Humus is the organic residue in the soil resulting from decomposition of plant and animal residues in soil, or it is the highly complex organic residual matter in soil which is not readily degraded by microorganism, or it is the soft brown/dark coloured amorphous substance composed of residual organic matter along with dead microorganisms.
Composition of Humus:
In most soil, percentage of humus ranges from 2-10 percent, whereas it is up to 90 percent in peat bog. On average humus is composed of Carbon (58 %), Nitrogen (3-6 %, Av.5%), acids – humic acid, fulvic acid, humin, apocrenic acid, and C: N ratio 10:1 to 12:1. During the course of their activities, the microorganisms synthesize number of compounds which plays important role in humus formation.
Functions/Role of Humus:
It improves physical condition of soil
Improve water holding capacity of soil
Serve as store house for essential plant nutrients
Plays important role in determining fertility level of soil
It tend to make soils more granular with better aggregation of soil particles
Prevent leaching losses of water soluble plant nutrients
Improve microbial/biological activity in soil and encourage better development of plant-root system in soil
Act as buffering agent i.e. prevent sudden change in soil PH/soil reaction
Serve as source of energy and food for the development of soil organisms
It supplies both basic and acidic nutrients for the growth and development of higher plants
Improves aeration and drainage by making the soil more porous