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C.Chenuet al.
Composition and Properties of Clay-OM Associations
3.14
The Influence of Cultivation
on the Composition and
Properties of Clay-Organic
Matter Associations in Soils
C. C
HENU
1
, M. A
RIAS
2
AND
E. B
ESNARD
1
1
Unité de Science du Sol,INRA, 78026 Versailles, France; and
2
Universidade de Santiago,DepartamentodeEdafoloxia, 15706
Santiago de Compostela, Spain
Introduction
One of the main questions about the effect of land use on soil properties is
which soil constituents are affected and what is the impact of land use
change on soil properties. Cultivation decreases soil organic matter (SOM)
stocks, in particular labile fractions, such as particulate organic matter
(Cambardella and Elliott, 1992). Organic matter in the < 2
m fraction of
soils is less depleted by cultivation (Christensen, 1992; Balesdent
et al
.,
1998). This is ascribed to the slow turnover rate of < 2
µ
µ
m SOM, due
to
its
chemical
nature
and
presumably
also
to
its
protection
from
decomposition by the clay minerals (Balesdent
et al
., 1998).
The basic units of soil aggregates are elementary associations of clay
minerals and oxides with organic matter (Emerson
et al
., 1986). Clay-
associated organic matter is identified in most studies with the organic
matter present in the < 2
m fraction of soils. However, in this fraction,
organic matter can be associated with clay particles or present as discrete
entities (Chenu
et al
., 1998).
The aims of this chapter are to assess the effect of cultivation on the
organic matter present in the < 2
µ
m particle size fraction, and in particular
on the forms of organic matter present in this fraction and their degree
of association with clay particles, and on the physical properties of this
fraction. We focused on clay dispersibility because it seriously affects large
soil pores and leads to surface sealing and associated problems (Kay and
Dexter, 1990).
µ
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