Soil organic matter includes all living soil organisms together with the remains of dead organisms in their various degrees of decomposition. The organic carbon content of a soil is made up of heterogeneous mixtures of both simple and complex substances containing carbon. The sources for organic matter are crop residues, animal and green manures, compost and other organic materials. A decline in organic matter is caused by the reduced presence of decaying organisms, or an increased rate of decay as a result of changes in natural or anthropogenic factors. Organic matter is regarded as a vital component of a healthy soil; its decline results in a soil that is degraded.
Soil organic carbon content is affected mostly by climate, texture, hydrology, land use and vegetation.
Recent trends in land use and climate change have resulted in soil organic carbon loss at a rate equivalent to 10 % of the total fossil fuel emissions for Europe as a whole. In general, soils with low organic carbon content can be found in warm, dry climates and soils with a higher organic carbon content can be found in colder, wetter climates. Almost half of European soils have low organic matter content, principally in southern Europe but also in areas of France, the United Kingdom and Germany.
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