@ Eetela, it is the most difficult exercise to enrich the organic carbon in the soil. To my experience if you can enrich 10% more of the present status, you are very lucky. The practices for enrichment of organic carbon in the soil are:
Grow high yield, high biomass crops and pastures, and in continuous cropping systems maximise crop frequency to increase organic matter returns to the soil.
Maintain soil fertility with inorganic and organic fertilisers to maximise production.
If available locally, import manure/compost or other organic amendments.
Increasing of organic carbon content in soils it may take 10-20 years that is also depends upon the soil internal & external profile characteristics. We can increase the organic carbon by applying manures, bone meal, FYM and vermicompost..