Relative importance of soil organic matter, soil litter and litter fall in the tropics

Organic matter in soils (SOM) is represented by plant and animal residues in various stages of decomposition, containing typically 58% of Carbon. Carbon content of soils is considered as a major indicator of soil quality, including water retention capacity. However, only organic particles passing through the 2 mm sieve are considered. Moreover, soil litter is generally given less importance in the interpretation of soil quality. Under tropical forest conditions it is not rare to find soils with less than 1% carbon although soil litter is undergoing an active humification process, continuously supplied with litter fall. Several coefficients taking both annual litter fall and soil litter into account, provide more dynamic interpretation tools of soil quality under tropical conditions as illustrated with several examples from Latin-America and Africa.