Factors Affecting Soil Organic Matter
1. Climate: Temperature and rainfall exert a dominant influence on the amounts of N and OM found in soils.
a) Temperature: The OM and N content of comparable soils tend to increase if one moves from warmer to cooler areas. The decomposition of OM is accelerated in warm climates as compared to cooler climates. For each 10 C decline in mean annual temperature, the total OM and N increases by two to three times.
b) Rainfall: There is an increase in OM with an increase in rainfall. Under comparable conditions, the N and OM increase as the effective moisture becomes greater.
2. Natural Vegetation: The total OM is higher in soils developed under grasslands than those under forests.
3. Texture: Fine textured soils are generally higher in OM than coarse textured soils.
4. Drainage: Poorly drained soils because of their high moisture content and relatively poor aeration are much higher in OM and N than well drained soils.
5. Cropping and Tillage: The cropped lands have much low N and OM than comparable virgin soils. Modern conservation tillage practices helps to maintain high OM levels as compared to conventional tillage.
6. Rotations, residues and plant nutrients: Crop rotations of cereals with legumes results in higher soil OM. Higher OM levels, preferably where a crop rotation is followed.