Soil Fertility and Nutrient management (1+1)

Formation of humus

Definition of humus
Humus is defined as they are more or less stable fraction of the soil organic matter remaining after the major portions of added plant and animal residues have decomposed. Usually it is dark or brown in colour. They are high molecular weight compounds, complex, resistant, polymeric compounds. They are amorphous and colloidal organic substances.

Composition of humus
Humus is a heterogeneous mixture of complex organic compounds. It is mainly made up of 58% C, 3-6% of N- and C:N ratio of 10:1 to 12:1.

Humus formation
Humic substances are produced when plant residues and other organic debris are broken down and/or chemically altered by microorganisms and subsequently recombine under the influence of enzymes. Humus formation is a complex two stage process in which organic residues of plant and animal origin undergo profound transformation.
1. The decomposition of the original components of tissues and their conversion by microorganisms in to simpler chemical compounds and partially to products of complete mineralization (CO2, NO2, NO3, NH3, CH4, H2O etc.)
2. The synthesis of organic compounds with the formation of high molecular weight humic substances of specific nature.
Ex. Lignin --------------broken into polyphenols, phenolic acids
       Proteins-----------polypeptides and amino acids
       Carbohydrates ------------ simple sugars
       High molecular weights humic acids (HAs) and Fulvic acids (FAs).