Implications of Soil Biodiversity for Sustainable Organic Matter Management - Sustainable Management of Soil Organic Matter - page 365

The heavy metals did not appear to affect crop yields although the numbers
and diversity of one group of bacteria, the rhizobia, are known to have been
affected (Hirsch et al ., 1993). With changes in EU regulations concerning
the disposal of sewage sludge at sea, its addition to agricultural soil is likely
to increase, with the possibility of a resulting increase in metal contamina-
tion. Thus, this change in environmental policy and agricultural practice
may increase the metal content, and consequently reduce soil quality.
The catabolic diversity of culturable bacteria as determined via
BIOLOG™ assays (Fig. 5.3.1) reveals a difference between the two soils.
The Shannon diversity is higher in the Sewage plot, which indicates more a
more diverse population using more varied carbon sources compared with
the FYM plot.
The number of culturable microbes estimated on agar media from the
bacterial or fungal colony-forming units (c.f.u.) g −1 soil were consistently
higher in the FYM plot compared with the Sewage plot (Fig. 5.3.2). This is
consistent with the finding that the total microbial biomass carbon was
higher in the FYM plot than in the Sewage plot (Brookes and McGrath,
1984). None of the media showed large differences between the two plots,
indicating that overall the community structure was not greatly affected.
The most noticeable increase was seen in the pseudomonads from FYM
on PSA medium, where the c.f.u. were tenfold higher than those from
the Sewage plot. Since this group contains many root-colonizing bacteria
implicated in healthy plant growth (Rovira et al ., 1965), is important for soil
fertility, the genetic diversity of the population was investigated.
Fig. 5.3.1. Catabolic diversity of C utilization in the soil, as Shannon index for two soils receiving
FYM or sewage sludge.