Implications of Soil Biodiversity for Sustainable Organic Matter Management - Sustainable Management of Soil Organic Matter - page 374

variations in carbohydrate content as earthworm cast materials contain high
levels of carbohydrates (Altemuller and Joschko, 1992). In the inoculation
trial on restored (R9) land, earthworms increased soil carbohydrates and
aggregate stability (Table 5.4.3) by similar proportions at both sampling
depths. Clay showed a trend similar to that for silt + clay stability, so
only the latter data are given. On earthworm input plots, stability was
most closely related to carbohydrate contents and inputs also decreased
consistently C resp :C org ratios (Scullion and Malik, 2000).
Carbohydrates accounted for 16.0 and 16.1% of the total organic
content of the earthworm input soils at the upper and lower sampling
depths, respectively, compared with 10.6 and 7.7% in the control. Input
soils 9 years after their replacement showed proportions of carbohydrates
similar to those of UD soils but somewhat lower levels. Input soils had
higher levels of stability and of carbohydrates than corresponding soils
on the older (R21) site.

Carbon indices

Ratios of different soil C fractions provide an indication of the status of car-
bon cycling in soils and have been suggested as an index of soil recovery
(Insam and Domsch, 1988). Data in Table 5.4.4 show that for grassland,
but not woodland, there was a significantly higher proportion of soil C as
microbial C in undisturbed compared with restored soils; restored soils of
different age did not differ consistently in this respect. Within similar man-
agement regimes, UD soils generally had lower C resp :C mic and C resp :C org
ratios compared with restored soils, perhaps indicating respectively less
stress on microorganisms and greater protection of organic matter. It is
likely that the high labile organic fraction in UD soils was linked to similarly
high aggregation levels. Within restored soils, there was little difference in
C resp :C mic , but the more recently restored soils had markedly higher

Table 5.4.3. Organic fractions and aggregation (R9 site) as affected by earthworm inputs 8 years

previously.

0-7.5 cm 7.5-15 cm

%Z + Cl
stability

%Z + Cl
stability

Treatment %LOI %CARB %NCARB %LOI %CARB %NCARB

Control 8.49 0.90 7.59 21.9 3.91 0.30 3.61 13.1

Worm input 8.00 1.28 6.72 33.7 4.36 0.70 3.66 26.9

Significance
level (P=)

0.2189 0.0001 0.2188 0.0004 0.0993 0.0000 0.0993 0.0000