Modelling indicates that about 90% of the organic matter present in soils turns over on
decadal to centennial timescales (Coleman et al., 1996; McGill, 1996). Most organic matter in
soil is derived from plant roots, plant debris and microbially re-worked substances. The
presence of soil organic matter is important for a range of useful soil properties, which has
been comprehensively reviewed by Krull (2004). The process of microbial energy acquisition
(and concomitant CO2 release) from substrate is accompanied by a release of various
nutrient elements, which may be conserved in the soil in microbial biomass or the particulate
residues of substrate decomposition. A portion of certain nutrients may also be released in
soluble form, and a fraction may be lost from the soil through leaching or run-off; which is
essential to crop nutrition. This is particularly the case where external nutrient provision (from
fertiliser or manure) is limited or absent.
Modelling indicates that about 90% of the organic matter present in soils turns over on
decadal to centennial timescales (Coleman et al., 1996; McGill, 1996). Most organic matter in
soil is derived from plant roots, plant debris and microbially re-worked substances. The
presence of soil organic matter is important for a range of useful soil properties, which has
been comprehensively reviewed by Krull (2004). The process of microbial energy acquisition
(and concomitant CO2 release) from substrate is accompanied by a release of various
nutrient elements, which may be conserved in the soil in microbial biomass or the particulate
residues of substrate decomposition. A portion of certain nutrients may also be released in
soluble form, and a fraction may be lost from the soil through leaching or run-off; which is
essential to crop nutrition. This is particularly the case where external nutrient provision (from
fertiliser or manure) is limited or absent.
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