Implications of Soil Biodiversity for Sustainable Organic Matter Management - Sustainable Management of Soil Organic Matter - page 363

direct economic consequences for agriculture, particularly if diversity
provides a buffer against environmental changes. Biodiversity should be
preserved in its present state as an insurance for future generations, until its
significance is more fully understood (Bengtsson, 1998).
Materials and Methods
Site description and soil analysis
The Market Garden Experiment at Woburn Experimental Farm, Woburn,
UK is a sandy loam (typic Udipsamment), pH 6.5 with 10% clay, 51%
coarse sand. Two plots were sampled: the farmyard manure (FYM) plot,
which received 10.4 t organic matter ha −1 year −1 ; and the sewage sludge
(Sewage) plot, which received 16.4 t of metal-contaminated organic matter
ha −1 year −1 between 1942 and 1961. The plots are under grass and have
similar C : N ratios. Soil was sampled with a 10 mm corer to the depth of
250 mm, and ten replicate samples were taken from each plot, bulked and
sieved through a 2 mm sieve. Microbial studies were performed on fresh
soil; samples for other analyses were stored at 4°C. Total carbon, nitrogen
and heavy metal contents were measured as described previously (Brooks
and McGrath, 1984; McGrath and Cunliffe, 1985).
Catabolic diversity of the culturable bacteria
Using the BIOLOG™ system (Garland and Mills, 1991), a 1 g sub-sample
of the bulked soil was taken and the diluted soil extracts were exposed to 95
different carbon substances. The capacity of the soil microbes to metabolize
these compounds was measured by colour development in comparison with
a control containing only water. This provided C substrate utilization data
which were used to assess any functional changes in culturable bacterial
communities by using the Shannon Weaver equation (Magurran, 1988).
Population size and phenotypic diversity
Microbial counts were obtained using standard procedures (Alef and
Nanninpieri, 1995). Diluted soil suspensions (obtained as above) were
plated out on a range of selective media: 1/10 tryptone soya agar (TSA),
general selection for fast-growing heterotrophic bacteria; potato dextrose
agar (PDA), fungi; yeast mannitol (YM), slower growing heterotrophs e.g.
rhizobia; Pseudomonas selective agar (PSA), fluorescent pseudomonads;