Agriculture Reference
In-Depth Information
decomposition of carbon compounds with downward movement. In applying the model
to this soil, diffusion due to bioturbation and soil homogenisation by the soil fauna
accounted for most of the movement. Since burial occurs more slowly than decomposition,
the rapidly decaying components are confined in the upper part of the soil. In contrast,
old organic matter is more homogeneously distributed throughout the entire profile.
3.2.2
FACTORS REGULATING ABUNDANCE
The total amount of organic matter accumulated in any soil varies with the rate of
supply of biological materials and the nature of its timing. It also depends on soil age,
whether the soil environment is conducive to rapid organic matter decomposition,
the chemical composition of the material to be decomposed and the capacity of soil to
retain organic matter. This latter capacity is largely dependent on the types and
concentrations of the soil clays.
Time
Balesdent
et al.
(1987) considered that organic stocks in recent volcanic soils (Andisols)
in Martinique comprised two pools of different ages. The first had a mean age of 38 years
and corresponds to the decomposable plant material, soil biomass and physically-
stabilised pools of Jenkinson and Rayner (1977). The mean age of the second pool
was estimated at 1,400 years and included the chemically-stabilised organic matter.
Accumulation of organic matter in the second pool was considered to cease after
ca.
