soil gives CO₂, NH₄⁺, NO₃^-, H₃PO_4, SO₄^--, H₂O resistance residues, and numerous other nutrients that are essential for the plants but if the soil is not supplied with the sufficient oxygen, the undesirable end products like CH₄, Organic acids (R-COOH), H₂S, which is the toxic gas for the plant and the microorganism and the ethylene is produced.

The microbes in the soil absorb the nutrients which are released during the decomposition, particularly N₂ and C and therefore, use them for their growth and the reproduction. The more the number of the microbes the more is the decomposition rates.

Microbial Decomposition of the Humus

On the basis of the resistance to the degradation and the solubility of the acids and the alkali the humic substances are classified into the 3 Chemical groups.

1. Fulvic acid

These are lightest in the color, soluble in the acid and alkali, lower in the molecular weight, and the most susceptible to the microbial attack that contains more amount of the cellulose and the hemicellulose.

2. Humic acid

These are medium in the molecular weight and the color and are soluble in the alkali but insoluble in the acids and intermediate in the resistance to the degradation.

3. Humin

These are the darkest in color, highest in the molecular weight and are insoluble in both the acid and alkali and are most resistant to the microbial attack. The protein and lignin are also in the maximum amount.

C:N ratio and its Significance

The organic matter in the soil contains the nitrogen and the carbon as well. The nitrogen content in the micro-organisms and in the organic matter is given in proportion to the carbon content called C-N ratio. The carbon content in the organic matter remains in the relatively amount between 42- 50% while the nitrogen content varies in the various folds. This shows that the C: N ratio expresses the relative content of the nitrogen in the organic matter.

Like the human being, the soil microbes also have some dietary requirement for their different activities. If the nitrogen in the soil is less than the microbes compete for the nitrogen with the higher plant. If the competition occurs then, there will be the reduction in the growth of the plant. The C: N ratio is given as

In this, the plant residue with the 20:1, C: N ratio have the sufficient supply to the decomposing microbes and also release nitrogen to the plant use. The residues with 20:1 to 30: 1, C: N ratio supply the decomposition but not enough for the plant use. The residues with C: N ratio wider than 30: 1 decomposes slowly because they lack sufficient nitrogen for the microbes.

There will be the continuous competition between the microbes and the higher plants for the amount of the nitrogen, which reduces the growth of the higher plants. So to prevent such competition straw and the similar residues may be burned for the ash which is rich in phosphorus and the nitrogen instead of incorporating them into the soil. The C: N ratio of the organic matter can be narrowed by composting them. The decaying of the material causes the release of the carbon dioxide in the atmosphere but only a little of the nitrogen is lost as nitrate by the leaching process. Most of the released form of the nutrients is recycled by the microbes and are then conserved. Therefore while there is the loss of the carbon, the amount of the nitrogen remains about the constant resulting in the narrow C: N ratio. The rotten materials decomposing in the soil can also provide nitrogen and the other essential nutrients in the soil which is the rich nutrient for the microbes and the higher plants.

Major types of the Soil In Nepal

The soil is formed after the thousands to the millions of the year by the weathering of the rocks, the sand, gravel, and the regoliths are the parent material formed by the deposition which may develop the clay, silt, oxygen, plants and the animals. These organisms born, grow, die and becomes mixed in the soil and the ecosystem continues.

There are mainly eight types of the soil found in Nepal:

1. Entisols

These soil do not have the well-developed pedogenic layer and are very common in the mountainous area and the recent alluvial deposits. Along the time, the soil changes in colour and the chemical constituents. The lower part of the soil will remain somewhat same as before while the upper part is mixed with the organic matter and the minerals giving the dark-colored layer of the A horizon and the lower unchanged layer is called C horizon. Such soil with only A and the C horizons are known as entisols and are also known as young soil. The parent materials are active alluvium and alluvium on shale. The texture types are loamy fine sand and ruby loam. They occur in the lower terai, susceptible mountains, and middle mountains.

2. Inceptisols

The pedagogical horizons are present in this type and are more developed than inceptisols. The parent materials are alluvium on phyllite, schist, quartzite, limestone, slate, frost etc. Such soil is found in Terai, high and middle Himalayas and Mountains, dun valleys etc.

3. Mollisol

These have loose and dark color and have the characteristics of the grassland and the evergreen forest where there is high organic content and more than 50 cm thick. The parent materials are deep alluvium aquic, udic. It is found in terai upper piedmont.

4. Alfisols

These are found in the high rainfall areas mainly in the forest with A, B, C horizons and is a basic cation. The parent material is old alluvium derived from phyllite. Its texture type is loamy to clay and occurs in siwaliks, high Himalayas, and mountains.

5. Spodosols

It has grey colour with the E horizons. The parent material is the loamy marine deposits. The texture is loamy and occurs in the cold wet climate usually under acidic coniferous forest or vegetation that develops acidic soil in the High Himalayas and the mountains.

6. Ultisols

Since the surface horizons are highly leached, the clay accumulation is in B horizons. The parent material is Lacustrine with the sandy loam texture. It is found in Siwaliks.

7. Aridisols

The parent material of aridisol is Glacial and alluvial-colluvial fan with texture type gravelly loam sand and occurred in the high Himalaya,

8. Histosols

Such soils are the organic soils having more than 12% Organic carbon content. Its occurrence is in the upper Narayani terraces, Jiri, Kalimati and the Tansen.

References:

Santra, S. (2004). Environmental Science . India: New Central Book Agency (p) Ltd.

T., R. (2008). Towards a Sustainable Future . India: PHI (p)Limited.

Keller, E.A.Environmental Geology. Columbus, Ohio: Charles E. Miller Publishing Company,Bell,and Howell Company, 1985.