Factors affecting decomposition of organic matter
1. Temperature: Cold periods retard plant growth and OM decomposition. Warm summers may permit plant growth and humus accumulation.
2. Soil moisture: Extremes of both arid and anaerobic conditions reduce plant growth and microbial decomposition. Near or slightly wetter than field capacity moisture conditions are most favorable for both processes.
3. Nutrients: Lack of nutrients particularly N slows decomposition.
4. Soil PH: Most of the microbes grow best at pH 6 – 8, but are severely inhibited below pH 4.5 and above pH 8.5.
5. Soil Texture: Soils higher in clays tend to retain larger amounts of humus.
6. Other Factors: Toxic levels of elements (Al, Mn, B, Se, Cl), excessive soluble salts, shade and organic phytotoxins in plant materials.