Organic Matter and Sustainability - Sustainable Management of Soil Organic Matter - page 21

Fig. 1.1.4. 5 kPa tension (THV5), and

soil organic carbon content (SOC%) for West Midland topsoils under three agricultural land uses
(expanded from Hollis et al., 1977 using unpublished SSLRC data).

The relationship between volumetric water content at −

In terms of the long-term sustainability of soil, it is important to
consider the magnitude of change in SOC over time. Data from the
National Soil Inventory (McGrath and Loveland, 1992) and subsequent
re-investigation at the same sites (DETR, 1999, p. 212), has shown that
there is a significant change in the distribution of sites in the organic carbon
groups for both arable/ley grass sites and for permanent grass sites (Table
1.1.3). The absolute magnitude of the change in the mean value of OC in
the two data sets is 0.5% (arable/ley grass) and 0.8% (permanent grass)
during ~15 years. Thus, whatever one might derive from the evidence in
terms of critical levels of SOC/SOM, the need to consider change in these
levels is likely to arise at decadal intervals.
The work reviewed thus far is in terms of total SOM or SOC. Tisdall
and Oades (1982) summarized a considerable amount of earlier work,
which had shown that 'active' or 'fresh' components of SOM were at least,
or sometimes more, important in controlling soil physical behaviour than