Implications of Soil Biodiversity for Sustainable Organic Matter Management - Sustainable Management of Soil Organic Matter - page 372

Non-carbohydrate (NCARB) content was calculated as the difference
between percentage loss on ignition and percentage total carbohydrates.
Biomass carbon was estimated by fumigation extraction (Vance et al .,
1987), with C in extracts determined on a Shimadzu Organic Carbon
analyser (Model TOC-5050). Respired CO 2 was measured (Sparling,
1981) C for 2 h using gas chromatography

(PYE-Unicam series 104). For organic C ratios, loss on ignition (for C org ),
extractable biomass carbon (C mic ) and respiration (C resp ) were converted to
carbon equivalents using standard factors (Vance et al ., 1987; Howard and
Howard, 1990).
Aggregate stability was measured after shaking air-dry soil (< 2 mm) in
water for 1 h (Scullion, 1994). The percentage of silt + clay and clay
remaining in aggregates (> 63 and > 2

after incubation at 20 °

m, respectively) was calculated by
reference to total silt + clay and clay (MAFF, 1986). This procedure was
also carried out for soils pre-treated with sodium chloride or sodium
periodate, with the difference between pre-treatments taken as the
contribution of carbohydrates to stable aggregation (Cheshire et al .,
1983); periodate treatment was found to destroy between 95 and 98% of
carbohydrates (Malik, 1996).

µ

Results and Discussion

Organic matter and aggregation

There was a consistent increase in all organic matter fractions in
restored soils between years 9 and 21 (Table 5.4.1), with the latter soils
having higher total organic levels near the surface than UD soils. Since
soils immediately following restoration had ~4% LOI (Scullion, 1994), the
average annual gain in soil organic matter, allowing for changes in bulk
density, can be estimated at > 3000 kg ha −1 .

Table 5.4.1. Mean values for organic matter fractions in undisturbed (UD) and restored (R) soils.

0-7.5 cm 7.5-15 cm

Sites %LOI %CARB %NCARB %LOI %CARB %NCARB

UD 10.9 1.66 9.3 7.6 0.92 6.7

R21H 13.2 1.05 12.2 5.6 0.21 5.4

R21L 11.3 0.84 10.5 5.4 0.19 5.1

R9H 7.2 0.74 6.4 4.4 0.12 4.3

R9L 6.8 0.73 6.1 4.1 0.11 4.0

LSD 5% 1.58 0.25 1.33 0.85 0.13 0.72