Agriculture Reference
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restored soils under grassland management were related to the develop-
ment of stable aggregation in these soils. A second experiment evaluated
the role of earthworms in these changes, again under grassland manage-
ment. The third study assessed differences in soil C cycling between some
of the grassland sites used in the first study and similar soils under
woodland. All sites were in the same location (UK Grid Ref. SN259214) in
South Wales and were part of a long-term research programme (Scullion,
1994). The region had high rainfall, with both undisturbed and restored
clay loam soils having poor to imperfect drainage. Soil conditions at
replacement and management regimes were recorded carefully as part of
the overall research programme, ensuring that comparisons between sites
could be made with confidence.
In the first study, soils on undisturbed (UD) land and on land restored
for 9 (R9) and 21 (R21) years were compared in terms of their organic
composition and carbohydrate contribution to stable aggregation. It was
anticipated that as restored soils aged, their organic content and composi-
tion would approach that of UD soils. Earthworm activity and resulting
physical protection of organic matter within stable aggregates were
expected to mediate this process (Scullion, 1994). Five fields were selected
including two examples of different (9 and 21 years) stages in the recovery
process; an undisturbed field was included to represent the end point of this
process. The two fields from each restoration phase had different nutrient
inputs, organic returns and earthworm populations. Both fields on the
9-year site received 100 kg N as urea and 8 t of poultry manure ha
−1
year
−1
,
and had low earthworm populations. However, the high input field (R9H)
was treated with 100 t of sewage sludge (7.1% total C, 0.6% total N,
0.8% total P
2
O
5
as applied) ha
−1
at restoration; the low input field (R9L)
received only the basal fertilizer dressing at this stage. On the older site, the
high (R21H) input field was treated with 100 kg N as urea and 8 t poultry
manure ha
−1
year
−1
, whilst the low (R21L) input field received half of
each of these annual inputs; earthworm populations were moderate on the
high input and large on the low input field. The undisturbed field, with
the largest earthworm population, received nutrient inputs similar to those
of R21H. All fields were under grass-clover leys and, with the exception of
R21H which was cut for silage, were grazed by sheep. Differences were
expected between each pair of fields on restored soils in the amount and
quality of organic matter, and in associated soil structural development.
On the more recently restored (R9) site, the influence of earthworms
on organic content, composition and aggregation was evaluated by
comparison of control and earthworm input plots (Scullion, 1994). This
experiment aimed to assess the influence of earthworm activity on changes
in soil organic matter and aggregation in restored soils. Four 'blocks',
including one control and one earthworm input plot (each 400 m
2
)
were designated prior to the introduction of earthworms, with treatments
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