Humus is a complex, dark brown mixture of organic matter that forms in soil through the decomposition of plant and animal residues by soil microorganisms. There are two main types of biochemical reactions involved in humus formation: decomposition, where microbes break down plant materials like lignin, and synthesis, where microbes transform the simpler breakdown products into humus. The specific factors that influence humus formation include soil parent material, climate, temperature, rainfall, time, plant and animal life present, microorganisms, topography, altitude, and slope.

1. HUMUS FORMATION
I PG MICROBIOLOGY
SRCW

2. “Humus is defined as a complex and rather resistant
mixture of brown or dark brown amorphous and
colloidal substances modified from the original tissues
or synthesized by the various soil organisms”

4. DECOMPOSITION
SYNTHESIS
2 GENERAL TYPES OF
BIOCHEMICAL
REACTIONS

5. DECOMPOSITION
• PLANT RESIDUES BROKEN DOWN BY MICROBES LIGNIN
• OTHER SIMPLER ORGANIC COMPOUNDS BROKEN DOWN

6. SYNTHESIS

7. SOIL
PARENT ROCK
CLIMATE
TEMPERATURE
RAINFALL
TIME
FLORA
FAUNA
MICROBES
RELIEF
ALTITUDE
SLOPE
FACTORS RESPONSIBLE FOR FORMATION