Agriculture Reference
In-Depth Information
compounds such as root exudates or earthworm intestinal mucus (see the 'Sleeping Beauty
paradox'‚ Chapter III.2.4.3). However‚ their activities are mediated through a set of
hierarchically-organised factors: climate‚ soil characteristics - especially the abundance
and types of clays and nutrient status - and the quality of the organic materials input.
The functioning of the soil system is defined by:
(i) the decomposition rates of dead organic materials‚ and the balance between mineral-
isation (which releases nutrients available to plants and micro-organisms) and humification
(which forms reserves of soil organic matter and colloidal organic compounds);
(ii) the degree of synchronisation and synlocalisation of nutrient release with plant
demand (definitions in Swift‚ 1986; van Noordwijk and de Willigen‚ 1986);
(iii) the soil physical structure which determines the rates and patterns of gas exchange‚
soil water movement into and through the soil‚ and erosion rates.
This chapter first describes the general mechanisms and regulation of decomposition‚
the most important process of soil function. Subsequently‚ functioning of the major
biological systems of regulation‚ the litter-systems‚ rhizospheres‚ drilospheres and
termitospheres are then detailed‚ with particular emphasis on their compositions‚
structures and the effects of the major groupings of organisms on soil physical proper-
ties and organic matter dynamics.
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